In this study, a paired ion electrospray ionization (PIESI) mass spectrometry method was developed for sensitive detection of 9-fluorenylmethyl chloroformate (Fmoc)-derivatized amino acids. The structure-optimized ion-pairing reagent was introduced post column to form positively charged complexes which can be detected in the positive ion mode. These complexes are more surface-active than the original analytes, and meanwhile, the intensity of sodium adducts was significantly reduced. The limit of detection of the amino acids obtained with the optimal ion-pairing reagent was 0.5 to 20 pg which was 5–100 times lower than the negative mode. In addition, two mass spectrometry platforms—linear ion trap and triple quadrupole—were used to compare the PIESI improvements. Eventually, the method was applied to successfully detect the level of amino acids in human urine samples with high accuracy and the added benefit of minimizing matrix effects.

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在这项研究中，开发了一种配对离子电喷雾电离（PIESI）质谱方法，用于灵敏检测9-芴基甲基氯甲酸酯（Fmoc）衍生的氨基酸。在柱后引入结构优化的离子对试剂，以形成带正电的络合物，可以在正离子模式下对其进行检测。这些配合物比原始分析物具有更高的表面活性，同时钠加合物的强度也大大降低。使用最佳离子对试剂获得的氨基酸的检出限为0.5到20 pg，比阴性模式低5-100倍。此外，还使用了两个质谱分析平台（线性离子阱和三重四极杆）来比较PIESI的改进。最终，

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