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Sodium-ion batteries represent a promising alternative to lithium-ion systems. However, the rapid growth of sodium-ion battery technology requires a sustainable and scalable synthetic route to high-grade sodium hexafluorophosphate. This work demonstrates a new multi-gram scale synthesis of NaPF6 in which the reaction of ammonium hexafluorophosphate with sodium metal in THF solvent generates the electrolyte salt with the absence of the impurities that are common in commercial material. The high purity of the electrolyte (absence of insoluble NaF) allows for concentrations up to 3 M to be obtained accurately in binary carbonate battery solvent. Electrochemical characterization shows that the degradation dynamics of sodium metal-electrolyte interface are different for more concentrated (>2 M) electrolytes, suggesting that the higher concentration regime (above the conventional 1 M concentration) may be beneficial to battery performance.

Ionic liquids (ILs) such as 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) are considered suitable co-extraction reagents of tri-n-butyl phosphate (TBP) for selective extraction of lithium from magnesium-rich salt lake brine. However, ILs are very expensive and the loss of cations can cause the contamination of the aqueous solution. The corresponding inorganic salts of ILs such as sodium hexafluorophosphate (NaPF6) should play the same role as ILs in the extraction of Li+ by TBP, and importantly, they are cheaper and more environmentally friendly. In this study, the effects of NaPF6 concentration, phase ratio, initial pH of the aqueous phase, temperature, and MgCl2 concentration on the extraction of lithium were investigated. It was found that NaPF6 was as good as [C4mim][PF6] in the extraction of Li+ from Mg-rich solution by TBP, and their extraction mechanisms are also the same, which is certified by comparing the Fourier transform infrared spectroscopy (FT-IR) and slope analysis. Hydrochloric acid (HCl) is more effective than sodium carbonate (Na2CO3) in the stripping of Li+, but Na2CO3 can avoid the regeneration of the organic phase and increase the reusability of both TBP/[C4mim][PF6] and TBP/NaPF6 systems. In TBP/NaPF6 system, the schematic of Li extraction/stripping from brine with high Mg/Li ratios using (a) HCl as stripping agent and (b) Na2CO3 as stripping agent

The paper reports effect of dispersion of titanium dioxide (TiO2) nanofiller on the sodium ion conducting nanocomposite polymer electrolyte membranes consisting of TiO2 dispersed membranes of poly(vinylidenedifluoride-co-hexafluoropropylene) (PVdF-HFP) soaked in a liquid electrolyte of sodium hexafluorophosphate (NaPF6) in ethylene carbonate (EC) and propylene carbonate (PC). The TiO2 dispersed membranes have been prepared by phase inversion technique. The structural and morphological properties of the polymer electrolyte membranes have been investigated using x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The membranes have been found to be highly porous with maximum porosity ~ 72% and liquid electrolyte uptake ~ 270%. Ionic conductivity of the electrolyte membranes containing different concentrations of TiO2 has been measured by complex impedance spectroscopy. The maximum room temperature ionic conductivity has been found to be ~ 1.3 × 10−3 S cm−1. The ionic conductivity measured with temperature has been found to follow VTF behavior. The ion transport numbers of the membranes have been studied using dc polarization, complex impedance, and cyclic voltammetry. The membranes have been found to be predominantly ionically conducting with Na+ transport number ~ 0.31. The electrochemical stability window of the membranes has also been measured using cyclic voltammetry and found to be 3.5 V.

Cathode materials that operate at high voltages are required to realize the commercialization of high-energy-density sodium-ion batteries. In this study, we prepared different composites of sodium cobalt mixed-phosphate with multiwalled carbon nanotubes (Na4Co3(PO4)2P2O7–MWCNTs) by the sol–gel synthesis technique. The crystal structure and microstructure were characterized by using PXRD, TGA, Raman spectroscopy, SEM and TEM. The electrochemical properties of the Na4Co3(PO4)2P2O7–20 wt% MWCNT composite were explored using two different electrolytes. The composite electrode exhibited excellent cyclability and rate capabilities with the electrolyte composed of 1 M sodium hexafluorophosphate in ethylene carbonate:dimethyl carbonate (EC:DMC). The composite electrode delivered stable discharge capacities of 80 mA h g−1 and 78 mA h g−1 at room and elevated (55 °C) temperatures, respectively. The average discharge voltage was around 4.45 V versus Na+/Na, which corresponded to the Co2+/3+ redox couple. The feasibility of the Na4Co3(PO4)2P2O7 cathode for sodium-ion batteries has been confirmed in real time using a full cell configuration vs. NaTi2(PO4)3–20 wt% MWCNT, and it delivers an initial discharge capacity of 78 mA h g−1 at 0.2C rate.

Room temperature sodium-sulfur (Na-S) batteries are promising energy storage devices for meeting increasing energy demands. An electrolyte with reasonably high ionic conductivity (≥10−4 S cm−1) is one of the key requirements for room temperature Na-S batteries. In this work, a sodium ion conducting flexible porous gel polymer electrolyte membrane of TiO2 (Titanium dioxide) dispersed Poly(vinylidene fluoride-hexafluoropropylene) soaked in a liquid electrolyte of NaPF6 (sodium hexafluorophosphate) in EC (ethylene carbonate): PC (Propylene carbonate) has been prepared. The electrolyte is obtained through phase inversion method and shows an ionic conductivity of 1.3 × 10−3 S cm−1. A proto-type Na-S battery has been fabricated and characterized using the prepared electrolyte membrane. The battery shows an open circuit voltage of ∼2.1 V and discharge capacity of 231 mA h g−1. However, battery shows capacity fading during charge-discharge cycle.

Solid-state sodium ion batteries are frequently referred to as the most promising technology for next-generation energy storage applications. However, developing a suitable solid electrolyte with high ionic conductivity, excellent electrolyte–electrode interfaces, and a wide electrochemical stability window, remains a major challenge. Although solid-polymer electrolytes have attracted great interest due to their low cost, low density and very good processability, they generally have significantly lower ionic conductivity and poor mechanical strength. Here, we report on the development of a low-cost composite solid polymer electrolyte comprised of poly(ethylene oxide), poly(vinylpyrrolidone) and sodium hexafluorophosphate, mixed with indium arsenide nanowires. We show that the addition of 1.0% by weight of indium arsenide nanowires increases the sodium ion conductivity in the polymer to 1.50 × 10−4 Scm−1 at 40 °C. In order to explain this remarkable characteristic, we propose a new transport model in which sodium ions hop between close-spaced defect sites present on the surface of the nanowires, forming an effective complex conductive percolation network. Our work represents a significant advance in the development of novel solid polymer electrolytes with embedded engineered ultrafast 1D percolation networks for near-future generations of low-cost, high-performance batteries with excellent energy storage capabilities.

