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This paper describes the development and validation of a sequential injection (SI) anodic stripping voltammetry (ASV) method using the hanging mercury drop electrode for accumulation of the heavy metal cations Cu(II), Pb(II) and Cd(II). The method was applied to wastewater samples after proper acid digestion in open vessels to eliminate matrix effects. For a deposition time of 90 s at the flow rate of 10 μl s−1, the detection limits of the method were 0.06, 0.09 and 0.16 μmol L−1 for Cd, Pb and Cu, respectively. Under these conditions the linear dynamic range was between 0.20 and 9.0 μmol L−1 and the sampling frequency was 30 analyses per hour. The relative standard deviation of the method was 3%( n=7) at the concentration level of 2.0 μmol L−1. The accuracy of the method was evaluated by spiking the samples with known amounts of the metal cations, and by comparison with an independent analytical technique, the inductively coupled plasma atomic emission spectroscopy (ICP-AES). Average recoveries were around of 84%, and the results showed no evidence of systematic errors in comparison to the ICP-AES. [ABSTRACT FROM AUTHOR]

Current research indicates that replacing organic solvents with room-temperature ionic liquids may lead to remarkable improvements in well-known processes. Ionic liquids have already been utilized as alternative solvents in organic synthesis and catalysis, and also in electrochemistry and in separation sciences. Their wide applicability will soon result in their production on an industrial scale. Therefore, analytical methods applicable to various matrices for product control and environmental monitoring will be very much in demand. In this study, the usefulness of π...π interactions between alkylimidazolium and pyridinium cations and the aromatic π...π active moiety of the stationary phase was investigated for the selective separation and analysis of some ionic liquids. With phenyl-bonded phases, very good separations of the cations were achieved. Special attention was paid to the short-chain hydrophilic entities, known to be poorly separated on conventional reversed-phase columns. Further, the nature of the interactions occurring in the system under study was investigated by varying the content of methanol/acetonitrile used as organic modifiers in the mobile phases. The analytical method developed here is simple and reproducible, and its quantitative analytical performance was excellent. The paper also discusses the applicability of the method for monitoring degraded cations of 1-butyl-3-methylimidazolium salts obtained in the Fenton process. [ABSTRACT FROM AUTHOR]

Owing to their favorable properties, ionic liquids have recently gained recognition as possibly environmentally benign solvents. Now among the most promising industrial chemicals, they have already been labeled “green”, but this appellation seems due entirely to their very low vapor pressure. This growing interest in the various applications of ionic liquids will soon result in their presence in the environment. Therefore, reliable analytical tools for the environmental analysis of ionic liquids need to be developed urgently. This paper presents a newly developed analytical procedure for the enrichment of 1-alkyl- and 1-aryl-3-methylimidazolium ionic liquids from water samples. The method is based on cation exchange solid-phase extraction followed by selective elution. Pre-concentrated samples are subjected to high-performance liquid chromatography (HPLC) with an advanced methodology for qualitative and quantitative analysis. The overall procedure was verified by using standard spiked samples of tap water, seawater, and freshwater. [ABSTRACT FROM AUTHOR]

This paper reports the assessment of total arsenic and six arsenic species (As(III), As(V), MMA, DMA, AsBet, AsCol) as contaminants of mussel samples collected around the island of Sardinia and in the Gulf of Venice. The samples were analysed using cation- and anion-exchange HPLC-HG-AFS for speciation and ICP-AES for the total As determination. To ensure the robustness of the routine analytical method, the technique was validated using a candidate reference material, BCR-710, and good agreement was obtained. It was recognised that higher total arsenic concentration in mussels does not necessarily result in higher toxicity of mussel samples. [ABSTRACT FROM AUTHOR]

Hydride generation (HG) coupled to cryotrapping was employed to introduce, separately and with high selectivity, four gaseous arsanes into a direct analysis in real time source for high-resolution mass spectrometry (DART-HR-MS). The arsanes, i.e., arsane (AsH3), methylarsane (CH3AsH2), dimethylarsane ((CH3)2AsH), and trimethylarsane ((CH3)3As), were formed under HG conditions that were close to those typically used for analytical purposes. Arsenic containing ion species formed during ambient ionization in the DART were examined both in the positive and negative ion modes. It was clearly demonstrated that numerous arsenic ion species originated in the DART source that did not accurately reflect their origin. Pronounced oxidation, hydride abstraction, methyl group(s) loss, and formation of oligomer ions complicate the identification of the original species in both modes of detection, leading to potential misinterpretation. Suitability of the use of the DART source for identification of arsenic species in multiphase reaction systems comprising HG is discussed. [ABSTRACT FROM AUTHOR]

In this work, the suitability of atmospheric pressure photoionization (APPI) has been assessed for the determination of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) by gas chromatography–high-resolution mass spectrometry (GC-HRMS). The APPI of target compounds has been tested in both positive and negative ion modes. Under positive ion mode, the analytes generated the molecular ion, which was favoured using dopants that promote charge exchange gas-phase reactions (i.e., benzene), while in negative ion mode, the ion [M−Cl+O]− for PCDFs and dl-PCBs were mainly formed, providing the best results using benzene and diethyl ether as dopants, respectively. Concerning PCDDs, highly chlorinated congeners were mainly ionized by means of the [M−Cl]− ion, whereas [M−Cl+O2]− was the base peak for tetraCDD and [M−Cl+O]− for penta- and hexaCDDs. Method quality parameters, in accordance with the current EU Regulation guidelines for food and feed analysis, showed the good performance of the two GC-APPI-HRMS (Orbitrap) methods since they provided high detection capability (low fg levels), good linearity, and satisfactory precision (RSD% < 9%). In addition, the GC-APPI-HRMS (Orbitrap) methods were validated by analysing selected environmental and feed samples and the results were compared to those obtained using conventional GC-EI-HRMS, demonstrating the good performance in the analysis of the target compounds. Hence, the GC-APPI-HRMS technique can be proposed as alternative to the conventional methods for the determination of PCDD/Fs and dl-PCBs in environmental and feed matrices. [ABSTRACT FROM AUTHOR]

