Journal
ELECTROPHORESIS
Volume 27, Issue 21, Pages 4240-4248Publisher
WILEY
DOI: 10.1002/elps.200600149
Keywords
acid barrage stacking; anti-salt injection; CE; 9-fluorenylmethyl chloroformate-amino acids; physiological samples
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An acid barrage stacking (ABS) method has been shown to be feasible for online antisalt injection in CE of 9-fluorenylmethyl chloroformate (FMOC)-labeled amino acids (AAs) detected by common UV absorption. The operation was performed on normal polar CE by sucking in an extra plug of acid following a sample zone, serving as a selective acid barrage to block the backward migration of weak anionic analytes due to a sudden mobility reduction via acid-base reaction which does not affect strong co-ions such as Cl- to penetrate the barrage freely. By CE-UV of FMOC-AAs in various NaCl solutions, the effectiveness of ABS was firmly validated, able to stand up to 500 mM NaCl and to stack analytes by 10(3)-fold calculated from the UV detection limits, that is 0.01 mu M for ABS and 10 mu M for non-stacking injection. The method was also validated by determining trace Glu and Asp in real samples of rat brain microdialysate, rat serum and human saliva. The intraday RSDs were 0.33-4.9% for migration time and 1.8-9.6% for peak area. The recoveries measured by spiking technique were 82-115% for Glu and 86-116% for Asp. Working equations were obtained by plotting peak height vs. concentration at 0.1-50 mu M, with correlation coefficients of > 0.999. The contents of Glu and Asp were thus found at 0.26-0.83 mu M and 0.24-0.64 mu M respectively, in rat brain microdialyste; 37-40 mu M and 8.4-10 mu M, respectively, in rat serum; and 3.5-5.8 mu M and 1.0-4.1 mu M, respectively in human saliva. They were consistent with the data from other methods.
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