A solid polymer electrolyte composed of poly(ethylene oxide) and sodium hexafluorophosphate has been synthesized with a varying fraction of succinonitrile via solution cast technique. Impedance spectroscopy, transference number measurements, and linear sweep voltammetry were used to study the electrochemical properties. The 10 wt.% succinonitrile system exhibited the highest ionic conductivity of ~ 2 × 10−5 S cm−1 which is two orders of magnitude higher than the pristine polymer salt system. The high ionic transference number (~ 1) confirms that ion conduction is dominated by ions and displays the voltage stability window of about 4 V. The dielectric permittivity and the relaxation time ( $$ {\tau}_{\upvarepsilon^{\prime }},\kern0.5em {\tau}_{\mathrm{M}},{\tau}_{\mathrm{h}} $$ ) values corresponding to the segmental motion of the polymer chain varies with the variation of succinonitrile content. The relaxation time and double-layer capacitance are in good agreement with the conductivity. Finally, an ion transport mechanism has been proposed to provide a better understanding of ion migration.

Solid polymer electrolytes consisted of poly (ethylene oxide) (PEO) and poly (vinyl) pyrrolidone (PVP) with sodium hexafluorophosphate (NaPF6) salt has been prepared by solution cast technique. The influence of salt concentration and temperature on the complex permittivity, complex conductivity, loss tangent, and complex modulus have been analyzed systematically. The complex permittivity decreases with the increase of frequency and high value of dielectric permittivity in the low-frequency window is attributed to the electrode polarization effect. The peak in the loss tangent plot shift toward high frequency with the addition of salt and increase of temperature clearly indicates the decrease of the relaxation time. The temperature dependent analysis suggests that dielectric properties, dc conductivity, and the molecular chain segmental dynamics increase with the increase of temperature owing to the thermal activation of dielectric properties. The ion migration and dc conductivity are effectively improved by the addition of salt. Aforementioned estimated results strongly convincing its use for the device applications

Dual ion batteries based on Na+ and PF6– received considerable attention due to their high operating voltage and the abundant Na resources. Here, cheap and easily obtained graphite that served as a cathode material for dual ion battery delivered a very high average discharge platform (4.52 V vs Na+/Na) by using sodium hexafluorophosphate in propylene carbonate as electrolyte. Moreover, the all-carbon dual ion batteries with graphite as cathode and hard carbon as anode exhibited an ultrahigh discharge voltage of 4.3 V, and a reversible capacity of 62 mAh·g–1 at 40 mA·g–1. Phase changes have been investigated in detail through in situ X-ray diffraction and in situ Raman characterizations. The stable structure provides long life cycling performance, and the pseudocapacitance behavior also demonstrates its benefits to the rate capability. Thus, dual ion batteries based on sodium chemistry are very promising to find their applications in future.

In this work electrospun amorphous polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) based separator is shown to have a superior gel electrolyte material suitable to the sodium-ion cell. The 16 wt.% polymer solution was electrospun under a voltage of 18 kV to get an amorphous electroactive β-phase structure. The amorphous β-phase is indexed by an X-ray diffractometer (XRD). The ionic conductivities, electrolyte uptakes, and linear sweep voltammetry (LSV) of the amorphous gel polymer electrolyte (AGPE) are investigated by saturating the separator membrane in a liquid electrolyte solution of 0.6 M sodium hexafluorophosphate (NaPF6) dissolved in ethylene carbonate (EC)/ propylene carbonate (PC) (1:1, vol.%). The AGPE displayed a high ionic conductivity of 1.28 × 10−3 S cm−1 and wide electrochemical stability up to 4.6 V vs Na/Na+ at room temperature. Further, the cells Na/AGPE/Na0.66Fe0.5Mn0.5O2 displayed an excellent cycling performance with little capacity loss.

The physicochemical properties of the phosphonium-based organic ionic plastic crystal (OIPC), triisobutylmethylphosphonium bis(fluorosulfonyl)amide (P1i444FSI) in mixtures with sodium salts consisting of different anion structures, sodium bis(fluorosulfonyl)amide (NaFSI), sodium bis(trifluromethanesulfonyl)amide (NaNTf2) and sodium hexafluorophosphate (NaPF6) were investigated. The phase behaviour, ionic conductivity and electrochemical performance at a sodium concentration of 20 mol% for each anion system were compared. 20 mol% P1i444FSI/NaPF6 displays complicated phase behaviour with additional phase transitions and a higher melting temperature compared to pure P1i444FSI, indicating the formation of a new compound which is different from pure P1i444FSI or NaPF6. The system consisting of 20 mol% NaNTf2 exists as a supercooled liquid across the whole temperature range with a glass transition at − 73 °C. At temperatures corresponding to their liquid state, the ionic conductivity values for both 20 mol% NaFSI and NaNTf2 systems are substantially higher than the NaPF6 system and are approximately similar. Na symmetrical cell cycling at room temperature and 50 °C for these two systems at current densities of 0.1 and 0.25 mA cm− 2 exhibited stable and reversible sodium stripping and plating behaviour with very low polarisation potentials. In contrast, for cells based on the 20 mol% NaPF6 electrolyte, an extended time or higher current density is required in order to form a stable SEI layer before stable cell polarisation behaviour is reached.

This paper reports the electrochemical behavior and catalytic property of electrode-supported thin films of polystyrene-block-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS-b-PAEFc) in an ethanol (EtOH) solution. The electrochemical properties of PS-b-PAEFc films with different PAEFc volume fractions (fPAEFc = 0.47, 0.30, and 0.17) in 0.1 M ethanolic sodium hexafluorophosphate (NaPF6) were compared with those in an acetonitrile (MeCN) solution of 0.1 M tetrabutylammonium hexafluorophosphate. Pristine PS-b-PAEFc films did not afford significant faradaic currents in the EtOH solution because EtOH is a nonsolvent for both PS and PAEFc. However, the films could be rendered redox-active in the EtOH solution by applying potentials in the MeCN solution to induce the redox-associated incorporation of the supporting electrolytes into the films. Atomic force microscopy images verified the stability of PAEFc microdomains upon electrochemical measurements in these solutions. Cyclic voltammograms measured in the ...

