Single HPLC Method Research Articles

Understanding the Stress Testing Characteristics of Apixaban, Structural Elucidation of a Novel Degradation Impurity, and Stability-Indicating Method Development for Quantification of Related Substances.

People who have non-valvular atrial fibrillation may benefit from taking a new oral anticoagulant called apixaban, which has recently been given the green light by the U.S. Food and Drug Administration. During stress testing, apixaban was found to have a high degree of degradability when subjected to both acidic and basic conditions, and one significant unknown impurity was observed in addition to the major known impurities. Our aim is the isolation and characterization of degradation product observed in stress/forced degradation studies, and also the development of a single HPLC method that is both reliable and accurate for quantifying all 10 related impurities of apixaban. Preparative HPLC was used to isolate the degradation product, and 1H NMR, 13C NMR, and MS were used to elucidate the structure of the product. Additionally, a single reverse-phase (RP) HPLC method was developed for quantification of all related impurities of apixaban. Based on the spectral characterization data, the identified unknown degradation impurity was found to be a pH-independent hydrolysis degradation impurity of apixaban. The developed method is specific, linear, accurate, robust, and rugged. The isolated and characterized impurities were the same as those found during stress testing. The developed method has been validated for its intended purpose in accordance with the regulatory requirements that were outlined. The unknown impurity is a new apixaban degradation impurity that helps us understand its toxicity. The scientific community will benefit from the developed analytical method information as it relates to understanding drug product impurity profiling.

Structural Elucidation of Novel Degradation Impurity and Development, Validation of a Single HPLC Method for all Putative Impurities of Clobetasol Propionate in a Foam Drug Product.

Clobetasol Propionate is a highly strong corticosteroid that is used in a variety of topical medication formulations, including foam, ointment, lotion, spray and shampoo; with a dosage strength of 0.05% (w/w). The goal of this research was to identify and characterize a substantial unknown impurity (UK) detected during the stability testing of a Clobetasol Propionate foam pharmaceutical product in accelerated conditions (40°C and 75% relative humidity). Developing a single, robust and accurate HPLC method that is LC-MS compatible for quantifying all 14 potential Clobetasol Propionate impurities in therapeutic drugs is another goal. Preparative column chromatography was used to separate the impurity, and spectroscopic techniques like IR, NMR and MS were used to characterize its structure. The structure of isolated UK was effectively characterized and defined using spectroscopic data evaluation. The chromatographic method has also been validated according to the International Conference on Hominization's Q (2) quality guidelines. The isolated and characterized impurity had the same equivalence as the impurity found during stability testing. Precision, accuracy, linearity, robustness and ruggedness are all met in the method validation data.

Development and validation of a stability-indicating, single HPLC method for sacubitril-valsartan and their stereoisomers and identification of forced degradation products using LC-MS/MS.

The aim of this research work was to develop and validate a stability-indicating, single reversed-phase HPLC method for the separation of five impurities, including enantiomers, diastereomers, and degradation products in sacubitril-valsartan tablets. The method was developed using a Chiralcel OJ-RH column (150 × 4.6mm, 5μm) at 45°C with a gradient program of (T/%B) 0.01/25, 10.0/25, 25/38, 37.0/45, 39.0/25, and 45.0/25 at a flow rate of 0.8ml/min. Mobile phase A consisted of 1ml of trifluoroacetic acid in 1000 ml of Milli-Q water. Mobile phase B consisted of 1ml of trifluoroacetic acid in a mixture of acetonitrile and methanol in the ratio of 950:50 (v/v). Sacubitril, valsartan, and their five impurities were monitored at 254 nm. Degradation was not observed when sacubitril-valsartan was subjected to heat, light, hydrolytic, and oxidation conditions. In acid degradation study (1N HCl/60°C/2h) impurity 1 (m/z 383.44) was formed, and in base degradation study (0.1N NaOH/40°C/1h) impurities 1 and 5 (m/z 265.35) were formed; both impurities were confirmed using LC-MS. The degradation products, enantiomers, and diastereomers were well separated from sacubitril and valsartan, proving the stability-indicating power of the method. The developed method was validated per the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines. The inter- and intra-day percentage relative standard deviation for sacubitril, valsartan, and their five impurities was less than 5.2%, recovery of the five impurities was between 93 and 105%, and linearity was ≥0.999. The limit of detection was 0.030-0.048 μg/ml, and the limit of quantification was 0.100-0.160 μg/ml.

