Quantitative Isotope Dilution Research Articles

A rapid and sensitive method for the determination of inorganic chloride in oil samples

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.

Unbiased Measurement of Phosphate and Phosphorus Speciation in Surface Waters.

Trace-level phosphate analysis and phosphorus speciation in surface water remained challenging due to adsorption and phosphate uptake by microorganisms. In this study a two-dimensional ion chromatography separation coupled to electrospray ionization high-resolution mass spectrometry (2D-IC-ESI-MS) allowed isotope dilution quantitation of phosphate with simultaneous analysis of 11 phosphate-containing metabolites and two inorganic condensed phosphates. Samples were collected from Lake St. Clair, Lake Ontario, and Georgian Bay (ON, Canada). Comparative experiments showed lower phosphate results for samples not immediately spiked and for external calibration quantitation. Field spiking with 18O-labeled phosphate combined with isotope dilution quantitation allows measurement of the phosphate levels existent at the collection time instead of the phosphate concentrations remaining in the samples at the analysis time. This is a significant advantage against the traditional colorimetric and ion chromatographic (IC) analysis methods, which are unable to compensate for the adsorption loss occurring in standards and samples, especially when phosphate is present at levels below 20 μg L-1 as P (61 μg L-1 as PO43-). Two phosphate-containing metabolites, adenosine 5'-monophosphate (AMP) and d-glucose 6-phosphate (Glucose-P), were detected in a subset of samples collected from Lake St. Clair, with no statistically significant correlation between them and the simultaneously measured phosphate. Directly bioavailable P (phosphate), indirectly bioavailable P (phosphatase-hydrolyzed P) and nonbioavailable P (nonhydrolizable P) fractions were quantified by measuring phosphate, phosphate after phosphatase addition and total phosphorus. The proposed 2D-IC-ESI-MS method developed for a QExactive MS instrument with field spiking of the internal standard provides accurate phosphate results and eliminates quantitation errors caused by phosphate adsorption. This setup allows simultaneous collection of targeted and nontargeted analysis data and thus the detection of trace polar organic phosphorus metabolites as well.

N6-(2-Deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine Adducts of 1,3-Butadiene: Synthesis, Structural Identification, and Detection in Human Cells.

1,3-Butadiene (BD) is an environmental and occupational toxicant classified as a human carcinogen. BD is metabolically activated by cytochrome P450 monooxygenases to 3,4-epoxy-1-butene (EB), which alkylates DNA to form a range of nucleobase adducts. Among these, the most abundant are the hydrolytically labile N7-guanine adducts such as N7-(2-hydroxy-3-buten-1-yl)-guanine (N7-EB-dG). We now report that N7-EB-dG can be converted to the corresponding ring open N6-(2-deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine (EB-Fapy-dG) adducts. EB-Fapy-dG lesions were detected in EB-treated calf thymus DNA and in EB-treated mammalian cells using quantitative isotope dilution nanoLC-ESI+-MS/MS. EB-Fapy-dG adduct formation in EB-treated calf thymus DNA was concentration dependent and was greatly accelerated at an increased pH. EB-FAPy-dG adduct amounts were 2-fold higher in base excision repair-deficient NEIL1-/- mouse embryonic fibroblasts (MEF) as compared to isogenic controls (NEIL1+/+), suggesting that this lesion may be a substrate for NEIL1. Furthermore, NEIL1-/- cells were sensitized to EB treatment as compared to NEIL1+/+ fibroblasts. Overall, our results indicate that ring-opened EB-FAPy-dG adducts form under physiological conditions, prompting future studies to determine their contributions to genotoxicity and mutagenicity of BD.

Quantitative Isotope-Dilution High-Resolution-Mass-Spectrometry Analysis of Multiple Intracellular Metabolites in Clostridium autoethanogenum with Uniformly 13C-Labeled Standards Derived from Spirulina.