Therapeutic drug monitoring (TDM) is necessary in the clinical management of linezolid to improve its efficacy and reduce the risk of time- and dose-dependent toxicity. A novel and ultrahigh-throughput analytical method for the determination of linezolid in human plasma was developed based on direct analysis in real-time tandem mass spectrometry (DART-MS/MS) without chromatographic separation. After solid-phase extraction with Waters Oasis HLB, the linezolid and internal standard linezolid-d3 were detected by positive ion electrospray ionization followed by multiple reaction monitoring (MRM) of the transition at m/z 338.1 → 296.2 and 341.2 → 297.3, respectively. The use of DART-MS obviates the need for chromatographic separation and allowed determination of linezolid in a total run time of only 24 s per sample. The method was linear in the concentration range 0.20–25 μg mL−1 with intraday and interday precision <14.5% and accuracy ranging from −3.85% to 12.7%. The method was successfully applied to a pharmacokinetic study of linezolid in healthy male volunteers after oral administration of a 600 mg tablet. DART-MS/MS provides a rapid and sensitive method for the determination of linezolid that does not require chromatographic separation. It is eminently suitable to meet the high-throughput challenge of clinical TDM. [ABSTRACT FROM AUTHOR]

Quantification of ultra-trace analytes in complex biological samples using micro-solid-phase extraction followed by direct detection with internal extractive electrospray ionization mass spectrometry (μSPE–iEESI–MS) was demonstrated. 1-Hydroxypyrene (1-OHP) and papaverine at attomole levels in human raw urine samples were analyzed under negative and positive ion detection mode, respectively. The μSPE was simply prepared by packing a disposable syringe filter with octadecyl carbon chain (C18)-bonded micro silica particles, which were then treated as the "bulk sample" after the analytes were efficiently enriched by the C18 particles. Under the optimized experimental conditions, the analytes were readily eluted by isopropanol/water (80/20, V/V) at a high voltage of ± 4.0 kV, producing analyte ions under ambient conditions. The limit of detection (LOD) was 0.02 pg/L (9.2 amol) for 1-hydroxypyrene and 0.02 pg/L (5.9 amol) for papaverine. The acceptable linearity (R2 > 0.99), signal stability (RSD ≤ 10.7%), spike recoveries (91–95%), and comparable results for real urine samples were also achieved, opening up possibilities for quantitative analysis of trace compounds (at attomole levels) in complex bio-samples. [ABSTRACT FROM AUTHOR]

The existing Air Quality Directive 2008/50/EC establishes within the European Union (EU) member states limit values for fine air particulate matter (PM2.5) including the possibility to discount natural sources of pollution when assessing compliance with the legislation. In proving this, EU member states shall determine, amongst others, the rural background concentration of some anions (Cl−, NO3− and SO42−) and cations (Na+, NH4+, K+, Ca2+ and Mg2+). To deliver reliable data and to comply with the data quality objectives of the legislation, environmental control laboratories should use certified reference materials (CRMs) to validate or verify the performance of their analytical methods. Since no CRMs for anions and cations in PM2.5 are presently available, we present the commutability issues encountered during the first attempt to develop such a material. We demonstrate that a dust, collected in a road tunnel and previously used for the production of two CRMs of a PM10-like material, does not behave as an authentic fine particulate matter collected according to EN12341:2014 when measured by an established method proposed by the European Committee for Standardization (CEN/TR 16269:2011). The water-soluble fractions of SO42−, NH4+, K+, Ca2+ and Mg2+ in a PM2.5-like candidate CRM produced from that road tunnel dust are only fully extracted after 3 h of sonication and not after 30 min, as stated in the method. Moreover, we found that the particle size of the test material influenced the extraction yield of K+, Ca2+ and Mg2+, suggesting that these ionic species were incorporated in the core of the particles and inaccessible to the extraction procedure. These particular features make the material unsuitable for the measurements of ions with the CEN method. The difference in the extraction time can be seen as a commutability issue and the candidate CRM should be considered as not commutable with routine samples. This demonstrates that commutability studies should not only be considered for clinical CRMs, but also for inorganic CRMs when they are intended to be used to quantify operationally defined analytes. [ABSTRACT FROM AUTHOR]

In this study, four hydrophilic ionic liquids (ILs) containing 1-alkyl-3-methylimidazolim cation and either salicylate or chloride anions were synthetized and studied as new task-specific ionic liquids (TSILs) suitable for aqueous biphasic system (ABS) formation and selective one-step extraction of copper(II). TSILs are designed so that the anion is responsible for forming the complex with metal(II) and preventing hydrolysis of metal cations at very strong alkaline pH, whereas the cation is responsible for selective extraction of metal(II)-salicylate complexes. It was found that 1-butyl-3-methylimidazolium salicylate could be used for selective extraction of Cu(II) in the presence of Zn(II), Cd(II), and Pb(II) at very alkaline solution without metal hydroxide formation. It was assumed that formation of metal(II)-salicylate complexes prevents the hydrolysis of the metal ions in alkaline solutions. The determined stability constants for Cu(II)-salicylate complexes, where salicylate was derived from different ionic liquids, indicated that there was no significant influence of the cation of the ionic liquid on the stability of the complexes. The ABS based on 1-butyl-3-methylimidazolium salicylate has been applied as the sample preparation step prior to voltammetric determination of Cu(II). The effect of volume of aqueous sample and IL and extraction time were investigated and optimum extraction conditions were determined. The obtained detection limits were 8 ng dm. The optimized method was applied for the determination of Cu(II) in tap water, wastewater, and urine. The study indicated that application of the ABS based on 1-butyl-3-methylimidazolium salicylate ionic liquid could be successfully applied as the sample preparation method for the determination of Cu(II) from various environmental samples. [ABSTRACT FROM AUTHOR]

