Sample preparation and determination of acetylcholine in corneal epithelium cells using liquid chromatography-tandem...

A sample preparation method with subsequent liquid chromatography (LC)-mass spectrometry (MS)-MS analysis for acetylcholine in corneal epithelium is developed. The sample preparation is developed with a focus on compatibility with the LC-MS-MS system and the stability of acetylcholine because acetylcholine esterase is present in the tissue. It appears that both acetylcholine as well as the internal standard (IS) used (acetyl-beta-methylcholine) have fragments at m/z values in the tandem MS spectrum, which correspond with the m/z values of fragments of endogenous substances. Acetylcholine and (3-carboxypropyl)triethylammonium both have 146-->87 and 146-->60 transitions. Acetyl-beta-methylcholine and an unknown compound both have 160-->101 and 160-->60 transitions. This makes it necessary to use a chromatographic step, which has a baseline separation between these endogenous compounds, acetylcholine, and the IS. The analytical procedure has linearity from 1 ng/mL (30 pg/mg corneal epithelium tissue) to at least 250 ng/mL (7.55 ng/mg corneal epithelium tissue). The limits of detection and quantitation are 15 and 45 pg on column, respectively. Relative standard deviation and bias values are within the range of acceptance for all concentration levels.