Sensitive Detection and Quantification of Oxygenated Compounds in Complex Samples Using GC-Combustion-MS.

This work introduces a new element-selective gas chromatography detector for the accurate quantification of traces of volatile oxygen-containing compounds in complex samples without the need for specific standards. The key to this approach is the use of oxygen highly enriched in 18O as the oxidizing gas in a combustion unit (800 °C) that allows us to directly and unambiguously detect the natural oxygen present in the GC-separated compounds through its incorporation into the volatile species formed after their combustion and their subsequent degradation to 16O in the ion source. The unspecific signal due to the low 16O abundance in the oxidizing gas could be compensated by measuring the m/z 12 that comes as well from the CO2 degradation. Equimolarity was proved with several O-containing compounds with different sizes and functionalities. A detection limit of 28 pg of injected O was achieved, which is the lowest ever reported for any GC detector, which barely worsened to 55 and 214 pg of O when the oxygenate partially or completely coeluted with a very abundant matrix compound. Validation was attained by the analysis of a SRM to obtain accurate (99-103%) and precise (1-4% RSD) results. Robustness was tested after spiking a hydrotreated diesel with 10 O-compounds at the ppm level, which could be discriminated from the matrix crowd and quantified (mean recovery of 102 ± 9%) with a single generic standard. Finally, it was also successfully applied to easily spot and quantify the 33 oxygenates naturally present in a complex wood bio-oil sample.

Potential of GC-Combustion-MS as a Powerful and Versatile Nitrogen-Selective Detector in Gas Chromatography.

Here, we show the potential and applicability of the novel GC-combustion-MS approach as a nitrogen-selective GC detector. Operating requirements to achieve reproducible and compound-independent formation of volatile NO species as a selective N-signal during the combustion step are described. Specifically, high temperatures (≥1000 °C) and post-column O2 flows (0.4 mL min-1 of 0.3% O2 in He) turned out to be necessary when using a vertical oven without makeup flow (prototype #1). In contrast, the use of a horizontal oven with 1.7 mL min-1 He as an additional makeup flow (prototype #2) required milder conditions (850 °C and 0.2 mL min-1). A detection limit of 0.02 pg of N injected was achieved, which is by far the lowest ever reported for any GC detector. Equimolarity, linearity, and peak shape were also adequate. Validation of the approach was performed by the analysis of a certified reference material obtaining accurate (2% error) and precise (2% RSD) results. Robustness was tested with the analysis of two complex samples with different matrices (diesel and biomass pyrolysis oil) and N concentration levels. Total N determined after the integration of the whole chromatograms (524 ± 22 and 11,140 ± 330 µg N g-1, respectively) was in good agreement with the reference values (497 ± 10 and 11,000 ± 1200 µg N g-1, respectively). In contrast, GC-NCD results were lower for the diesel sample (394 ± 42 µg N g-1). Quantitative values for the individual and families of N species identified in the real samples by parallel GC-MS and additional GC × GC-MS analyses were also obtained using a single generic internal standard.

Quantitative multiplexed elemental (C, H, N and S) detection in complex mixtures using gas chromatography.

We present a novel and single detection approach that enables sensitive, accurate and compound-independent quantification of N, S and H in the individual compounds present in complex samples. Integration of the whole chromatographic profile gives the total content of the elements. Simultaneous universal detection is also achieved using the C profile.

GC-ICP-MS/MS Instrumental Setup for Total and Speciation Sulfur Analysis in Gasolines using Generic Standards.

Quantitative characterization of sulfur-containing petroleum derivatives is mainly limited by the large number of potential targets present and the matrix effects suffered due to the high-carbon-containing matrices. Herein we describe the instrumental modifications required in a commercial GC-ICP-MS/MS instrument, and their corresponding optimization, for turning it into a compound-independent quantitative technique for both total and speciation sulfur analysis in gasolines. Additionally, carbon-derived matrix effects were made negligible for direct and fast total S analysis, making the use of relatively complex isotope-dilution strategies not necessary anymore. An absolute detection limit of 0.3 pg of S was achieved, which is, to the best of our knowledge, more than 1 order of magnitude below the ones reported for other sulfur GC selective detectors. The precision was below 3% RSD. Total analysis was performed by flow-injection analysis through a transfer line and external calibration, whereas speciation analysis was carried out by chromatographic separation and internal standardization. In both cases, simple generic standards were used, which enabled us to get rid of specific S-containing standards, which were sometimes not available or unstable. The proposed method was successfully applied to total and speciation sulfur analysis of a commercial gasoline sample and validated with a certified-reference-material (ERM-EF213) gasoline. The approach has proved to be simple, fast, robust, and convenient for implementation in routine laboratories, as demonstrated by the successive analyses of 50 gasoline samples in 3 h without any instrumental drift.