A nanocomposite solid polymer electrolyte has been synthesized using polyethylene oxide (PEO), sodium hexafluorophosphate (NaPF6), and organomodified montmorillonite (DMMT) nano-clay, with an aim to improve the ionic conductivity, voltage stability window, transference number and dielectric properties. The DMMT intercalated PNCs exhibits an ionic conductivity of three order (∼10−5 S cm−1) higher as compared to the pure polymer (∼10−8 S cm−1). The DMMT based PNCs have ion transference number close to unity (0.99) and wide voltage stability window (∼ 5 V). The dielectric constant and dc conductivity increases with nanoclay addition. The relaxation peak in loss tangent plot shift toward high frequency on nanoclay addition and indicates the decrease of relaxation time. The evaluated relaxation time τe′, τtan δ, τh, τm are in good correlation with each other and exhibits minima for the nanoclay based PNCs which infers the faster segmental motion of polymer chain and supports the enhanced ionic conductivity.

To bridge the gap between current lithium-ion battery technology and alternative cell chemistries such as, e.g., sodium-ion batteries, the majority of the research in this field focuses on the improvement of the cell’s energy density by the development of new active materials for reversible storage of sodium ions. On the other hand, the power density, which is determined by the ionic transport and thermodynamic parameters in the electrolyte, namely the conductivity, the thermodynamic factor, the transference number, and the diffusion coefficient, is attracting little attention. In this contribution, we determine these electrolyte properties for 0.1 M to 2 M LiPF6 and NaPF6 in a mixture of ethylene carbonate and diethyl carbonate (EC:DEC (1:1 v:v)) and use them in 1D simulations to show their impact on the theoretical discharge rate performance of the lithium and sodium cell chemistry. We show that the increased cation size of sodium and its corresponding weaker solvent interactions are beneficial for high power applications and that the improved ionic transport properties would allow for a substantial increase of either the (dis)charge currents or the electrode areal loading, compared to the well-established lithium system.

In the present work, a novel, simple, and efficient method for the iron (Fe) speciation and determination in different water and food samples was developed using in situ solvent formation microextraction (ISFME) technique followed by spectrophotometric analysis. The procedure is based on the complexation of Fe (II) with 1, 10-phenanthroline. A hydrophilic ionic liquid (IL), 1-Hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4]), was added to the aqueous media and then ion-pairing agent, sodium hexafluorophosphate (NaPF6), was added in order to obtain a hydrophobic IL ([Hmim][PF6]) as the extraction solvent. The hydrophobic extraction solvent formed under these conditions was completely dispersed into the sample solution. After centrifugation, the fine droplets of the extractant phase settled to the bottom of the conical-bottom glass centrifuge tube. The absorbance of the enriched analyte in the final solution was determined by UV–Vis spectrophotometer against a reagent blank. Total iron was determined after the reduction of Fe (III) to Fe (II) by using ascorbic acid as reducing agent. To obtain the best extraction results, some experimental parameters affecting the extraction efficiency were optimized. Under optimum conditions, the calibration curve was linear in the concentration range of 1.0–60.0 μg L¯1, with the square correlation coefficient (r) equal to 0.998. The limit of detection and the enrichment factor were 0.3 μg L¯1 and 80, respectively. The method was successfully applied to the analysis of iron in water and food samples.

Ultrasound-assisted (UA) hollow fiber (HF) liquid-phase microextraction (LPME) coupled with flame atomic absorption spectrometry (FAAS) has been developed to preconcentrate and determine ultra-trace amounts of cobalt (Co) and nickel (Ni) ions in human urine. To the best of our knowledge, no previous reports have described the coupling of UA-ionic liquid (IL)-HF-LPME with an FAAS system to analyze metal ions in biological samples. In this study, the ILs 1-hexyl-3-methylimidazolium hexafluorophosphate, sodium hexafluorophosphate, and 1-(2-pyridylazo)-2-naphthol were used as extraction, ion-pairing, and chelating agents, respectively. With the assistance of an ultrasonic probe, the analyte exchange between the phases increased, and the extraction efficiency of Co and Ni ions improved significantly. The collected extraction phase was subsequently analyzed directly through FAAS. Under optimized conditions, the detection limits of Co and Ni ions were 0.09 and 0.03 μg L−1, respectively. The precision of the analysis of Co and Ni ions was within a relative standard deviation of 10% under normal operating conditions. The ultrasonic assistance provided enrichment factors of 66 and 82 for Co and Ni ions, respectively. The recoveries of Co and Ni ions spiked in urine samples ranged from 93.8 to 104.3%. The practicality of the proposed method was demonstrated through satisfactory analyses of samples of a standard reference material and real human urine.

Fundamental characterization of battery electrolyte is vital for rechargeable batteries. This work reports the chemical stability of sodium hexafluorophosphate (NaPF6)-based non-aqueous electrolytes containing different solvent mixtures (e.g., cyclic and acyclic carbonates) in the presence of water for Na-ion batteries. A degradation study is conducted using NaPF6-based electrolytes, highlighting two electrolyte additives, 2,2,2-trifluoroethoxy-2,2,2-ethoxy phosphazene (FM2) and fluoroethylene carbonate (FEC), on degradation and cell performance of Na-ion batteries. Hydrolysis of NaPF6 in acidic condition is particularly prone to form hydrofluoric acid (HF), and can be observed in electrolytes made with battery grade carbonate solvents (

Tin phosphide (Sn4P3) is here investigated as an anode material in half-cell, symmetrical, and full-cell sodium-ion batteries. Results from the half-cells using two different electrolyte salts of sodium bis(fluorosulfonyl)imide (NaFSI) or sodium hexafluorophosphate (NaPF6) show that NaFSI provides improved capacity retention but results from symmetrical cells disclose no advantage for either salt. The impact of high and low desodiation cut-off potentials is studied and the results show a drastic increase in capacity retention when using the desodiation cut-off potential of 1.2 V as compared to 2.5 V. This effect is clear for both NaFSI and NaPF6 salts in a 1 : 1 binary mixture of ethylene carbonate and diethylene carbonate with 10 vol% fluoroethylene carbonate. Hard X-ray photoelectron spectroscopy (HAXPES) results revealed that the thickness of the solid electrolyte interphase (SEI) changed during cycling and that SEI was stripped from tin particles when tin phosphide was charged to 2.5 V with NaPF6 based electrolyte.

