Santamaria-Fernandez Rebeca, Carter David, Hearn Ruth
LGC, Queens Road, Teddington, Middlesex, TW11 0LY, UK.
Anal Chem. 2008 Aug 1;80(15):5963-9. doi: 10.1021/ac800621u. Epub 2008 Jun 20.
A new method for the measurement of SI traceable carbon isotope amount ratios using a multicollector inductively coupled mass spectrometer (MC-ICPMS) is reported for the first time. Carbon (13)C/(12)C isotope amount ratios have been measured for four reference materials with carbon isotope amount ratios ranging from 0.010659 (delta(13)C(VPDB) = -46.6 per thousand) to 0.011601 (delta(13)C(VPDB) = +37 per thousand). Internal normalization by measuring boron (11)B/(10)B isotope amount ratios has been used to correct for the effects of instrumental mass bias. Absolute (13)C/(12)C ratios have been measured and corrected for instrumental mass bias and full uncertainty budgets have been calculated using the Kragten approach. Corrected (13)C/(12)C ratios for NIST RM8545 (Lithium Carbonate LSVEC), NIST RM8573 (L-Glutamic Acid USGS40), NIST RM8542 (IAEA-CH6 Sucrose) and NIST RM8574 (L-Glutamic Acid USGS41) differed from reference values by 0.06-0.20%. Excellent linear correlation (R = 0.9997) was obtained between corrected carbon isotope amount ratios and expected carbon isotope amount ratios of the four chosen NIST RMs. The method has proved to be linear within this range (from (13)C/(12)C = 0.010659 to (13)C/(12)C =0.011601), and therefore, it is suitable for the measurement of carbon isotope amount ratios within the natural range of variation of organic carbon compounds, carbonates, elemental carbon, carbon monoxide, and carbon dioxide. In addition, a CO2 gas sample previously characterized in-house by conventional dual inlet isotope ratio mass spectrometry has been analyzed and excellent agreement has been found between the carbon isotope amount ratio value measured by MC-ICPMS and the IRMS measurements. Absolute values for carbon isotope amount ratios traceable to the SI are given for each NIST RM, and the combined uncertainty budget (including instrumental error and each parameter contributing to Russell expression for mass bias correction) has been found to be < 0.1% for the four materials. The advantage of the method versus conventional gas source isotope ratio mass spectrometry measurements is that carbon isotope amount ratios are measured as C(+) instead of CO2(+), and therefore, an oxygen (17)O correction due to the presence of (12)C(17)O(16)O(+) is not required. Organic compounds in solution can be measured without previous derivatization, combustion steps, or both, thus making the process simple. The novel methodology opens new avenues for the measurement of absolute carbon isotope amount ratios in a wide range of samples.
首次报道了一种使用多接收电感耦合等离子体质谱仪（MC-ICPMS）测量可溯源至国际单位制（SI）的碳同位素丰度比的新方法。已对四种参考物质的碳（13）C/（12）C同位素丰度比进行了测量，其碳同位素丰度比范围为0.010659（δ（13）C（VPDB）=-46.6‰）至0.011601（δ（13）C（VPDB）=+37‰）。通过测量硼（11）B/（10）B同位素丰度比进行内部归一化，以校正仪器质量偏倚的影响。已测量了绝对（13）C/（12）C比值，并对仪器质量偏倚进行了校正，并使用克拉滕方法计算了完整的不确定度预算。NIST RM8545（碳酸锂LSVEC）、NIST RM8573（L-谷氨酸USGS40）、NIST RM8542（IAEA-CH6蔗糖）和NIST RM8574（L-谷氨酸USGS41）的校正后（13）C/（12）C比值与参考值的差异为0.06 - 0.20%。在所选择的四种NIST标准物质的校正碳同位素丰度比与预期碳同位素丰度比之间获得了极好的线性相关性（R = 0.9997）。该方法已证明在此范围内（从（13）C/（12）C = 0.010659至（13）C/（12）C = 0.011601）是线性的，因此，它适用于测量有机碳化合物、碳酸盐、元素碳、一氧化碳和二氧化碳自然变化范围内的碳同位素丰度比。此外，对一个先前通过传统双进样口同位素比率质谱仪在内部进行表征的CO2气体样品进行了分析，发现MC-ICPMS测量的碳同位素丰度比值与IRMS测量结果之间具有极好的一致性。给出了每种NIST标准物质可溯源至SI的碳同位素丰度比的绝对值，并且发现这四种物质的合成不确定度预算（包括仪器误差和对质量偏倚校正的罗素表达式有贡献的每个参数）<0.1%。该方法相对于传统气体源同位素比率质谱测量的优势在于，碳同位素丰度比是以C（+）而不是CO2（+）进行测量的，因此，不需要对由于（12）C（17）O（16）O（+）的存在而进行的氧（17）O校正。溶液中的有机化合物无需预先衍生化、燃烧步骤或两者皆无需即可进行测量，从而使该过程变得简单。这种新方法为在广泛的样品中测量绝对碳同位素丰度比开辟了新途径。
