Thermal Ionization Isotope Dilution Mass Research Articles

Development of an Isotope Dilution Mass Spectrometric Method for Dimethylthallium Speciation and First Evidence of Its Existence in the Ocean

A sensitive analytical method for the determination of dimethyl thallium (Me2Tl+) in environmental samples by positive thermal ionization isotope dilution mass spectrometry (PTI-IDMS) was developed. For the necessary low detection limit and for species selective determination, PTI-IDMS was connected with species-unspecific enrichment of thallium from ocean water samples by a strongly basic anion exchanger and a species-specific extraction step, respectively. For isotope dilution, a 203Tl-enriched Me2Tl+ spike solution was synthesized and characterized with respect to its isotopic composition and concentration. The spike solution was stable for the 30-month period of investigations under dark storage conditions at pH = 2 and 4 °C. The detection limit of the developed method is 0.4 ng L-1 for 500 mL ocean water samples and the species selectivity of Me2Tl+, compared with that of inorganic thallium, is >500. In different surface water samples of the Atlantic Ocean from 50°N to 64°S and in one depth profile down to 4000 m, Me2Tl+ concentrations in the range of <0.4 to 3.2 ng L-1 were determined. This is the first time that dimethyl thallium could be detected in environmental samples. Positive detection of the organothallium compound was found in about 20% of all samples analyzed. By also analyzing the total thallium content with PTI-IDMS it was found that in these cases 3−48% of thallium exists in the methylated form. From its occurrence in the remote areas of the South Atlantic, from positive correlation with the bioactivity in the corresponding ocean water, and from the fact that Me2Tl+ is not known as an anthropogenic substance, it follows that a biogenic origin must be assumed.

Use of thermal ionization isotope dilution mass spectrometry (TI-IDMS) as an oligo-element method for the determination of photographically relevant trace elements in AgCl emulsions

Thermal ionization isotope dilution mass spectrometry (TI-IDMS) was used as an oligo-element method for the determination of Cr, Cd and Pb in photographic AgCl emulsions. After addition of an appropriate amount of isotopically enriched spikes (53Cr, 116Cd and 206Pb) to the solid samples, the latter were completely dissolved in NH3 solution, permitting isotopic exchange to take place. Thereafter, AgCl was selectively removed by precipitation, whereby ultrasonic treatment was used to enhance the recovery of the elements of interest. Despite the use of concentrated HNO3 and H2O2 during further sample processing, preliminary experiments indicated the presence of a substantial remainder of the organic matrix (gelatine). Hence, the analytes of interest were isolated by means of electrolytic deposition on Pt electrodes. Subsequently, the deposits were dissolved from the Pt electrodes using a mixture of concentrated HNO3 and H2O2 and the solutions evaporated to dryness. The solid residues were taken up in diluted HNO3 and loaded onto Re filaments. In order to improve the ionization yield, prior to the sample, a silicagel suspension containing AlCl3 was loaded onto the filament and after sample loading, both H3BO3 (for Cr and Pb) and H3PO4 (for Cd and Pb) were added as further ionization aids. Finally, the isotope ratios of interest (52Cr/53Cr, 114Cd/116Cd and 206Pb/208Pb) were determined using thermal ionization mass spectrometry, whereby all three analyte elements were vaporized from the same filament. The limits of detection obtained using this procedure range from 0.4 ng (for Cd) to 4 ng (for Pb). Four different AgCl emulsions were analyzed. For Cr, the concentration found was quite similar for all emulsions analyzed, as it varied between ∼ 40 and ∼ 100 ng/g only. For Cd, very low values were found for all samples analyzed (≤ 3 ng/g). Finally, for Pb a much larger variation from ∼ 10 ng/g up to ∼ 5.5 μg/g was observed. For the sample with the highest Pb content, an excellent agreement could be established between the results obtained using quadrupole-based ICP-IDMS and those using TI-IDMS. For the determination of Cr by means of quadrupole-based ICP-IDMS, an instrument equipped with a ShieldTorch system was used to avoid spectral overlap of the 52Cr+ and 40Ar12C+ ion signals. Also in this case, the results obtained are in very good agreement with those obtained using TI-IDMS. The comparison between TI-IDMS and ICP-IDMS also made clear that sample inhomogeneity limits the between-sample precision attainable.

Definitive method certification of clinical analytes in lyophilized human serum: NIST Standard Reference Material (SRM) 909b

