George M. Hanna

Isolation and identification of process impurities in trimethoprim drug substance by high-performance liquid chromatography, atmospheric pressure chemical ionization liquid chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy.

Twenty-two lots of recently synthesized trimethoprim drug substance, from five different manufacturers, in three different countries of origin, China, Israel and the United States, were investigated for the presence of impurities. A liquid chromatographic system, using gradient elution, and a mobile phase consisting of 0.25% TEA/0.1% formic acid (pH 5.8)--acetonitrile, was used to separate and detect two significant, recurring impurities in trimethoprim drug substance. The two impurities were isolated by preparative liquid chromatography and identified, using a combination of liquid chromatography/mass spectroscopy and nuclear magnetic resonance, as 2,4-diamino-5-(4-ethoxy-3,5-dimethoxybenzyl) pyrimidine and 2,4-diamino-5-(3-bromo-4,5-dimethoxybenzyl) pyrimidine. These impurities were not detected by the compendial method and were present at significant levels in 17 of the lots tested. Total impurity concentrations were in the range of 0.1-2.1%.

Optimization of enantiomeric separation for quantitative determination of the chiral drug propranolol by 1H-NMR spectroscopy utilizing a chiral solvating agent.

High-field 1H-NMR methodology for enantiomeric composition determination of the chiral drug propranolol utilizing a chiral solvating agent is reported. Optimal experimental conditions for the resolution of enantiomers were determined by studying the interaction of substrate concentration, chiral solvating agent concentration and temperature. The success of the method is based on the selection of a chiral solvating agent that has the following two characteristics. First, it possesses functional groups that are complimentary to those of the chiral substrate for significant interaction to occur. Second, it has a group of diamagnetic anisotropy near its stereogenic center for translating spatial environments of solute nuclei into different magnetic environments that are measurable by NMR spectroscopy. Optical purities were determined on the basis of the intensities of the methyl proton resonances. The analysis of synthetic enantiomeric mixtures of propranolol by the proposed NMR method resulted in assay values, which agreed closely with the known quantities of each enantiomer in the mixtures tested. The mean +/- SD recovery values for the (R)-(+)-enantiomer was 100.0+/-0.6% of added antipode (n = 7).

1H-NMR Spectroscopic Assay Method for Metoclopramide Hydrochloride in Tablets and Injections

AbstractA simple, accurate and specific proton nuclear magnetic resonance (1H-NMR) spectroscopic method has been developed for the assay of metoclopramide hydrochloride in tablets and injections. In deuterium oxide, the analyte and acetamide, the internal standard, produced corresponding resonance signals at 1.35 ppm and 2.03 ppm of utility for quantitative purposes. The average ± SD recovery of drug from 10 synthetic formulations was 99.7 ± 0.7% of the added amount. The assay of commercial products by the proposed method resulted in average assay values of 100.43 (range = 98.8-100.8, n = 6)% of declared for tablets, and of 99.45 (range = 99.6-100.4, n = 4)% of declared for injections. These results were validated by a high performance liquid chromatographic (HPLC) method.

Determination of enantiomeric composition of ibuprofen in bulk drug by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide chelate

The enantiomeric composition of ibuprofen was determined in a simple and reliable manner by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide chelate. Optimum complexation with the europium (III) chelate took place in CCl4 after conversion of the enantiomeric sample into a mixture of methyl esters. The optimization of the experimental conditions in terms of substrate concentration and lanthanide chelate to substrate molar ratio led to two sets of signals of utility for quantitative purposes. Analysis of synthetic enantiomeric mixtures by the proposed method demonstrated excellent agreement between the assay results and the known masses of each enantiomer present in the mixture samples. The average +/- S.D. recovery values were 99.39 +/- 0.92 and 99.42 +/- 0.68% (n = 10) of (S)-(+)-ibuprofen depending on whether the quantitation was based on the alpha-methyl protons or ester methyl protons, respectively.

Determination of the optical purity of timolol maleate by proton nuclear magnetic resonance spectroscopy with a chiral Pr(III) shift reagent.

A 1H NMR spectroscopic method with chiral shift chelate is presented for the determination of the optical purity of timolol maleate. Optimum experimental conditions were established by studying the interactions of solvents (CCl4, CDCl3), substrate concentration, and the type and concentration of chiral lanthanide chelate (Pr(hfc)3, Eu(hfc)3). Larger induced shift (delta delta) and enantiomeric shift difference (delta delta delta) values, and more detailed spectral differences were obtained with Pr(hfc)3 than with Eu(hfc)3. By monitoring the spectral changes of the resonance signals for the enantiomeric -C(CH3)3 protons, suitable conditions for quantitative determinations were found when 0.1 molar equivalents of Pr(hfc)3 were complexed with 0.074 M of substrate. Enantiomeric compositions were calculated from the relative intensities of the enantiomeric -C(CH3)3 proton resonances. Based on the analysis of six synthetic enantiomeric mixtures, the mean +/- SD recovery of (R)-(+)-timolol by the proposed method was 99.5 +/- 1.17% of the amount added.

