Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Abstract

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l −1 disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l −1 EDTA and 0.5 mmol l −1 Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/ z 48 as 32 S 16 O + by using its reaction with O 2 in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/ z 32 caused by 16 O 16 O + and 14 N 18 O + on 32 S + by detecting 32 S + as the oxide ion 32 S 16 O + at m/ z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047–0.058 μg S ml −1, which corresponded to the absolute detection limit of 1.3–1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92–128% for various species.