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.     

Sulfur trace determination in petroleum products by isotope dilution ICP-MS using direct injection by thermal vaporization (TV-ICP-IDMS)

An accurate, sensitive, and fast method for direct determination of total sulfur in petroleum products after thermal vaporization of an isotope-diluted sample was developed by using ICP-MS. ³⁴S-labelled dibenzothiophene spike was used for the isotope dilution step. The isotope-diluted sample was injected into a thermal vaporizer which was directly connected by a heated transfer line to the plasma torch. Sample transport was achieved by using a helium gas flow, and the isotope ratio ³⁴S/³²S was determined within seconds after injection. No other sample preparation other than the simple and fast isotope dilution step, which enables accurate and sensitive determination of sulfur at high sample throughputs, is necessary. Thus, this technique fits all needs for routine analyses. Validation of the TV-ICP-IDMS method was carried out by analyzing the certified gas oil reference materials BCR672 and BCR107. Comparison of results for noncertified low- and high-boiling samples, obtained from an ICP-IDMS microwave-assisted digestion method, also resulted in very good agreement. The low detection limit of 40 ng/g and the large dynamic range of TV-ICP-IDMS fulfill all necessities to allow analysis of sulfur in different petroleum products, e.g., even at the low concentration level of ‘sulfur-free’ gasoline.     

Continuous-wave room-temperature laser oscillation of Cr(3+):MgO

Continuous-wave laser oscillation of Cr(3+):MgO at room temperature was realized under argon-ion laser pumping at 476 and 514 nm. The free-running laser wavelength was 840 nm, and with different mirror sets laser oscillation at 824, 830, 870, and 878 nm was also realized. With different crystals a maximum output power of 48 mW and a lowest threshold with respect to the absorbed pump power of 80 mW were realized. The slope efficiencies with respect to the absorbed pump power were as high as 2.3%. No thermal effects were observed for absorbed pump powers as great as 2.7 W.     

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. Received: 5 July 1996/Accepted: 7 August 1996