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As an alternative to classical tetrahydroborate (BH₄⁻), chemical vapour generation (CVG) can also be attained using alkylation-based derivatization chemistries. In paragraphs 4.2 and 4.3, two classes of alkylating reagents are presented: the tetraalkylborates (BR₄⁻) and the trialkyloxonium (R₃O⁺) salts. The first have been applied for metal speciation, whereas the latter have found applications for headspace GC-MS analysis of several inorganic anions. Properties and reactivity of these two chemicals are presented under typical analytical conditions, i.e. conversion of trace amount of analyte with a large excess of reagent in an aqueous medium. We also report possible interferences, side reactions and ways to tackle them. Most notably, these alkylation chemistries allow the separation of the derivative from the matrix providing for clean sample introduction and very competitive detection limits. In most applications, potential matrix effects and other perturbation of the analytical signal have been addressed by the use of isotope dilution quantitation. Finally, paragraph 4.4 is a brief discussion about Grignard reagents used in metal speciation. Such applications of Grignard chemistry typically require injection of a solvent extract in a GC system, therefore they cannot be properly classified as CVG techniques. However, Grignard chemistry applied to metal speciation is closely related to the tetraalkylborates and we retained useful to mention it in this chapter.

The determination of inorganic anions in uranium ore concentrates (UOCs) is useful to nuclear forensics for establishing the provenance of sample materials. In this collaborative study, quantitation of inorganic anions was carried out on three UOC reference materials from the National Research Council Canada: UCLO-1 (https://doi.org/10.4224/crm.2020.uclo-1), UCHI-1 (https://doi.org/10.4224/crm.2020.uchi-1), and UPER-1 (https://doi.org/10.4224/crm.2020.uper-1). The analytes were extracted into water and characterized by ion chromatography with combined standard uncertainties (uc) between 1.6 and 11%. The highest contributor to uc was homogeneity. Sulfate was the most abundant anion (2000–12,000 mg/kg SO42−). Other anions were in the 15–500 mg/kg range.

Trace element determination and speciation at the part-per-trillion level (ng L−1) are challenging for most elemental detectors and become harder when complex samples are analyzed. Solid phase microextraction (SPME) can provide matrix separation along with analyte preconcentration which are essential steps to obtain interference free and measurable signals for quantitation of inorganics at these low levels. Fiber SPME was introduced first and it is still an indispensable tool for Hg and Sn speciation, and for the analysis of volatile organometallic metabolites. In recent years, several other SPME approaches have been employed for inorganic analysis, including in-tube SPME, capillary microextraction, hollow fiber SPME, micropipette tip SPME, SPME on a stir bar, SPME on a microfluidic device and dispersive SPME. A significant advancement in coatings has closely followed the developments of novel SPME formats: at this time a number of nanocomposites and polymers were available enabling the microextraction of most transition metal ions, directly in solution, without the need for derivatization.

In this study we demonstrate that the method of standard additions can provide unreliable results in chemical analysis when the linear calibration model is forced to fit the data. A well designed standard addition experiment can still yield results biased by 10% when the analyst relies only on the linear model. Recently, the Joint Committee for Guides in Metrology (GUM-6) has emphasized the need to address the uncertainty inherent to the choice of measurement models and here we show how model averaging can provide a practical way to account for model uncertainty in the method of standard additions.

We would like to invite you to participate in the Analytical Challenge, a series of puzzles to entertain and challenge our readers. This special feature of “Analytical and Bioanalytical Chemistry” has established itself as a truly unique quiz series, with a new scientific puzzle published every three months. Readers can access the complete collection of published problems with their solutions on the ABC homepage at http://www.springer.com/abc. Test your knowledge and tease your wits in diverse areas of analytical and bioanalytical chemistry by viewing this collection. In the present challenge, bisphenol A is the topic. And please note that there is a prize to be won (a Springer book of your choice up to a value of €100,- given to one winner selected randomly). Please read on...

The aqueous-phase reaction of dimethylarsinc acid (DMAs(V)) with NaBH4 (THB) was studied under non-analytical conditions (1000 mu g/mL As, 0.1 M HCl, 1% NaBH4) with the aim of identifying intermediates and reaction products. The use of direct analysis in real time (DART) with high-resolution mass spectrometry (HRMS), in combination with two different chemical vapor generation systems, allowed the identification of some species not detected by GC-MS such as Me2As-AsMe-AsMe(2)and the arsonium species [Me3As-AsMe2](+) and [Me2As-AsMe2-AsMe2](+). Many other methylated species of arsenic containing up to four arsenic atoms have been observed. Unfortunately, the oxidation mechanism that took place in the DART source interfered with the identification of some of those species formed in solution following THB reduction. The species identified by DART-HRMS, together with those previously identified by GC-MS (Me2AsH, Me2AsOH, Me3As, Me3AsO, Me2AsAsMeH, Me2AsAsMe2, and Me2As-O-AsMe2), enabled the formulation of hypotheses on the possible reaction pathways and revealed an aqueous-phase reactivity of DMAs(V) which could not be explained on the basis of current knowledge.

Analytical chemists resort to derivatization for improving the detection performance of certain categories of analytes. Within this context, alkylation reactions are regarded as an important asset for many methods based on GC-MS and LC-MS. Trialkyloxonium tetrafluoroborates (R[Formula: see text][BF4]-) are powerful alkylating agents with ionic liquid properties: they are nonvolatile salts soluble in water which are easier and safer to handle with respect to common alkylating agents like diazomethane. R[Formula: see text][BF4]- can perform the alkylation in both organic and aqueous media at pH conditions ranging from acidic to alkaline. Recent analytical applications of trialkyloxonium derivatizations include the high-precision determination of inorganic anions in complex matrices, the qualitative confirmation of chemical warfare agent degradation products in soils, the profiling of carboxylic acids in urine, and the detection of protein post-translational modifications induced by carbon dioxide. The common denominator for all methods presented can be found in the simplicity of the alkylation protocol which, in most of the cases, requires a single step addition of the reagent directly to the sample. Graphical Abstract Alkylation with trialkyloxonium salts for GC-MS and LC-MS analysis.