A reference material of a PM-like atmospheric dust material has been prepared using a newly developed method. It is intended to certify values for the mass fraction of SO , NO , Cl (anions) and Na, K, NH , Ca, Mg (cations) in this material. A successful route for the preparation of the candidate reference material is described alongside with two alternative approaches that were abandoned. First, a PM-like suspension was allowed to stand for 72 h. Next, 90% of the volume was siphoned off. The suspension was spiked with appropriate levels of the desired ions just prior to drop-wise shock-freezing in liquid nitrogen. Finally, freeze drying of the resulting ice kernels took place. In using this approach, it was possible to produce about 500 g of PM-like material with appropriate characteristics. Fine dust in 150-mg portions was filled into vials under an inert atmosphere. The final candidate material approaches the EN12341 standard of a PM-material containing the ions mentioned in Directive 2008/50/EC of the European Union. The material should be analysed using the CEN/TR 16269:2011 method for anions and cations in PM collected on filters. The method described here is a relatively rapid means to obtain large quantities of PM. With access to smaller freeze dryers, still 5 to 10 g per freeze-drying cycle can be obtained. Access to such quantities of PM-like material could potentially be used for different kinds of experiments when performing research in this field. [ABSTRACT FROM AUTHOR]

Porcine relaxin is a 6 kDa peptide hormone of pregnancy with important physiological and pharmacological effects. It contains a number of analogs of which porcine relaxin B29 is one of the most important. To support the development of porcine relaxin B29 as a new drug, we established an UPLC-MS/MS method for its quantitation in dog plasma. Sample preparation by protein precipitation and ion exchange solid phase extraction was followed by UPLC on an XBridge™ BEH300 C18 column at 40 °C in a run time of only 5.5 min. Detection was performed on a Qtrap 6500 mass spectrometer using ESI in the positive ion mode with MRM of the transitions at m/z 831.7 [M+7H] → 505.4 and m/z 1162.4 [M+5H] → 226 for pRLX B29 and internal standard (recombinant human insulin), respectively. The method was linear over the concentration range 30-2000 ng/mL with no matrix effects. Intra- and inter-day precisions were < 15% with accuracies in the range 98.8-100.6%. The method was successfully applied to a pharmacokinetic study in beagle dogs after administration of a 0.15 mg/kg intravenous dose. [ABSTRACT FROM AUTHOR]

Chemical cross-linking/mass spectrometry (MS) is gradually developing into a routine method to investigate protein conformation and to decipher protein interaction networks. To increase identification rates of the frequently low abundant cross-linked products in LC/MS/MS experiments, fast and reliable sample preparation protocols are indispensable. We present simplified solid phase extraction methods using C/SCX StageTips and mixed-mode OASIS MCX cartridges for a single-step enrichment of cross-linked products prior to LC/MS/MS analysis. Our improved protocols result in 3.5 to 4.6 times higher numbers of cross-link identifications for the model protein bovine serum albumin compared to non-processed samples. [ABSTRACT FROM AUTHOR]

Most luminescent biosensors for heavy metals are fluorescent and rely on intensity measurements, whereas a few are ratiometric and rely on spectral changes. Bioluminescent biosensors for heavy metals are less common. Firefly luciferases have been coupled to responsive promoters for mercury and arsenium, and used as light on biosensors. Firefly luciferase bioluminescence spectrum is naturally sensitive to heavy metal cations such as zinc and mercury and to pH. Although pH sensitivity of firefly luciferases was shown to be useful for ratiometric estimation of intracellular pH, its potential use for ratiometric estimation of heavy metals was never considered. Using the yellow-emitting Macrolampis sp2 firefly luciferase and site-directed mutagenesis, we show that the residues H310 and E354 constitute two critical sites for metal sensitivity that can be engineered to increase sensitivity to zinc, nickel, and mercury. A linear relationship between cation concentration and the ratio of bioluminescence intensities at 550 and 610 nm allowed, for the first time, the ratiometric estimation of heavy metals concentrations down to 0.10 mM, demonstrating the potential applicability of firefly luciferases as enzymatic and intracellular ratiometric metal biosensors. [ABSTRACT FROM AUTHOR]

Fiber organic electrochemical transistors (FECTs) based on polypyrrole and nanofibers have been prepared for the first time. FECTs exhibited excellent electrical performances, on/off ratios up to 10 and low applied voltages below 2 V. The ion sensitivity behavior of the fiber organic electrochemical transistors was investigated. It exhibited that the transfer curve of FECTs shifted to lower gate voltage with increasing cations concentration, the sensitivity reached to 446 μA/dec in the 10-10 M Pb concentration range. The ion selective properties of the FECTs have also been systematically studied for the detection of potassium, calcium, aluminum, and lead ions. The devices with different cations showed great difference in response curves. It was suitable for selectively monitoring Pb with respect to other cations. The results indicated FECTs were very effective for electrochemical sensing of lead ion, which opened a promising perspective for wearable electronics in healthcare and biological application. [ABSTRACT FROM AUTHOR]

