Flexible Method for Analysis of Lidocaine and Its Metabolite in Biological Fluids.

A robust liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the determination of lidocaine (LIDO) and its metabolite (monoethylglycinexylidide (MEGX)) in serum. One hundred microliters of bovine serum were spiked with LIDO-d10 as internal standard and deproteinized with acetonitrile prior to solid-phase extraction purification using strong cation exchange cartridge. The chromatographic separation was achieved on a BetaBasic-18 column with a mobile phase consisting of aqueous 0.1% formic acid and 0.1% formic acid in acetonitrile. The instrumental linearity was verified from 0.4 to 1,000 ng/mL obtaining determination coefficients (r(2)) of >0.99. The limit of quantification (LOQ) was set at 1 ng/mL for both LIDO and MEGX. The coefficients of variation for within- and between-batch imprecision, including LOQ, were ≤10% and the percentage of inaccuracy was <15%. The absolute recoveries were >75% for both analytes. Experiments demonstrated the method applicability to sera of different animal species and also to plasma, urine and milk matrices.