ABU RUSTUM - Academia.edu (original) (raw)

Papers by ABU RUSTUM

Research paper thumbnail of Applying Charged Aerosol Detection to Aminoglycosides

Charged Aerosol Detection for Liquid Chromatography and Related Separation Techniques

Research paper thumbnail of Simultaneous Determination of Esafoxolaner, Eprinomectin, Praziquantel, BHT and Their Related Substances in a Topical Finished Product by a Single Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) Method

SSRN Electronic Journal, 2021

Research paper thumbnail of Alternative and Improved Stability-Indicating HPLC Method for the Assay of Eprinomectin and Determination of Its Related Compounds in Bulk Batches of Eprinomectin Drug Substance

Journal of AOAC INTERNATIONAL, 2021

Background Eprinomectin is used as an active pharmaceutical ingredient (API) in various drug prod... more Background Eprinomectin is used as an active pharmaceutical ingredient (API) in various drug products by the animal health industry. Several major related impurities of eprinomectin API are not separated and coelute by the current United States Pharmacopeia (USP) method for eprinomectin. Objective The aim was to develop and validate a true and reliable stability-indicating reversed-phase (RP) HPLC method for assay and determination of related substances of eprinomectin in bulk batches of eprinomectin API. Method HPLC analysis is carried out using a Kinetex C8 column (100 mm × 4.6 mm i.d. , 2.6 μm particle size) maintained at 30°C with water–acetonitrile–isopropanol (48 + 42 + 10, v/v/v) as mobile phase A and 100% acetonitrile as mobile phase B. Analytes are separated by gradient elution at a flow rate of 0.7 mL/min and detected by UV at 252 nm. The total run time of the method is 30 min. Eprinomectin assay and estimation of all eprinomectin-related substances are obtained in a singl...

Research paper thumbnail of Investigation to Identify the Root Cause of Out-of-Specification Results for Color of a Topical Pour-on Drug Product: A Case Study

Chromatographia, 2021

One topical pour-on drug product formed a slightly yellow color and continued to increase the int... more One topical pour-on drug product formed a slightly yellow color and continued to increase the intensity over the shelf life of the product. This caused out-of-specification (OOS) results for the color of the drug product. Based on the experimental results obtained using high-performance liquid chromatography, high-resolution mass spectrometry, and a color measurement spectrophotometer, the root cause of color formation in the OOS sample was identified and confirmed to be 3,3′,5,5′-tetra-t-butyl-4,4’-stilbenequinone (2BHT-QM), an oxidative degradation product of t-butylated hydroxytoluene (BHT) which is used in this drug product as an antioxidant. The content of 2BHT-QM in the OOS sample was estimated to be about 0.9–1 ppm by two independent analytical methods. The results from our investigation clearly indicated that BHT can cause color change in liquid or semi-liquid formulation (drug product) and we report this for the first time. The investigation approach and rationale of described in this paper should be helpful for similar investigations when BHT is used in liquid or semi-liquid formulations.

Research paper thumbnail of Determination of Individual Homologues and Total Content of Benzalkonium Chloride by Reversed-Phase High-Performance Liquid Chromatography Using a Short Butyl Column

Journal of AOAC INTERNATIONAL, 2009

Benzalkonium chloride (a mixture of alkylbenzyldimethylammonium chlorides that usually contains C... more Benzalkonium chloride (a mixture of alkylbenzyldimethylammonium chlorides that usually contains C-10, C-12, C-14, and C-16 homologues), commonly known as BKC, is used as a bacteriostatic agent in many household, food, and drug products. In this paper, we report a simple, rapid, robust, and stability-indicating reversed-phase HPLC method using a short butyl (C4) column for the simultaneous determination of each individual homologue content, as well as the total concentration of individual homologues in commercial bulk raw material batches of BKC samples. The chromatographic separation was performed on a 5 cm ACE C4 column with mobile phase consisting of water, acetonitrile, and potassium chloride. Even though using a short column can potentially cause some challenges to resolving certain critical pairs of peaks, we have successfully separated all of the analyte peaks (including those from stressed, degraded products) on a short column using an optimal mobile phase.

Research paper thumbnail of Development and Validation of an HPLC Stability-Indicating Method for Identification and Assay of Elemental Iron(II) in Pharmaceutical Drug Products Using Reversed-Phase HPLC

Journal of AOAC INTERNATIONAL, 2011

Ferrous sulfate tablets are a supplementary iron source for people who suffer from iron defciency... more Ferrous sulfate tablets are a supplementary iron source for people who suffer from iron defciency anemia. A simple, fast, and QCfriendly HPLC method was developed and validated to determine elemental iron in ferrous sulfate drug products. A TSK-GEL Super octadecylsilyl column (50 × 4.6 mm id, 2 µm particle size) with a mobile phase consisting of 0.06 M methanesulfonic acid in water–acetonitrile (40 + 60, v/v) and UV detection at 282 nm were used for this method. Separation of the elemental iron peak from the matrix was achieved within 5 min. This method was successfully validated according to International Conference on Harmonization guidelines, and shown to be stability-indicating for the shelf-life samples of ferrous sulfate tablets, as well as selective for the analyte of interest.