A passive sampler for determining the time-weighted average total ammonia (i.e. molecular ammonia and the ammonium cation) concentration ( C) in freshwaters, which incorporated a polymer inclusion membrane (PIM) as a semi-permeable barrier separating the aqueous source solution from the receiving solution (i.e. 0.8 mol L HCl), was developed for the first time. The PIM was composed of dinonylnaphthalene sulfonic acid (DNNS) as a carrier, poly (vinyl chloride) (PVC) as a base polymer and 1-tetradecanol as a modifier. Its optimal composition was found to be 35 wt% commercial DNNS, 55 wt% PVC and 10 wt% 1-tetradecanol. The effect of environmental variables such as the water matrix, pH and temperature were also studied using synthetic freshwaters. The passive sampler was calibrated under laboratory conditions using synthetic freshwaters and exhibited a linear response within the concentration range 0.59-2.8 mg L NH (0.46-2.1 mg N L) at 20 °C. The performance of the sampler was further investigated under field conditions over 7 days. A strong correlation between spot sampling and passive sampling was achieved, thus providing a proof-of-concept for the passive sampler for reliably measuring the C of total ammonia in freshwaters, which can be used as an indicator in tracking sources of faecal contamination in stormwater drains. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In Campylobacterales and related ε-proteobacteria with N-linked glycosylation (NLG) pathways, free oligosaccharides (fOS) are released into the periplasmic space from lipid-linked precursors by the bacterial oligosaccharyltransferase (PglB). This hydrolysis results in the same molecular structure as the oligosaccharide that is transferred to a protein to be glycosylated. This allowed for the general elucidation of the fOS-branched structures and monosaccharides from a number of species using standard enrichment and mass spectrometry methods. To aid characterization of fOS, hydrazide chemistry has often been used for chemical modification of the reducing part of oligosaccharides resulting in better selectivity and sensitivity in mass spectrometry; however, the removal of the unreacted reagents used for the modification often causes the loss of the sample. Here, we develop a more robust method for fOS purification and characterize glycostructures using complementary tandem mass spectrometry (MS/MS) analysis. A cationic cysteine hydrazide derivative was synthesized to selectively isolate fOS from periplasmic fractions of bacteria. The cysteine hydrazide nicotinamide ( Cyhn) probe possesses both thiol and cationic moieties. The former enables reversible conjugation to a thiol-activated solid support, while the latter improves the ionization signal during MS analysis. This enrichment was validated on the well-studied Campylobacter jejuni by identifying fOS from the periplasmic extracts. Using complementary MS/MS analysis, we approximated data of a known structure of the fOS from Campylobacter concisus. This versatile enrichment technique allows for the exploration of a diversity of protein glycosylation pathways. [ABSTRACT FROM AUTHOR]

The interest in compound-specific isotope analysis for product authenticity control and source differentiation in environmental sciences has grown rapidly during the last decade. However, the isotopic analysis of very polar analytes is a challenging task due to the lack of suitable chromatographic separation techniques which can be used coupled to isotope ratio mass spectrometry. In this work, we present the first method to measure carbon isotope compositions of the widely applied herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) by liquid chromatography coupled to isotope ratio mass spectrometry. We demonstrate that this analysis can be carried out either in cation exchange or in reversed-phase separation modes. The reversed-phase separation yields a better performance in terms of resolution compared with the cation exchange method. The measurement of commercial glyphosate herbicide samples show its principal applicability and reveals a wide range of δC values between −24 and −34 ‰ for different manufacturers. The absolute minimum amounts required to perform a precise and accurate determination of carbon isotope compositions of glyphosate and AMPA were in the sub-microgram range. The method proposed is sensitive enough to further perform the experiments that are necessary to better understand the carbon isotope fractionation associated to the natural degradation of glyphosate into AMPA. Furthermore, it can be used for contaminant source allocation and product authenticity as well. [ABSTRACT FROM AUTHOR]

In the present work a sensitive and accurate method by ion chromatography and conductimetric detection has been developed for the determination of biogenic amines in food samples at microgram per kilogram levels. The optimized extraction procedure of trimethylamine, triethylamine, putrescine, cadaverine, histamine, agmatine, spermidine, and spermine from real samples, as well as the separation conditions based on a multilinear gradient elution with methanesulfonic acid and the use of a weak ionic exchange column, have provided excellent results in terms of resolution and separation efficiency. Extended calibration curves (up to 200 mg/kg, r > 0.9995) were obtained for all the analyzed compounds. The method gave detection limits in the range 23-65 μg/kg and quantification limits in spiked blank real samples in the range 65-198 μg/kg. Recovery values ranged from 82 to 103 %, and for all amines, a good repeatability was obtained with precision levels in the range 0.03-0.32 % ( n = 4). The feasibility and potential of the method were tested by the analysis of real samples, such as tinned tuna fish, anchovies, cheese, wine, olives, and salami. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A study on the interactions between CHHg and some S, N and O donor ligands (2-mercaptopropanoic acid (thiolactic acid (H TLA)), 3-mercaptopropanoic acid (H MPA), 2-mercaptosuccinic acid (thiomalic acid (H TMA)), d,l-penicillamine (H PSH), l-cysteine (H CYS), glutathione (H GSH), N, N′-bis(3-aminopropyl)-1-4-diaminobutane (spermine ( SPER)), 1,2,3,4,5,6-benzenehexacarboxylic acid (mellitic acid (H MLT)) and ethylenediaminetetraacetic acid (H EDTA)) is reported. The speciation models in aqueous solution and the possible structures of the complexes formed are discussed on the basis of potentiometric, calorimetric, UV spectrophotometric and electrospray mass spectrometric results. For the CHHg-S donor ligand systems, the formation of ML and MLH complex species is observed, together with a diprotonated MLH species for CYS, PSH and GSH and the mixed hydrolytic one ML(OH) for TLA and MPA. The dependence of the stability on ionic strength and on temperature is also analysed. In the other CHHg-L systems (L = MLT, SPER and EDTA), ML, MLH and MLH complex species are formed, together with the MLH species for SPER, the mixed hydrolytic ML(OH) one for SPER and EDTA, and the ML for EDTA only. On the basis of the speciation models proposed, the sequestering ability of the ligands towards methylmercury(II) cation is evaluated. All S donor ligands show a good sequestering power (at 10 mol L level, in the pH range 4 to 8) following the trend MPA < PSH < GSH < TLA < CYS < TMA, while significantly lower is the sequestering ability of MLT, SPER and EDTA (at 10-10 mol L level, in the pH range 4 to 8). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The feasibility of using gold electrodes modified with short-chain ssDNA oligonucleotides for determination of uranyl cation is examined. Interaction between UO and proposed recognition layer was studied by means of voltammetric and quartz crystal microbalance measurements. It was postulated that ssDNA recognition layer functions via strong binding of UO to phosphate DNA backbone. The methylene blue was used as a redox marker for analytical signal generation. Biosensor response was based on the difference in electrochemical signal before and after subjecting it to sample containing uranyl ion. The lower detection limit of 30 nmol L for UO was observed for a sample incubation time of 60 min. Proposed ssDNA-modified electrodes demonstrated good selectivity towards UO against common metal cations, with only Pb and Ca showing considerable interfering effect. [ABSTRACT FROM AUTHOR]

