Capillary electrophoresis coupled to LED‐induced fluorescence detection is a robust and sensitive technique used for amino acids (AA) analysis in biological media, after labeling with 3‐(4‐carboxybenzoyl)quinoline‐2‐carboxaldehyde (CBQCA). We wanted to quantitate in plasma tryptophan (Trp), tyrosine (Tyr), valine (Val), and isoleucine (Ile). Among the different labeled AA‐CBQCA, Trp has the lowest fluorescence yield, which makes its detection and quantification very difficult in biological samples such as plasma. We tried to improve Trp analysis by CE/LED‐induced fluorescence detection to its maximal sensitivity by using large volume sample stacking as a preconcentration step in our analytical protocol. At pH 9.5, this step caused a drop in resolution during the separation of the four AAs and it was therefore necessary to work at pH 10. We have found that Tyr, Val, Ile, and Trp are detected and well separated from the other AAs, but Trp cannot be quantified in plasma samples, mainly because of the low fluorescence yield of the Trp‐CBQCA derivative. The recorded LOD is 0.18 μM for Trp‐CBQCA in standard solution with a resolution between Trp and Tyr of 1.2, while the LOD is 6 μM in plasma with the same resolution.

中文翻译：

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用于直接分析血浆中氨基酸的 3-(4-Carboxybenzoyl)quinoline-2-carboxaldehyde 标记不适用于通过 CE/荧光同时定量色氨酸、酪氨酸、缬氨酸和异亮氨酸

在用 3-(4-羧基苯甲酰基)喹啉-2-甲醛 (CBQCA) 标记后，毛细管电泳与 LED 诱导的荧光检测耦合是一种可靠且灵敏的技术，可用于生物介质中的氨基酸 (AA) 分析。我们想定量血浆中的色氨酸 (Trp)、酪氨酸 (Tyr)、缬氨酸 (Val) 和异亮氨酸 (Ile)。在不同标记的 AA-CBQCA 中，色氨酸的荧光产率最低，这使其在血浆等生物样品中的检测和定量非常困难。我们试图通过在我们的分析方案中使用大体积样品堆叠作为预浓缩步骤，通过 CE/LED 诱导荧光​​检测将 Trp 分析提高到最大灵敏度。在 pH 9.5 时，此步骤会导致四种 AA 分离过程中的分离度下降，因此必须在 pH 10 下工作。我们发现 Tyr、Val、Ile 和 Trp 被检测到并与其他氨基酸很好地分离，但血浆样品中的 Trp 无法量化，主要是因为 Trp-CBQCA 衍生物的荧光产率低。标准溶液中 Trp-CBQCA 的记录 LOD 为 0.18 μM，Trp 和 Tyr 之间的分辨率为 1.2，而在具有相同分辨率的血浆中 LOD 为 6 μM。