Photochemical generation of volatile fluoromethane in a dilute acetic acid medium is demonstrated. Radical halogen atom transfer (XAT) from an intermediate Cu–F transition metal fluorocomplex to abundant ˙CH3 generated by UV homolysis of acetic acid, rather than direct formation of free ˙F radicals, is hypothesized as being the synthetic route. The presence of Cu(II) is indispensable for CH3F formation. GC-MS identification of the gaseous products released from a photolysed 2% (v/v) solution of acetic acid containing 60 mg L−1 added Cu(II) as a sensitizer confirms synthesis of CH3F as the volatile fluorinated species, which is not detectable in the absence of Cu(II). Reaction efficiency remains unchanged whether the sample medium is exposed to V-UV radiation (185 nm) or germicidal UV-C radiation (primarily 254 nm and longer wavelengths) from the source. Experimental optimization of generation conditions (pH, irradiation time, UV wavelength, acetic acid concentration, metal ion sensitizer and concentration) was undertaken with a view to elucidation of mechanism as well as maximizing synthetic yield. Although the low yield (

Natural water certified reference materials (CRMs) are mostly available in a liquid form, and they are produced starting from suitable environmental samples. Many precautions are usually needed to avoid biological or physical degradation, including filtration, acidification, and sterilization. In this study, the drawbacks associated with liquid-based seawater CRMs were tackled by developing a salt-based seawater proxy for nutrients that could be reconstituted in water solution just before use. Phosphate, silicate, and nitrate were chosen as target analytes. Sea salt mimicking the composition of seawater was spiked with an aqueous solution of the analytes and homogenized using a high-energy planetary ball mill (uhom https://doi.org/10.4224/crm.2022.salt-1) demonstrated good short- and long-term stability for nutrients. When the SALT-1 was reconstituted in water at the 4.0% w/w level, the resulting solution had similar properties with respect to typical seawater in terms of major constituents (± 20%), trace metals, density (1.023 g/mL), pH (8.8–9.0), and optical properties relevant to the photometric characterization. Phosphate and silicate were quantified by photometry (molybdenum blue method, batch mode), whereas nitrate was quantified by isotope dilution GC−MS (uchar w/w salt level, the nutrient amount concentration was w(phosphate, PO43−) = 1.615 ± 0.030 μmol/L, w(silicate as SiO2) = 8.89 ± 0.31 μmol/L, and w(nitrate, NO3−) = 18.98 ± 0.45 μmol/L at the 95% confidence (k = 2). Overall, the SALT-1 CRM exhibits similar nutrient profile and general analytical characteristics as the MOOS-3 CRM. However, the SALT-1 has much reduced preparation, storage, and distribution cost, likely much better long-term stability, and it could enable the production of lower cost and more accessible seawater reference materials. Graphical abstract

The volatile synthetic products of photochemical vapor generation (PVG) of Os(IV) and W(VI) have been confirmed by GC-MS. Osmium tetroxide has been identified as the species generated from an oxidizing medium of dilute nitric acid, and tungsten hexacarbonyl is produced during PVG from a reducing medium of formic acid. Attempts to ascertain the PVG products of Os and Ru generated in high yield from reducing media (i.e., acetic and formic acids, respectively in the presence of metal sensitizers) were unsuccessful, possibly due to their instability or reactivity with the GC support, and thus remain to be identified using more direct approaches such as Direct Analysis in Real Time (DART)-MS. The mass spectra for OsO₄ and W(CO)₆, reported here for the first time, serve to aid the further development/refinement of mechanistic models for PVG.

Optimisation and validation of a novel isotope dilution gas chromatography mass spectrometry (GC–MS) method for determination of inorganic chloride (Cl⁻) in crude oils is presented. The use of stable isotope dilution calibration approach decreases losses and biases and it is considered a higher order measurement approach. Samples were diluted with a 1:1 blend of isopropyl alcohol : toluene with 5% water, mixed with ³⁷Cl⁻ internal standard, water extracted and derivatized with triethyloxonium tetrafluoroborate at room temperature. This reagent converted Cl⁻ into stable ethyl chloride (EtCl) which was detected by headspace GC–MS. A limit of quantitation of 100 µg kg⁻¹ and limit of detection of 30 µg kg⁻¹ were observed in crude oil samples when initial dilution was not required. The performance of this novel method was compared with combustion ion chromatography, ion chromatography with conductivity detection after microwave-induced combustion, and ASTM D3230 method on a set of medium and heavy crude oil samples. Despite the challenges of the measurement, a reasonable level of agreement was observed among methods over the range of 0.38 ± 0.02 to 993 ± 103 mg kg⁻¹ of Cl⁻. Presented headspace GC–MS method proved to be suitable for analysis of all types of crude oils samples with an excellent reproducibility (RSD < 6%) and high sample throughput (7 min GC–MS run time).