Owing to its low cost and high natural abundance, sodium metal is among the most promising anode materials for energy storage technologies beyond lithium ion batteries. However, room-temperature sodium metal anodes suffer from poor reversibility during long-term plating and stripping, mainly due to formation of nonuniform solid electrolyte interphase as well as dendritic growth of sodium metal. Herein we report for the first time that a simple liquid electrolyte, sodium hexafluorophosphate in glymes (mono-, di-, and tetraglyme), can enable highly reversible and nondendritic plating–stripping of sodium metal anodes at room temperature. High average Coulombic efficiencies of 99.9% were achieved over 300 plating–stripping cycles at 0.5 mA cm–2. The long-term reversibility was found to arise from the formation of a uniform, inorganic solid electrolyte interphase made of sodium oxide and sodium fluoride, which is highly impermeable to electrolyte solvent and conducive to nondendritic growth. As a proof of concept, we also demonstrate a room-temperature sodium–sulfur battery using this class of electrolytes, paving the way for the development of next-generation, sodium-based energy storage technologies., Room-temperature sodium metal anodes can be cycled in a highly reversible and nondendritic manner using sodium hexafluorophosphate in glymes, paving the way for the development of next-generation sodium-based batteries.

MgO-templated mesoporous carbons annealed from 900 to 1,500 °C were examined as active materials for negative electrodes in a propylene carbonate electrolyte containing 1 M sodium hexafluorophosphate. The carbons annealed at 1,000 °C exhibited 180 mAh g−1 at a rate of 0.1 A g−1 in a potential range of 2.00–0.01 V versus Na+/Na. The carbons showed good rate capability as well as cyclability. It is considered that mesopores plays a role of easy diffusion pathway for ions, and also significantly relates to both electric double layer capacitance and faradaic reactions involving Na ions. X-ray diffraction patterns, nuclear magnetic resonance spectra and Raman spectra were discussed for characterization of the carbons. Raman spectra indicated a reversible interaction of reduced Na with carbons. However, Na intercalation in the carbon layers was not confirmed for the carbon annealed at 1,000 °C. This is because the Na intercalation sites in the carbon layers are very few due to the disordered structure caused by the relatively low temperature annealing.

Direct analysis of melamine using reverse phase chromatography is a challenge because this compound's small size and strong polar nature leads to abnormal peak symmetry as well as poor retention. Here, we introduce a simple and reliable reverse phase liquid chromatographic method using sodium hexafluorophosphate to modify an acidic aqueous eluent, resulting in improved chromatographic behaviors of melamine in complex food matrices. Variables affecting the retention mechanism, including chaotrope type, concentration and stationary phase, were investigated. Under optimum conditions, melamine retention, separation efficiency, peak shape and reproducibility were significantly improved as compared to other methods that use ionic liquids or a micellar mobile phase. No interference affected melamine detection when infant formula was applied as the food matrix. Analytical reliability was demonstrated through estimation of validation parameters such as specificity, linearity, precision, accuracy and recovery. This method is suitable for routine analysis of melamine in infant formula. More noteworthy, this is the first time that an organic solvent-free mobile phase using chaotropic salt, meeting the concept of green chemistry, has been proposed.

A novel homogeneous liquid-liquid microextraction technique based on use of ionic liquids (ILs), termed in situ solvent formation microextraction (ISFME) is developed for separation/preconcentration of Co(II) ions. In this method, small amount of sodium hexafluorophosphate (NaPF6, as an ion-pairing agent) was added to the sample solution containing very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4], as hydrophilic IL). A cloudy solution was formed as a result of formation of fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF6]. After centrifuging, the fine droplets of the extractant phase settled to the bottom of the conical-bottom glass centrifuge tube. ISFME is a simple and rapid method for extraction and preconcentration of cobalt ions from water samples that can be applied for the sample solutions containing very high concentrations of salt. Furthermore, this technique is much safer in comparison with the organic solvent extraction. Reliability of the introduced methodology was evaluated by analyzing water reference material. ISFME was successfully applied to determining cobalt(II) in real water samples. Schiff base ligand, 3,3′-(1E,1E′)-(propane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(4-bromophenol) (L) was chosen as a complexing agent. Analysis was carried out using atomic absorption spectrometry. Type and amount of IL, pH and the other parameters were optimized. Under the optimum conditions, the limit of detection (LOD) was 0.06 ng/mL and the relative standard deviation (RSD) was 1.8% for 10 ng/mL cobalt.

A simple and efficient method for the determination of methyl tert-butyl ether (MTBE) in water samples is presented. The analytical method is based on use of 1-octyl-3-Methyl-imidazolium chloride [OMIM][Cl] and sodium hexafluorophosphate (NaPF6) as an extractant solvent ([OMIM][PF6] is established and finally MTBE separated/preconcentrated by an in situ solvent formation microextraction (ISFME) technique. Later on, the extractant containing the analyte is recovered by centrifugation and thermally desorbed. The analyte is finally determined by gas chromatography/flame ionization detection (ISFME-GC/FID). The main variables involved in the extraction and thermal desorption steps have been studied in depth. Once evaluated, the analytical method has been characterized in terms of linearity, sensitivity, precision, and accuracy. The limit of detection was 0.09 μg L−1 while the precision, expressed as relative standard deviation, was 1.9% (n = 7). In addition, acceptable recovery values were obtained in samples...

Piezoelectric resonator measurements show that there is a minimum of interfacial viscosity of sodium hexafluorophosphate aqueous solution (approximately 1% of the bulk viscosity) at the potential of zero charge of gold electrode. Drag force measurements confirm interfacial viscosity dependence on the potential obtained from piezoelectric resonator measurements but the minimum is lower (approximately 5% of the bulk viscosity). Potential dependence of interfacial viscosity has been determined in the absence of confinement of fluid between a probe and surface what provides useful comparison to probe-based methods where confinement is inherent to the measurement and where additional model assumptions are needed to separate confinement effects. By controlling the applied potential it is possible to control the viscosity of liquid layer close to the solid interface, what increases the ability to actively manipulate a wall-bounded liquid flow field to effect a desired change.

