It remains an issue to directly quantify trace biologically important carboxyl compounds in body fluids. Herein we propose an innovative method to determine α-lipoic acid, 2-(β-carboxyethyl)-6-hydroxy-2,7,8-trimethylchroman, prostaglandin E₂, cholic acid, and chenodeoxycholic acid in saliva. The method consists of two successive steps: fast and direct labeling of the target analytes with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide followed by ultrahigh-performance liquid chromatography–tandem mass spectrometry analysis. The method exhibited a wide linear range from 2.5 to 2500 pg/mL, with linear coefficients greater than 0.9963 and limits of detection and quantification as low as 0.10 and 0.33 pg/mL, respectively. The method precision was evaluated, with relative standard deviations ranging from 2.12% to 10.63% for intraday assays and from 2.98% to 12.88% for interday assays. The recoveries were measured by our spiking saliva samples with standards at three different levels, and ranged from 72.5% to 98.0%. Real applicability was validated by direct quantification of trace target analytes in human saliva, with simple pretreatment, use of a small sample volume, and a short analysis time.

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直接定量体液中的痕量生物学上重要的羧基化合物仍然是一个问题。在本文中，我们提出了一种创新的方法来测定唾液中的α-硫辛酸，2-（β-羧乙基）-6-羟基-2,7,8-三甲基苯并二氢吡喃，前列腺素E ₂，胆酸和鹅去氧胆酸。该方法包括两个连续步骤：用N-（3-二甲基氨基丙基）-N快速和直接标记目标分析物'-乙基碳二亚胺，然后进行超高效液相色谱-串联质谱分析。该方法的线性范围从2.5到2500 pg / mL，线性系数大于0.9963，检出限和定量限分别低至0.10 pg / mL和0.33 pg / mL。评估了方法的精确度，日内测定的相对标准偏差为2.12％至10.63％，日间测定的相对标准偏差为2.98％至12.88％。回收率是通过将唾液样品加标为三种不同水平的标准来测量的，范围从72.5％到98.0％。通过直接定量人类唾液中的痕量目标分析物，简单的预处理，使用少量的样品以及较短的分析时间，验证了其实际适用性。

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