Systematic comparison of post-column isotope dilution using LC-CO-IRMS with qNMR for amino acid purity determination

Analytical and Bioanalytical Chemistry - Determination of the purity of a substance traceable to the International System of Units (SI) is important for the production of reference materials...     

Iodine determination in milk by isotope dilution analysis

Iodine is an essential trace element in the human diet. It is utilized in the synthesis of L-monoiodothyrosine, which is a precursor of the thyroid hormones, thyroxin and triiodothyronin. In this study, a method that can determine iodine concentrations in milk has been developed. The method is based on substoichiometric isotope dilution analysis (IDA). Iodine concentrations were measured in milk, which has been collected from three big cities and environment municipalities of Aegean Region. The iodine concentration ranges were within 436.8 and 896.7 μg/kg in milk samples. Mean iodine concentration was not greatly changed from season to season, between 1998 and 2002. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mass-spectrometric determination of uranium by means of isotope dilution analysis

The paper describes experience concerning the determination of uranium in nuclear fuels by mass-spectrometric isotope dilution analysis. As a spike, the solution of²³³U was used. The method was applied to the uranium content determination in non-irradiated and irradiated samples of nuclear fuels.     

Multi-element determination in environmental samples by mass spectrometric isotope dilution analysis using thermal ionization

Summary A procedure for multielement analysis using mass spectrometry with thermal ionization and the isotope dilution technique was developed. The analytical procedure was checked by investigating the Standard Reference Material no. 1575 Pine Needles supplied by the National Bureau of Standards, USA. The concentrations of the elements Fe, Ni, Cu, Zn, Ga, Rb, Sr, Cd, Tl, and Pb were simultaneously determined in this material. The total amount of ions observed in the mass spectrum originating from the material investigated is discussed. It follows that it might be possible to increase the number of elements determinable simultaneously to 19.

---

Multielementbestimmung in Umweltproben nach der massenspektrometrischen Isotopenverdünnungsmethode mit thermischer IonisationTeil I: Fichtennadeln

Zusammenfassung Ein Verfahren für die Multielement-analyse nach der massenspektrometrischen Isotopenverdünnungsmethode mit thermischer Ionisation wurde entwickelt. Eine Überprüfung des Analysenverfahrens erfolgte durch die Untersuchung des Standardreferenzmaterials Nr. 1575 Pine Needles, National Bureau of Standards, USA. In diesem Material konnten die Konzentrationen der Elemente Fe, Ni, Cu, Zn, Ga, Rb, Sr, Cd, Tl und Pb simultan bestimmt werden. Die insgesamt im Massenspektrum beobachteten, zur Probe gehörenden Ionen werden diskutiert. Hieraus folgt, daß es möglich sein könnte, die Zahl der gleichzeitig zu bestimmenden Elemente bis auf 19 zu vergrößern.

     

High accuracy isotope dilution analysis for the determination of ethanol using gas chromatography-combustion-isotope ratio mass spectrometry

A procedure was established for the determination of ethanol in water samples by isotope dilution analysis. After spiking the sample with labelled [13C2]ethanol, it was analysed by gas chromatography-combustion-isotope ratio mass spectrometry. Results are reported for two certified reference materials and also ethanol solutions prepared for a CITAC (Co-operation on International Traceability in Analytical Chemistry) interlaboratory comparison. The certified reference materials were certified using the dichromate titration method at nominal levels of 80 and 200 mg per 100 mL. The CITAC solutions were prepared gravimetrically at nominal levels of 50, 80 and 200 mg per 100 mL. The results of the analysis agree well to within 0.5% of the gravimetric values of the different samples. The relative expanded standard uncertainties (with a coverage factor equal to 2) associated with the results varied between 0.18 and 0.37%, a range that encompassed the gravimetric values for the different samples. A complete uncertainty budget was also drawn up so that the different contributions could be identified and quantified. The main contributions were due to variations in the measured isotope amount ratios and a 'between' blend component introduced to quantify the contribution of factors such as the degree of matching of the isotope amount ratios between standards and samples used in the isotope dilution analysis.     

The determination of zinc by substoichiometric isotope dilution

Recently, R??I?KA et al. proposed a determination of zinc in highly pure germanium dioxide by a substoichiometric extraction technique. In the present work, the effects on the substoichiometric extraction of equilibrium time, pH and interfering ions were investigated by radioactive tracer techniques and spectrophotometric measurements. The sensitivity of the procedure is limited by the blanks and the addition of oxalate ions can give rise to inaccurate results. The specific activity of ⁶⁵Zn was also determined by substoichiometric extraction.     