New synthesized 1,4-disubstituted thiosemicarbazide derivatives were analyzed in the RP system, modified with the addition of salts; chaotropic (sodium hexafluorophosphate - Na PF(6)), cosmotropic (sodium phosphate - NaH(2)PO(4)), and neutral (NaCl) on Zorbax XDB C18 column. The effect of the eluent composition on the analytes retention (k), system efficiency (N), peak symmetry (A(s)), and LOD values were all examined and compared to unmodified organic-aqueous mobile phase system. It was established that eluent modified with chaotropic salts addition was also the most advantageous according to other peak parameters such as the theoretical plates numbers and asymmetry factors. The lower LOD values were achieved in comparison to unmodified organic-aqueous eluent system. Compatibility of lipophilicity parameters calculated by the use of computer software with experimental ones measured by RP-HPLC was also the best for chaotropic modified mobile phase. To explain the observed phenomena, molecular modeling was performed for chosen representative compound in different environment representing examined mobile phase composition.

A robust extraction method against the variations of sample ionic strength viz. ionic liquid-based ultrasound-assisted in situ solvent formation microextraction (IL-UA-ISFME) was coupled for the first time with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), and successfully used as a more sustainable approach for the determination of meloxicam (MEL) in human plasma. Herein, a hydrophobic IL (1-butyl-3-methylimidazolium hexafluorophosphate) was formed by adding a hydrophilic IL (1-butyl-3-methylimidazolium tetrafluoroborate) to aqueous sample solution containing an ion-exchange reagent (sodium hexafluorophosphate). The target analyte was transferred into the IL medium while the extraction solvent was completely dispersed into the sample using ultrasonic irradiation and then, the settled enriched phase was injected to HPLC. Firstly, main factors affecting the microextraction performance were evaluated and optimized. The linearity was in the range of 5-1,500 ng mL-1 with regression coefficient corresponding to 0.997. Limits of detection (LOD; signal-to-noise ratio (S/N) = 3) and quantification (LOQ, S/N = 10) were 1 and 5 ng mL-1, respectively. An acceptable recovery range of 82.1-93.6% and satisfactory intra-assay (3.6-4.8%, n = 6) and inter-assay (3.3-5.1%, n = 9) precision as well as remarkable sample clean up exhibited good efficiency of the method. The freeze-thaw stability study was performed for samples and standard solutions. To study the applicability of the proposed method, it was employed for the determination of MEL in human plasma after oral administration of the drug and some pharmacokinetic data were achieved. The technique proved to be accurate and reliable for the screening intentions.

A simple in situ solvent formation microextraction method based on use of ionic liquid (IL) as an extractant solvent and sodium hexafluorophosphate (NaPF6) as an ion-pairing agent was proposed for the concentration of trace levels of lead. In this method lead was complexed with N-phenylbenzo-hydroxamic acid (PBHA) and extracted into an ionic liquid phase. After phase separation, the enriched analyte in the final solution is determined by flame atomic absorption spectrometry. ISFME is a fast, simple and suitable method for extraction and concentration of inorganic such as metal ions from sample solutions containing a high concentration of salts. The influences of the analytical parameters on the microextraction efficiency were investigated and optimized. Under the optimum conditions, the limit of detection (3s) and the enhancement factor were 0.1 μg L−1 and 70, respectively. The relative standard deviation (R.S.D) was obtained 1.3%. The accuracy of the method was confirmed by analyzing certified reference materials. The presented method was successfully applied for the determination of lead in water samples.

A hydrophilic radical polymer, poly(2,2,6,6-teteramethylpiperidinyloxyl-4-yl acrylamide) (PTAm), was synthesized via oxidation of the corresponding precursor polymer, poly(2,2,6,6-teteramethylpiperidine-4-yl acrylamide). Electrochemical properties of the PTAm layer were characterized in three aqueous electrolytes of sodium chloride (NaCl), sodium tetrafluoroborate (NaBF4), and sodium hexafluorophosphate (NaPF6) to optimize its activity as an organic cathode. The counter anion species significantly affected the capacity and the cycle performance of the PTAm layer. The PTAm layer in the presence of BF4 −1 displayed quantitative redox capacity beyond 1 μm layer thickness and maintained the discharging capacity of 110 mAh g−1 (97% vs. the calculated capacity) even after 1000 cycle charging/discharging, which could be ascribed to its appropriate affinity to the aqueous electrolyte without any dissolution into the electrolyte. A totally organic-based rechargeable cell was fabricated using PTAm and poly(N-4,4′-bipyridinium-N-decamethylene dibromide) as the cathode and the anode, respectively, and the aqueous electrolyte of NaBF4. The cell gave a plateau voltage at 1.2 V both on charging and discharging and an excellent charging/discharging cyclability of >2000 with high coulombic efficiency of >95%.

In this work, hydrolysis of three different hexafluorophosphate salts in purified water was investigated. Aqueous samples of lithium hexafluorophosphate (LiPF(6)), sodium hexafluorophosphate (NaPF(6)) and potassium hexafluorophosphate (KPF(6)) were prepared and stored for different times. Ion chromatography (IC) with UV as well as non-suppressed and suppressed conductivity detection was used for the analysis of the reaction products. For the detection and identification of the formed decomposition products, an IC method using IonPac AS14A 250 mm × 4.0 mm i.d. column and 2.5 mM KHCO(3)-2.5 mM K(2)CO(3) eluent was established. Besides hexafluorophosphate, four other anionic species were detected in fresh and matured aqueous solutions. The hydrolysis products fluoride (F(-)), monofluorophosphate (HPO(3)F(-)), phosphate (HPO(4)(2-)) and difluorophosphate (PO(2)F(2)(-)) were found and were unambiguously identified by means of standards or electrospray ionization mass spectrometry (ESI-MS). It was shown that stability of hexafluorophosphate solutions depends on the nature of the counter ion and decreases in the order potassium>sodium>lithium.

Sodium hexafluorophosphate, perchlorate and tetrafluoroborate were applied as the ion-pair reagents in reversed-phase chromatography of several imidazolium-based ionic liquids. The optimization of the retention was performed by changing the kind of organic modifier (methanol, acetonitrile), concentration and the kind of the ion-pair reagents in the mobile phase and the column kind (Zorbax SB-C18, Zorbax SB-Phenyl, Zorbax SB-CN, Zorbax SB-NH2 and Supelcosil LC-F). The selectivity of the proposed chromatographic systems according to the cation kind was compared on the basis of the resolution of ionic liquid mixture. The perturbation method was applied to identify the anion kind. The formation of ion-associated complexes between promethazine as counter-cation and chaotropic anions controlling their retention was confirmed.

