Separation and determination of carnosine‐related peptides using capillary electrophoresis with laser‐induced fluorescence detection

A capillary electrophoresis (CE) method with laser‐induced fluorescence (LIF) detection was developed for the separation and detection of carnosine‐related peptides (carnosine, anserine, and homocarnosine). A sensitive and fluorogenic regent, 3‐(4‐carboxybenzoyl) quinoline‐2‐carboxaldehyde (CBQCA) was selected as a precapillary labeling reagent for imidazole dipeptides to form isoindole derivatives. The optimized molar ratio between CBQCA and peptide was found to be 75:1, and 50 mmol/L borate buffer (pH 9.2) was used for the derivatization in order to achieve good efficiency. Three imidazole dipeptides were baseline‐separated within 20 min by using 112 mmol/L sodium borate (pH 10.4–10.8) as running buffer. Concentration detection limits (signal‐to‐noise ratios) for carnosine, anserine, and homocarnosine were 4.73, 4.37, and 3.94 nmol/L, respectively. This method has been applied to the analysis of human cerebrospinal fluid (CSF) and meat dry powder of pig and sheep. Recoveries were in the range of 82.9–104.8% for homocarnosine in CSF. For carnosine and anserine, the recoveries are 98.3% and 80.2% in meat dry powder of pig and 111.2% and 112.8% in meat dry powder of sheep, respectively.