We have investigated the applicability of commercially available lyophilized spirulina ( Arthrospira platensis), a microorganism uniformly labeled with 13C, as a readily accessible source of multiple 13C-labeled metabolites suitable as internal standards for the quantitative determination of intracellular bacterial metabolites. Metabolites of interest were analyzed by hydrophilic-interaction liquid chromatography coupled with high-resolution mass spectrometry. Multiple internal standards obtained from uniformly (U)-13C-labeled extracts from spirulina were used to enable isotope-dilution mass spectrometry (IDMS) in the identification and quantification of intracellular metabolites. Extraction of the intracellular metabolites of Clostridium autoethanogenum using 2:1:1 chloroform/methanol/water was found to be the optimal method in comparison with freeze-thaw, homogenization, and sonication methods. The limits of quantification were ≤1 μM with excellent linearity for all of the calibration curves ( R2 ≥ 0.99) for 74 metabolites. The precision and accuracy were found to be within relative standard deviations (RSDs) of 15% for 49 of the metabolites and within RSDs of 20% for all of the metabolites. The method was applied to study the effects of feeding different levels of carbon monoxide (as a carbon source) on the central metabolism and Wood-Ljungdahl pathway of C. autoethanogenum grown in continuous culture over 35 days. Using LC-IDMS with U-13C spirulina allowed the successful quantification of 52 metabolites in the samples, including amino acids, carboxylic acids, sugar phosphates, purines, and pyrimidines. The method provided absolute quantitative data on intracellular metabolites that was suitable for computational modeling to understand and optimize the C. autoethanogenum metabolic pathways active in gas fermentation.

Odor-Active Compounds in the Special Flavor Hops Huell Melon and Polaris.

The volatiles isolated from samples of the special flavor hop varieties, Huell Melon and Polaris, and from the aroma hop variety, Hallertau Tradition, by solvent extraction and solvent-assisted flavor evaporation (SAFE) were subjected to a comparative aroma extract dilution analysis (cAEDA), which resulted in 46 odor-active compounds in the flavor dilution (FD) factor range of 16 to 2048. On the basis of high FD factors, myrcene, (3R)-linalool, and 2- and 3-methylbutanoic acid were confirmed as important variety-independent hop odorants. (1R,4S)-Calamenene was identified for the first time as an odor-active compound in hops. Clear differences in the FD factors and their subsequent objectification by stable isotope dilution quantitation suggested that high concentrations of the esters ethyl 2-methylbutanoate, ethyl 2-methylpropanoate, and propyl 2-methylbutanoate cause the characteristic fruity, cantaloupe-like odor note in Huell Melon hops, whereas the fruity and minty odor notes in Polaris are associated with high amounts of 3-methylbutyl acetate and 1,8-cineole.

Rapid determination of nitrate in vegetables by gas chromatography mass spectrometry

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 μg/g range with a detection limit of 2 μg/g. Due to the use of primary isotope dilution quantitation, traceable results of high-precision were attained.

Odour-active compounds in the traditional Armenian soup seasoning herb Heracleum transcaucasicum

The volatile fraction isolated from dried shoots of Heracleum transcaucasicum Manden (syn. Heracleum pastinacifolium C. Koch) by solvent extraction and solvent-assisted flavour evaporation was screened for odour-active compounds by application of an aroma extract dilution analysis. In the flavour dilution (FD) factor range of 1–2048, 51 odorants were detected, among which soup seasoning-like smelling sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) showed the highest FD factor (2048). Its characteristic odour, which closely matched the overall aroma of the dried shoots, in combination with its high FD factor and the absence of any further odour-active compound exhibiting a similar smell, suggested that sotolon constitutes the character impact compound in the aroma of H. transcaucasicum. Stable isotope dilution quantitation using (13C2)sotolon as internal standard revealed a concentration of ~12 mg/kg sotolon in dried H. transcaucasicum shoots, which is several orders of magnitude higher than its odour detection threshold. Further quantitation experiments revealed that during traditional culinary use, sotolon is transferred from H. transcaucasicum shoots in odour-active amounts to Armenian karshm soup.

Insights into the Key Aroma Compounds in Mango (Mangifera indica L. 'Haden') Fruits by Stable Isotope Dilution Quantitation and Aroma Simulation Experiments.