A high-precision isotope dilution GC–MS method was employed for the determination of nitrate in processed vegetables. The samples were extracted in water, derivatized with triethyloxonium tetrafluoroborate and analyzed by headspace GC–MS (15 samples/h). The method was applied to estimate the effect of drying on the content of nitrate in vegetables. The absolute amount of nitrate in a spinach sample before and after drying did not change even when the material was baked at 105 °C. Elevated levels of nitrate were found in commercial vegetable powders where the nitrate mass fraction exceed the percent level: 1.2–2.3% NO3− was found in spinach powders, 1.3–1.6% in kale powders, and 1.4% in a beetroot powder. The likely reduction of the antioxidant properties seen in vegetable powders along with their high nitrate content suggest the need to study the risk of endogenous N-nitrosation associated with these products.

The aqueous-phase reaction of dimethylarsinc acid (DMAs(V)) with NaBH

International audience; Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.

The high toxicity of cyanide, along with its widespread industrial use, has fuelled interest in the development of analytical methods for its determination in complex matrices. In this study, we propose a novel approach for the measurement of total cyanide in soil samples based on single-step derivatization with pentafluorobenzyl bromide (F₅Bn−Br) followed by quantitation with gas chromatography mass spectrometry in negative chemical ionization mode. The reaction between CN⁻ and F₅Bn−Br resulted in the identification of several derivatives such as F₅Bn−CN, (F₅Bn)(F₅Ph)CH−CN, and (F₅Bn)₂(F₅Ph)C−CN. The relative proportion between such compounds was dependent on experimental conditions. When a 100 μL aliquot of an alkaline-aqueous extract was reacted with 700 μL of 1.3% F₅Bn−Br in acetone, the tri-alkylated derivative was the most abundant. In such conditions a detection limit of 0.5 ng/g of CN⁻ was attained. Soil samples were initially spiked with an alkaline solution of K¹³C¹⁵N internal standard and suspended in 7.5% aqueous NaOH. Determination of total cyanide was achieved by digestion of the alkaline extract with H₃PO₄ to produce HCN which was then trapped in 0.1% NaOH in a sealed double vial system, followed by reaction with F₅Bn−Br. Isotope dilution calibration was chosen for quantitation, and the validity of the novel method was demonstrated by analysis of soil Certified Reference Materials (CRMs) and by spike recovery tests., yes

A sensitive and accurate method is developed for the simultaneous ultra-trace determination of tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), methylmercury (MeHg) and inorganic mercury (iHg) in waters including seawater by dynamic headspace in-tube extraction (dHS-ITEX) and GC-ICPMS detection. Quantitation of TBT, DBT, iHg and MeHg was achieved by isotope dilution mass spectrometry using 117Sn-enriched TBT and DBT, 201Hg-enriched iHg and enriched Me198Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution at the same time using natural abundance TBT, DBT, iHg and MeHg primary standards by exactly matching the analyte and enriched spikes. Quantitation of MBT was realized by standard addition calibration with 117Sn-enriched DBT serving as the internal standard. The proposed method achieved detection limits of 0.06, 0.08 and 1.1 pg g−1 (as Sn) for TBT, DBT and MBT and 0.08 and 0.4 pg g−1 (as Hg) for MeHg and iHg, respectively. Validation of the proposed method was demonstrated by quantitative spike recoveries of 94–105% at 5 to 50 pg g−1 levels achieved in drinking water, river water and seawater, demonstrating the accuracy of the method. The obtained detection limits are sufficiently low to perform measurements in support of the Water Framework Directive. The developed method was applied for the determination of butyltins, iHg and MeHg in drinking water (AQUA-1), river water (SLRS-6) and seawater (CASS-6 and NASS-7) samples. Values of 0.124 ± 0.041 and 0.157 ± 0.060 pg g−1 (1SD, n = 4) for MeHg in CASS-6 and NASS-7 and values of 1.74 ± 0.61, 22.15 ± 0.13, and 31.42 ± 0.30 pg g−1 (1SD, n = 4) for iHg in SLRS-6, CASS-6 and NASS-7 were obtained, respectively. A value of 2.27 ± 0.45 pg g−1 as Sn for MBT was detected in NASS-7 seawater, whereas other butyltins were below the detection limits in the waters.

A novel method for the determination of nitrite and nitrate in meat products is presented. The samples were ground and extracted in hot water with the presence of ¹⁵NO₂⁻ and ¹⁵NO₃⁻ internal standards. The solution was buffered with sodium bicarbonate and reacted with triethyloxonium tetrafluoroborate to convert nitrite and nitrate into EtNO₂ and EtONO₂. Such derivatives could be detected by headspace GC/MS in positive chemical ionisation mode with 0.05 µg g⁻¹ NO₂⁻ and 1.0 µg g⁻¹ NO₃⁻ LOD. The method was used for NO₂⁻ and NO₃⁻ quantitation in the 0.5-300 and 2.5-300 µg g⁻¹ ranges. The method was applied for the analysis of fifteen meat products. Despite minimal sample preparation, the headspace sampling ensured a clean chromatography for over 135 analyses (throughput ten samples per hour). The proposed method offers selective GC/MS detection combined with high-precision isotope dilution calibration, it is suitable for metrological applications and can support regulations on meat safety (European Commission, 2011).