Research paper thumbnail of Measurement of ibuprofen in human whole blood by reversed-phase ion-paired high-performance liquid chromatography using a pH-stable polymeric column

Journal of Chromatography B: Biomedical Sciences and Applications, 1990

Research paper thumbnail of Determination of 5-fluorouracil in plasma and whole blood by ion-pair high-performance liquid chromatography

Journal of Chromatography B: Biomedical Sciences and Applications, 1988

5Fluorouracil in blood or plasma was determined by extraction and column liquid chromatography. A... more 5Fluorouracil in blood or plasma was determined by extraction and column liquid chromatography. Acetonitrile was added to blood or plasma and the mixture was stirred and centrifuged. Zinc sulfate addition was followed by stirring and centrifuging. The acetonitrile was salted out with ammonium sulfate, and an aliquot was evaporated with nitrogen. The residue was dissolved in mobile phase and chromatographed. The stationary phase was a styrene-divinylbenzene copolymer, and the mobile phase was 10 n&f tetrabutylammonium hydroxide-methanol (74:26). 5-Fluorouracil was detected by UV absorption at 266 nm. Time of the assay was less than 30 min. The detection limit was 10 ng/ml and the relative standard deviation was 4 to 10% depending on the concentration.

Research paper thumbnail of Investigation of dimethyl sulfide formation during GC analysis of permethrin API: study of the reaction kinetics and estimation of the activation energy of the reaction

RSC Adv., 2016

Dimethyl sulfide was formed via a reaction between dimethyl sulfoxide and 3-phenoxylbenzyl chlori... more Dimethyl sulfide was formed via a reaction between dimethyl sulfoxide and 3-phenoxylbenzyl chloride during gas chromatography analysis of the active pharmaceutical ingredient permethrin (PMN). The kinetics and the activation energy of the reaction are presented herein.

Research paper thumbnail of Development and validation of a fast static headspace GC method for determination of residual solvents in permethrin

Journal of Pharmaceutical and Biomedical Analysis, 2016

A fast static headspace gas chromatography (HS-GC) method was developed to separate all residual ... more A fast static headspace gas chromatography (HS-GC) method was developed to separate all residual solvents present in commercial active pharmaceutical ingredient (API) batches of permethrin. A total of six residual solvents namely 2-methylpentane, 3-methylpentane, methylcyclopentane, n-hexane, cyclohexane and toluene were found in typical commercial batches of permethrin; and three of them are not in the list of ICH solvents. All six residual solvents were baseline separated in five minutes by the new method presented in this paper. The method was successfully validated as per International Conference on Harmonisation (ICH) guidelines. Evaluation of this method was conducted to separate 26 commonly used solvents in the manufacturing of various APIs, key intermediates of APIs and pharmaceutical excipients. The results of the evaluation demonstrated that this method can also be used as a general method to determine residual solvents in various APIs, intermediates and excipients that are used in pharmaceutical products.

Research paper thumbnail of Development and Validation of a Fast Stability-Indicating Ion-Paired Reversed-Phase HPLC Method for the Assay of Thiabendazole and Estimation of Its Related Compounds

Journal of AOAC INTERNATIONAL, 2017

Thiabendazole is a benzimidazole-based anthelmintic active pharmaceutical ingredient for the trea... more Thiabendazole is a benzimidazole-based anthelmintic active pharmaceutical ingredient for the treatment of intestinal pinworm and Strongyloides infections. Thiabendazole is also used as a fungicide to control fungal diseases in fruits and vegetables. In this paper, we report, for the first time, the development and validation of a novel stability-indicating reversed-phase ion-paired HPLC method for the assay of thiabendazole and estimation of its related compounds. Chromatographic separation was achieved by using an isocraticelution at a flow rate of 1.5 mL/min using an ACE 5 C18 (4.6 × 50 mm, 5 μm particle size) columnmaintained at 35°C and with UV detection at 300 nm. The mobile phase consisted of 25% acetonitrile and75% 10 mM 1-octanesulfonic acid sodium salt aqueous solution containing 0.1% methanesulfonic acid. The total run time was only 4 min. The new method was successfully validated according to the International Conference on Harmonization guidelines. The stability-indicati...

