Abstract: Infant formula samples were analyzed to determine their free L-carnitine content by using flow injection (FI) with an incorporated immobilized carnitine acetyltransferase bioreactor. The methodology was based on the spectrophotometric determination through its reaction with carnitine acetyltransferase coupled with acetyl coenzyme A (acetyl-CoA) and dithiobenzoate. The merging zones technique was used to minimise acetyl CoA consumption. Linearity was observed over the concentration range 10^-80 mg L-1 with L-carnitine as standard (r = 0.9998) and the rate of analysis was 50 h-1 infant formula samples. The enzymatic FI method afforded a low RSD (2.2%). Comparisons were made with other methods of known accuracy. The enzymatic reactors were stable for 3 months when used daily at the optimum pH.

Abstract: A fluorometric flow injection method for determining carnitine with use of immobilized enzymes carnitine dehydrogenase (EC 1.1.1.108) and diaphorase (EC 1.8.1.4) was developed and applied to the assay of carnitine in serum of patients treated with valproic acid. After fractionation and hydrolysis of carnitines in serum samples by perchloric acid and potassium hydroxide, liberated carnitine was converted to resorufin by immobilized carnitine dehydrogenase and diaphorase in the presence of β-NAD+ (1.0 mmol/L), resazurin (12.5 µmol/L), and Tris acetate (0.6 mol/L, pH 9.0) at 37°C. The fluorescence intensity of resorufin was monitored at lambda Ex 560 nm and lambda Em 580 nm. The calibration curve was linear for carnitine amounts from 0.1 to 1.0 nmol. Quantitative analytical recovery and satisfactory within- and between-run imprecision of carnitine in each carnitine fraction were obtained. Interference by bilirubin, serum albumin, and hemoglobin was negligible. Carnitine deficiencies were detected in about 20% of the valproic acid-treated patients (n = 198). The present method should be useful for monitoring carnitine deficiencies in clinical laboratories.