Characterization of mercury contamination in petroleum hydrocarbons (PHs) is necessary in order to assess the risk of corrosion of the processing infrastructure and to assess the level of human exposure to Hg-containing substances. Here we present an accurate and sensitive method for determination of Hg species in PHs by headspace sampling with a possibility of on-line pre-concentration using in-tube extraction (ITEX) combined with gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS) analysis. Mercury species were first extracted from the PHs matrix into an aqueous phase via dithizone chelation and subsequently converted with sodium tetrapropyl borate into volatile derivatives which could be sampled from the headspace prior to GC-ICP-MS analysis. For concentrations in the ng kg–1 range, the on-line ITEX method was applied, whereas the μg kg–1 range was accessible by static headspace. Quantitation of Hg species was carried out by a double isotope dilution method, with quantitative recoveries of methylmercury (MeHg, average 101 ± 5%) and inorganic mercury (InHg, average 97 ± 7%) by direct headspace injection. Average recoveries of Hg spikes after on-line ITEX pre-concentration were 95 ± 3% for MeHg and 98 ± 8% for InHg. The detection limits for MeHg and InHg were 428 and 46 ng kg–1 when measured by static headspace, and 2.4 ng kg–1 and 1.7 ng kg–1 by on-line ITEX pre-concentration. The accuracy of the pre-concentration method was demonstrated by analysis of a crude oil standard reference material (NIST 2722) certified for InHg.

The recent interest in the determination of selenocyanate (SeCN⁻) in wastewater systems has spurred the development of analytical methods for its determination at the ultratrace level. Since most of the current procedures require complex and costly instrumental configurations, we have developed a simple and rapid gas chromatography tandem mass spectrometry (GC/MS/MS) method able to detect SeCN⁻ in water samples with a LOD of 0.1 ng/g Se. A 1 mL volume of aqueous sample was buffered with sodium bicarbonate and treated with triethyloxonium tetrafluoroborate for conversion of the analyte into volatile EtSeCN. The derivatization yield was higher than 90%, and it could tolerate concentrations of chloride or sulfate up to 2%. The EtSeCN was extracted in chloroform and could be detected in electron ionization and also in negative chemical ionization mode with a further gain in signal-to-noise ratio by a factor of 2. The method was applied for the analysis of natural waters with quantitation of SeCN⁻ in the low ng/g region. The Se¹³C¹⁵N⁻ internal standard could be used for isotope dilution. Quantitative spike recoveries of 1 ng/g Se were obtained from seawater and river water, and 1 ng/g Se could be quantified within a standard uncertainty of 15%.

A high-precision exact-matching quadruple isotope dilution method (ID4MS) was employed for the quantitation of nitrate in an air-dried spinach powder Certified Reference Material (CRM). The analyte was extracted in hot water following addition of 15NO[Formula: see text] internal standard. The blend was then treated with sulfamic acid to remove nitrite and with triethyloxonium tetrafluoroborate to promote aqueous conversion of nitrate into volatile EtONO2. The derivative was analyzed by headspace GC-MS with 3-min elution time. The method performance was validated with a series of tests which demonstrated adequate selectivity and ruggedness. This method supported the development of novel SPIN-1 CRM giving a modest contribution to its uncertainty (uchar = 0.85%). With respect to previous attempts, the SPIN-1 was proven stable, homogeneous (uhom = 0.44%), and suitable for spinach monitoring under EU regulations. On dried basis, the nitrate content of SPIN-1 was found to be 22.53 ± 0.43 mg/g (Uc = 1.9%, k = 2). The material was also used in an inter-laboratory study where four laboratories employed a total of ten measurement methods. Graphical Abstract SPIN-1 Certified Reference Material for nitrate in spinach powder.

A novel isotope dilution method for the analysis of inorganic chloride in fuel oil matrix is presented. The samples were diluted by isopropyl alcohol:toluene, mixed with 37Cl− internal standard and reacted with triethyloxonium tetrafluoroborate at room temperature. This reagent promoted conversion of Cl− into stable ethyl chloride (EtCl) which was selectively detected by headspace GC–MS/MS with no matrix effects. A limit of detection of 0.2 mg kg−1 Cl− was obtained in fuel oil. The method was tested on the NIST SRM 1634c (trace elements in residual fuel oil) and validated through a series of robustness tests. Over 18 days, the variation in the signal response was less than 10% and the RSD for quantitative isotope dilution results was below 3%. Overall, the method is fast, simple and allows robust quantitation of inorganic chloride directly in the non-aqueous media.

Isotopic internal standards are widely employed for accurate quantitation in chemical and clinical analysis. Although this type of internal standardization – also referred to as isotope dilution mass spectrometry (IDMS) – has calibration curves that are inherently nonlinear, most analysts fit linear model to calibration data and use R2 as a metric to decide whether the calibration curves are reasonably linear. We show that this approximation can lead to significant errors even in cases when R2 > 0.99. We present a simulation approach – available as supplementary Excel spreadsheet – able to predict the IDMS calibration curves and estimate the errors that are introduced by the linear simplification. The simulation does not require experimental input and was validated using examples to cover cases of large, intermediate, and unnoticeable nonlinear calibration curves. This spreadsheet can be a valuable tool to plan IDMS experiments and to assess if a linear model is fit for purpose.

Volatile Cu species were on-line generated by photochemical reduction in a formic acid medium utilizing a unique flow-through photochemical reactor. Digests of biological samples in 18% formic were introduced to the photochemical vapor generation (PVG) reactor under conditions wherein copper-containing species were initially retained on the reactor wall following a purge of the line with air and desorbed in the presence of a plug of 60% formic acid to yield volatile species which were transported to a gas–liquid separator and introduced to multi-collector inductively coupled plasma spectrometry (MC-ICPMS). Sensitivity of the proposed method could be further improved if a sample solution is repeatedly introduced using several cycles comprising loading and drying steps. However, the unstable volatile Cu species generated by PVG together with the early release of Cu during drying step resulted in a poor measurement precision of near 30% (n = 4, RSD) and a non-linear correlation between the signal intensity and the Cu2 + concentration. Despite the above shortcomings, the accurate and precise determination of Cu concentrations in biological samples was achieved by applying isotope dilution (ID) calibration. A method detection limit of 8 ng g− 1 normalized to a nominal test mass of 0.25 g of sample was obtained based on ID quantification. Method validation was demonstrated by analysis of three biological certified reference materials of TORT-3, SRM 1566b and DOLT-5 with satisfying results. Concentrations of 490.8 ± 0.6, 71.88 ± 0.06 and 34.95 ± 0.04 μg g− 1 (1SD, n = 4) with precisions of 0.12, 0.08 and 0.13% RSD for Cu were obtained in TORT-3, SRM 1566b and DOLT-5, respectively, in good agreement with certified values.