Research paper thumbnail of Development and Validation of a Normal Phase Chiral HPLC Method for Analysis of Afoxolaner Using a Chiralpak® AD-3 Column

Journal of chromatographic science, 2016

Afoxolaner is a new antiparasitic molecule from the isoxazoline family that acts on the insect ac... more Afoxolaner is a new antiparasitic molecule from the isoxazoline family that acts on the insect acarine gamma-aminobutyric acid and glutamate receptors. Isoxazoline family of compounds has been employed as active pharmaceutical ingredient in drug products prescribed for control of fleas and ticks in dogs. Afoxolaner with a chiral center at isoxazoline ring exists as a racemic mixture. A normal phase chiral high performance liquid chromatography analytical method has been developed to verify that afoxolaner is a racemic mixture as demonstrated by specific rotation, as well as to determine enantiomeric purity of single enantiomer samples. A Chiralpak(®) AD-3 column (150 × 4.6 mm I.D.) maintained at 35°C was used in the method. Analytes were analyzed with an isocratic elution using n-Hexane/IPA/MeOH (89:10:1, v/v/v) as the mobile phase with a detection wavelength of 312 nm. Desired separation of the two enantiomers was achieved in <10 minutes with resolution and selectivity factors o...

Research paper thumbnail of Rapid and Sensitive Hplc Determination of Ranitidine in Plasma. Application to Pharmacokinetics Study

Journal of Liquid Chromatography, 1988

A rapid and sensitive reversed-phase high-performance liquid chrormatography (RP-HPLC) method for... more A rapid and sensitive reversed-phase high-performance liquid chrormatography (RP-HPLC) method for the separation and quantification of the H2-receptor antagonist drug ranitidine in human plasma is described.The extraction of ranitidine from plasma by an organic solvent was eliminated in this method. Instead, the pre-chromatography isolation of the drug was done by adding approximately 50 mg of zinc sulfate and 200 μL of acetonitrile in 1.0 mL of plasma. A short column packed with pH-stable (1–13) reversed phase PLRP-S particles was used with an isocratic elution of 5.0mM dibasic potassium phosphate plus 0.50mM tetraethyl ammonium hydroxide/ acetonitrile, 80:20 (v/v). The ranitidine was monitored at 315 nm and 0.20 to 0.002 absorption units full scale (AUFS). The completion time of the assay was less than 15 minutes and had a limit of detection of 1.0 ng/mL for a 100-μL injection volume.After an oral dose of 150 mg of ranitidine, plasma samples were collected at several time points and were analyzed by using this method to determine various pharmacokinetic parameters.

Research paper thumbnail of A Practical Synthesis of the PDE4 Inhibitor, SB-207499, from a Cyclohexanone Precursor

Organic Process Research & Development, 2003

Research paper thumbnail of (1) Rapid High Performance Liquid Chromatography of Cyclosporin A, Cimetidine, Cyclophosphamide, 5-FLUOROURACIL and 5- …

This research has developed simple and rapid analytical methods to quantitate the drugs 5-Azaciti... more This research has developed simple and rapid analytical methods to quantitate the drugs 5-Azacitidine, Cimetidine, Cyclophosphamide, Cyclosporin A and 5-Fluorouracil from biological samples by using HPLC. 5-Azacitidine is isolated from plasma with acetonitrile ...

Research paper thumbnail of A general static-headspace gas chromatographic method for determination of residual benzene in oral liquid pharmaceutical products

Journal of Pharmaceutical and Biomedical Analysis, 2011

Sodium benzoate is used in oral liquid pharmaceutical products for its anti-microbial properties.... more Sodium benzoate is used in oral liquid pharmaceutical products for its anti-microbial properties. The benzoate salts present in liquid pharmaceutical products can potentially generate residual levels of free benzene during manufacturing of the drug product and or during the shelf-life of the product under its storage conditions. To ensure the safety and quality of the pharmaceutical products (containing benzoate in the formulation), a selective and sensitive analytical method is required to monitor residual benzene in oral liquid pharmaceutical products. In this paper, we report the development and validation of a general static-headspace gas chromatographic (SH-GC) method to determine residual benzene in oral liquid pharmaceutical products. The liquid pharmaceutical drug product sample is dissolved in dimethylsulfoxide (DMSO) in a GC headspace vial. A DB-624 capillary column (30 m × 0.32 mm I.D. and 1.8 m film thickness) was used under isothermal conditions with a flame ionization detection (FID). The benzene peak was well separated from all other volatile compounds that are present in the formulation of a number of liquid drug products. This method was successfully validated using a representative oral liquid pharmaceutical drug product. The limit of detection of the method for benzene is 0.5 ppm which met the 2 ppm limit of current ICH guideline for residual benzene in pharmaceutical products.

Research paper thumbnail of Comparison study of porous, fused-core, and monolithic silica-based C18 HPLC columns for Celestoderm-V Ointment® analysis

Journal of Pharmaceutical and Biomedical Analysis, 2009

In this paper, three C18 columns with different substrates (i.e., porous ACE-3 C18, 3 microm, fus... more In this paper, three C18 columns with different substrates (i.e., porous ACE-3 C18, 3 microm, fused-core Halo C18, 2.7 microm, and monolithic Chromolith C18 were compared for the analysis of a pharmaceutical product, Celestoderm-V Ointment, that contains one active pharmaceutical ingredient, betamethasone-17-valerate and one critical pair of low level impurities, betamethasone-E-enolaldehyde and betamethasone-Z-enolaldehyde. Key column performance for the analysis of pharmaceutical products including selectivity, efficiency, separation impedance, resolution factor, sample loading capacity, linearity and lifetime from the three columns were determined. The potential applications of these three C18 columns for different methods for Celestoderm-V Ointment analysis are also recommended.

