Simple Quantitative HPLC Method for Measuring Physiologic Amino Acids in Cerebrospinal Fluid without Pretreatment

Because the cerebral spinal fluid (CSF) bathes the whole central nervous system, its contents reflect changes occurring in the central neurons. Quantitative analysis of amino acids present in CSF has been helpful in improving our understanding of disease conditions associated with pain (1)(2)(3). Amino acids in CSF can be determined either by postcolumn derivatization with ninhydrin or o -phthalaldehyde (OPA) by commercially available amino acid analyzers or by precolumn derivatization with different reagents, such as dansyl chloride, phenylisothiocyanate, fluorenylmethyl chloroformate, dabsyl chloride, and OPA, followed by HPLC separation (4)(5)(6). Precolumn derivatization with OPA has been used predominantly for analysis of amino acids in CSF (1)(2)(7). However, OPA reacts only with primary amines, and the OPA adducts are unstable (4)(8). The preanalytical processes, including sample storage conditions and the pretreatment used for amino acid analysis in physiologic fluids, have not been standardized, making it difficult to compare results among laboratories (5)(9)(10)(11)(12). Pretreatment with different deproteination methods, including strong acids (3)(4)(9)(10), organic solvents (13)(14)(15), or ultrafiltration (2)(16)(17), has been shown to adversely affect the quantitative results for amino acids (16)(18).Dabsyl chloride has been used to convert primary and secondary amines to their colored derivatives with subsequent separation by HPLC (19). This method has been used for analysis of amino acids and other compounds from physiologic fluid and tissue extracts (8)(15)(16)(20). However, use of this method for CSF samples has not been reported. We report an improved method using dabsyl chloride in the presence of the nonionic neutral surfactants Triton X-100 (Sigma) or Tween 20 (Bio-Rad), which …