An automated method for determination of trace level amino acids in 2-muL s
amples using on-column sample; preconcentration, gradient elution on 50-mum
inner diameter (i.d.) capillary columns packed with 5-mum reversed-phase p
articles, and electrochemical detection is described. The 50-mum i.d. capil
lary columns were efficiently coupled directly to an autosampler without in
creasing zone dispersion by preconcentrating derivatized amino acids at the
head of the capillary column and minimizing gradient dwell volume. Using t
his system, the relative standard deviations (RSDs) of retention time for a
16 component amino acid mixture were between 0.2 and 0.8%. Using an automa
ted microinjection method, as little as 0.3 muL of derivatized sample was c
onsumed to perform a 0.25-muL injection with peak area RSDs of 3.0-8.4%, al
lowing conservation of a majority of the derivatized sample for future anal
ysis. Precision was improved to peak area RSDs of 1.8-4.1% when consuming 1
.0 muL of sample per injection. Detection limits were < 0.2 nM for most ami
no acids. The linear solvent strength theory was used to optimize the gradi
ent and allowed resolution of 15 amino acids in 13 min. The final gradient
separation was demonstrated to be selective for the neurotransmitter amino
acids in the presence of 44 primary amines commonly found in physiological
samples. The system was used to characterize amino acid secretion from sing
le pancreatic islets of Langerhans under different physiological conditions
with 2 min of temporal resolution. <(c)> 2001 John Wiley & Sons, Inc.