Thirty-four aroma-active compounds, previously identified with high flavor dilution factors by application of an aroma extract dilution analysis, were quantified in tree-ripened fruits of mango (Mangifera indica L. 'Haden'). From the results, the odor activity value (OAV) was calculated for each compound as the ratio of its concentration in the mangoes to its odor threshold in water. OAVs > 1 were obtained for 24 compounds, among which ethyl 2-methylbutanoate (fruity; OAV 2100), (3E,5Z)-undeca-1,3,5-triene (pineapple-like; OAV 1900), ethyl 3-methylbutanoate (fruity; OAV 1600), and ethyl butanoate (fruity; OAV 980) were the most potent, followed by (2E,6Z)-nona-2,6-dienal (cucumber-like), ethyl 2-methylpropanoate (fruity), (E)-β-damascenone (cooked apple-like), ethyl hexanoate (fruity), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like), 3-methylbut-2-ene-1-thiol (sulfurous), γ-decalactone (peach-like), β-myrcene (terpeny), (3Z)-hex-3-enal (green), 4-methyl-4-sulfanylpentan-2-one (tropical fruit-like), and ethyl octanoate (fruity). Aroma simulation and omission experiments revealed that these 15 compounds, when combined in a model mixture in their natural concentrations, were able to mimic the aroma of the fruits.

Convenient preparation of deuterium‐labeled analogs of peptides containing N‐substituted glycines for a stable isotope dilution LC‐MS quantitative analysis

N-substituted glycines constitute mimics of natural amino acids that are of great interest in the peptide-based drug development. Peptoids-oligo(N-substituted glycines) have been recently demonstrated to be highly active peptidomimetics in biological systems, resistant to proteolytic degradation. We developed a method of the deuterium labeling of peptidomimetics containing N-substituted glycine residues via H/D exchange of their α-carbon hydrogen atoms. The labeling was shown to be easy, inexpensive, and without the use of derivatization reagents or the need for a further purification. The deuterons introduced at the α-carbon atoms do not undergo a back exchange under acidic conditions during liquid chromatography mass spectrometry (LC-MS) analysis. The LC-MS analysis of a mixture of isotopologues revealed a co-elution of deuterated and nondeuterated forms of the peptidomimetics, which may be useful in the quantitative isotope dilution analysis of peptoids and other derivatives of N-substituted glycines.

Sulfur and nitrogen mustards induce characteristic poly(ADP-ribosyl)ation responses in HaCaT keratinocytes with distinctive cellular consequences.

Mustard agents are potent DNA alkylating agents with mutagenic, cytotoxic and vesicant properties. They include bi-functional agents, such as sulfur mustard (SM) or nitrogen mustard (mustine, HN2), as well as mono-functional agents, such as "half mustard" (CEES). Whereas SM has been used as a chemical warfare agent, several nitrogen mustard derivatives, such as chlorambucil and cyclophosphamide, are being used as established chemotherapeutics. Upon induction of specific forms of genotoxic stimuli, several poly(ADP-ribose) polymerases (PARPs) synthesize the nucleic acid-like biopolymer poly(ADP-ribose) (PAR) by using NAD(+) as a substrate. Previously, it was shown that SM triggers cellular poly(ADP-ribosyl) ation (PARylation), but so far this phenomenon is poorly characterized. In view of the protective effects of PARP inhibitors, the latter have been proposed as a treatment option of SM-exposed victims. In an accompanying article (Debiak et al., 2016), we have provided an optimized protocol for the analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to further analyze mustard-induced PARylation and its functional consequences, in general. Thus, in the present study, we performed a comprehensive characterization of the PARylation response in HaCaT cells after treatment with four different mustard agents, i.e., SM, CEES, HN2, and chlorambucil, on a qualitative, quantitative and functional level. In particular, we recorded substance-specific as well as dose- and time-dependent PARylation responses using independent bioanalytical methods based on single-cell immuno-fluorescence microscopy and quantitative isotope dilution mass spectrometry. Furthermore, we analyzed if and how PARylation contributes to mustard-induced toxicity by treating HaCaT cells with CEES, SM, and HN2 in combination with the clinically relevant PARP inhibitor ABT888. As evaluated by a novel immunofluorescence-based protocol for the detection of N7-ETE-guanine DNA adducts, the excision rate of CEES-induced DNA adducts was not affected by PARP inhibition. Furthermore, while CEES induced moderate changes in cellular NAD(+) levels, annexin V/PI flow cytometry analysis revealed that these changes did not affect CEES-induced short-term cytotoxicity 24h after treatment. In contrast, PARP inhibition impaired cell proliferation and clonogenic survival, and potentiated micronuclei formation of HaCaT cells upon CEES treatment. Similarly, PARP inhibition affected clonogenic survival of cells treated with bi-functional mustards such as SM and HN2. In conclusion, we demonstrate that PARylation plays a functional role in mustard-induced cellular stress response with substance-specific differences. Since PARP inhibitors exhibit therapeutic potential to treat SM-related pathologies and to sensitize cancer cells for mustard-based chemotherapy, potential long-term effects of PARP inhibition on genomic stability and carcinogenesis should be carefully considered when pursuing such a strategy.

