Isotope Dilution For Determination Research Articles

Isotope dilution determination for the trace level of 4(5)-methylimidazole in beverages using dispersive liquid-liquid microextraction coupled with ESI-HPLC–MS/MS

In this study, a rapid and reliable pretreatment method called dispersive liquid-liquid microextraction (DLLME) was developed for the determination of 4(5)-methylimidazole (4-MeI) in beverages. The clean-up samples were analyzed by a high performance liquid chromatography coupled with triple quadrupole mass spectrometer (HPLC–MS/MS) using a reversed-phase C18 column (250 mm × 4.6 mm, 5 μm). The matrix effects and the fault of DLLME operation were corrected by the isotope dilution technique. The developed method exhibited the limit of quantification (0.3 μg L−1) and excellent linearity (R2 = 0.999). In addition, the recovery values of 4-MeI in carbonated beverage were ranging from 102.60% to 113.22%, in soft drinks were ranging from 103.24% to 108.85%. The content 4-MeI was detected in thirteen beverage samples treated with DLLME and solid phase extraction method (SPE) (ranging from 6.4 to 165.5 μg L−1). The consistent result of 4-MeI content detected by DLLME and SPE method concluded that the established method on the basis of DLLME was rapid, robust and accurate for the trace 4-MeI determination in beverages.

Comparison of Dilution, Filtration, and Microwave Digestion Sample Pretreatments in Elemental Profiling of Wine by ICP-MS.

Wine elemental composition varies by cultivar, geographic origin, viticultural and enological practices, and is often used for authenticity validation. Elemental analysis of wine by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is challenging due to the potential for non-spectral interferences and plasma instability arising from organic matrix components. Sample preparation mitigates these interferences, however, conflicting recommendations of best practices in ICP-MS analysis of wine have been reported. This study compared direct dilution, microwave-assisted acid digestion, and two filtration sample pretreatments, acidification prior to filtration and filtration followed by acidification, in elemental profiling of one white and three red table wines by ICP-MS. Of 43 monitored isotopes, 37 varied by sample preparation method, with significantly higher results of 17 isotopes in the microwave-digested samples. Both filtration treatments resulted in lower results for 11 isotopes compared to the other methods. Finally, isotope dilution determination of copper based on natural abundances and the 63Cu:65Cu instrument response ratio agreed with external calibration and confirmed a significant sample preparation effect. Overall, microwave digestion did not compare favorably, and direct dilution was found to provide the best compromise between ease of use and result accuracy and precision, although all preparation strategies were able to differentiate the wines.

Accretion timescale and impact history of Mars deduced from the isotopic systematics of martian meteorites

High precision Sm−Nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on Mars associated with the formation of their mantle sources. These data are used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic. Ages determined from the Sm−Nd isotopic systematics of individual samples are strongly dependent on the assumed Nd isotopic composition of the bulk planet. This assumption is problematic given differences observed between the Nd isotopic composition of Earth and chondritic meteorites and the fact that these materials are both commonly used to represent bulk planetary Nd isotopic compositions. Ages determined from the slope of 146Sm−142Nd whole rock isochrons are not dependent on the assumed 142Nd/144Nd ratio of the planet, but require the sample suite to be derived from complementary, contemporaneously-formed reservoirs. In this work, we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a 143Nd−142Nd whole rock isochron and is also independent of any a priori assumptions regarding the bulk isotopic composition of the planet. This expression is also applicable to mineral isochrons and has been used to successfully calculate 143Nd−142Nd model crystallization ages of early refractory solids as well as lunar samples. This permits ages to be obtained using only Nd isotopic measurements without the need for 147Sm/144Nd isotope dilution determinations. When used in conjunction with high-precision Nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504±6Ma. Because the Sm−Nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification, the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the Solar System. Recent thermal models, however, suggest that Mars-sized bodies cool rapidly in less than ∼5Ma after accretion ceases, even in the presence of a thick atmosphere. Assuming these models are correct, an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504Ma. Late accretional heating of Mars could either be associated with protracted accretion occurring at a quasi-steady state or alternatively be associated with a late giant impact. If this scenario is correct, then accretion of Mars-sized bodies takes up to 60Ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation. This further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets, and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed.