Isotope Dilution Mass Spectrometry for Highly Precise Determination of Dissolved Inorganic Carbon in Seawater Aiming at Climate Change Studies.

Dissolved inorganic carbon (DIC) is one of the most important parameters to be measured in seawaters for climate change studies. Its quantitative assessment requires analytical methodologies with overall uncertainties around 0.05% RSD for clear evaluation of temporal trends. Herein, two alternative isotope dilution mass spectrometry (IDMS) methodologies (online and species-specific) using an isotope ratio mass spectrometer (IRMS) and two calculation procedures for each methodology have been compared. As a result, a new method for the determination of DIC in seawaters, based on species-specific IDMS with isotope pattern deconvolution calculation, was developed and validated. A 13C-enriched bicarbonate tracer was added to the sample and, after equilibration and acidification, the isotope abundances at CO2 masses 44, 45, and 46 were measured on an IRMS instrument. Notably, early spiking allows correcting for evaporations and/or adsorptions during sample preparation and storage and could be carried out immediately after sampling. Full uncertainty budgets were calculated taking into account all the factors involved in the determination (initial weights, concentration and isotope abundances of standards, and final IRMS measurements). The average DIC value obtained for CRM seawater agreed very well with the certified value. Propagated precision obtained ranged from 0.035 to 0.050% RSD for individual sample triplicates. Reproducibility, assessed by three independent experiments carried out in different working days, was excellent as well (-0.01% and 0.057%, error and full combined uncertainty, respectively). Additionally, the approach proposed improves on established methods by simplicity, higher throughput (15 min per sample), and lower volume requirements (10 mL).

Instrumental Setup for Simultaneous Total and Speciation Analysis of Volatile Arsenic Compounds in Gas and Liquefied Gas Samples.

Although analysis of metals and metalloids, such as arsenic, is widely spread in many different fields, their analysis in gas and liquefied gas samples is still a challenge. A new GC-ICP-MS set up has been developed for their simultaneous total and speciation analysis in gas and liquefied gas samples without the need of a preconcentration step. An arsine in nitrogen standard was used for optimization and evaluation of the system. Good linearity and detection limits in the very low ppt level for both total and speciation analyses were found. Liquefied butane pressurized under nitrogen and doped with arsine and a propylene real sample from a cracker plant were analyzed using both external calibration and standard additions methods. The good match between both quantifying approaches demonstrated almost negligible matrix effects, even for the total analysis. Application of the approach to check repartition of volatile elements or species between gas and liquid phases was performed in the real propylene sample. Finally, its potential applicability for the simultaneous total and speciation analysis of other elements, such as Hg, was also proved.

Comparison of gas chromatography-combustion-mass spectrometry and gas chromatography-flame ionization detector for the determination of fatty acid methyl esters in biodiesel without specific standards.

GC-FID has been effectively used as a universal quantification technique for volatile organic compounds for a long time. In most cases, the use of the ECN allows for quantification by GC-FID without external calibration using only the response of a single internal standard. In this paper we compare the performance characteristics of GC-FID with those of post-column (13)C Isotope Dilution GC-Combustion-MS for the absolute quantification of organic compounds without the need for individual standards. For this comparison we have selected the quantification of FAMEs in biodiesel. The selection of the right internal standard was critical for GC-FID even when ECN were considered. On the other hand, the nature of the internal standard was not relevant when GC-Combustion-MS was employed. The proposed method was validated with the analysis of the certified reference material SRM 2772 and comparative data was obtained on real biodiesel samples. The analysis of the SRM 2772 biodiesel provided recoveries in the range 100.6-103.5% and 96.4-103.6% for GC-combustion-MS and GC-FID, respectively. The detection limit for GC-combustion-MS was found to be 4.2ng compound/g of injected sample. In conclusion, the quantitative performance of GC-Combustion-MS compared satisfactorily with that of GC-FID constituting a viable alternative for the quantification of organic compounds without the need for individual standards.

Detection of transgenerational barium dual-isotope marks in salmon otoliths by means of LA-ICP-MS.