Isotope dilution is among the most accurate quantitation approaches in chemical analysis. This calibration method is often employed using a plurality of mathematical formulations. While most analysts find the calibration curve approach most appealing, there is a lack of rigorous general procedures involving calibration curves in isotope dilution and analysts resort to empirical polynomial calibration functions. In this contribution we discuss the adoption of regression analysis, commonly known as least squares methods, to solve isotope dilution equations of varied complexity. This manuscript introduces general regression-based methods to isotope dilution applicable to all known variants of classical isotope dilution known to date, including the fusion of the isotope dilution and standard additions methods.

The determination of the mass fractions of bromide, sulfate, and lead as well as the isotopic composition of the lead (expressed as the molar mass and the amount fractions of all four stable lead isotopes) in an aqueous solution of sodium chloride with a mass fraction of 0.15 g/g was the subject of this comparison. Even though the mass fractions ranged from 3 μg/g (bromide) to 50 ng/g (lead), almost all results reported agreed with the according KCRVs. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

[object Object]In order to elucidate controversial results emerging in chemical vapor generation (CVG) for trace element determination, we conducted a series of experiments devoted to the identification of intermediates formed by acid hydrolysis of amine-boranes. For the first time, direct analysis in real time coupled with high-resolution mass spectrometry (DART-Orbitrap) was applied for detection of this class of compounds. Mass spectra of both solid amine-boranes and their aqueous solutions (pH ~ 8, no hydrolysis) were acquired for understanding their ionization pathway. Mass spectra of aqueous solutions of t-BuNH2·BH3 and Me2NH·BH3 were acquired under conditions that are employed in CVG (0.017-4.0 mol L-1 HCl, 0.167-0.2 mol L-1 borane reagent). The results disclose a reactivity driven by pH of amine-boranes undergoing hydrolysis. At low acidity, the hydrolysis proceeds according to the currently accepted displacement mechanisms (i.e., R3N·BH3 + H3O+ -> R3NH+ + H2OBH3). At higher acidity, N-tert-butyl, cyclotriborazane, and bis(dimethylamino)boronium were identified, for the first time, during the hydrolysis of t-BuNH2·BH3 and Me2NH·BH3, respectively. Formation of these intermediates was ascribed to a hydrolysis pathway starting with the ionization of the amine-borane, (i.e., R3N·BH3 + H3O+ -> [(H2O)R3NBH2] + + H2). The new evidence explains the anomalous behavior observed in CVG by amine-borane derivatization, and updates the currently accepted mechanisms for the acid hydrolysis of amine-boranes

Thiocyanate is a heme peroxidase substrate that scavenges oxidants produced during inflammation and regulates host defense. In cystic fibrosis (CF) patients, increased airway thiocyanate levels are associated with improved lung function. Research on airway thiocyanate is limited, however, because convenient non-invasive airway sampling methods, such as exhaled breath condensate (EBC), yield low concentrations that are difficult to detect with available assays. In the present study, we developed a method for the determination of thiocyanate in dilute samples using isotope dilution headspace gas chromatography-coupled high-resolution, accurate-mass mass spectrometry (GC-HRMS). The method reliably quantified as little as 4 pmol thiocyanate in EBC and could detect even lower amounts. We successfully measured thiocyanate in EBC from seven healthy donors, with a mean ± SD of 27 ± 16 nM and a median inter-assay coefficient of variation of 10.4% over six months. The method was applied to other biological fluids (plasma from the same visit as EBC donation; bronchoalveolar lavage fluid [BALF] from infants with CF; and healthy adult mouse BALF), giving reliable quantification of samples ranging from 10 nM to 100 µM. Thiocyanate concentrations in fluids besides EBC were (from lowest to highest): 0.73 ± 0.39 µM in BALF of healthy adult mice (n = 6); 1.4 ± 1.4 µM in BALF from infants with CF (n = 24); 46 ± 22 µM in the plasma of adult volunteers (n = 7). These results demonstrate the utility of this new method for clinical determination of thiocyanate in EBC and other biological fluids.

In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN) in seawater combining high-precision isotope dilution GC–MS with persulfate digestion. A 2 mL sample aliquot was digested with an alkaline solution of persulfate to convert nitrogen containing compounds to nitrate. Digested samples were spiked with 15NO3− internal standard and treated with aqueous triethyloxonium to convert the analyte into volatile EtONO2. This derivative was readily separated from the matrix under gaseous form and could be sampled from the headspace before GC–MS analysis. The resulting chromatograms showed a stable flat baseline with EtONO2 as the only eluting peak (retention time 2.75 min on a DB 5.625 column). Such an approach provides specificity and obviates the shortcomings of current detection methods employed to analyze seawater samples after digestion with persulfate. In negative chemical ionization mode, the method reached a detection limit of 0.5 μmol/kg TDN (7 ng/g N) and could be applied to quantify seawater samples with 1–25 μmol/kg TDN. On the upper end of the range, quantitation could be repeated within 1%, whereas on a 6 μmol/kg TDN sample repeatability was 2.3% on eight measurements. The method was employed in two proficiency testing exercises providing results in agreement with consensus values. We investigated the impact of reagent blank and we implemented a blank-matching optimal design to account for such contribution. Finally, we performed a study on the yield of persulfate oxidation for organic and inorganic nitrogen compounds typically present in seawater. Whilst nitrite and ammonium are fully converted to nitrate, more complex organic molecules showed recoveries varying from 70% to 100%.

