A high-performance liquid chromatographic method with electrochemical detection (LC/EC) was developed to measure
cystine and cysteinyl-
penicillamine disulfide in the urine of patients screened or treated for
cystinuria. Urine was acidified, centrifuged to remove urinary
protein, diluted and injected. The
disulfides were separated on a reversed-phase column, reduced at the upstream
electrode of a dual electrochemical detector with
gold-
mercury amalgam (Au/Hg)
electrodes and the resultant
thiols measured at the downstream
electrode. The sample preparation is simple, the analysis rapid, specimens can be easily batched and the specificity of the method is better than those of two other separative procedures with which it was compared. The coefficient of variation for
cystine in cystinuric urine is 6.7%, 5.5% and 3.2% for levels of 0.09, 0.52 and 1.02 mmol/l respectively, and for cysteinyl-
penicillamine disulfide 2.6% and 7.5% for levels of 0.45 and 0.98 mmol/l respectively. Urine for analysis of these
disulfides should not be collected within 24 hours of administration of the radiopaque agent
diatrizoate but no other interference to the assay has been noted. This method is suitable as a screen for
cystinuria in patients with renal tract
calculi, for ongoing monitoring of cystinuric patients and to check patient compliance with
d-penicillamine therapy.