Research paper thumbnail of Development and validation of a stability-indicating RP-HPLC method to separate low levels of dexamethasone and other related compounds from betamethasone

Journal of Pharmaceutical and Biomedical Analysis, 2009

Betamethasone (BM) is an active pharmaceutical ingredient (API) or an intermediate which is used ... more Betamethasone (BM) is an active pharmaceutical ingredient (API) or an intermediate which is used to manufacture various finished pharmaceutical products. Betamethasone is also used as a starting material to manufacture other APIs that are related to this steroid family. It is quite a challenging task to separate dexamethasone (DM) peak (the alpha epimer) and other structurally related compounds from BM. A stability-indicating reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed which can separate and accurately quantitate low levels of DM and other related compounds from BM and also from each other. This method was successfully validated for the purpose of conducting stability studies of betamethsone in quality control (QC) laboratories. The stability-indicating capability of this method was demonstrated by adequate separation of DM and all the degradation product peaks from BM peak and also from each other in aged stability samples of betamethasone. A gradient mobile phase system consisting of (A) water:acetonitrile (90:10, v/v) and (B) acetonitrile:isopropanol (80:20, v/v) was used with an ACE Phenyl column (10 cm x 4.6 mm, 3 microm particles, 100 A pore size) and an ultraviolet (UV) detection at 240 nm.

Research paper thumbnail of Determination of chiral purity of ethyl nipecotate using a Chiralcel-OG column

Journal of Chromatography A, 1995

The R-(-)-and S-(+)-enantiomers of ethyl nipecotate tartaric acid salt were separated by chiral h... more The R-(-)-and S-(+)-enantiomers of ethyl nipecotate tartaric acid salt were separated by chiral high performance liquid chromatography on a commercially available chiral stationary phase using a non-polar mobile phase. Samples of ethyl nipecotate tartaric acid salt were analysed on a Chiralcel-OG column as the free base of ethyl nipecotate after extraction. The mobile phase was hexane-2-propanol-2-methyl-2-propanol (94:4:2, v/v/v), to which ca. 0.5 ml/1 of dimethylamine was added. The method is able to separate the two enantiomers with a resolution factor (R) of approximately 1.3 and a selectivity factor (a) of 1.15. The limit of quantification of the S-(+)-enantiomer is 0.2% in the R-(-)-enantiomer. The method was validated by the standard addition method and determining the recovery of the S-(+)-enantiomer in the R-(-)-enantiomer. The precision of the method was determined by analysing seven individual sample preparations. The analysis was done by two analysts on different days, using different equipment and reagents.

Research paper thumbnail of Development of a high performance size exclusion chromatography method to determine the stability of Human Serum Albumin in a lyophilized formulation of Interferon alfa-2b

Journal of Chromatography A, 2008

Intron Powder for Injection is a lyophilized formulation of Interferon alfa-2b marketed for treat... more Intron Powder for Injection is a lyophilized formulation of Interferon alfa-2b marketed for treatment of Hepatitis C and some cancer indications. Human Serum Albumin (HSA) is used as a lyoprotectant and cryoprotectant at 1.0 mg/mL in the product formulation. No stability-indicating method, which can quantitate HSA and its dimer or oligomer aggregates in the formulated product, has been published to date. This paper describes the development and validation of a stability-indicating high performance size exclusion chromatography (HPSEC) method for the assay of HSA and estimation of HSA related compounds in lyophilized Intron Powder for Injection. The method employs a YMC-Pack Diol-200 ® column (7.8 mm × 30 cm, 5 m porous particles with 250Å pore size), UV detection at 214 nm, and a mobile phase of 0.1 M phosphate buffer at pH 7.0 with 0.1 M sodium sulfate. The mobiles phase runs in an isocratic mode at 1.0 mL/min and the total chromatographic run time is 30 min. The method was validated for specific, linearity, accuracy, sensitivity, and robustness. It was shown to be specific for HSA and HSA aggregates (dimer and oligomers) with a limit of quantitation of 0.0005 mg/mL or 0.05% of HSA label claim in the presence of active therapeutic protein, Interferon alfa-2b, and the other pharmaceutical excipients, glycine, sodium phosphate dibasic, sodium phosphate monobasic. The method is stability indicating and is suitable for assay of HSA from 0.0005 mg/mL to 1.5 mg/mL. (0.05-150% of HSA label claim) and for estimation of HSA related aggregates (dimer, and oligomer) from 0.0005 mg/mL to 0.15 mg/mL (0.05-15% of HSA label claim). The method is robust for routine use in product quality control. The method was applied to the analysis of batches of lyophilized Intron Powder for Injection of low, middle and high strength from the beginning, middle and end of shelf-life. The results indicated that HSA is stable in the product through out its shelf-life.

