On-line capillary electrophoresis-electrospray ionization mass spectrometry analysis of urinary porphyrins

A rapid, high-resolution and high-efficiency novel method for the simultaneous determination of mesoporphyrin (MP), coproporphyrin (CP) and uroporphyrin (UP) in human urine by capillary electrophoresis coupled with electrospray ionization mass spectrometry (CE-ESI-MS) was developed. The simple laboratory-made interface was developed by using a micro-tee connection and a liquid junction. The porphyrins were well separated by CE with a positive 12 kV voltage in a 20 mM ammonium acetate buffer (pH 10.5) containing 40% v/v acetonitrile. The sheath liquid was composed of acetonitrile-water (50:50 v/v) containing 5 mM ammonium acetate and 0.1% v/v formic acid (pH 3.0) with a flow rate of 5 mu L/min. The porphyrins were identified with the criteria of migration time and m/z values, and quantified with the measurement of peak area of [M+H](+) ion. Limits of detection for MP, CP and UP were 85 nM, 140 nM and 300 nM, respectively. The correlation coefficients of calibration curves were between 0.9956 and 0.9862. The intra-day precisions in terms of relative standard deviations (n = 12) of the method were 1.1-3.9% for migration times and 2.3-14.1% for peak areas. The porphyrin recoveries of spiked urine samples were between 73% and 96%. The liquid junction interface for CE-ESI-MS was demonstrated to be applicable for the potential quantitative analysis of clinical samples.