Reversed-phase chromatography of zimelidine and similar dibasic amines. I. Analysis in biological material

Zimelidine, a new antidepressant, and its pharmacologically active metabolite, norzimelidine, have been determined quantitatively in biological material. The compounds are extracted from alkali-treated body fluid or tissue homogenate into diethyl ether-n-hexane (8:2, v/v), and re-extracted into a small volume of acidic aqueous phase (ca. 100 microliter), which is injected onto the chromatographic column. The chromatographic support is Nucleosil C18 (5 micron) and the mobile phase is phosphate buffer (pH 2)-acetonitrile (91:9, v/v) with the addition of an aliphatic amine, N,N-dimethyl-N-octylamine (4.10(-4) M), which improves the chromatographic performance. By using glass-lined stainless-steel tubes instead of the common precision-bore stainless-steel columns, peak symmetries were improved. Detection limits in plasma are in the range 2.3--4.7 nmol/1 for extractions from 1 ml. It is demonstrated that the quality of the quantitations are improved by use of an internal standard, norzimelidine E-isomer. The precisions obtained for both compounds at the concentration levels of 300 and 1500 nmol/1 are ca. 5--6% and 2% respectively for within-run variations, and 8--9% and 5% respectively for day-to-day-variations.