Research paper thumbnail of Applying Charged Aerosol Detection to Aminoglycosides

Charged Aerosol Detection for Liquid Chromatography and Related Separation Techniques

Research paper thumbnail of Simultaneous Determination of Esafoxolaner, Eprinomectin, Praziquantel, BHT and Their Related Substances in a Topical Finished Product by a Single Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) Method

SSRN Electronic Journal, 2021

Research paper thumbnail of Alternative and Improved Stability-Indicating HPLC Method for the Assay of Eprinomectin and Determination of Its Related Compounds in Bulk Batches of Eprinomectin Drug Substance

Journal of AOAC INTERNATIONAL, 2021

Background Eprinomectin is used as an active pharmaceutical ingredient (API) in various drug prod... more Background Eprinomectin is used as an active pharmaceutical ingredient (API) in various drug products by the animal health industry. Several major related impurities of eprinomectin API are not separated and coelute by the current United States Pharmacopeia (USP) method for eprinomectin. Objective The aim was to develop and validate a true and reliable stability-indicating reversed-phase (RP) HPLC method for assay and determination of related substances of eprinomectin in bulk batches of eprinomectin API. Method HPLC analysis is carried out using a Kinetex C8 column (100 mm × 4.6 mm i.d. , 2.6 μm particle size) maintained at 30°C with water–acetonitrile–isopropanol (48 + 42 + 10, v/v/v) as mobile phase A and 100% acetonitrile as mobile phase B. Analytes are separated by gradient elution at a flow rate of 0.7 mL/min and detected by UV at 252 nm. The total run time of the method is 30 min. Eprinomectin assay and estimation of all eprinomectin-related substances are obtained in a singl...

Research paper thumbnail of Investigation to Identify the Root Cause of Out-of-Specification Results for Color of a Topical Pour-on Drug Product: A Case Study

Chromatographia, 2021

One topical pour-on drug product formed a slightly yellow color and continued to increase the int... more One topical pour-on drug product formed a slightly yellow color and continued to increase the intensity over the shelf life of the product. This caused out-of-specification (OOS) results for the color of the drug product. Based on the experimental results obtained using high-performance liquid chromatography, high-resolution mass spectrometry, and a color measurement spectrophotometer, the root cause of color formation in the OOS sample was identified and confirmed to be 3,3′,5,5′-tetra-t-butyl-4,4’-stilbenequinone (2BHT-QM), an oxidative degradation product of t-butylated hydroxytoluene (BHT) which is used in this drug product as an antioxidant. The content of 2BHT-QM in the OOS sample was estimated to be about 0.9–1 ppm by two independent analytical methods. The results from our investigation clearly indicated that BHT can cause color change in liquid or semi-liquid formulation (drug product) and we report this for the first time. The investigation approach and rationale of described in this paper should be helpful for similar investigations when BHT is used in liquid or semi-liquid formulations.

Research paper thumbnail of Determination of Individual Homologues and Total Content of Benzalkonium Chloride by Reversed-Phase High-Performance Liquid Chromatography Using a Short Butyl Column

Journal of AOAC INTERNATIONAL, 2009

Benzalkonium chloride (a mixture of alkylbenzyldimethylammonium chlorides that usually contains C... more Benzalkonium chloride (a mixture of alkylbenzyldimethylammonium chlorides that usually contains C-10, C-12, C-14, and C-16 homologues), commonly known as BKC, is used as a bacteriostatic agent in many household, food, and drug products. In this paper, we report a simple, rapid, robust, and stability-indicating reversed-phase HPLC method using a short butyl (C4) column for the simultaneous determination of each individual homologue content, as well as the total concentration of individual homologues in commercial bulk raw material batches of BKC samples. The chromatographic separation was performed on a 5 cm ACE C4 column with mobile phase consisting of water, acetonitrile, and potassium chloride. Even though using a short column can potentially cause some challenges to resolving certain critical pairs of peaks, we have successfully separated all of the analyte peaks (including those from stressed, degraded products) on a short column using an optimal mobile phase.

Research paper thumbnail of Development and Validation of an HPLC Stability-Indicating Method for Identification and Assay of Elemental Iron(II) in Pharmaceutical Drug Products Using Reversed-Phase HPLC

Journal of AOAC INTERNATIONAL, 2011

Ferrous sulfate tablets are a supplementary iron source for people who suffer from iron defciency... more Ferrous sulfate tablets are a supplementary iron source for people who suffer from iron defciency anemia. A simple, fast, and QCfriendly HPLC method was developed and validated to determine elemental iron in ferrous sulfate drug products. A TSK-GEL Super octadecylsilyl column (50 × 4.6 mm id, 2 µm particle size) with a mobile phase consisting of 0.06 M methanesulfonic acid in water–acetonitrile (40 + 60, v/v) and UV detection at 282 nm were used for this method. Separation of the elemental iron peak from the matrix was achieved within 5 min. This method was successfully validated according to International Conference on Harmonization guidelines, and shown to be stability-indicating for the shelf-life samples of ferrous sulfate tablets, as well as selective for the analyte of interest.