High Precision Isotope Dilution Determination of Potassium by Thermal Ionisation Mass Spectrometry

Two independent articles published more than a decade ago pointed to the potential of the somewhat neglected K-Ca system for very precise K-Ca dating and thermochronology, but have not been followed up since. In the first of these articles, highly precise determination of K and hence the K/Ca ratio in lunar granites showed the feasibility of K-Ca dates of micas with an analytical precision known so far in only U-Pb and Ar/Ar dating. In the second article, it was shown that responses of the K-Ca and Rb-Sr isotopic systems in micas subjected to a slow post-metamorphic cooling could provide new insights into thermochronology. Crucial to the follow-up of these two promising leads is the development of a simple and user-friendly method for routine high precision K determination in real samples, such as the one described in this report. Deux articles independants publies il y a plus d’une decennie et dont les resultats n’ont pas ete suivi depuis ont souligne le potentiel du presque oublie systeme K-Ca pour des datations et de la thermochronologie tres precises. Dans le premier de ces articles, une grande precision dans la determination de K et donc dans celle du rapport K/Ca dans les granites lunaires a permis de fournir des âges K-Ca des micas avec une precision d’analyse connu jusqu’alors uniquement pour les methodes U-Pb et Ar/Ar. Dans le deuxieme article, il a ete montre que les reponses des systemes isotopiques K-Ca et Rb-Sr dans des micas soumis a un lent refroidissement metamorphique pourraient offrir de nouvelles perspectives dans le domaine de la thermochronologie. La mise au point d’une methode simple et conviviale pour la determination a haute precision et en routine des teneurs en K d’echantillons reels, telle que celle decrite dans le present rapport est cruciale pour le suivi de ces deux pistes prometteuses.

Isotope Dilution Determinations of Lu, Hf, Zr, Ta and W, and Hf Isotope Compositions of NIST SRM 610 and 612 Glass Wafers

Isotope dilution determinations of Lu, Hf, Zr, Ta and W are reported for nine test portions (five for W) of NIST SRM 610 and 612 glass wafers. Additionally, all test portions were analysed for their Hf isotope compositions. In general, high field strength elemental (HFSE) distributions in NIST SRM 610 and 612 were reproducible to ∼± 1%, except for Zr (± 5%) in NIST SRM 612, and absolute reported concentrations agreed with previously published values, but with higher precision. The slightly worse reproducibility of Zr in NIST SRM 612 compared to other HFSE is interpreted to result from analytical scatter, rather than sample inhomogeneity. The analyses demonstrated elemental homogeneity for both glass wafers for samples of 1–2 mg with respect to the precision of the method, i.e., ± 1% or better. Average Hf isotope compositions for both glass wafers agreed within uncertainty and the weighted average of all determinations yielded a mean 176Hf/177Hf ratio of 0.282111 ± 0.000009 (95% confidence level). However, although mean values for NIST SRM 610 and 612 agreed within analytical limits, NIST SRM 610 test portions showed a tendency of systematically elevated isotope composition of ∼ 0.5 ɛHf units when compared to NIST SRM 612, which may indicate a slightly more radiogenic Hf isotope composition of NIST SRM 610. The results of this study suggest that NIST SRM 610 and 612 are valuable calibrators for HFSE in situ analyses within the given uncertainties.

Isotope dilution determination of polycyclic aromatic hydrocarbons in olive pomace oil by gas chromatography–mass spectrometry