We report on a new method for the microextraction and determination of zinc (II). The ion is accumulated via ionic-liquid cold-induced aggregation dispersive liquid-liquid microextraction (IL-CIA-DLLME) followed by flame atomic absorption spectrometry (FAAS). The ionic liquid (IL) 1-hexyl-3-methylimidazolium hexafluorophosphate is dispersed into a heated sample solution containing sodium hexafluorophosphate as a common ion source. The solution is then placed in an ice-water bath upon which a cloudy solution forms due to the decrease of the solubility of the IL. Zinc is complexed with 8-hydroxyquinoline and extracted into the IL. The enriched phase is dissolved in a diluting agent and introduced to the FAAS. The method is not influenced by variations in the ionic strength of the sample solution. Factors affecting the performance were evaluated and optimized. At optimum conditions, the limit of detection is 0.18 μg L−1, and the relative standard deviation is 3.0% (at n = 5). The method was validated by recovery experiments and by analyzing a certified reference material and successfully applied to the determination of Zn (II) in water and food samples.

For a Na/Ni 3 S 2 cell operating at room temperature, three kinds of tetra (ethylene glycol) dimethyl ether (TEGDME) electrolytes, containing sodium trifluoromethane sulfonate (NaCF 3 SO 3 ), sodium hexafluorophosphate (NaPF 6 ), and sodium perchlorate (NaClO 4 ) salts, respectively, were prepared. Na/Ni 3 S 2 cells with 1 M NaCF 3 SO 3 in TEGDME showed a discharge plateau potential of 0.85 V and a first discharge capacity of 448 mAh/g. The discharge capacity decreased to 250 mAh/g after 40 cycles, which represented the best cycling performance among the three electrolytes.

In an effort to utilize the cationic cobalt(III) complex as a binding agent for fluoroanions, the reaction of carbonatobis(1,10-phenanthroline)cobalt(III) chloride with sodium tetrafluoroborate and sodium hexafluorophosphate in water (1:1 M ratio) leads to the formation of [Co(phen)2CO3]BF4 (1) and [Co(phen)2CO3]PF6·3H2O (2). These cobalt(III) complex salts have been characterized by elemental analyses, spectroscopic techniques (multinuclear NMR, UV/Visible and FT-IR), solubility product and conductance measurements. X-ray structure determination of these complex salts revealed the presence of ionic structures i.e., one complex cation [Co(phen)2CO3]+ and one BF 4 - anion in 1 and one complex cation [Co(phen)2CO3]+, one PF 6 - anion and three water molecules of crystallisation in 2. The packings in both complex salts are stabilized by C H⋯F, C H⋯O(carbonato) hydrogen bonds and anion⋯π interactions beside electrostatic forces of attraction. In addition to these non-covalent interactions, O H⋯O(water) and π–π stacking interactions are also observed in 2. The formation of complex salts of definite composition with tetrafluoroborate and hexafluorophosphate ions suggest that [Co(phen)2CO3]+ may be used as binding agent for weakly coordinating fluoroanions i.e. BF 4 - and PF 6 - .

Highly hydrophilic compounds belonging to biogenic amines were analysed in the reversed-phase system, modified with the addition of ionic liquids: 1-ethyl-3-methyl-imidazolium hexafluorophosphate (EMIM PF(6)) and chaotropic salt NaPF(6) on Discovery HS C18 column at acidic conditions. The effect of the additives concentration and the presence of organic solvent on the analytes' chromatographic parameters such as retention factor, tailing factor and theoretical plates number were all determined. On the basis of k versus ionic liquid concentration in aqueous-organic mobile phase with constant amount of phosphate buffer, retention mechanism was studied. It was established that the presence of organic solvent with low dielectric constant and ionic liquid with both chaotropic ions allows achieving typical Langmuir shape of this relationship. Investigated mobile phase additives are comparable according to efficiency and selectivity towards biogenic amines analysis. However, the sensitivity was found to be better for the eluent system modified with chaotropic salt.

Electrochemically driven actuation of polypyrrole in aqueous sodium hexafluorophosphate (NaPF 6 ) solution has been shown to produce repeated large strains (>6%) at low voltages and with high conductivity, making it one of the most promising electroactive conducting polymers. Little is known about the voltage dependent stiffness of this version of the polymer. This information is important in determining the strain as a function of load. In this paper the complex Young's modulus (storage and loss components) of a hexafluorophosphate-doped polypyrrole film in aqueous NaPF 6 electrolyte at different oxidation states, under various loads and as a function of the frequency of the applied load, is investigated. Uniformity of doping was ensured by allowing enough time to reach steady state charge levels, and the creep during measurements was minimized by using preconditioning cycles. The results of this study show that storage modulus decreases (from 1 GPa to 0.80 GPa) as the polypyrrole oxidation potential increases (from −0.4 V to +0.4 V versus Ag/AgCl reference electrode). The loss modulus, on the other hand, increases from 55 MPa to 80 MPa. An increasing trend in the Young's modulus is also observed with the applied load. The storage modulus increases from 0.65 GPa to 1 GPa by increasing the applied load from 0.2 MPa to 2.5 MPa. The modulus is found to increase with time through the experiment, which may be due to stretch alignment of the polymer. It is also observed that complex Young's modulus increases in proportion to the logarithm of frequency.

In situ UV–vis–NIR and Raman spectra were recorded for three polypyrroles of different compositions established by the specific redox responses of the polymers. Polypyrrole has been electrodeposited in the reversibly oxidized state and concomitantly doped with a small octahedral counterion from aqueous solution of sodium hexafluorophosphate, sodium hexafluorosilicate or sodium hexafluoroaluminate. The dopant anions differ from each other by the charge valency, having at the same time very similar ionic radii. The spectra of the resulting three polypyrroles were found to differ noticeably. An origin of the differences was discussed. The doping level and/or structure of a polymer phase can be invoked to explain the observed spectral changes of the polymer due to the anion dopants. As expected, the most counterion sensitive are the N–H bond and the polaron and bipolaron electronic levels. Polypyrrole doped with hexafluoroaluminate has generated the spectra that differ markedly from that recorded for polypyrrole hexafluorosilicate and polypyrrole hexafluorophosphate. The spectroscopic results are in agreement with earlier findings concerning electrochemical properties of polypyrrole hexafluoroaluminate and polypyrrole hexafluorosilicate. Raman bands that are usually assigned to the ring deformation vibrations were shown to decrease significantly in energy on oxidation of polypyrrole (900–1000 cm −1 ). Raman bands intensities are complex function of laser energy and electrode potentials so their analysis on the anion effects should be performed rather at a constant length of laser excitation.