The present study evaluates the use of an individual-specific transgenerational barium dual-isotope procedure and its application to salmon specimens from the Sella River (Asturias, Spain). For such a purpose, the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in combination with multiple linear regression for the determination of the isotopic mark in the otoliths of the specimens is presented. In this sense, a solution in which two barium-enriched isotopes ((137)Ba and (135)Ba) were mixed at a molar ratio of ca. 1:3 (N Ba137/N Ba135) was administered to eight returning females caught during the spawning period. After injection, these females, as well as their offspring, were reared in a governmental hatchery located in the council of Cangas de Onís (Asturias, Spain). For comparison purposes, as well as for a time-monitoring control, egg and larva data obtained by solution analysis ICP-MS are also given. Otoliths (9-month-old juveniles) of marked offspring were analysed by LA-ICP-MS demonstrating a 100 % marking efficacy of this methodology. The capabilities of the molar fraction approach for 2D imaging of fish otoliths are also addressed.

Development of a dual-isotope procedure for the tagging and identification of manufactured products: application to explosives.

A novel chemical tagging approach, based on a dual-isotope procedure, is presented. The method has been applied to explosives tagging. The method is based on the addition to the explosive of two enriched isotopes of the same element, which may be already present within it, at a given molar ratio. This dual-isotope approach will give a unique fingerprint to the tagged explosive. Further, the authentication of the tagged explosive or its residues will be obtained by comparison of the ratio of molar fractions experimentally measured by inductively coupled plasma mass spectrometry (ICP-MS) with the molar fraction ratio of the tagging mixture. The novelty of this tagging method relies on working with isotope abundances and molar fraction ratios instead of the classical isotope ratios, and this fact constitutes the strong point of the described approach since the molar ratio is not affected by physical, chemical, or biochemical processes, and it is also not disturbed by environmental contamination with the natural abundance element. Furthermore, the use of molar fraction ratios overcomes the nonhomogeneous distribution of the tagging element within the explosive. As the tagging element can be present at trace or ultratrace levels, a very small amount of enriched isotopes needs to be added, denoting a low cost solution. Also, the use of enriched stable isotopes of nontoxic elements will have negligible health effects or affect the environment.

Individual-specific transgenerational marking of fish populations based on a barium dual-isotope procedure.

The present study focuses on the development and evaluation of an individual-specific transgenerational marking procedure using two enriched barium isotopes, (135)Ba and (137)Ba, mixed at a given and selectable molar ratio. The method is based on the deconvolution of the isotope patterns found in the sample into four molar contribution factors: natural xenon (Xe nat), natural barium (Ba nat), Ba135, and Ba137. The ratio of molar contributions between Ba137 and Ba135 is constant and independent of the contribution of natural barium in the sample. This procedure was tested in brown trout ( Salmo trutta ) kept in captivity. Trout were injected with three different Ba137/Ba135 isotopic signatures ca. 7 months and 7 days before spawning to compare the efficiency of the marking procedure at long and short term, respectively. The barium isotopic profiles were measured in the offspring by means of inductively coupled plasma mass spectrometry. Each of the three different isotopic signatures was unequivocally identified in the offspring in both whole eggs and larvae. For 9 month old offspring, the characteristic barium isotope signatures could also be detected in the otoliths even in the presence of a high and variable amount of barium of natural isotope abundance. In conclusion, it can be stated that the proposed dual-isotope marking is inheritable and can be detected after both long-term and short-term marking. Furthermore, the dual-isotope marking can be made individual-specific, so that it allows identification of offspring from a single individual or a group of individuals within a given fish group.

Use of the stable isotope (57) Fe to track the efficacy of the foliar application of lignosulfonate/Fe(3+) complexes to correct Fe deficiencies in cucumber plants.

BACKGROUND: During the last decade, environmental concerns regarding the use of recalcitrant synthetic chelates to overcome iron chlorosis has increased and new ligands such as lignosulfonates (LS) have been evaluated. However, the efficacy of these products is variable. In this work a hardwood (eucalyptus) and softwood (spruce) LS were compared to try to relate their physico-chemical characteristics and their efficacy. Also two more products derived from the eucalyptus lignosulfonate were tested. RESULTS: All the LS tested presented a good ability to complex Fe, but only the spruce LS was capable to maintain significant amounts of soluble Fe above pH 8. According to the FTIR data, structural changes related to the Fe source (Fe(2+) or Fe(3+) ) used to form the complex occurred in the LS molecule and might influence their efficacy. Cucumber (Cucumis sativus L. cv Ashley) chlorotic plants were used to test lignosulfonate efficacy when applied through foliar sprays in comparison with FeSO(4) and EDTA/(57) Fe(3+) . The (57) Fe content of plants sprayed with LS was very low in respect to the EDTA treatment, but this was not reflected in the biomass and re-greening rates. Eucalyptus LS modifications improve its efficacy for iron chlorosis recovery to levels similar to those found for the spruce LS. Two applications of the LS are recommended. CONCLUSIONS: Lignosulfonates did not require surfactants for their application; they did not burn the leaves, and had a stimulating effect on the vegetative growth of the plants. So these by-products could be a good alternative when applied through foliar sprays for cucumber plants.