A gas chromatographic (GC) method with mass spectrometry detection (MS) for the determination of eight polycyclic aromatic hydrocarbons (PAHs) in olive pomace oil has been developed. The oil was diluted with n-pentane and extracted by liquid-liquid partition with dimethyl sulphoxide (DMSO). After water addition and back-extraction with cyclohexane, a thin-layer chromatography on silica gel was performed as a further purification step. The PAHs spot was scraped off from the plate and the final extract was concentrated and analysed by GC-MS in full scan mode. The eight PAHs under investigation were determined in the presence of the corresponding labelled compounds added as internal standards to the sample at the beginning of the analytical process. The identified PAHs were then quantified by the isotope dilution methodology assuring the compensation of the concentration of each analyte for any variation in the sample preparation. The method precision was satisfactory with relative standard deviation (R.S.D.) values in the range 3.6-12.7% for all PAHs. The average recovery rates ranged from 69.0 to 97.5%. Accuracy was also calculated for benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene by analysing a certified reference material (CRM 458, coconut oil) with adequate results. All response curves exhibited a linear fit from 0.1 to 10 microg ml(-1) and the determination coefficients R2 were better than 0.9942. The limits of detection (0.1-0.4 microg kg(-1)) were acceptable when compared with the maximum permitted limit of 2 microg kg(-1) for each of the eight considered PAHs and 5 microg kg(-1) for the sum of the eight PAHs established by the Italian legislation. Measurement uncertainty was finally calculated identifying and quantifying the uncertainty components of the analytical process. The relative expanded uncertainties (Uc), expressed as percent values were in the range 8.5-11.4% thus appropriate for residues quantification in the range of concentrations considered in the present study.

High resolution ID-ICP-MS certification of an estuary water reference material (LGC 6016) and analysis of matrix induced polyatomic interferences.

Reliable trace metal analysis of environmental samples is dependent upon the availability of high accuracy, matrix reference standards. Here, we present Cd, Cu, Ni, Pb and Zn isotope dilution determination for an estuary water certified reference material (LGC 6016). This work highlights the need for high-accuracy techniques in the development of trace element CRMs rather than conventional inter-laboratory trials. Certification of the estuary water LGC6016 was initially determined from a consensus mean from 14 laboratories but this was found to be unsatisfactory due to the large discrepancies in the reported concentrations. The material was re-analysed using isotope dilution ICP-MS techniques. Pb and Cd were determined using a conventional quadrupole ICP-MS (Elan 5000). Cu, Zn and Ni were determined using a magnetic sector ICP-MS (Finnigan Element), which allowed significant polyatomic interferences to be overcome. Using the magnetic sector instrument, precise mass calibration to within 0.02 amu permitted identification of the interferences. Most interferences derived from the sample matrix. For example, the high Na content causes interferences on 63Cu, due to the formation of 40Ar23Na and 23Na2 16O1H, which in a conventional quadrupole instrument would relate to an erroneous increase in signal intensity by up to 20%. For each analyte a combined uncertainty calculation was performed following the Eurachem/GTAC and ISO guideline. For each element a combined uncertainty of 2-3% was found, which represents a 10-fold improvement compared to certification by inter-laboratory comparison. Analysis of the combined uncertainty budget indicates that the majority of systematic uncertainty derives from the instrumental isotope ratio measurements.

Simultaneous Determination of Multiple Aldehydes in Biological Tissues and Fluids Using Gas Chromatography/Stable Isotope Dilution Mass Spectrometry

Biological oxidative stress has been associated with various degenerative disorders and disease states, and accurate and sensitive methods are needed to determine the extent of oxidation occurringin vivo.Peroxidation of polyunsaturated fatty acids forms complex mixtures of aldehydes and other breakdown products because various oxidants are involved and lipid composition is not uniform. Quantitative analysis of multiple lipid peroxidation products yields a more complete measure of biological oxidation than measurement of a single aldehyde, particularly when aldehydes exhibit marked differences in reactivity. This report describes extensions of an established gas chromatography/mass spectrometry method to include stable isotope dilution determination in tissue and plasma of three aldehydic products of lipid peroxidation: hexanal, nonanal, and 4-hydroxy-2-nonenal. Use of deuterated internal standards for each analyte improved precision and accuracy compared to a single internal standard for all three aldehydes. Improvements are attributed to differences in extraction and derivatization efficiencies for individual analytes owing to substantial differences in reactivity. Electron ionization of oxime-tert-butyldimethylsilyl derivatives gave greater specificity for detecting all three aldehydes than was possible using electron-capture ionization ofO-pentafluorobenzyl oxime derivatives. Exchange of the deuterium label of [2,3-2H]HNE internal standard was determined to be minimal during the analyses.