In this research, a novel microextraction technique based on ionic liquids (ILs) termed in situ solvent formation microextraction (ISFME) is developed. In this method, small amount of sodium hexafluorophosphate (NaPF6, as an ion-pairing agent) was added to the sample solution containing very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4], as hydrophilic IL). A cloudy solution was formed as a result of formation of fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF6]. After centrifuging, the fine droplets of the extractant phase settled to the bottom of the conical-bottom glass centrifuge tube. ISFME is a simple and rapid method for extraction and preconcentration of metal ions from water samples and can be applied for the sample solutions containing very high concentrations of salt. Furthermore, this technique is much safer in comparison with the organic solvent extraction. Reliability of the introduced methodology was evaluated by analyzing water reference material. ISFME was successfully applied to determining mercury (II) in several real water samples. Michler thioketone (TMK) was chosen as a complexing agent. Analysis was carried out using spectrophotometric detection method. Type and amount of IL, temperature and the other parameters were optimized. Under the optimum conditions, the limit of detection (LOD) was 0.7 ng mL−1 and the relative standard deviation (R.S.D.) was 1.94% for 40 ng mL−1 mercury.

Chromatographic behavior of two main classes of neuroleptics, derivatives of phenothiazine and thioxanthene in RP systems modified by anionic additives: sodium perchlorate and sodium hexafluorophosphate possessing chaotropic properties, was examined. Influence of the method of pH lowering (by addition of acids: trifluoroacetic or perchloric or by adding the appropriate concentration of phosphate buffer) and the kind of organic modifier in the mobile phase (methanol, acetonitrile) were estimated. Stability of complexes created between protonated drugs and anions of added salts was evaluated by comparison of their desolvation parameters (K), limiting retention factors for unsolved molecules calculated on the basis of chromatographic data. Experimentally obtained parameters were used in QSAR studies. It appeared that chosen parameters reflect not only physico-chemical properties of analytes but also contain information about the strength of their antipsychotic activity. Multidimensional cluster analysis has been performed. On the basis of the results obtained, it could be concluded that chaotropic systems can generate useful parameters for further QSAR studies.

The aim of this study was to systematically investigate the phenomena affecting the retention behavior of structurally diverse basic drugs in ion-interaction chromatographic systems with chaotropic additives. To this end, the influence of three factors was studied: pH value of the aqueous phase, concentration of sodium hexafluorophosphate, and content of acetonitrile in the mobile phase. Mobile phase pH was found to affect the thermodynamic equilibria in the studied system beyond its effects on the analytes' ionization state. Specifically, increasing pH from 2 to 4 led to longer retention times, even with analytes which remain completely protonated. An explanation for this phenomenon was sought by studying the adsorption behavior of acetonitrile and chaotropic additive onto stationary phase. It was shown that the magnitude of the developed surface potential, which significantly affects retention - increases with pH, and that this can be attributed to the larger surface excess of acetonitrile. To study how analytes' structural properties influence their retention, quantitative structure-retention modeling was performed next. A support vector machine regression model was developed, relating mobile phase constituents and structural descriptors with retention data. While the ETA_EtaP_B_RC and XlogP can be considered as molecular descriptors which describe factors affecting retention in any RP-HPLC system, TDB9p and RDF45p are molecular descriptors which account for spatial arrangement of polarizable atoms and they can clearly relate to analytes' behavior on the stationary phase surface, where the electrostatic potential develops. Complementarity of analytes' structure with that of the electric double layer can be seen as a key factor influencing their retention behavior. Structural diversity of analytes and good predictive capabilities over a range of experimental conditions make the established model a useful tool in predicting retention behavior in the studied chromatographic system.

Ion pair extraction from water into oil in a (ferrocenylmethyl)trimethylammonium bromide (FcTMABr)–sodium hexafluorophosphate (NaPF6) system was studied kinetically by injection and manipulation of a single oil droplet of 10−8 cm3 and electrochemistry of the single droplet contacting a microelectrode. The FcTMA+ concentration extracted into the oil phase at the distribution equilibrium was dependent on the FcTMABr, NaPF6, and NaCl concentrations in the water phase. The initial rate of the ion pair extraction was directly proportional to the FcTMABr concentration in water, while it was independent of the NaPF6 and NaCl concentrations in water. These results indicate that the ion pair extraction rate is governed by the ion transfer of FcTMA+ from water into the droplet, maintaining the electroneutrality in the droplet by the PF6− transfer.

This work explores the coordination chemistry of a bis(pyrrolidone) ether ligand. Pyrrolidones are commercially important functional groups because of the high polarity and hence high hydrophilicity and surface affinity. An array of alkali metal ion complexes of a podand bearing two pendant pyrrolidone functionalities, namely 1-{2-[2-(2-oxo-pyrrolid-1-yl)-ethoxy]-ethyl}-pyrrolid-2-one (1) are reported. Reaction of this ligand with sodium hexafluorophosphate gives two discrete species of formulae [Na(1)2]PF6 (3) and [Na3(H2O)2(μ-1)2](PF6)3 (4), and a coordination polymer {[Na3(μ3-1)3(μ2-1)](PF6)3}n (5). The same reaction in methanol gives a 1 : 1 complex, namely [Na2(μ-1)2(MeOH)2](PF6)2 (6). Use of tetraphenyl borate as a less coordinating counter ion gives [Na2(1)2(H2O)4](BPh4)2 (7) and [Na2(1)4](BPh4)2 (8). Two potassium complexes have also been isolated, a monomer [K(1)2]PF6 (9) and a cyclic tetramer [K4(μ4-H2O)2(μ-1)4](PF6)4 (10). The structures illustrate the highly polar nature of the amide carbonyl moiety within bis(pyrrolidone) ethers with longer interactions to the ether oxygen atom. The zinc complex is also reported and {[ZnCl2(μ-1)]}n (11) exhibits bonding only to the carbonyl moieties. The ether oxygen atom is not necessary for Na(+) complexation as exemplified by the structure of the sodium complex of the analogue 1,3-bis(pyrrolid-2-on-1-yl)butane (2). Reaction of compound 1 with lithium salts results in isolation of the protonated ligand.