Semi-automated solid phase extraction method for the mass spectrometric quantification of 12 specific metabolites of organophosphorus pesticides, synthetic pyrethroids, and select herbicides in human urine

Organophosphate and pyrethroid insecticides and phenoxyacetic acid herbicides represent important classes of pesticides applied in commercial and residential settings. Interest in assessing the extent of human exposure to these pesticides exists because of their widespread use and their potential adverse health effects. An analytical method for measuring 12 biomarkers of several of these pesticides in urine has been developed. The target analytes were extracted from one milliliter of urine by a semi-automated solid phase extraction technique, separated from each other and from other urinary biomolecules by reversed-phase high performance liquid chromatography, and detected using tandem mass spectrometry with isotope dilution quantitation. This method can be used to measure all the target analytes in one injection with similar repeatability and detection limits of previous methods which required more than one injection. Each step of the procedure was optimized to produce a robust, reproducible, accurate, precise and efficient method. The required selectivity and sensitivity for trace-level analysis (e.g., limits of detection below 0.5ng/mL) was achieved using a narrow diameter analytical column, higher than unit mass resolution for certain analytes, and stable isotope labeled internal standards. The method was applied to the analysis of 55 samples collected from adult anonymous donors with no known exposure to the target pesticides. This efficient and cost-effective method is adequate to handle the large number of samples required for national biomonitoring surveys.

Plasma Levels of Conjugated Bile Acids in Newborns After a Short Period of Parenteral Nutrition

Patients receiving parenteral nutrition (PN) frequently exhibit liver dysfunction. The authors previously reported that plant sterols of lipid emulsions added to the nutritional solution of newborns receiving PN accumulate in plasma and cell membranes and may contribute to the development of cholestasis. Conjugated bile acids (BA) have been shown to be useful markers of cholestasis. Plasma levels of several BA in newborns were quantified after administration of PN for less than 2 weeks. Plasma samples from 15 healthy control infants (CN), 22 patients who had received PN for 3-15 days (T1), and 9 patients scheduled to receive PN (T0) were analyzed. After a simple extraction procedure, plasma BA were analyzed by liquid chromatography-tandem mass spectrometry using a quantitative isotope dilution method. The concentrations of BA did not differ significantly between controls and patients before PN (CN vs T0), with the exception of glycocholic acid (GCA; 2.30 ± 2.60 µM vs 7.29 ± 5.39 µM, respectively). There was a significant difference in several BA between controls and patients after PN (2.30 ± 2.60 µM vs 7.61 ± 6.46 µM for GCA, respectively; 4.02 ± 3.49 µM vs 11.88 ± 11.05 µM for taurocholic acid [TCA], respectively; and 4.81 ± 3.49 µM vs 13.58 ± 12.22 µM for taurochenodeoxycholic + taurodeoxycholic + tauroursodeoxycholic acids [TCDCA+TDCA+TUDCA], respectively). In newborns receiving PN, a short period of PN is associated with an early increase of some conjugated BA. These results suggest that GCA, TCA, and TCDCA+TDCA+TUDCA levels could be used as early markers of PN-related cholestasis.

