CE assay for simultaneous determination of charged and neutral impurities in dexamphetamine sulfate using a dual CD system

Abstract

A CE assay for the simultaneous determination of charged and uncharged potential impurities (1S,2S-(1)-norpseudoephedrine, 1R,2S-(À)-norephedrine, phenylacetone and phenylacetone oxime) of dexamphetamine sulfate including the stereoisomer levoamphetamine was developed and validated. The optimized background electrolyte consisted of a 50 mM sodium phosphate buffer, pH 3.0, containing 80 mg/mL sulfobutylether-b-CD and 25 mg/mL sulfated b-CD. Separations were performed in 40.2/35 cm, 50 mm id fused-silica capillaries at a temperature of 201C and an applied voltage of -10 kV. 1R,2S-(À)-ephedrine was used as internal standard. The assay was validated in the range of 0.05-1.0% for the related substances and in the range of 0.05-5.0% for levoamphetamine. The LOD was 0.01-0.02% depending on the analyte. The assay also allowed the separation of the E,Z-stereoisomers of phenylacetone oxime. The effect of the degree of substitution of sulfobutylether-b-CD was investigated. In commercial samples of dexamphetamine sulfate between 3.2 and 3.7% of levoamphetamine were found. Furthermore, phenylacetone and phenylacetone oxime could be observed at the LOD, indicating the synthetic origin of the investigated samples. The effect in attention deficit hyperactivity disorder is believed to be mediated via several mechanisms including the binding of the drug to the pre-synaptic dopamine transporter inducing a reversed transport process as well as stimulation of pre-synaptic inhibitory autoreceptors, resulting in reduced activity in dopaminergic and noradrenergic pathways [4]. Dexamphetamine can be synthesized by various methods, for example, starting from chiral precursors such as D-phenylalanine [5] or from chiral b-hydroxyphenylethylamines such as 1R,2S-(À)-norephedrine or 1S,2S-(1)-norpseudoephedrine [6,7]. Alternatively, the compound can be obtained from racemic amphetamine synthesized from phenylacetone (1-phenyl-2-propanone, benzyl methyl ketone) by Leuckart reaction or by reduction of the oxime [8,9] followed by fractional crystallization with L-(1)-tartaric acid [10]. Thus, charged as well as neutral starting materials or synthetic by-products as well as the enantiomer levoamphetamine (2R-(À)-amphetamine) may be present as related substances in the drug.Dexamphetamine sulfate is described in monographs by the United States Pharmacopeia 32 (USP 32) [11]

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis

“…Analysis of commercial samples of dexamphetamine sulfate by both methods revealed the presence of 3.2–3.8% levoamphetamine while all other impurities were either below the LOQ or could not be detected at all. Compared to the dual CD method , the MEEKC method showed higher LODs because of the increased baseline noise observed for MEEKC. However, all chemicals including sulfated β‐CD are rather inexpensive so that MEEKC may present a valuable alternative for the analysis of dexamphetamine.…”

“…An example is the analysis of dexamphetamine with regard to the levorotatory enantiomer and other related substances including the charged impurities 1 R ,2 S ‐(−)‐norephedrine and 1 S ,2 S ‐(+)‐norpseudoephedrine as well as the uncharged compounds phenylacetone and phenylacetone oxime. In the first study, the separation was achieved using a dual CD system composed of the charged CD derivatives sulfobutylether‐β‐CD (SBE‐β‐CD) and sulfated β‐CD . The optimized BGE consisted of 50 mM sodium phosphate buffer, pH 3.0, containing 80 mg/mL SBE‐β‐CD and 25 mg/mL sulfated β‐CD.…”

Chiral electromigration techniques in pharmaceutical and biomedical analysis

“…The first assay used HDAS-β-CD as chiral selector in a 50-mM sodium phosphate buffer, pH 2.5 allowing the determination of levoamphetamine as well as the charged potential impurities 1S,2S-(+)-norpseudoephedrine and 1R,2S-(−)-norephedrine in commercial dexamphetamine samples [91]. The second method employed a dual CD system combining 25 mg/ml sulfated β-CD and 80 mg/ml SBE-β-CD in a 50-mM sodium phosphate buffer, pH 2.5 and reversed polarity of the applied voltage [92]. This set-up also enabled the analysis of the neutral impurities phenylacetone and phenylacetone oxime besides the charged impurities.…”

“…The application of CE in drug impurity analysis has been summarized [79,80]. Table 1 clearly reflects the general trend that CDs are by far the most widely used chiral selectors although some studies utilized other additives such as BSA [81], maltodextrin [82], (+)-18C6H4 [83], ligand exchange [84] or the chiral ionic liquid ethylcholine bis(trifluoromethylsulfonyl) Baclofen α-CD (18 mM) 0.1 M sodium borate, pH 9.9, 1% acetonitrile 2-10 μg/ml, analysis of racemic bulk drug and tablets [103] Benzimidazole derivatives Chloroquine SBE-β-CD (30 mg/ml) 100 mM sodium phosphate, pH 2.5 0.02%, analysis of laboratory sample [108] Clopidogrel Sulfated β-CD (5%) 10 mM triethylamine/phosphoric acid 0.08-0.33 μg/ml, minor enantiomer and related substances [109] Dexamphetamine HDAS-β-CD (10 mg/ml) 0.1 M sodium phosphate buffer, pH 2.5 0.06%, minor enantiomer and charged related substances [91] Dexamphetamine Sulfated β-CD (25 mg/ml), SBE-β-CD (80 mg/ml) 50 mM sodium phosphate buffer, pH 2.5 0.01-0.02%, minor enantiomer and related substances [92] Dexamphetamine Sulfated β-CD (5.5%) 1.5% SDS, 0.5% ethyl acetate, 3.5% 1-butanol, 2.5% 2-propanol and 92% 50 mM sodium phosphate buffer, pH 3.0 0.05-0.2%, minor enantiomer and related substances [93] Econazole HP-γ-CD (40 mM) 50 mM SDS in 20 mM phosphate buffer, pH 8.0…”

Study of the enantioseparation capability of chiral dual system based on chondroitin sulfate C in CE

“…With two different chiral selectors introduced simultaneously, chiral dual system often leads to a significant enhancement of selectivity and resolution (synergistic effect) due to differences in the complexation mechanisms of the two selectors with the analyte enantiomers . The use of dual CD systems has been reported in some studies, in which different combinations of charged and neutral CDs are employed .…”