Using a dual-stable isotope tracer method to study the uptake, xylem transport and distribution of Fe and its chelating agent from stereoisomers of an Fe(III)-chelate used as fertilizer in Fe-deficient Strategy I plants.

A dual-stable isotope tracer experiment was carried out with Fe-deficient sugar beet plants grown hydroponically and resupplied with differentially Fe labeled racemic and meso Fe(iii)-chelates of the ethylendiamine di(o-hydroxyphenylacetic) acid (o,oEDDHA). No short-term Fe isotope exchange reactions occurred in the nutrient solution and plants did not discriminate between (54)Fe and (57)Fe. After 3-6 h, stable Fe isotopes, chelating agents and chelates were analyzed in roots, xylem sap and leaves by ICP-MS and HPLC-ESI/TOFMS. Ferric chelate reductase rates, xylem transport and total uptake were 2-fold higher with the meso isomer than with the racemic one. Both chelating agent isomers were incorporated and distributed by plants at similar rates, in amounts one order of magnitude lower than those of Fe. After 6 h of Fe resupply, most of the Fe acquired was localized in roots, whereas most of the chelating agent was in leaves. In a separate experiment, Fe-deficient sugar beet and tomato plants were treated with different concentrations of Fe(iii)-o,oEDDHA (with a meso/racemic ratio of 1). The xylem sap Fe concentration at 24 h was unaffected by the chelate concentration, with xylem Fe(iii)-o,oEDDHA accounting for 1-18% of total Fe and xylem meso/racemic ratio close to 1. Although most of the Fe coming from Fe(iii)-o,oEDDHA was taken up through a reductive dissociative mechanism, a small part of the Fe may be taken up via non-dissociative mechanisms.

Internal correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis.

A method has been developed for the accurate determination of platinum by isotope dilution analysis, using enriched (194)Pt, in environmental samples containing comparatively high levels of hafnium without any chemical separation. The method is based on the computation of the contribution of hafnium oxide as an independent factor in the observed isotope pattern of platinum in the spiked sample. Under these conditions, the ratio of molar fractions between natural abundance and isotopically enriched platinum was independent of the amount of hafnium present in the sample. Additionally, mass bias was corrected by an internal procedure in which the regression variance was minimised. This was possible as the mass bias factor for hafnium oxide was very close to that of platinum. The final procedure required the measurement of three platinum isotope ratios (192/194, 195/194 and 196/194) to calculate the concentration of platinum in the sample. The methodology has been validated using the reference material "BCR-723 road dust" and has been applied to different environmental matrices (road dust, air particles, bulk wet deposition and epiphytic lichens) collected in the Aspe Valley (Pyrenees Mountains). A full uncertainty budget, using Kragten's spreadsheet method, showed that the total uncertainty was limited only by the uncertainty in the measured isotope ratios and not by the uncertainties of the isotopic composition of platinum and hafnium.

Isotope pattern deconvolution as a tool to study iron metabolism in plants.

Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution multicollector or collision cell ICP-MS allows the determination of the tracer/tracee ratio with simultaneous internal mass bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber plants using 57Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap, after exposure of the cucumber plants to the mentioned 57Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured by ICP-MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low 57Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis, using a collision cell quadrupole ICP-MS instrument, after addition of 57Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample.

Large volume injection in ion chromatography Separation of rubidium and strontium for on-line inductively coupled plasma mass spectrometry determination of strontium isotope ratios.

Large volume injection, up to 5 mL, was evaluated and optimised for the on-line ion chromatographic separation of Rb and Sr before ICP-MS measurement of Sr isotope ratios. Flat-topped chromatographic peaks, ideally suited for multicollector ICP-MS isotope ratio measurements, could be obtained when the composition of the mobile phase (nitric acid and 18-crown-6 ether) was identical to the matrix of the sample. Under those conditions rubidium eluted at the dead volume of the column while strontium produced a flat-topped transient signal with several minutes of stable plateau. On-line data acquisition during several minutes at the plateau of Sr signal allowed high precision Sr isotope ratio measurement. The developed procedure was evaluated for Sr isotope ratio measurements on different types of samples, including cider, apples, apple leaves, and soil extracts, in the frame of a long-term project aiming at origin authentication using strontium isotope ratio measurements. It was observed that sample matrix caused broadening of the strontium chromatographic peak and loss of flat-topped peak profile. Under those circumstances the addition of the complexing crown-ether 18-crown-6 both to samples and chromatographic eluent provided two distinct advantages. First, a drastic increase in the retention of strontium was observed which could be modulated by increasing the concentration of nitric acid in the eluent up to 900 mM. This increase in the eluent HNO(3) concentration allowed the application of the method to acid soil digests and other high acidity samples. Second, the matrix of the sample did not affect any more the chromatographic peak profile and similar chromatographic separations could be obtained for samples and standards maintaining the flat-topped Sr peak profile. Sample preparation consisted of a simple 1:10 dilution of the cider or pre-treated solid samples by adding HNO(3) (900 mM) and 18-crown-6 ether (5mM) to obtain similar composition in the sample solution and the HPLC eluent.