The National Institute of Standards and Technology (NIST) has developed several Standard Reference Materials (SRMs) based on human serum. NIST SRM 909b, Human Serum, is a lyophilized human serum material with concentrations for seven organic and six inorganic analytes at two levels certified solely by definitive methods (DMs). This material provides the vehicle by which high precision, high accuracy measurements made with DMs at NIST can be transferred through the measurement hierarchy to other laboratories. Isotope dilution gas chromatographic-mass spectrometric (GC-IDMS) methods were applied to measure cholesterol, creatinine, glucose, urea, uric acid, triglycerides, and total glycerides. Thermal ionization isotope dilution mass spectrometry (TI-IDMS) was used for determination of lithium, magnesium, potassium, calcium, and chloride. In addition, chloride was determined by coulometry, providing a comparison between two DMs. Sodium, which lacks a stable isotope that would permit isotope dilution mass spectrometric (IDMS) measurement, was determined by gravimetry. SRM 909b includes certified values for total glycerides and triglycerides, which were not certified in the previous lot of this material (SRM 909a). Improvement in uniformity of vial fill weight in the production of SRM 909b resulted in smaller certified uncertainties over previous freeze-dried serum SRMs. Uncertainties at the 99% level of confidence for relative expanded uncertainty (%) for certification of the organic analytes on a mmol/L/g basis ranged from 0.44% for urea (level II) to 5.04% for glucose (level II). (In-house studies have shown glucose to be a relatively unstable analyte in similar lyophilized serum materials, degrading at about 1% per year.) Relative expanded uncertainties (99% C.I.) for certification of inorganic analytes on a mmol/L/g basis ranged from 0.25% for chloride (level I) to 0.49% for magnesium (level II).

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples.

Accurate and precise determination of chromium by isotope dilution mass spectrometry in some environmental materials

A method for the determination of chromium with the help of thermal ionization isotope dilution mass spectrometry was developed. In this type of mass spectrometry a stable signal depends mainly on the purity of the loaded sample. Therefore, the main effort was the development of a method for the separation of the chromium from the matrix. A separation procedure based on ion exchange is described. Two alternative thermal ionization methods were investigated. With the first one (the so-called triple filament technique) the measurable amount of chromium ranges from 10 ng to 10 μg. The second technique (a single filament technique) needs 0.1–10 μg. For economical reasons the last technique was chosen. Combined with a blank value of 0.4 ± 0.2 μg and a sample intake of 1–2 g the detection limit of the described method is approximately 0.5μg/g. To test the method a number of certified reference materials were analyzed.

Comparison of heavy metal analyses in hydrofluoric acid used in microelectronic industry by ICP-MS and thermal ionization isotope dilution mass spectrometry

An isotope dilution mass spectrometric (IDMS) method with the thermal ionization (TI) technique has been developed for the determination of trace impurities of Cr, Fe, Ni, Cu, Zn, Ag, Cd, Tl, Pb, Th, and U in high-purity HF (50% by weight) used in the semiconductor industry. The evaporation step of the HF solution was carried out in an apparatus which did not significantly contribute to contaminations of the heavy metals to be analysed. This apparatus allowed fast evaporation of the HF solution of up to 200 ml/h and therefore also a fast trace heavy metal/matrix separation was carried out. The evaporation step was also used in connection with inductively coupled plasma mass spectrometry (ICP-MS) when applying the isotope dilution technique and an external calibration for quantification, respectively. The detection limits for TI-IDMS were (in pg/g): Cr=30, Fe=400, Ni=70, Cu=20, Zn=1100, Ag=70, Cd=10, Tl=1, Pb=16, Th=3, and U=1. With ICP-MS in combination with the evaporation step, detection limits of less than 50 pg/g have been achieved for Cr, Ni, and Zn and of <5 pg/g for the other elements except Fe, which could not be determined in concentrations less than 100 ng/g. On the other hand, the detection limits were much higher when the HF matrix was not removed before measuring by ICP-MS. A comparison of the different ICP-MS methods (isotope dilution technique and external calibration for both HF evaporated samples and those with HF matrix) with the results of TI-IDMS has been carried out. An excellent agreement was achieved between the results of TI-IDMS and the two ICP-MS methods using the HF evaporation step, whereas the ICP-MS techniques without HF evaporation essentially deviated from these results. Fe was the only trace element of all investigated heavy metals which could only be analysed by TI-IDMS in high purity HF in a concentration of about 3 ng/g. Although ICP-MS with isotope dilution and external calibration resulted in comparable analytical data, the ICP-IDMS method has some practical advantages such as time-saving and more reliable results.

Mass Spectrometry Element Analysis-Advances and New Perspectives in a Modern Analytical Method

Abstract Mass spectrometry is an extremely sensitive method for the determination of elements down to the sub-pg level. The different ionization methods used for mono-and multi-element analyses are discussed. Spark source mass spectrometry has been the most commonly multi-element technique in the past. However, inductively coupled plasma and glow-discharge mass spectrometry will probably replace spark source mass spectrometry in the future. Accurate trace element determinations can only be obtained with isotope dilution mass spectrometry. Because of a lack of accurate methods, isotope dilution is one of the few definitive calibration techniques that can be used for trace element analyses. The formation of negative and positive thermal ions on a hot metal surface is the most frequently applied ionization method in isotope dilution mass spectrometry. All elements which can be analyzed by this method are listed. A selected number of trace determinations with thermal ionization isotope dilution mass spectrometry are discussed, e.g. the analysis of ultra-low amounts of heavy metals in Antarctic snow, of halide traces in geochemical materials, and of nitrite and nitrate in food samples. Determinations of element species with the isotope dilution technique will become more and more important in the future.