Measurement of labile Cu in soil using stable isotope dilution and isotope ratio analysis by ICP-MS

Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium (<7 days) with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool by using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, due to the short half-life of the ⁶⁴Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed a technique using enriched ⁶⁵Cu stable isotope and measurement of ⁶³Cu/⁶⁵Cu ratios by quadrupole inductively coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils using E value techniques. Mass spectral interferences in detection of ⁶³Cu/⁶⁵Cu ratios in soil extracts were found to be minimal. Isotope ratios determined by quadrupole ICP-MS compared well to those determined by high-resolution (magnetic sector) ICP-MS. E values determined using the stable isotope technique compared well to those determined using the radioisotope for both uncontaminated and Cu-contaminated soils.     

Redox substoichiometry in isotope dilution analysis

Isotope dilution analysis using the redox substoichiometric principle has been applied to the determination of antimony content in metallic zinc. As the substoichiometric reaction, the oxidation of trivalent to pentavalent antimony with potassium permanganate was used, followed by separation of these species by the BPHA extraction of trivalent antimony. Determination of antimony contents less than 0.5 μg was found to be possible with good accuracy, without separation of zinc ions. The antimony content in metallic zinc was determined to be 19.7±0.8 ppm, in good agreement with the results obtained by the other analytical methods.     

The determination of lead in blood using isotope dilution inductively coupled plasma mass spectrometry

Isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) was applied to the certification of Pb in four levels of NIST blood SRM, 955a. This standard reference material (SRM) represents a significant improvement over the previous blood reference material and will greatly aid method development. The lowest level, 47.76 ng/g Pb was determined with analysis uncertainty (95% CI, ID-ICP-MS uncertainties) of less than 1% and the highest level, 517.9 ng/g Pb to 0.3%. Uncertainty in the lowest level was due to sample inhomogeneity and variability in the analytical blank as the RSD on ratio measurements was typically better than 0.2%. Properly applied isotope dilution coupled with careful isotope ratio measurements on the ICP-MS offers precision and accuracy for blood Pb analyses beyond what is currently obtainable with routine methods.     

The determination of nitrogen in metals by isotope dilution

A wet chemical procedure for determining the amount of nitrogen in a metal or alloy has been developed which utilizes the isotope dilution technique. Ammonium sulfate, either enriched or depleted in ¹⁵N, is added to the metal sample during solution procedures. Ammonium ions resulting from the hydrolysis of bound nitrogen in the metals mix with that of the tracer and the total is then oxidized to N₂ in which form the element is analyzed in the mass spectrometer. The method has been tested on a variety of metals and alloys including thorium, lanthanum, yttrium, titanium, chromium, manganese, various steels, nickel-chromium, ferrotitaniuin, ferromanganese and ferrochromium. The range of nitrogen in these materials was from -2 ppm to almost 6%. Average precision was generally better than ± 5%.     

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 ¹⁹⁴Pt, 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. Figure Simultaneous correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

The determination of rubidium by the method of stable isotope dilution

The rubidium contents of a granite (G-1), a diabase (W-1) and sea-water have been determined by mass spectrometric isotope dilution analysis. The values found are: G-1, 214 p.p.m-; W-1, 21.3 p.p.m.; sea water, 121.4 μg/l. These results show excellent agreement with values obtained at Harwell by neutron activation analysis, and the coefficient of variation for four determinations is usually ±1–2%.Rubidium ions were produced in the mass spectrometer by either a side filament or a centre filament technique. The former method enables rubidium and lithium determinations to be combined; the results obtained by the second method suggest that concentrations of the order of 1 p.p.m. may be determined for a sample of only a few mg with little chemical treatment beyond that required to decompose the sample.     

Quantitative element analysis by isotope dilution in diode laser graphite furnace atomic absorption spectrometry

The paper reviews the application of the isotope dilution technique in optical atomic absorption spectrometry by use of a low-pressure graphite tube furnace as atomizer and diode lasers as radiation sources. The principles and the methodology to obtain accurate quantitative results despite of the occurrence of interferences are presented. The successful application of different Doppler-limited and Doppler-free spectrometric techniques is also presented. The perspectives but also the limitations of this new method are discussed.     

Stable isotope dilution assays in mycotoxin analysis

The principle and applications of stable isotope dilution assays (SIDAs) in mycotoxin analysis are critically reviewed. The general section includes historical aspects of SIDAs, the prerequisites and limitations of the use of stable isotopically labelled internal standards, and possible calibration procedures. In the application section actual SIDAs for the analysis of trichothecenes, zearalenone, fumonisins, patulin, and ochratoxin A are presented. The syntheses and availability of labelled mycotoxins for use as internal standards is reviewed and specific advances in food analysis and toxicology are demonstrated. The review indicates that LC–MS applications, in particular, require the use of stable isotopically labelled standards to compensate for losses during clean-up and for discrimination due to ion suppression. As the commercial availability of these compounds continues to increase, SIDAs can be expected to find expanding use in mycotoxin analysis.