Direct determination of dialkyl phosphates by strong anion‐exchange liquid chromatography/atmospheric pressure chemical ionization mass spectrometry using a quadrupole ion trap instrument

The direct determination of dialkyl phosphates (DAPs) in water by strong anion-exchange (SAX) liquid chromatography/atmospheric pressure chemical ionization (APCI) mass spectrometry was investigated. The SAX high-performance liquid chromatography (HPLC) column was eluted with methanol/water gradients containing ammonium formate (AF) separating the DAPs which included six dimethyl- and diethyl-substituted phosphates, thiophosphates, and dithiophosphates. The high buffer concentrations required for separation were compatible with -ve APCI, but in +ve APCI the DAPs were unstable giving anomalous ions such as [M+15]+ and [M+29]+. These ions are believed to result from ion molecule reactions with CH3OH2+ in the plasma. DAPs are very stable in -ve APCI being detected as abundant [M-H](-) ions, even with 200 mM AF. At higher AF concentration formate clusters ([M+45](-) and [M+91](-)) were seen. Fragmentation by collision-activated dissociation (CAD) was more efficient for deprotonated ethyl-substituted DAPs which lost ethylene followed by ethanol. APCI instrument detection limits were in the low ng/mL range and the response was highly linear. Isotope dilution quantitation using d10-diethyl dithiophosphate (DEDTP) as an internal standard produced an instrument detection limit of 2 ng DEDTP/mL and method detection limit (MDL) of 9.3 ng/mL with accuracy of 99% (spike concentration, 25 ng/mL). DAP mixtures required storage in cold, dry conditions and alcohol solvents should be avoided because of solvolysis reactions.

Optimization of a Multiresidual Method for the Determination of Waterborne Emerging Organic Pollutants Using Solid-Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry and Isotope Dilution Mass Spectrometry

A high-throughput, liquid chromatography/tandem mass spectrometry (LC/MS-MS) method has been developed for the determination of 51 emerging organic pollutants (EOPs) in environmental waters. The method was validated for the analysis of 38 pharmaceutically active, 10 endocrine disrupting, and three perfluoroalkylated compounds. Method performance parameters, including sample preservatives, pH values used in the solid-phase extraction (SPE), sample storage, sample extract storage time, and matrix effects were discussed in detail for different aquatic matrices, including drinking water, wastewater, and surface water. Isotope-labeled compounds were used as injection internal standards (IIS) or isotope dilution quantitation standards (IDQS) to improve the data quality, investigate the behavior of matrix effects during SPE sample preparation and LC/MS-MS analysis, and to validate isotope dilution mass spectrometric (IDMS) determination of selected compounds. Method detection limits were determined to be in the low ng/L range forthe compounds evaluated. By application of this method to the analysis of effluents and samples downstream of a wastewater treatment plant, more than 35 target EOPs were quantified. We demonstrated method ruggedness by quality control and quality assurance (QC/QA) data, showed that matrix effects were dependent on modes of electrospray ionization, and could not be removed via SPE or cleanup procedures, exerting the same effect to target compounds in both raw and extracted samples. Both 13C- and 2H-labeled IDQS could be added to samples before sample extraction, and their recoveries used to correct matrix effects in LC/MS-MS EOP analyses.

Quantitative Analysis of 39 Polybrominated Diphenyl Ethers by Isotope Dilution GC/Low-Resolution MS

A GC/low-resolution MS method for the quantitative isotope dilution analysis of 39 mono- to heptabrominated diphenyl ethers was developed. The effects of two different ionization sources, electron impact (EI) and electron capture negative ionization (ECNI), and the effects of their parameters on production of high-mass fragment ions [M - xH - yBr](-) specific to PBDEs were investigated. Electron energy, emission current, source temperature, ECNI system pressure, and choice of ECNI reagent gases were optimized. Previously unidentified enhancement of PBDE high-mass fragment ion [M - xH - yBr](-) abundance was achieved. Electron energy had the largest impact on PBDE high-mass fragment ion abundance for both the ECNI and EI sources. By monitoring high-mass fragment ions of PBDEs under optimized ECNI source conditions, quantitative isotope dilution analysis of 39 PBDEs was conducted using nine (13)C(12) labeled PBDEs on a low-resolution MS with low picogram to femtogram instrument detection limits.

Quantitative analysis of 4-aminobiphenyl-C8-deoxyguanosyl DNA adducts produced in vitro and in vivo using HPLC-ES-MS.