We would like to invite you to participate in the Analytical Challenge, a series of puzzles to entertain and challenge our readers. This special feature of “Analytical and Bioanalytical Chemistry” has established itself as a truly unique quiz series, with a new scientific puzzle published every three months.

Isotope-based quantitation is routinely employed in chemical measurements. Whereas most analysts seek for methods with linear theoretical response functions, a unique feature that distinguishes isotope dilution from many other analytical methods is the inherent possibility for a nonlinear theoretical response curve. Most implementations of isotope dilution calibration today either eliminate the nonlinearity by employing internal standards with markedly different molecular weight or they employ empirical polynomial fits. Here we show that the exact curvature of any isotope dilution curve can be obtained from three-parameter rational function, y = f(q) = (a0 + a1q)/(1 + a2q), known as the Padé[1,1] approximant. The use of this function allows eliminating an unnecessary source of error in isotope dilution analysis when faced with nonlinear calibration curves. In addition, fitting with Padé model can be done using linear least squares.

Photochemical vapor generation (PVG) provides an alternative to chemical vapor generation techniques but suffers severe interference in the presence of oxidizing species, notably nitrate and nitrite. Although the mechanism is not completely understood, scavenging of photogenerated free electrons and hydrogen radicals by NO2− and NO3− likely plays a role in terminating analyte reduction reactions which lead to hydridization, carbonylation or alkylation of analytes. In this study, several strategies for the elimination of nitrate and nitrite from samples prior to PVG were examined. Since the Se(IV)-acetic acid PVG system proved to be extremely sensitive to low levels of these oxidants, wherein 50% loss of generation efficiency is realized at [NO3−] > 2.5 mM, it was used as a test case. To this end, a number of practical approaches to the reduction of nitrate and nitrite were evaluated, including: utilizing sulfamic acid, hydrazine sulfate, sodium thiosulfate and V(III), as well as removal by photo-reduction and quantitative precipitation by nitron. Whereas none of these approaches could be implemented with impunity, a methodology based on UV photolysis of a basic solution containing 2% hydrazine sulfate provided high NO3− removal efficiencies. Residual NO2− was quantitatively eliminated by addition of sulfamic acid to the acidified solution, allowing efficient generation of volatile Se(CH3)2 species. The methodology was tested by application to Certified Reference Material SLRS-3 (river water, acidified to pH 1.6 with nitric acid), achieving 83 ± 2% Se(IV) spike recoveries using PVG sample introduction coupled with ICP-MS for detection, illustrating effective control over interferences and recovery of Se(IV).

Cyanocobalamin (CNCbl) is an active form of vitamin B12, commonly employed for the preparation of multivitamin supplements and fortified food. In this study, we present a novel analytical method for its determination based on stable isotope dilution liquid chromatography electrospray tandem mass spectrometry (ID LC-MS/MS). Isotopically enriched 13C15NCbl was synthesized in-house and used as internal standard. The method was validated using NIST SRM 3280 multivitamin reference material and by comparison with an independent methodology based on LC-ICPMS. The proposed method provided a detection limit of 57 pg/g and could be applied for the determination of trace level of CNCbl in multivitamin supplements with a relative standard uncertainty better than 3%. The novel ID LC-MS/MS is a primary ratio method that could become a reference for CNCbl determination in multivitamins and food supplements. The method was applied for the characterization of two NRC multivitamin tablet Certified Reference Material (CRM) candidates, VITA-1 and VITB-1 whose CNCbl levels were quantified as 2.64 ± 0.09 and 1.75 ± 0.12 μg/g, respectively.

Download PDF Advanced Elsevier Analytica Chimica Acta Volume 980, 8 August 2017, Pages 33-40 Analytica Chimica Acta Rapid determination of nitrate in vegetables by gas chromatography mass spectrometry Author links open overlay panelBeatriceCampanellaaMassimoOnoraEneaPaglianob https://doi.org/10.1016/j.aca.2017.04.053 Get rights and content Highlights o Novel isotope dilution GC-MS method for high-precision determination of nitrate in vegetable. o Stable calibration plot for more than one month. o Simple: based on aqueous chemistry at room temperature. o Rapid: only 1.8 min of chromatography. o Cost effective: less than 0.5 USD of chemicals per analysis. Abstract In this study we present a novel isotope dilution gas chromatography method for the determination of nitrate in vegetables. The analyte was extracted in water at 70?C and mixed with 15N isotopically enriched nitrate internal standard. The sample was centrifuged and the supernatant reacted with sulfamic acid for removal of nitrite, and with triethyloxonium tetrafluoroborate for converting nitrate into volatile EtONO2. This simple aqueous chemistry allowed for separation of analyte from sample matrix in the form of a gaseous derivative which could be sampled in the headspace before GC-MS analysis. This key-feature of the method made possible the collection of clean chromatograms within an elution time of only 1.8 min. Detection of EtONO2 could be performed using electron impact ionization with a standard GC-MS setup. The method was optimized and validated for the analysis of nitrate in fresh vegetables in the 10-10,000 ?g/g range with a detection limit of 2 ?g/g. Due to the use of primary isotope dilution quantitation, traceable results of high-precision were attained.