Determination of the optical purity of indacrinone by proton nuclear magnetic resonance spectroscopy using chiral lanthanide chelates.

A simple, specific and reliable 1H-NMR spectroscopic method for the quantitative determination of the optical purity of indacrinone is described. After conversion of the S(+)- and R(-)-enantiomers to their methyl ester derivatives, they were coordinated with chiral europium(III) or praseodymium(III) shift reagents in CCl4/C2HCl3 (2:1). The optical purity was calculated from the relative intensities of the enantiomeric resonance signals for the protons of the methyl groups at position C(2) of the indanone ring. Mean +/- SD (n = 6) recoveries of S(+)-indacrinone from synthetic enantiomeric mixtures amounted to 99.75 +/- 0.63% when using europium(III) and 100.01 +/- 0.55% when using praseodymium(III).

Optical Purity Determination of threo-Methylphenidate Hydrochloride Using a Chiral Europium Nuclear Magnetic Resonance (NMR) Shift Reagent

A 1H-NMR spectroscopic method for the determination of the optical purity of threo-methylphenidate hydrochloride is presented. Complexation of the free-base form of the substrate with a chiral Eu(III) shift reagent resulted in two distinct enantiomeric ester methyl proton signals of utility for quantitative work. The accuracy of the method was validated by analyzing six synthetic mixtures of various proportions of ( + )- and (–)-threo-methylphenidate. In addition to yielding assay results that were in close agreement with the known weights of each enantiomer in the mixture, and a mean recovery of the (–)-threo-enantiomer of better than 99.0%, the proposed method was capable of accurately measuring as little as 2% of one enantiomer in the presence of the other.

Determination of the enantiomeric composition of carprofen by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide-shift reagent

The enantiomeric composition of carprofen has been determined in a rapid and reliable manner by proton nuclear magnetic resonance spectroscopy with a chiral lanthanide-shift chelate. Carprofen was converted into a mixture of enantiomeric methyl ester derivatives which were then complexed with tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium(III) in CDCl(3). The concentration of substrate in the test sample was 0.15M and the chiral-shift reagent:substrate molar ratio was 0.453. Determination of the enantiomers was based on the relative intensities of the signals for the alpha-methyl protons. The mean recovery +/-SD for six determinations of S(+)-carprofen from synthetic enantiomeric mixtures was 99.3 +/- 1.7%.

Determination of Garbaghol Ophthalmic Solution by Proton Magnetic Resonance Spectroscopy

AbstractBy using proton magnetic resonance spectroscopy, carbachol can be assayed in commercial ophthalmic solutions with a minimum of steps and reagents, and with a high degree of accuracy. The sample is freeze-dried to a powder which is first mixed with acetamide, the internal standard, and next is dissolved in methanol. An aliquot of the solution is evaporated to dryness, the residue is dissolved in deuterium oxide, the solution is mixed with the reference standard, and the spectrum is recorded. The quantity of carbachol in the dosage form is calculated from the integral value at ca. 3.27 ppm (carbachol) and ca. 2.01 ppm (acetamide). The mean recovery value ± SD for carbachol added to synthetic formulations was 100.0 ± 0.5% (n = 10), CV = 0.5%. The mean assay values for commercial 15 and 30 mg/ml ophthalmic solutions were 100.2 (n = 3) and 99.9 (n = 3)% of declared, respectively. The proposed method precludes interferences by synthetic celluloses, which are added to carba-chol ophthalmic solutions to b...

Nuclear Magnetic Resonance Analysis of Phenytoin and Sodium Phenytoin in Solid Dosage Forms

AbstractA rapid and specific nuclear magnetic resonance (NMR) spectroscopic method was developed for determining phenytoin and its sodium salt in capsules and tablets. Acetamide was used as the internal standard and 0.5% sodium deuteroxide in deuterium oxide served as the NMR solvent. The concentration of drug per unit dose was calculated from the integration values for the resonance signals of phenytoin at about 7.40 ppm and of the internal standard at about 1.97 ppm. The average recovery value of phenytoin added to synthetic samples, in concentrations ranging from 84 to 122 mg, was 99.9 ± 0.2% (SD) with a coefficient of variation of 0.2%. The method using commercial products gave results comparable to those obtained by the titrimetric and gravimetric methods of USP XX. Excipients of tablets and capsules such as sucrose and lactose did not interfere with the determinations. The proposed method was found suitable for measuring the content uniformity of capsules and tablets, and offered a positive means of...