A Critical Review of Inductively Coupled Plasma-Mass Spectrometry for Geoanalysis, Geochemistry, and Hydrology. Part I. Analytical Performance

Abstract Present-day inductively coupled plasma-mass spectrometry (ICP-MS) instrumentation is described briefly. Emphasis is placed on performance characteristics for geoanalysis, geochemistry, and hydrology. Applications where ICP-MS would be indispensable are indicated. Determination of geochemically diagnostic trace elements (such as the rare earth elements [REE], U and Th), of isotope ratios for fingerprinting, tracer and other geo-isotope applications, and benchmark isotope dilution determinations are considered to be typical priority applications for ICP-MS. It is concluded that ICP-MS furnishes unique geoanalytical and environmental data that are not readily provided by conventional spectroscopic (emission and absorption) techniques.

Substoichiometric isotope dilution determination of manganese in biological smples using 2-thenoyltrifluoroacetone in isobutyl methyl ketone

A substoichiometric isotope dilution method was developed for the determination of microgram amounts of manganese. The method involves the use of carrier-free 54Mn with Mn(II) carrier and its complexation with 2-thenoyltrifluoroacetone (TTA) at pH 8.5, the complex then being extracted into isobutyl methyl ketone. A minimum of 50 ng of manganese can be determined. The method was applied to the determination of manganese in several standard reference materials and biological samples such as tea leaves, spices and condiments. The method is simple and fast and yields results with high accuracy and precision.

A thin-layer chromatographic method for the quantitative separation and estimation of S-adenosylmethionine and S-adenosylethionine in rat liver

A procedure is described for the simultaneous isolation, separation, and quantitation of S-adenosylmethionine (AdoMet) and S-adenosylethionine (AdoEt) in rat liver. These compounds are isolated by precipitation with ammonium reineckate, are separated by thin-layer chromatography, and are quantitated by an isotope dilution determination. The procedure was tested with commercial standards added to liver homogenate ranging up to 160 μg AdoMet/g liver and 173 μg AdoEt/g liver; at all of the concentrations tested, the recoveries were linear and accurate. AdoMet recoveries were linear in the presence of 11.6 or 307 μg AdoEt/g liver, and AdoEt recoveries were linear in the presence of 37.8 or 191 μg AdoMet/g liver. AdoMet and AdoEt levels were measured in the livers of rats fed diet containing 0 or 0.3% dl-ethionine for 2 weeks. In the ethionine-treated animals, AdoMet concentrations were lower than in the controls; and, conversely, AdoEt increased from 0 to 259 μg/g liver.

Mass Spectrometric Isotope Dilution Determination of Cadmium in Geochemical Reference Samples

Twenty seven geochemical reference samples have been analysed for cadmium using the stable isotope dilution technique. These include four USGS, one NBS, five CRPG, eleven ANRT and six NIMROC samples. Each sample has been analysed at least in duplicate.The four USGS samples have previously been measured in this laboratory by Rosman and De Laeter, but the present results are believed to be more accurate than the earlier data. Our results for the other twenty three samples are much lower than most of the published data. There is also evidence of cadmium inhomogeneities in some of the samples.

Blood and urine levels of N,N-dimethyltryptamine following administration of psychoactive dosages to human subjects

Psychoactive doses (0.7 mg/kg) of the hallucinogen N,N-dimethyltryptamine (DMT) were administered intramuscularly to 11 normal subjects. A gas chromatographic-mass spectrometric isotope dilution determination of DMT concentrations in whole blood and urine revealed that only a fraction of the injected dose was recovered and the blood DMT concentrations had a very similar time course o the subjectively reported “high”.