Research paper thumbnail of Measurement of ibuprofen in human whole blood by reversed-phase ion-paired high-performance liquid chromatography using a pH-stable polymeric column

Journal of Chromatography B: Biomedical Sciences and Applications, 1990

Research paper thumbnail of Determination of 5-fluorouracil in plasma and whole blood by ion-pair high-performance liquid chromatography

Journal of Chromatography B: Biomedical Sciences and Applications, 1988

5Fluorouracil in blood or plasma was determined by extraction and column liquid chromatography. A... more 5Fluorouracil in blood or plasma was determined by extraction and column liquid chromatography. Acetonitrile was added to blood or plasma and the mixture was stirred and centrifuged. Zinc sulfate addition was followed by stirring and centrifuging. The acetonitrile was salted out with ammonium sulfate, and an aliquot was evaporated with nitrogen. The residue was dissolved in mobile phase and chromatographed. The stationary phase was a styrene-divinylbenzene copolymer, and the mobile phase was 10 n&f tetrabutylammonium hydroxide-methanol (74:26). 5-Fluorouracil was detected by UV absorption at 266 nm. Time of the assay was less than 30 min. The detection limit was 10 ng/ml and the relative standard deviation was 4 to 10% depending on the concentration.

Research paper thumbnail of Investigation of dimethyl sulfide formation during GC analysis of permethrin API: study of the reaction kinetics and estimation of the activation energy of the reaction

RSC Adv., 2016

Dimethyl sulfide was formed via a reaction between dimethyl sulfoxide and 3-phenoxylbenzyl chlori... more Dimethyl sulfide was formed via a reaction between dimethyl sulfoxide and 3-phenoxylbenzyl chloride during gas chromatography analysis of the active pharmaceutical ingredient permethrin (PMN). The kinetics and the activation energy of the reaction are presented herein.

Research paper thumbnail of Development and validation of a fast static headspace GC method for determination of residual solvents in permethrin

Journal of Pharmaceutical and Biomedical Analysis, 2016

A fast static headspace gas chromatography (HS-GC) method was developed to separate all residual ... more A fast static headspace gas chromatography (HS-GC) method was developed to separate all residual solvents present in commercial active pharmaceutical ingredient (API) batches of permethrin. A total of six residual solvents namely 2-methylpentane, 3-methylpentane, methylcyclopentane, n-hexane, cyclohexane and toluene were found in typical commercial batches of permethrin; and three of them are not in the list of ICH solvents. All six residual solvents were baseline separated in five minutes by the new method presented in this paper. The method was successfully validated as per International Conference on Harmonisation (ICH) guidelines. Evaluation of this method was conducted to separate 26 commonly used solvents in the manufacturing of various APIs, key intermediates of APIs and pharmaceutical excipients. The results of the evaluation demonstrated that this method can also be used as a general method to determine residual solvents in various APIs, intermediates and excipients that are used in pharmaceutical products.

Research paper thumbnail of Development and Validation of a Fast Stability-Indicating Ion-Paired Reversed-Phase HPLC Method for the Assay of Thiabendazole and Estimation of Its Related Compounds

Journal of AOAC INTERNATIONAL, 2017

Thiabendazole is a benzimidazole-based anthelmintic active pharmaceutical ingredient for the trea... more Thiabendazole is a benzimidazole-based anthelmintic active pharmaceutical ingredient for the treatment of intestinal pinworm and Strongyloides infections. Thiabendazole is also used as a fungicide to control fungal diseases in fruits and vegetables. In this paper, we report, for the first time, the development and validation of a novel stability-indicating reversed-phase ion-paired HPLC method for the assay of thiabendazole and estimation of its related compounds. Chromatographic separation was achieved by using an isocraticelution at a flow rate of 1.5 mL/min using an ACE 5 C18 (4.6 × 50 mm, 5 μm particle size) columnmaintained at 35°C and with UV detection at 300 nm. The mobile phase consisted of 25% acetonitrile and75% 10 mM 1-octanesulfonic acid sodium salt aqueous solution containing 0.1% methanesulfonic acid. The total run time was only 4 min. The new method was successfully validated according to the International Conference on Harmonization guidelines. The stability-indicati...

