Heilmann Jens, Heumann Klaus G
Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University, Duesbergweg 10-14, 55099, Mainz, Germany.
Anal Bioanal Chem. 2008 Jan;390(2):643-53. doi: 10.1007/s00216-007-1574-7. Epub 2007 Sep 14.
A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step 34S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental 34S-enriched sulfur. Thiophene was determined in gasoline, 'sulfur-free' gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 microg g(-1) was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.
通过将毛细管气相色谱与四极杆电感耦合等离子体质谱联用(GC-ICP-IDMS),开发了一种用于准确测定低沸点和高沸点石油产品中硫物种的物种特异性同位素稀释技术。在同位素稀释步骤中,从富含34S的元素硫出发,以毫克规模合成了34S标记的噻吩、二苯并噻吩以及混合的二苯并噻吩/4-甲基二苯并噻吩加标化合物。测定了汽油、“无硫”汽油和石脑油中的噻吩。通过分析参考物质NIST SRM 2296,物种特异性GC-ICP-IDMS的准确性通过与认证值的出色吻合得到了证明。检测限始终受同位素色谱图背景噪声的限制,测定噻吩的绝对检测限为7 pg,在所用实验条件下相当于7 ng硫/克样品。测定了不同高沸点石油产品(如瓦斯油、柴油和取暖油)中的二苯并噻吩和4-甲基二苯并噻吩。在这种情况下,两种硫物种的浓度范围很广,从约<0.04到超过2000 μg g-1。通过GC-ICP-MS和GC-EI-MS平行实验(EI-MS为电子轰击电离质谱),证明了共洗脱烃类对ICP-MS硫信号有重大影响,这会显著影响外部校准得到的结果,但不会影响同位素稀释技术得到的结果。