增益(Gain)校正有助于消除MC-ICP-MS不同高阻放大器之间的阻值差异,进而提高同位素分析的精度和准确度,但有关Gain的偏移和校正频率对同位素测试的影响和作用原理还缺乏系统认识.本研究结合本实验室Neptune Plus MC-ICP-MS的Gain校正数据,以实际测试的汞同位素数据为例,评估了放大器Gain校正系数偏移对同位素测试的影响.结果显示,当测试标样和样品的校正系数偏移幅度一致时,汞同位素测试结果基本无变化;当偏移幅度存在明显差异且单一放大器校正系数的相对偏移幅度超过-0.070‰～0.058‰时,汞同位素的测试结果大于分析误差.Gain校正系数单日的相对变化幅度(-0.028‰～0.028‰)可保证汞同位素测试结果小于分析误差,但长期的偏移却会导致汞同位素变化远超分析误差.此外,仪器的硬件、温度和真空度等也是Gain校正系数变化的重要影响因素,因此建议定期维护仪器,并每日进行Gain校正,以保证测试结果的稳定和准确.
Effect of high-impedance amplifier calibration drift on isotope measurement by MC-ICP-MS-an example of mercury isotope analysis
Gain calibration helps to eliminate the difference in resistance values between different high-impedance amplifiers of MC-ICP-MS and thus improves the accuracy and precision of isotope analysis.However,the principles and effects of Gain drift and calibration frequency on isotope analysis are not yet systematically understood.In this study,based on the Gain calibration data of Neptune Plus MC-ICP-MS in our laboratory,taking the actual Hg isotope analysis as an example,the effect of Gain calibration coefficient drift on isotope measurement was evaluated.The results showed that the Hg isotope measurements were essentially unchanged when the calibration coefficient of Gain for the standard and sample measurements drifted the same.However,the deviation of Hg isotope ratios exceeded the range of analytical error when the drift amplitudes in standard and sample measurements were significantly different and the relative variation of the single amplifier calibration coefficient exceeded-0.070‰～0.058‰.The relative variation of Gain calibration coefficient for a single day(-0.028‰～0.028‰)can ensure the variation of Hg isotope ratios are within the analytical error range,but the long-term drift will cause the Hg isotope variation to be far beyond the analytical error.In addition,the hardware,temperature,and vacuum of the instrument are also important influencing factors for the variation of Gain calibration coefficient.Therefore,it is recommended to maintain the instrument regularly and perform Gain calibration daily to ensure the stability and accuracy of isotope analysis.
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