The combination of isotope dilution and mass spectrometry has become an ubiquitous tool of chemical analysis. Often perceived as one of the most accurate methods of chemical analysis, it is not without shortcomings. Current isotope dilution equations are not capable of fully addressing one of the key problems encountered in chemical analysis: the possible effect of sample matrix on measured isotope ratios. The method of standard addition does compensate for the effect of sample matrix by making sure that all measured solutions have identical composition. While it is impossible to attain such condition in traditional isotope dilution, we present equations which allow for matrix-matching between all measured solutions by fusion of isotope dilution and standard addition methods.

Quadruple isotope dilution mass spectrometry (ID 4 MS) has been applied for simultaneous determination of nitrite and nitrate in seawater. ID 4 MS allows high-precision measurements and entails the use of isotopic internal standards ( 18 O-nitrite and 15 N-nitrate). We include a tutorial on ID 4 MS outlining optimal experimental design which generates results with low uncertainties and obviates the need for direct (separate) evaluation of the procedural blank. Nitrite and nitrate detection was achieved using a headspace GCMS procedure based on single-step aqueous derivatization with triethyloxonium tetrafluoroborate at room temperature. In this paper the sample preparation was revised and fundamental aspects of this chemistry are presented. The proposed method has detection limits in the low parts-per-billion for both analytes, is reliable, precise, and has been validated using a seawater certified reference material (MOOS-2). Simplicity of the experimental design, low detection limits, and the use of quadruple isotope dilution makes the present method superior to the state-of-the-art for determination of nitrite and nitrate, and an ideal candidate for reference measurements of these analytes in seawater.

A method is described for the direct determination of dissolved phosphate and silicate in seawater using ion exclusion chromatography (IEC) coupled with sector field inductively coupled plasma mass spectrometry (SF-ICPMS). Dissolved silicate was determined by double isotope dilution using a (29)Si spike, whereas one point gravimetric standard addition with internal standard of the same (29)Si spike was employed to quantitate dissolved phosphate. Medium resolution was used for all measurements in order to resolve polyatomic interferences on Si and P isotopes. Concentrations of 1.670 ± 0.008 and 30.20 ± 0.09 μM (SD, n = 6) with precisions of 0.47 and 0.31% for the dissolved phosphate and silicate, respectively, were obtained in National Research Council Canada certified reference material MOOS-3 seawater, in good agreement with certified values of 1.60 ± 0.15 and 30.5 ± 0.8 μM (U, k = 2), respectively. The reported method is a rapid (10 min per run), simple, and accurate online technique that requires no sample pretreatment. Moreover, this procedure achieves0.5% precision (at above analyte concentrations) and method detection limits of 0.006 and 0.004 μM (0.18 as P and 0.11 ng g(-1) as Si), respectively, using a of 100 μL injection of seawater. The proposed technique is robust and well-suited for the determination of dissolved phosphate and silicate in seawater.

Since its introduction a century ago, isotope dilution analysis has played a central role in developments of analytical chemistry. This method has witnessed many elaborations and developments over the years. To date, we have single, double, and even triple isotope dilution methods. In this manuscript, we summarize the conceptual aspects of isotope dilution methods and introduce the quadruple dilution and the concept of exact matching triple and quadruple dilutions. The comparison of isotope dilution methods is performed by determination of bromide ions in groundwater using novel ethyl-derivatization chemistry in conjunction with GC/MS. We show that the benefits of higher-order isotope dilution methods are countered with a greater need for careful experimental design of the isotopic blends. Just as for ID2MS, ID3MS and ID4MS perform best when the isotope ratio of one sample/spike blend is matched with that of a standard/spike blend (exact matching). © 2013 Her Majesty the Queen in Right of Canada.

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Recent studies of the formation of arsane in the borohydride/arsenate reaction demonstrate the occurrence of condensation cascades whereby small quantities of di- and triarsanes are formed. In this study, the isotopic composition of these di- and triarsanes was examined using deuterium labelled borohydrides. A statistical model was employed to construct the mass spectra of all diarsane and triarsane isotopologues (As2H n D4-n and As3H n D5-n ) from the mass spectra of isotopically pure compounds (As2H4, As2D4, As3H5, and As3D5). Subsequent deconvolution of the experimental mixed spectra shows that incorporation of hydrogen closely follows the binomial distribution, in accord with arsane formation. The H/D distribution in arsane, diarsane, and triarsane isotopologues is binomial in the absence of any interference. However, this is significantly altered by the presence of some transition metals; presented here, for the first time, are the effects of Rh(iii). The presence of Rh(iii) in the As(iii)/[BD4]− system entails the incorporation of hydrogen into the arsanes arising from the solvent, altering the expected binomial H/D distribution.

The generation of arsane by reaction of either NaBH4 (THB) or NaBD4 (TDB) in aqueous solution with AsIII (1 mg L -1) has been studied in the presence of several transition and noble metals at trace levels. A continuous flow generation system coupled with both atomic absorption spectrometry (AAS) and gas chromatography mass spectrometry (GC-MS) were employed to measure the effect of AuIII (0.5 - 20 mg L-1) on reaction yield and isotopic composition of arsane. In a different set of batch experiments, GC-MS was employed to measure the effect of AuIII, PdII, PtII, NiII and Cu II on the isotopic composition of arsane. AuIII, Pd II and PtII induce a significant perturbation in the mechanism of hydride generation, promoting the incorporation of a large amount of hydrogen derived from the solvent into the final arsane. This effect takes place at metal concentration levels which hardly affect the generation efficiency of arsane and can likely be addressed by the action of intermediate species formed in the early stage of the reaction between the metal ion and the TDB-arsenic complex. Nanoparticles and colloids arising from the interaction of the metal and TDB are able to capture the final arsane but they do not promote H/D exchange on the already formed arsane. This evidence reveals the existence of a new type of interference in chemical generation of volatile hydrides - a "mechanistic interference" - in addition to the already known yield interferences. © 2011 Elsevier B.V. All rights reserved.