Research paper thumbnail of Development and Validation of a Normal Phase Chiral HPLC Method for Analysis of Afoxolaner Using a Chiralpak® AD-3 Column

Journal of chromatographic science, 2016

Afoxolaner is a new antiparasitic molecule from the isoxazoline family that acts on the insect ac... more Afoxolaner is a new antiparasitic molecule from the isoxazoline family that acts on the insect acarine gamma-aminobutyric acid and glutamate receptors. Isoxazoline family of compounds has been employed as active pharmaceutical ingredient in drug products prescribed for control of fleas and ticks in dogs. Afoxolaner with a chiral center at isoxazoline ring exists as a racemic mixture. A normal phase chiral high performance liquid chromatography analytical method has been developed to verify that afoxolaner is a racemic mixture as demonstrated by specific rotation, as well as to determine enantiomeric purity of single enantiomer samples. A Chiralpak(®) AD-3 column (150 × 4.6 mm I.D.) maintained at 35°C was used in the method. Analytes were analyzed with an isocratic elution using n-Hexane/IPA/MeOH (89:10:1, v/v/v) as the mobile phase with a detection wavelength of 312 nm. Desired separation of the two enantiomers was achieved in <10 minutes with resolution and selectivity factors o...

Research paper thumbnail of Rapid and Sensitive Hplc Determination of Ranitidine in Plasma. Application to Pharmacokinetics Study

Journal of Liquid Chromatography, 1988

A rapid and sensitive reversed-phase high-performance liquid chrormatography (RP-HPLC) method for... more A rapid and sensitive reversed-phase high-performance liquid chrormatography (RP-HPLC) method for the separation and quantification of the H2-receptor antagonist drug ranitidine in human plasma is described.The extraction of ranitidine from plasma by an organic solvent was eliminated in this method. Instead, the pre-chromatography isolation of the drug was done by adding approximately 50 mg of zinc sulfate and 200 μL of acetonitrile in 1.0 mL of plasma. A short column packed with pH-stable (1–13) reversed phase PLRP-S particles was used with an isocratic elution of 5.0mM dibasic potassium phosphate plus 0.50mM tetraethyl ammonium hydroxide/ acetonitrile, 80:20 (v/v). The ranitidine was monitored at 315 nm and 0.20 to 0.002 absorption units full scale (AUFS). The completion time of the assay was less than 15 minutes and had a limit of detection of 1.0 ng/mL for a 100-μL injection volume.After an oral dose of 150 mg of ranitidine, plasma samples were collected at several time points and were analyzed by using this method to determine various pharmacokinetic parameters.

Research paper thumbnail of A Practical Synthesis of the PDE4 Inhibitor, SB-207499, from a Cyclohexanone Precursor

Organic Process Research & Development, 2003

Research paper thumbnail of (1) Rapid High Performance Liquid Chromatography of Cyclosporin A, Cimetidine, Cyclophosphamide, 5-FLUOROURACIL and 5- …

This research has developed simple and rapid analytical methods to quantitate the drugs 5-Azaciti... more This research has developed simple and rapid analytical methods to quantitate the drugs 5-Azacitidine, Cimetidine, Cyclophosphamide, Cyclosporin A and 5-Fluorouracil from biological samples by using HPLC. 5-Azacitidine is isolated from plasma with acetonitrile ...

Research paper thumbnail of A general static-headspace gas chromatographic method for determination of residual benzene in oral liquid pharmaceutical products

Journal of Pharmaceutical and Biomedical Analysis, 2011

Sodium benzoate is used in oral liquid pharmaceutical products for its anti-microbial properties.... more Sodium benzoate is used in oral liquid pharmaceutical products for its anti-microbial properties. The benzoate salts present in liquid pharmaceutical products can potentially generate residual levels of free benzene during manufacturing of the drug product and or during the shelf-life of the product under its storage conditions. To ensure the safety and quality of the pharmaceutical products (containing benzoate in the formulation), a selective and sensitive analytical method is required to monitor residual benzene in oral liquid pharmaceutical products. In this paper, we report the development and validation of a general static-headspace gas chromatographic (SH-GC) method to determine residual benzene in oral liquid pharmaceutical products. The liquid pharmaceutical drug product sample is dissolved in dimethylsulfoxide (DMSO) in a GC headspace vial. A DB-624 capillary column (30 m × 0.32 mm I.D. and 1.8 m film thickness) was used under isothermal conditions with a flame ionization detection (FID). The benzene peak was well separated from all other volatile compounds that are present in the formulation of a number of liquid drug products. This method was successfully validated using a representative oral liquid pharmaceutical drug product. The limit of detection of the method for benzene is 0.5 ppm which met the 2 ppm limit of current ICH guideline for residual benzene in pharmaceutical products.

Research paper thumbnail of Comparison study of porous, fused-core, and monolithic silica-based C18 HPLC columns for Celestoderm-V Ointment® analysis

Journal of Pharmaceutical and Biomedical Analysis, 2009

In this paper, three C18 columns with different substrates (i.e., porous ACE-3 C18, 3 microm, fus... more In this paper, three C18 columns with different substrates (i.e., porous ACE-3 C18, 3 microm, fused-core Halo C18, 2.7 microm, and monolithic Chromolith C18 were compared for the analysis of a pharmaceutical product, Celestoderm-V Ointment, that contains one active pharmaceutical ingredient, betamethasone-17-valerate and one critical pair of low level impurities, betamethasone-E-enolaldehyde and betamethasone-Z-enolaldehyde. Key column performance for the analysis of pharmaceutical products including selectivity, efficiency, separation impedance, resolution factor, sample loading capacity, linearity and lifetime from the three columns were determined. The potential applications of these three C18 columns for different methods for Celestoderm-V Ointment analysis are also recommended.