Electrospray mass spectrometry (ES-MS) is a powerful tool for analysis of carcinogen-adducted DNA. In this study, we developed a quantitative isotope dilution method for analysis of N-(deoxyguanosine-8-yl)-4-aminobiphenyl (dG-C8-4-ABP), the principal nucleoside adduct derived from enzymatic hydrolysis of 4-aminobiphenyl (4-ABP)-modified DNA. The method used column switching valves to perform on-line sample concentration and cleanup, which permitted direct analysis of enzymatic DNA hydrolysates using narrow-bore liquid chromatography (LC). ES-MS detection was performed using a single quadrupole instrument by monitoring M+H+ and two fragment ions characteristic for dG-C8-4-ABP, along with M+H+ and a fragment ion for the deuterated internal standard. The detection limit for dG-C8-4-ABP in DNA hydrolysates was approximately 10 pg on-column, equivalent to 0.7 dG-C8-4-ABP adducts in 10(7) normal nucleotides for a sample containing 100 microg DNA. The method was applied to the analysis of calf thymus DNA modified in vitro through reaction with N-hydroxy-4-ABP and of hepatic DNA isolated from mice treated in vivo with two dose levels of 4-ABP.

The determination of geosmin and 2-methylisoborneol in water using isotope dilution high resolution mass spectrometry

Geosmin and 2-methylisoborneol (2-MIB) are extracted from water onto Ambersorb 572, desorbed into dichloromethane (DCM) and analyzed by gas chromatography-high resolution mass spectrometry (GC-HRMS) at a mass resolution of 7000. The use of the granular adsorbent Ambersorb 572 allows extraction by rolling the sample bottle, isolation of the adsorbent by filtration, desorption of the analytes into DCM in the autosampler vial and injection without plugging the syringe needle. Because there is no sample clean-up, HRMS is necessary to differentiate the analytes from chemical interferences when present. Isotope dilution quantitation with d 3-geosmin and d 3-2-MIB is required because the recoveries of geosmin and 2-MIB from water are highly variable. The Ambersorb 572/GC-HRMS method with isotope dilution quantitation was compared with the closed-loop stripping (CLS)/GC-low resolution mass spectrometry (LRMS) method with external standard quantitation. Increased productivity (up to 40 samples/day), faster turnaround times (48 h), better between-run precision (7.7% for geosmin and 5.5% for 2-MIB) and accuracy (±11% for geosmin and ±6% for 2-MIB) over the CLS/GC-LRMS method were achieved. Detection limits of 2.0 ng/L for geosmin and 2.0 ng/L for 2-MIB were obtained for the Ambersorb 572/GC-HRMS method. The method was successfully applied to 152 samples from Lake Ontario water supplies.

Syntheses of deuterium-labelled pristanic and phytanic acids

The syntheses of tetradeuterated pristanic and phytanic acids, suitable for isotope dilution quantitation or pristanic and phytanic acids in plasma, is described. The key reaction, a Favorsky rearrangement, which simultaneously generates a methyl branch and incorporates deuterium, should be suitable for the preparation of other isotopically-labelled branched chain acids.

Determination of nickel, gold and silver in gallium arsenide by radioactivation analysis based on the quantitative isotope dilution principle

A method of radioactivation analysis has been developed for the determination of Ni, Au and Ag impurities in gallium arsenide. The separation and substoichiometric extraction of these elements were studied and analytical procedures are suggested for their determination. All components are separated by suitable procedures and determined by substoichiometric methods. Ni is extracted as diethyldithiocarbamate into toluene, Au as a complex of rhodamine-B in chloroform, and Ag as dithizonate in carbon tetrachloride. The contents of Ni, Au and Ag in a gallium arsenide crystal with a carrier concentration of 1.8·1016/cm3 were 0.05–0.08, 0.006–0.008 and 0.002–0.005 ppm, respectively.

Determination of manganese, copper, zinc and cadmium in gallium arsenide by radioactivation analysis based on the quantitative isotope dilution principle

A method of radioactivation analysis has been developed for the determination of Mn, Cu, Zn and Cd impurities in gallium arsenide. After irradiation, arsenic and gallium are separated by distillation and solvent extraction, then the impurity elements are determined by substoichiometric methods. Mn is extracted as tetraphenylarsonium permanganate into chloroform, and other elements as dithizonates in carbon tetrachloride under various conditions. The contents of Mn, Cu, Zn and Cd in a gallium arsenide crystal with a carrier concentration of 1.8·1016/cc were 0.004, 0.02, 0.006 and 0.04 ppm, respectively.