A Closer Examination of 6-Aminoquinolyl-N-Hydroxysuccinimidyl Carbamate Amino Acid Derivatization in HPLC with Multiple Detection Modes
2021
Sung, Yu-Sheng | Berthod, Alain | Roy, Daipayan | Armstrong, Daniel W.
6-Aminoquinolyl-N-hydroxysuccinimidyl carbamate is a well-known reagent used to derivatize amino acids (AAs) into their aminoquinolyl carbamate (AQC) analogs. Originally, AQC derivatization was used to enhance UV detection of amino acids (and amines) and to provide a fluorescent derivative for further enhanced detection. Subsequently, it was found that AQC derivatization could also enhance mass spectrometry (MS) detection. It is sometimes assumed that since the AQC tag is identical for all amino acids, that their detection will be similar for a given detection mode. However, this is often not the case. Sometimes there are extreme exceptions, for example, cysteine and tryptophan, which are simply ignored in the literature. Herein, four detection modes were compared: two optical spectroscopic modes, 254 nm UV and fluorimetry, and two mass spectrometry (MS) modes, single ion analysis and multiple reaction monitoring (MRM). The most sensitive detection modes were fluorimetry and MRM which were able to detect down to the tens of femtomoles of injected AAs. But single quad MS and classical UV detection could quantitate most AQC-AAs down to the picomole level in most instances. The differences between detection modes and within each of the four detection modes are examined and discussed for the first time. The possible reasons for extreme differences in the detectability of specific amino acids are considered.
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