Research paper thumbnail of Development and validation of a stability-indicating RP-HPLC method to separate low levels of dexamethasone and other related compounds from betamethasone

Journal of Pharmaceutical and Biomedical Analysis, 2009

Betamethasone (BM) is an active pharmaceutical ingredient (API) or an intermediate which is used ... more Betamethasone (BM) is an active pharmaceutical ingredient (API) or an intermediate which is used to manufacture various finished pharmaceutical products. Betamethasone is also used as a starting material to manufacture other APIs that are related to this steroid family. It is quite a challenging task to separate dexamethasone (DM) peak (the alpha epimer) and other structurally related compounds from BM. A stability-indicating reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed which can separate and accurately quantitate low levels of DM and other related compounds from BM and also from each other. This method was successfully validated for the purpose of conducting stability studies of betamethsone in quality control (QC) laboratories. The stability-indicating capability of this method was demonstrated by adequate separation of DM and all the degradation product peaks from BM peak and also from each other in aged stability samples of betamethasone. A gradient mobile phase system consisting of (A) water:acetonitrile (90:10, v/v) and (B) acetonitrile:isopropanol (80:20, v/v) was used with an ACE Phenyl column (10 cm x 4.6 mm, 3 microm particles, 100 A pore size) and an ultraviolet (UV) detection at 240 nm.

Research paper thumbnail of Determination of chiral purity of ethyl nipecotate using a Chiralcel-OG column

Journal of Chromatography A, 1995

The R-(-)-and S-(+)-enantiomers of ethyl nipecotate tartaric acid salt were separated by chiral h... more The R-(-)-and S-(+)-enantiomers of ethyl nipecotate tartaric acid salt were separated by chiral high performance liquid chromatography on a commercially available chiral stationary phase using a non-polar mobile phase. Samples of ethyl nipecotate tartaric acid salt were analysed on a Chiralcel-OG column as the free base of ethyl nipecotate after extraction. The mobile phase was hexane-2-propanol-2-methyl-2-propanol (94:4:2, v/v/v), to which ca. 0.5 ml/1 of dimethylamine was added. The method is able to separate the two enantiomers with a resolution factor (R) of approximately 1.3 and a selectivity factor (a) of 1.15. The limit of quantification of the S-(+)-enantiomer is 0.2% in the R-(-)-enantiomer. The method was validated by the standard addition method and determining the recovery of the S-(+)-enantiomer in the R-(-)-enantiomer. The precision of the method was determined by analysing seven individual sample preparations. The analysis was done by two analysts on different days, using different equipment and reagents.

Research paper thumbnail of Development of a high performance size exclusion chromatography method to determine the stability of Human Serum Albumin in a lyophilized formulation of Interferon alfa-2b

Journal of Chromatography A, 2008

Intron Powder for Injection is a lyophilized formulation of Interferon alfa-2b marketed for treat... more Intron Powder for Injection is a lyophilized formulation of Interferon alfa-2b marketed for treatment of Hepatitis C and some cancer indications. Human Serum Albumin (HSA) is used as a lyoprotectant and cryoprotectant at 1.0 mg/mL in the product formulation. No stability-indicating method, which can quantitate HSA and its dimer or oligomer aggregates in the formulated product, has been published to date. This paper describes the development and validation of a stability-indicating high performance size exclusion chromatography (HPSEC) method for the assay of HSA and estimation of HSA related compounds in lyophilized Intron Powder for Injection. The method employs a YMC-Pack Diol-200 ® column (7.8 mm × 30 cm, 5 m porous particles with 250Å pore size), UV detection at 214 nm, and a mobile phase of 0.1 M phosphate buffer at pH 7.0 with 0.1 M sodium sulfate. The mobiles phase runs in an isocratic mode at 1.0 mL/min and the total chromatographic run time is 30 min. The method was validated for specific, linearity, accuracy, sensitivity, and robustness. It was shown to be specific for HSA and HSA aggregates (dimer and oligomers) with a limit of quantitation of 0.0005 mg/mL or 0.05% of HSA label claim in the presence of active therapeutic protein, Interferon alfa-2b, and the other pharmaceutical excipients, glycine, sodium phosphate dibasic, sodium phosphate monobasic. The method is stability indicating and is suitable for assay of HSA from 0.0005 mg/mL to 1.5 mg/mL. (0.05-150% of HSA label claim) and for estimation of HSA related aggregates (dimer, and oligomer) from 0.0005 mg/mL to 0.15 mg/mL (0.05-15% of HSA label claim). The method is robust for routine use in product quality control. The method was applied to the analysis of batches of lyophilized Intron Powder for Injection of low, middle and high strength from the beginning, middle and end of shelf-life. The results indicated that HSA is stable in the product through out its shelf-life.