Isotope Dilution Determinations and Other Studies of Cytidine Diphosphate Choline, Cytidine Diphosphate Ethanolamine, Deoxycytidine Diphosphate Choline, and Deoxycytidine Diphosphate Ethanolamine in Liver and Liver Tumors

Isotope Dilution Determinations and Other Studies of Cytidine Diphosphate Choline, Cytidine Diphosphate Ethanolamine, Deoxycytidine Diphosphate Choline, and Deoxycytidine Diphosphate Ethanolamine in Liver and Liver Tumors

Isotope dilution determination of chromium as doubly labelled110mAg2 51CrO4

A chromium determination is presented as a model of the doublylabelled compound technique in isotope dilution determinations. The specific radioactivities (aCr,aAg) of the parent soluble compounds and the activities (ACr,AAg) obtained (as gamma-photopeak areas) from an amountw of isolated110mAg251CrO4precipitate, are related byACr/FCraCr=AAg/FAgaag=w whereFCr andFAg are stoichiometric conversion factors, which gives the isotope dilution equation asAAg/aCr=kaAg0/aCr0+aAg0/aCr0·m·x, where the experimentally obtainedAAg/ACr ratios correspond to the dilution with a known quantity m of chromium compound of an unknown amountx in solution. Statistical analysis of the results for several knownx values gave m=0.102±0.003 and a standard straight line for unknown values ofx. The technique is also valid for fission product activity determinations, irrespective of their chemical separation yield.

Lipid mobilization in relation to body composition in man

The concentrations in plasma of free fatty acids, glycerol and immunoreactive insulin and the turnover rates of free fatty acids and glycerol were measured by constant infusion of albumin complexed palmatic-1- 14C and glycerol-2- 3H and correlated with body fat and body fat/body cell mass, obtained by isotope dilution determinations of total water and total exchangeable potassium, in a material of patients with a wide variation in body composition and without diabetes mellitus. Free fatty acid concentration and turnover rate correlated strongly as well as glycerol concentration and turnover rate. Free fatty acid turnover rate/glycerol turnover rate was above three, but not different at different body composition. Free fatty acid concentration showed a trend to positive correlation with body fat and body fat/body cell mass, while glycerol concentration showed a significant positive correlation with these parameters. Insulin was positively correlated with body fat and showed a trend to correlation with body fat/body cell mass. These results indicate that with increasing body fat, or obesity, lipid mobilization and lipolysis are increasing. No correlation between body cell mass and lipid mobilization or lipolysis was found. It therefore appears likely that some factor in adipose tissue is responsible for the increased lipid mobilization and lipolysis in obesity.

Formula omitted] ratios in australites

New isotope dilution determinations of Rb in seven australites, which cover the range in composition of the group, are 15–20% higher than previous determinations by Taylor (1960, 1962) and Taylor and Sachs (1961, 1964), and agree with those of Pinson et al. (1965). The average Rb in australites is increased from 84 to 100 ppm and the average K Rb ratio decreases from 225 to 186 (range 173–194). New K Rb ratios for Henbury subgreywacke average 199 and for Henbury impact glass average 174. A strong positive correlation exists between K and Rb in australites ( r = + 0.990). An inverse correlation apparently exists between K Rb and Rb (+K). The causes of low K Rb ratios are considered. The K Rb ratios in australites are consistent with derivation from a clay-rich sedimentary material analogous in composition to the Henbury subgreywacke. The variation in K Rb ratios between different tektite groups is considered due to variations in parent material.

THE ELECTRON CAPTURE TO NEGATIVE ELECTRON EMISSION BRANCHING RATIO FOR 142Pr DECAY

The ratio of electron capture to negative electron emission for the decay of [Formula: see text] has been found to be (1.64 ± 0.08) × 10−4. The half-life for electron capture, relative to the accepted beta emission half-life of 19.2 hours, is 13.3 ± 0.6 years. The ratio was found by mass-spectrometric stable isotope dilution determinations of the quantities of [Formula: see text] and [Formula: see text] produced by the decay.

Determination of small quantities of potassium and sodium in stony meteoritic material, rocks and minerals

A flame photometric method for the determination of potassium (0.005 0.1%) and sodium (0.01 1.0%) in stony meteorites and other silicate materials is described using a Beckman Model DU flame photometer. A simple scanning procedure eliminated background radiation and a small correction for the effect of magesium on potassium radiation was calculated. Results obtained by this procedure agree well with an evaporative technique and isotope dilution determinations.