Separation of serum LD isoenzymes by capillary electrophoresis

Separation and quantitative estimation of the isoenzymes of lactate dehydrogenase(LD) in serum were accomplished with capillary electrophoresis system. An uncoated fused silica capillary column 50 cm long, 75μm I.D. and substrate containing running buffer including L-lactic acid and NAD(+) were used for the separation of serum LD isoenzymes. The resulting product of "NADH" was detected at 340 nm. Injection of 10 nL of five fold diluted serum sample were performed by pressure injection within 2 seconds. The isoenzymes were separated at 10 kV of voltage for 5 min, by turning off the voltage applied for 30 min incubation at 24°C for reaction between substrate and isoenzymes, and applying voltage of 30 min. Under these conditions, the isoenzymes of LD were detected by a NADH generated as isoenzyme of LD-5 emerged at 20 min, LD-1 peak at 23.5 min with close to baseline separation of the other isoenzymes which emerge between LD-5 to LD-1, after the emergence to LD-1 peak, followed another peak, termed "sample shock": The results obtained by the proposed method correlated well with those by gel electrophoresis systemes (r=0.92∼0.98) for each five LD isoenzymes, respectively. Within-run precision CVs for 5 replicate analysis were 3.01 (LD-3, mean 14.6%)%∼7.82% (LD-4, mean 4.22%.), respectively.