Capillary ion electrophoresis-capacitively coupled contactless conductivity detection (CIE-C4D) with a polyvinyl alcohol chemically coated capillary (PVA capillary) was used to analyze inorganic cations (Na, K, NH, Mg, and Ca) commonly found in human saliva. The PVA capillary, which was made by our laboratory, minimized electro-osmotic flow in the wide pH range of the background electrolyte (BGE), and the PVA layer adsorbed to capillary wall did not affect the conductimetric background level. In this study, we determined an optimized BGE of 30 mM lactic acid/histidine plus 3 mM 18-crown-6 for the CIE-C4D system using the PVA capillary, which could simultaneously improve the separation of Mg and Ca from Na and that of K from NH. This system obtained highly reproducible separation of cations in human saliva samples within 8 min at 20 kV without deprotonation. The quantifiability of cations in human saliva samples on the CIE-C4D system was demonstrated through identification by ion chromatography with satisfactory results. [ABSTRACT FROM AUTHOR]

The potential of an in situ photopolymerized hexylacrylate-based monolithic stationary phase-bearing sulfonic acid groups was investigated by studying the chromatographic retention of small structurally related peptides (enkephalins) by nano-LC. Several retention mechanisms were highlighted. First, a reverse-phase chromatographic behavior toward neutral solutes due to hexylacrylate-moieties was demonstrated. Second, an evaluation of the influences of buffer pH suggested the involvement of a cation-exchange mechanism due to the presence of 2-acrylamido-2-methyl-1-propanesulfonic acid. This cation-exchange phenomenon was confirmed by the clear influence of Na concentration in the mobile phase on peptide retention. [ABSTRACT FROM AUTHOR]

In the study, a fast and selective method based on magnetic separation has been developed for the extraction of nicotine from human plasma using magnetic strong cation exchange (MSCX) resins as adsorbent. MSCX resins were prepared using hydrophobic FeO magnetite as magnetically susceptible component, styrene and acrylic acid as polymeric matrix components, and acetyl sulfonate as the sulfonation agent. The extraction procedure was carried out in a single step by stirring the mixture of diluted plasma sample and MSCX resins in the vortex for 5 min. Then, the resins with adsorbed nicotine were separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of nicotine such as the amount of MSCX resins, pH value of the extraction solvent, extraction time, and washing and eluting conditions were optimized. The nicotine eluted from the resins was determined by liquid chromatography-tandem mass spectrometry. The calibration curve obtained by analyzing matrix-matched standards shows excellent linear relationship ( r = 0.9998) in the concentration range of 10-2,500 ng mL. The limit of detection and quantification obtained are 2.9 and 9.7 ng mL, respectively. The relative standard deviations of intra- and inter-day obtained are in the range of 1.9-6.9% and 2.5-7.8% with the recoveries ranging from 78.7% to 99.1%. The proposed method was successfully applied to determine nicotine in human plasma phlebotomized from ten male smokers. Nicotine was detectable with the contents ranging from 44.4 to 221.9 ng mL in five samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

class of stationary phases for packed column supercritical fluid chromatography (SFC), referred to as immobilized ionic liquids (IILs), is evaluated with a two-part study: (1) a cation effect study and (2) an anion effect study. The former study compares six different IILs (tripropylphosphonium, tributylphosphonium, methyl-imidazolium, benzyl-imidazolium, triphenylphosphonium, and 4,4′-bipyridyl) on silica gel, evaluating their performance in SFC with all the counter anions as trifluoroacetate (TFA). In the latter study, the stationary phase consisted of a bonded tributylphosphonium cation and varying counter anions (acetate, TFA, chloride, NTf, and perchlorate). An order of retentivity was established for the cation effect study, and the favorable behavior of phosphonium-based stationary phases is reported for the first time in SFC. It was not possible to always assign a retentivity order for the anion effect study, but wide variations in selectivity are noted for different anions showing the tunable nature of this class of stationary phases. [ABSTRACT FROM AUTHOR]

The opioid tilidine is a prodrug which is hepatically metabolized to active nortilidine and bisnortilidine. Due to the increasing abuse of tilidine by drug users and the lack of a specific immunoassay, we developed an analytical method for the quantification of tilidine, nortilidine, and bisnortilidine in urine suitable for screening. In a following step, this method was used to establish data on excretion kinetics of the substances in order to evaluate the time window of detection after a single oral dose of tilidine/naloxone and also was applied to authentic urine samples from correctional facilities. Urine samples were mixed with internal standard solution and extracted on a weak cation exchanger at pH 6 using a Symbiosis Pico system. The chromatographic separation was achieved within a 3.5-min run time on a Phenylhexyl column (50 × 2.0 mm, 5 μm) via gradient elution (methanol and 0.2% formic acid) at a flow rate of 0.50 mL/min. The ESI-MS/MS was performed on a QTrap 3,200 in positive multiple reaction monitoring mode using two mass transitions per analyte. Validating the method resulted in a lower limit of quantification of 1.0 μg/L followed by a linear calibration range to 100 μg/L for each analyte ( r > 0.99). The analytical method allowed the detection of a single dose of a commercially available tilidine solution up to 7 days after administration. Using this highly sensitive method, 55 of 3,665 urine samples were tested positive. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma-mass spectrometry coupled with cation exchange matrix separation has been optimised for the direct determination of platinum group element (PGE) and trace element emissions from a diesel engine car. After matrix separation method detection limits of 1.6 ng g for Pd, 0.4 ng g for Rh and 4.3 ng g for Pt were achieved, the method was validated against the certified reference material BCR 723, urban road dust. The test vehicle was fitted with new and aged catalytic converters with and without diesel particulate filters (DPF). Samples were collected after three consecutive New European Driving Cycle (NEDC) of the particulate and 'soluble' phases using a home-made sampler optimised for trace element analysis. Emission factors for the PGEs ranged from 0.021 ng km for Rh to 70.5 ng km for Pt; when a DPF was fitted, the emission factors for the PGEs actually used in the catalysts dropped by up to 97% (for Pt). Trace element emission factors were found to drop by a maximum of 92% for Ni to a minimum of 18% for Y when a DPF was fitted; a new DPF was also found to cause a reduction of up to 86% in the emission of particulate matter. [ABSTRACT FROM AUTHOR]