Activity coefficients of the highly charged electrolytes Mgds, La2ds3, and [Co(en)3]2ds3 (en = ethylenediamine, ds2−=1,5-naphthalenedisulfonate anion), were determined at 298.15 K using liquid-membrane cells. These salts are found not to display large negative deviations from the Debye-Huckel limiting slope in the dilute regions, which characterize the corresponding sulfate salts. Theoretical calculations based on the primitive model (charged hard spheres in an unstructured dielectric medium) reproduce the behavior of these salts correctly up to concentrations of 0.01 mol⋅kg−1 or more (0.1 mol⋅kg−1 for Mgds), although ds2−, far from resembling a charged sphere, is a planar ion with charges distant from one another. The Pitzer model parameter values are reported for the activity and osmotic coefficients.

A novel method for compensation of the procedural blank in isotope dilution is presented. This method - entitled "blank-matching" - copes with the blank through experimental design. Both sample and calibration solutions are exposed to the same amount of isotopic standard and same procedural blank. The identical treatment of sample and calibrators eliminates the need for subtracting the procedural blank from the result obtained by isotope dilution. A further advantage of the method is that quantitation of the analyte in the procedural blank is not required. Blank-matching is simple and fast to implement and it permits direct determination of results without further corrections. This aspect has an important metrological outcome: blank-matching isotope dilution can be considered a primary method of analysis that does not involve the procedural blank as a potential source of bias.

Uncertainty of the result from the method of standard addition is often underestimated due to neglect of the covariance between the intercept and the slope. In order to simplify the data analysis from standard addition experiments, we propose x-y coordinate swapping in conventional linear regression. Unlike the ratio of the intercept and slope, which is the result of the traditional method of standard addition, the result of the inverse standard addition is obtained directly from the intercept of the swapped calibration line. Consequently, the uncertainty evaluation becomes markedly simpler. The method is also applicable to nonlinear curves, such as the quadratic model, without incurring any additional complexity.

A novel method for the determination of salivary thiocyanate is presented. Thiocyanate was converted into ethyl thiocyanate by single-step aqueous derivatization based on triethyloxonium tetrafluoroborate and measured by gas chromatography-mass spectrometry (15min runtime). The ethyl thiocyanate derivative is volatile and can be sampled from the headspace. The derivatization chemistry proposed allows for separation of the analyte from saliva matrix whose introduction in the measurement system is avoided. Quantitation of the analyte was obtained by isotope dilution, employing a 13C-enriched thiocyanate as internal standard. Technical details and fundamental aspects of derivatization chemistry and calibration strategy are presented.The method was validated by comparison with a standard method based on ion chromatography. The two independent methodologies produced results in agreement within 3%. Also a three level spike recovery test was carried out for validation purpose and quantitative recoveries were attained. The method is fast, simple, safe, and sensitive. Measurement of a 1. mL volume 50. ng/g of thiocyanate standard produced a signal-to-noise ratio of 250 for the analytical peak. This method is therefore suitable for ultra-trace determination of thiocyanate (low part-per-billion range). For the application described the full detection potential of the method was not required and the sample preparation presented has been designed for quantitation of saliva samples containing 1-400. ?g/g of thiocyanate with a combined standard uncertainty of 2% relative for saliva samples containing 25. ?g/g of thiocyanate. This method was applied for the determination of thiocyanate in human saliva samples.

Over the years, isotope dilution mass spectrometry (IDMS) has witnessed many reformulations. One of the earliest expressions for this quantitation model was given by the single isotope dilution (IDMS). In IDMS, the mass fraction of an analyte A is obtained from mass spectrometric analysis of a mixture (blend) of sample and an isotopically-enriched form of the analyte (B) which acts as an internal standard

Direct analysis in real time (DART) has been applied in conjunction with high-resolution Orbitrap mass spectrometry to characterize the aqueous reduction of monomethylarsenate by tetrahydroborate (B/As molar ratio ≈ 4 mol/mol). Under these conditions, the reaction gives rise to a complex mixture of arsenic compounds which result in the formation of a reddish precipitate. The use of the DART revealed the presence of a number of polymeric arsanes – up to eight arsenic atoms – associated with the liquid/solid phase of this reaction system. From a reactivity point-of-view, these polymers exhibit an uncommon ionization pathway. In fact, similar to the alkanes, the action of the DART results in the generation of [M − H] + ions. Furthermore, for each oligomer MeHAs–(AsMe) n –AsHMe ( n = 0–8), a series of oxidation products [(M + n O) − H] + were also identified and their formation has been discussed.

We report a novel derivatization chemistry for determination of fluoride based on the batch reaction of fluoride ions with triethyloxonium tetrachloroferrate(III) in a closed vessel to yield fluoroethane. Gaseous fluoroethane was readily separated from the matrix, sampled from the headspace, and determined by gas chromatography/mass spectrometry. The method was validated using rainwater certified reference material (IRMM CA408) and subsequently applied to the determination of fluoride in various matrixes, including tap water, seawater, and urine. An instrumental limit of detection of 3.2 μg/L with a linear range up to 50 mg/L was achieved. The proposed derivatization is a one-step reaction, requires no organic solvents, and is safe, as the derivatizing agent is nonvolatile. Determination of fluoride is affected by common fluoride-complexing agents, such as Al(III) and Fe(III). The effect of large amounts of these interferences was studied, and the adverse effect of these ions was eliminated by use of the method of standard additions.