High-performance liquid chromatographic separation of noreximide and norendimide in bulk material, tablets and animal feed

Noreximide, a sedative, is generally contaminated to some extent with its endo-isomer, norendimide, which produces excitation. A high-performance liquid chromatographic assay was developed to separate and quantitate these compounds on a 5-microns Ultrasphere ODS column with methanol-water (20:30) as mobile phase and detection at 254 nm. Assay of mixtures of these compounds in bulk material and tablets utilized isoniazide as internal standard. Peak area ratios were linear (r = 0.9999) over 1.4-66.2 micrograms of injected noreximide and 0.2-8.4 micrograms of injected norendimide. Overall percent recovery from simulated tablets containing noreximide alone was 99.6 +/- 0.8% (S.D., n = 3). Overall percent recoveries (+/- S.D.) from tablets containing a mixture of these compounds were 98.9 +/- 0.5% and 102.3 +/- 1.1% for noreximide and norendimide, respectively (n = 3). Noreximide in animal feed for long-term pharmacological studies was isolated by ether extraction and after work up, subjected to the same procedure, except that theophylline was the internal standard. Peak area ratios were linear over 0.2-19.3 micrograms of injected noreximide (r = 0.9999). Overall percent recoveries (+/- S.D., n = 3) of noreximide from spiked animal feed were 97.4 +/- 1.4% and 99.0 +/- 0.5% at the 500- and 5000-ppm levels, respectively. Limits of detection at the 95% confidence level (0.01 a.u.f.s., 20-microliters sample volume injected) were 1.67 microgram/ml and 2.56 micrograms/ml of noreximide and norendimide, respectively, in the final test solution.