Plasma protein adsorption is regarded as a key factor in the in vivo organ distribution of intravenously administered drug carriers, and strongly depends on vector surface characteristics. The present study aimed to characterize the 'protein corona' absorbed onto DC-Chol-DOPE cationic liposomes. This system was chosen because it is one of the most efficient and widely used non-viral formulations in vitro and a potential candidate for in vivo transfection of genetic material. After incubation of human plasma with cationic liposomes, nanoparticle-protein complex was separated from plasma by centrifugation. An integrated approach based on protein separation by one-dimensional 12% polyacrylamide gel electrophoresis followed by the automated HPLC-Chip technology coupled to a high-resolution mass spectrometer was employed for protein corona characterization. Thirty gel lanes, approximately 2 mm, were cut, digested and analyzed by HPLC-MS/MS. Fifty-eight human plasma proteins adsorbed onto DC-Chol-DOPE cationic liposomes were identified. The knowledge of the interactions of proteins with liposomes can be exploited for future controlled design of colloidal drug carriers and possibly in the controlled creation of biocompatible surfaces of other devices that come into contact with proteins in body fluids. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Nucleotides are a class of molecules that play an essential role in biological systems. A new method has been developed in the detection of nucleotides. These molecules can exist as monomers or constituents of oligomers and polymers. As such, they carry from one to several negative charges. In this study, different cationic ion-pairing reagents were used to complex with each of the 28 nucleotide monomers and nucleotide containing compounds. By using this method, this discrete set of anions was able to be detected in the positive-mode electrospray ionization mass spectrometry, as positively charged complexes. Tandem mass spectrometry experiments were also completed on the ion-pairing reagents that performed the best in the single ion monitoring (SIM) ion mode, and the sensitivity was lowered even further for most of the anions. Limits of detection for compounds such as thymidine diphosphate were improved as much as 100 times compared to the positive SIM mode, and 750 times when compared to the negative mode. A few nucleotides did not show a significant increase in sensitivity when analyzed in the positive ion mode, but in general the new method developed herein resulted in a much greater sensitivity than traditional detection in the negative mode. [ABSTRACT FROM AUTHOR]

The enrichment and processing of proteomic samples prior to multi-dimensional chromatography remain a challenge in ‘gel-free’ proteomics. We previously reported the development of a microfluidic device called the “proteomic reactor” that relied on enriching proteins by using strong cation exchange (SCX) followed by trypsin digestion in an interstitial volume as little as 50 nL. Here, we report a novel proteomic reactor that is based on polymeric strong anion exchange (SAX) material to analyse proteomic samples. We also compare the performance of the SAX proteomic reactor to our previously reported SCX proteomic reactor for analysing complex yeast proteomes. Our results indicate that the SAX protein reactor preferentially identifies more acidic peptides and proteins compared to the SCX reactor. We show that the SAX and SCX reactors are complementary and that their combination increases the number of unique peptides and proteins identified by 50%. Furthermore, we show that the number of protein identified can be increased further by up to 40% using different proteolytic enzymes on the proteomic reactor. [ABSTRACT FROM AUTHOR]

Methyl-capped poly(ethylene oxide) moieties were chemically bonded to silica gel using an amine-reactive modification reagent and evaluated as the stationary phase for ion chromatography. In this work, primary amino groups of an aminopropylsilica packing material were reacted with methyl-PEO12-NHS ester (succinimidyl-{[ N-methyl]-dodecaethyleneglycol} ester) in phosphate buffer (pH 7.0) at room temperature. The prepared poly(ethylene oxide)-bonded stationary was evaluated for the separation of inorganic anions, and the retention behavior of inorganic anions on the prepared stationary phase was examined. The elution order of the investigated anions was the same as that observed in common ion chromatography. Both cations and anions of the eluent affected the retention of the analyte anions. Ion exchange was involved for the retention of analyte anions, although the present stationary phase does not possess any discrete ion-exchange sites. The stationary phase was applied to the separation of trace anions contained in tap water and a rock salt. [ABSTRACT FROM AUTHOR]

A recently reported chiral strong cation exchanger (cSCX) type stationary phase was investigated for the LC separation of a series of Cinchona alkaloids and synthetic derivatives thereof to test its usefulness as alternative methodology for the separation of those important pharmaceuticals. The cSCX column-packing material was qualitatively compared on the one hand against a commercially available non-enantioselective SCX-material, PolySulfoethyl-A, and, on the other hand, against a modern C18 reversed-phase stationary phase which is commonly employed for Cinchona alkaloid analysis. Both SCX columns showed no pronounced peak-tailing phenomena which typically hamper Cinchona alkaloid RP analysis and require specific optimization. Thus, the cSCX-based assay provided new feasibilities for the separation of the Cinchona alkaloids in polar organic mode as opposed to conventional reversed-phase methodologies. In particular, a method for the simultaneous determination of eight Cinchona alkaloids (quinine, quinidine, cinchonine, cinchonidine, and their corresponding dihydro analogs) using the cSCX column in HPLC has been developed and exemplarily applied to impurity profiling of a commercial alkaloid sample. Furthermore, both SCX materials allowed successful separation of C9-epi and 10,11-didehydro derivatives from their respective educts in an application in synthetic Cinchona alkaloid chemistry. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A series of surface-confined ionic liquid (SCIL) stationary phases for high-performance liquid chromatography were synthesized in-house. The synthesized phases were characterized by the linear solvation energy relationship (LSER) method to determine the effect of residual linking ligands and the role of the cation and the anion on retention. Statistical analysis was utilized to determine whether the system coefficients returned from multiple linear regression analysis of chromatographic retention data for a set of 28 neutral aromatic probe solutes were significantly different. Examination of the energetics of retention via κ− κ plots agrees with the results obtained from the LSER analysis. Residual linking ligands were determined to contribute reversed-phase-type retention character to the chromatographic system. Furthermore, retention on the SCIL phases was observed to be more profoundly affected by the identity of the anion than by that of the cation. [ABSTRACT FROM AUTHOR]