The voltammetric reduction of 13- and 16-membered azo- and azoxycrowns is investigated in the presence of alkali metal cations (Na + or K + for 13- or 16-membered azocrowns, respectively). Two types of recognition behaviour have been observed. The first type consists in a positive shift of the redox potential (100–150 mV) upon addition of metal cation (single peak behaviour). The second type consists in the appearance of two separated redox peaks (150–320 mV more positive, two-wave situation). Better electrochemical recognition results were obtained using SW voltammetry with the peak potential for the complex up to 0.32 V (for the azoxycrown derivative) more positive of the original azocrown compound. For azo- and azoxycrowns exhibiting ‘two-wave’ behaviour, the binding enhancement (ratio of binding constants for reduced and neutral species) was 10 2 –10 5 M −1 . For other azocrown compounds with single peak recognition behaviour the binding constants for reduced species were estimated to be 10 4 –10 5 M −1 . In general, K + binds to 16-membered neutral azocrowns more strongly than Na + to 13-membered ones, whilst binding to the anion-radical has the opposite trend.

Modified-cold-induced aggregation microextraction (M-CIAME) was used for determination of gold in saline solutions. It is robust against the much higher concentration of salt (up to 40%). In this method sodium hexafluorophosphate (NaPF6) was added to the sample solution containing Au-TMK complex and a very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4]. Afterward the solution was cooled in an ice bath and a cloudy solution was formed. After centrifuging, the extractant phase was analyzed using a spectrophotometric detection method. Under the optimum conditions, the limit of detection (LOD) was 0.7 ng mL−1 and the relative standard deviation (RSD) was 1.65% for 50 ng mL−1 gold. The method was applied for the determination of trace amount of Au in mineral and seawater with satisfactory results.

This study determined the effect on the electrochemical quartz crystal microbalance's (EQCMs) response of substituting tetrafluoroborate and hexafluorophosphate as counter ions into a poly(vinylferrocene) (PVF) film that had been prepared initially with perchlorate ion as the counter ion in methylene chloride. This PVF+ClO4− film was redox cycled successively in aqueous 0.1 M sodium perchlorate, 0.1 M sodium hexafluorophosphate and 0.1 M sodium tetrafluoroborate solutions. Cyclic voltammetric EQCM experiments determined the changes in film mass and charge during the first and subsequent potential cycles. In all bathing solutions, the total mass change and charge consumed during the first oxidation cycle were larger than in subsequent potential cycles; thereafter there were negligible changes. This is rationalized by the trapping of one or more oxidized forms of PVF produced in the first oxidation cycle, and two possible detailed mechanisms are given. The extent of film oxidation was controlled kinetically, and it changed in the counter ion order tetrafluoroborate>perchlorate>hexafluorophosphate. Less film oxidation occurred at high potential scan rates for all counter ions. At the highest potential scan rate (0.080 V s−1) the amount of water entering the oxidized film from solution was greater in tetrafluoroborate, than in perchlorate, or than in hexafluorophosphate solutions. At slower potential scan rates these differences still existed but were less obvious. Free volume restraints within the film limited the total amount of counter ion and solvent that could be introduced under kinetically controlled conditions.

Thin polypyrrole layers (thickness: 0.2 to 0.3 μm) on gold were studied in aqueous solutions of sodium hexafluoroaluminate, sodium hexafluorosilicate, sodium hexafluorophosphate, and sodium chloride. Polypyrrole was prepared by the electrochemical oxidation of pyrrole in the chloride solution. The systems were examined by cyclic voltammetry and impedance spectroscopy. Transport/redox capacitances, effective charge diffusion coefficients, and charge transfer resistances were determined at several d.c. potentials of the polymer electrodes in a region of the reversible change of the redox/conductivity state of polypyrrole: the redox capacitance values of the oxidized polypyrrole are in the range of (0.7 to 0.9) × 10 3 F cm −3 , and the diffusion coefficients are in the range of 10 −8 to 10 −9 cm 2 s −1 ; the charge transfer resistances are higher for the secondary counterion systems than for the primary counterion system. Contributions from the bulk and interfacial phenomena of the polymer electrode to the electrochemical characteristics were separated and the overall mechanisms of the redox process of polypyrrole in studied electrolyte solutions are postulated. The thin layer polypyrrole electrode was found to respond more slowly to the electrical perturbations when working in the secondary counterion systems. The significance of the polycation-counterion-co-ion interactions in the mechanism of the transport of charges in the polymer electrode is pointed out. A contribution of sodium ions to the charge transport in the polypyrrole-hexafluoroaluminate system is postulated.

The determination of nickel in food samples and well water using cold induced aggregation microextraction combined UV-Vis spectrophotometry is described. The extraction of nickel was performed in the presence of dimethylglyoxime (DMG) as the complexing agent. In this method, sodium hexafluorophosphate (NaPF6) was added to the sample solution containing small amounts of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF6] as extraction solvent. Parameters governing the extraction efficiency such as amount of ionic liquid, pH, temperature and ionic strength were optimized. The applicability of the technique was evaluated by the determination of trace nickel in different types of vegetables. Under the optimum conditions, the calibration curve was linear in the concentration range 8-200 ng mL-1 with correlation coefficient (r²) of 0.9996. The limit of detection (LOD) of 0.47 ng mL-1 and enhancement factor of 186 were obtained for nickel. The relative standard deviation (RSD) was 3.7% for 40 ng L-1 nickel (n = 10). Este trabalho descreve a determinação de níquel em amostras de alimentos e de água usando microextração com agregação induzida à frio e determinação por espectrofotometria UV-Vis. A extração de níquel (II) foi feita na presença de dimetilglioxima (DMG) como agente complexante e hexafluorofosfato de sódio (NaPF6) foi adicionado às amostras contendo pequenas quantidades de 1-hexil-3-metilimidazol hexafluorofosfato [Hmim][PF6] como solvente extrator. Os parâmetros que governam a eficiência da extração, como o líquido iônico, o pH, a temperatura e a força iônica, foram otimizados. O método foi aplicado para a determinação de baixas concentrações de níquel em diferentes tipos de vegetais. Nas condições otimizadas a curva analítica mostrou-se linear no intervalo de concentração de 8-200 ng mL-1 apresentando coeficiente de correlação (r²) de 0,9996. O limite de detecção (LOD) calculado foi de 0,47 ng mL-1 com fator de enriquecimento de 186. O desvio padrão relativo (RSD) foi de 3,7% para 40 ng L-1 de níquel (n = 10).