Evaluation of strontium isotope abundance ratios in combination with multi-elemental analysis as a possible tool to study the geographical origin of ciders.

In order to evaluate alternative analytical methodologies to study the geographical origin of ciders, both multi-elemental analysis and Sr isotope abundance ratios in combination with multivariate statistical analysis were estimated in 67 samples from England, Switzerland, France and two Spanish regions (Asturias and the Basque Country). A methodology for the precise and accurate determination of the (87)Sr/(86)Sr isotope abundance ratio in ciders by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) was developed. Major elements (Na, K, Ca and Mg) were measured by ICP-AES and minor and trace elements (Li, Be, B, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Mo, Cd, Sn, Sb, Cs, Ba, La, Ce, W, Tl, Pb, Bi, Th and U) were measured by ICP-MS using a collision cell instrument operated in multitune mode. An analysis of variance (ANOVA test) indicated that group means for B, Cr, Fe, Ni, Cu, Se, Cd, Cs, Ce, W, Pb, Bi and U did not show any significant differences at the 95% confidence level, so these elements were rejected for further statistical analysis. Another group of elements (Li, Be, Sc, Co, Ga, Y, Sn, Sb, La, Tl, Th) was removed from the data set because concentrations were close to the limits of detection for many samples. Therefore, the remaining elements (Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba) together with (87)Sr/(86)Sr isotope abundance ratio were considered for principal component analysis (PCA) and linear discriminant analysis (LDA). Finally, LDA was able to classify correctly 100% of cider samples coming from different Spanish regions, France, England and Switzerland when considering Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba and (87)Sr/(86)Sr isotope abundance ratio as original variables.

Platinum, palladium, and rhodium in fresh snow from the Aspe Valley (Pyrenees Mountains, France).

Platinum, palladium, and rhodium have been measured in fresh snow samples from 14 locations within the Aspe Valley (Pyrenees Mountains, France) during two winter seasons, February 2003 and March 2004. Ultraclean procedures were employed for the sampling, sample treatment, and analysis in order to reduce sample contamination. Possible spectral interferences on platinum group element (PGE) analysis by inductively coupled plasma mass spectrometry (ICP-MS) were controlled and corrected. The detection limits obtained were 0.05, 0.45, and 0.075 pg g(-1) for Pt, Pd, and Rh, respectively. PGE content in fresh snow from the Pyrenees Mountains range from 0.20 to 2.51 pg g(-1) for Pt, 1.45-14.04 pg g(-1) for Pd, and 0.24-0.66 pg g(-1) for Rh. The higher PGE concentration, generally measured in sites located close to road traffic, exhibit potential resuspension of PGE-enriched particles emitted locally from the car exhaust, although no direct relationship could be observed with the number of vehicles. Measured atmospheric synoptic conditions allowed identification of the origin of air masses reaching the Aspe Valley and therefore provided information about the possible sources of platinum group elements. Higher PGE concentrations measured in 2004 samples, compared to the ones collected in 2003, indicate the influence of atmospheric synoptic conditions on the studied area. Fresh snow samples collected in 2003 could not be linked to a specific source, whereas 2004 samples could be influenced by PGE emissions from European vehicle fleet and Russian PGE-containing mining activities.

Scanning laser ablation-ICP-MS tracking of platinum group elements in urban particles.

While it has now been demonstrated that platinum group elements (PGE) are released from automobile catalysts into the environment, less is known about the form in which they are emitted and transported. Here we show that scanning laser ablation-inductively coupled plasma-mass spectrometry (scanning laser ablation-ICP-MS) can identify and track individual particles released from automobile catalysts present in environmental particulates and sediments. Particles with high PGE concentrations were found in the exhaust of gasoline and diesel vehicles equipped with catalytic converters. The PGE-Ce association in individual particles provides a definitive fingerprinting for tracking catalyst particles in environmental compartments, while relative PGE signal intensity is an indication of the catalyst type. Scanning laser ablation-ICP-MS of road and aquatic sediments revealed a few PGE containing catalyst particles and it was possible to identify catalyst types for the origin of these particles.