A rapid and simple method was developed for the determination of free amino acids (AAs) released from cyanobacteria. The procedure involves trapping of AAs from the centrifuged cyanobacterial culture fluid on a cation-exchange resin, their release together with the resin by direct treatment with the reaction medium, followed by immediate derivatization with a corresponding chloroformate. The extractive alkylation transfers the analytes into an organic phase, an aliquot of which is subjected to GC analysis. Identification and quantification of AAs was performed by GC/MS and GC/FID, respectively, using propyl chloroformate (PCF) as the derivatization reagent. For chiral analysis, the cyanobacteria extracts were treated with 2,2,3,3,3-pentafluoropropyl chloroformate (PFPCF) to create more volatile analytes. Separation of the AA enantiomers was accomplished on a Chirasil-Val capillary column and the D/ L enantiomeric ratios were determined. AAs of cyanobacteria are considered to be important for the assessment of energy flow in an aquatic food web, nutrition value of cyanobacteria in a food web and for cell–cell communication within cyanobacteria. The highest levels of AAs were found in the summer period at the beginning of the season (July). In the September and October samples, the amount of AAs was lower, the number of D-AAs decreased and the D/ L ratio was higher than in the July sample. Based on the obtained results it can be assumed that young populations excrete AAs in higher concentrations and a different composition compared to actively growing populations. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel method for rapid separation and determination of ascorbic acid and uric acid has been developed with a polycation-modified poly(dimethylsiloxane) (PDMS) microchip under a negative-separation electric field. Just by flushing the microchip with aqueous solutions of the polycations, poly(allylamine) hydrochloride, poly(diallyldimethylammonium chloride) or chitosan could be stably coated on the PDMS microchannel surface, which resulted in a reversed electroosmotic flow and thus the rapid and efficient separation of the two substrates. Factors influencing the separation, including polycation category, buffer solution, detection potential and separation voltage, were investigated and optimized. The cheapness, rapid analysis speed and the successful analysis of human urine make this microsystem attractive for application in clinics. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new capillary electrochromatography (CEC) column for the simultaneous analysis of cationic, neutral, and anionic compounds using CEC-ESI-MS is described. Three different silica monolith columns were prepared by changing the poly(ethylene glycol) (PEG) contents for comparison of the separation property of these columns. Different separation programs were used for the simultaneous separation of different charged compounds under the same conditions. The column prepared with 80 mg of PEG separated typical compounds within 15 min using 1 M formic acid as the electrolyte. The analytes migrated in the order of cationic, neutral, and anionic compounds, which means that the migration order was mainly determined by the electrophoresis. The hydrodynamic flow by pressure from the inlet side was significant for a stable analysis to be achieved. The effect of the composition of the sheath liquid was also examined. All analytes (14 amino acids, thiourea, urea, citric acid, and ATP) were detectable when 1% acetic acid in 50% (v/v) methanol was used as the sheath liquid. [ABSTRACT FROM AUTHOR]

An improvement of the peak parking technique is described for the serial determination of cations (Na+, % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaaru% avP1wzZbItLDhis9wBH5gaiuaacaWFobGaa8hsamaaDaaaleaacaWF% 0aaabaGaa83kaaaaaaa!4042! $$NH^{ + }_{4} $$ , K+, Mg2+, and Ca2+) and anions (Cl−, % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaaru% avP1wzZbItLDhis9wBH5gaiuaacaWFtbGaa83tamaaDaaaleaacaWF% 0aaabaGaa8Nmaiaa-1caaaaaaa!4103! $$SO^{{2 - }}_{4} $$ , and % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaaru% avP1wzZbItLDhis9wBH5gaiuaacaWFobGaa83tamaaDaaaleaacaWF% ZaaabaGaa8xlaaaaaaa!404A! $$NO^{ - }_{3} $$ ) using a single pump, a single eluent and a single detector. The present system used commercially-available unmodified cation exchange and anion exchange columns, which were attached to each switching valve. When 1.75 mM 5-sulfosalicylic acid was used as the eluent, serial separation of the above cations and anions was achieved in less than 20 min. The proposed ion chromatographic method was successfully applied to the serial determination of cations and anions in tap water and river water samples. The limits of detection at S/N=3 for an injection of 20 μl were 16–68 ppb (μg/l) for cations and 15–28 ppb for anions. [ABSTRACT FROM AUTHOR]

A comprehensive two-dimensional capillary liquid chromatographic (2D LC) method has been established for determination of neuropeptides in rat brain tissue. Rats were exposed to different levels of stress before sacrificing and the aim of this study was to design a powerful separation and detection technique capable of characterizing differences between cerebral neuropeptide expression as a function of stress level. Rat brain samples were homogenized and subjected to clean-up by solid-phase extraction (SPE) on both a reversed-phase (C18) and a weak cation-exchange (CBA) cartridge. The samples were divided in two fractions (A and B) depending on retention on the CBA column. Subsequently, 50 µL of the sample were injected on to a strong cation exchanger (SCX) at a mobile phase pH of 3, which enabled preconcentration of positively charged compounds. The trapped compounds were eluted using step gradients of ammonium formate in water-ACN (90:10,v/v). Before enrichment in the second dimension, the eluate from the first dimension was diluted with water containing 0.1% TFA. The compounds eluting from the first dimension were trapped in the second dimension using a dual precolumn system consisting of two short capillary columns packed with Kromasil C18, 10 µm particles. Subsequently, the trapped compounds were backflushed on to a 10 cm long, 320 µm I.D. analytical column packed with Kromasil C18 3.5 µm particles, on which they were efficiently separated. Detection was performed using an ion-trap mass spectrometer (ITMS) in both the MS and the MS-MS mode. Comparison of base-peak chromatograms (BPC) from MS analysis of stressed and non-stressed rats clearly revealed several differences in neuropeptide expression. The MS-MS data obtained combined with Mascot software were employed for peptide identification. [ABSTRACT FROM AUTHOR]

An ion chromatography method is described for the simultaneous determination of anions (Cl-, NO, and SO) and cations (Na+, NH, K+, Mg2+, and Ca2+) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min. [ABSTRACT FROM AUTHOR]

A capillary electrophoresis method with direct ultraviolet detection was developed for the analysis of organotin species. Despite the fact that direct detection of organotin compounds by ultraviolet absorption is difficult because most organotins possess poor chromophoric properties, the application of low wavelength (?=200 nm) and mixed organic-aqueous media enabled a significant enhancement in sensitivity. A mixed organic-aqueous system (10% methanol/40% acetonitrile/50% H2O) containing acetic acid and tetrabutylammonium perchlorate formed the basis for rapid, efficient and sensitive determinations of organotin cations such as tripropyltin, tributyltin, triphenyltin and diphenyltin. The concentration limits of detection (LOD) for the four organotin compounds were in the range of 0.4-14 µM, comparable to that obtained with the most sensitive indirect UV method reported until now, and took advantage of a stable baseline, a symmetric peak shape and an absence of disturbing system peaks. The relative standard deviations (n=7) for the relative peak time and peak area were 0.44-0.77 and 4.8-5.8%, respectively. In addition to sensitivity enhancements, the use of organic-aqueous systems instead of pure aqueous media resulted in improved selectivity and efficiency of separations. [ABSTRACT FROM AUTHOR]

A new type of silver composite electrode was examined, prepared from silver, graphite powder, and methacrylate resin. The effects of the presence of various cations (cadmium, copper, bismuth, thallium), anions (chlorides), surface-active substances (Triton X-100), and oxygen on the anodic-stripping voltammetric determination of lead were studied. It was found that the effect of underpotential deposition at the composite electrode differs from that produced at a metallic silver electrode, mainly at low concentrations of the deposited metal. The use of this type of silver composite electrode in differential pulse anodic-stripping voltammetry enables direct determination of lead in natural water samples without elimination of surface-active substances (LOD about 3 μg L-1). [ABSTRACT FROM AUTHOR]

Amino acids Trp, Gly, Ala, Leu are extracted efficiently from aqueous solution at pH 1.5–4.0 (Lys and Arg at pH 1.5–5.5) into the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) with dicyclohexano-18-crown-6 (CE). The most hydrophilic amino acids such as Gly are extracted as efficiently as the less hydrophilic (92–96%). The influence of pH, amino acid and crown ether concentration, volume ratio of aqueous and organic phases, and presence of some cations on amino acid recovery were studied. The ratio of amino acid to crown ether in the extracted species is 1:1 for cationic Trp, Leu, Ala, and Gly and to 1:2 for dicationic Arg and Lys. This ionic liquid extraction system was used successfully for the recovery of amino acids from pharmaceutical samples and fermentation broth, and was followed by fluorimetric determination. [ABSTRACT FROM AUTHOR]

Electrospray ionization mass spectrometry (ESI-MS) coupled to a microreactor is an excellent tool for the investigation of reactions in solution. Here, we report the first results of our investigations into preparatively interesting electron-transfer-initiated chain reactions in solution which proceed via radical cations as reactive intermediates. The tris(p-bromophenyl)aminium hexachloroantimonate (1)-mediated [2+2] cycloaddition of trans-anethole (2) to give 1,2-bis(4-methoxyphenyl)-3,4-dimethylcyclobutane (3) was investigated. The reaction proceeds as a radical cation chain reaction via transient intermediates 2&ding6C;+ and 3&ding6C;+ that could be detected and characterized unambiguously directly in the reacting solution by ESI-MS/MS. The identity of the intermediates was confirmed by comparison with authentic MS/MS spectra of 2&ding6C;+ and 3&ding6C;+ obtained by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). In addition, substrate and product can be monitored easily in the reacting solution by APCI-MS. [ABSTRACT FROM AUTHOR]

The monodisperse, macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads were synthesized by a single-step swelling and polymerization method. Based on this media, a weak cation exchange (WCX) stationary phase for HPLC was synthesized by a new chemically modified method. The prepared resin has advantages for biopolymer separation, high column efficiency, low column backpressure, high protein mass recovery, and good resolution for proteins. The measured bioactivity recovery for lysozyme was 98±5%. The dynamic protein loading capacity of the WCX packings was 17.3 mg g-1. The experimental results show that the synthesized WCX resin has very weak hydrophobicity. [ABSTRACT FROM AUTHOR]

Due to the better understanding of the processes taking place at the surface of the stationary phases, the number of ion-exchange materials for ion chromatography (IC) has increased tremendously over recent years. As a result, the multitude of commercially available columns today with their different selectivities for anion and cation chromatography is almost confusing. Hence, the aim of this article is to describe the different principles determining selectivity and ion-exchange capacity and to classify the various ion-exchange materials accordingly. To ensure a fair comparison of these columns, the selectivity differences are illustrated by showing separations of standards rather than individual samples. [ABSTRACT FROM AUTHOR]