Enantioselective Green HPLC Method for Simultaneous Determination of Enantiomer, and Potential Impurities in Apremilast Drug Substance

A single reversed-phase HPLC method was developed for the quantification of seven impurities of Apremilast and its enantiomer in the drug substance. An immobilized chiral stationary phase with a chiral selector “tris (3,5-dimethyl phenyl carbamate) derivative of amylose-Chiralpak IA-3 (250 mm × 4.6 mm, 3 μm) was employed to achieve the desired separation. A mobile phase consists of buffer (0.01M NH4HCO3, PH 8.0) and acetonitrile in the ratio 50:50 (v/v) and is pumped at a flow rate of 0.4 mL/min with an isocratic elution mode. The column oven temperature is set at 25°C, and the chromatographic output is monitored at 225 nm with a total run time of 45 min. A test concentration of 500 µg/mL of Apremilast in the mobile phase is used with an injection volume of 10 µL. Induced degradation studies were carried out to study the intrinsic chemical behavior of the drug. The degradation sample solutions were utilized to demonstrate the stability-indicating nature of the developed analytical method. The obtained mass number [M+H]+ for the primary degradation product formed in acid hydrolysis was identified as 418.36 and in base hydrolysis 478.12. The two impurities were identified as impurity-5(Deacetylated impurity), and impurity-2(open ring acid impurity), respectively, and the degradation pathways were established. Following ICH Q2 and USP<1225>guidelines, complete method validation was carried out. The RSD for the drug and impurities in interday and intraday studies are less than 4.0%, and the recoveries for the impurities are between 96.1-102.1% and linearity r ≥ 0.9997. LOQ results for the drug and impurities are between 0.052 µg/mL and 0.107 µg/mL, and LOD results are between 0.016 µg/mL and 0.032 µg/mL. The greenness of the method was evaluated by using an analytical eco scale, GAPI, and AGREE, and it was found that the method is green.

A Novel RP-HPLC Method for Estimating Fulvestrant, Benzoyl Alcohol, and Benzyl Benzoate in Injection Formulation

For the quantitative determination of Fulvestrant, Benzyl alcohol, and Benzyl benzoate in Fulvestrant injection, an original RP-HPLC approach was developed. The gradient method was developed using HPLC and a Phenomenex Luna C8, 150 × 4.6 mm, i.d 3.0 μm particle size column with a gradient programme of mobile phases A and B. With a flow rate of 1.5 mL/minute, injection volume of 10 μL, and column temperature of 35°C, UV wavelength detection at 254 nm for Benzyl alcohol and Benzoyl Benzoate and 280 nm for Fulvestrant, mobile phase-A consists of DI water and mobile phase-B consists of Acetonitrile. The current study describes a single HPLC method for developing a Fulvestrant (Active), Benzyl alcohol (Cosolvent), and Benzyl Benzoate (Cosolvent) assay for Fulvestrant injection. The assay method was determined to be suitable for quantifying three components in the pharmaceutical product and was verified according to ICH guidelines.

Physicochemical Compatibility Investigation of Mesalazine and Folic Acid Using Chromatographic and Thermoanalytical Techniques.

Inflammatory bowel disease is a common name for Crohn’s disease and ulcerative colitis. These inflammatory states cause damage in the sidewalls of the gastrointestinal tract, resulting in malabsorption of food and vitamins. Folic acid (Vitamin B9) is often associated with inflammatory bowel diseases since reduced overall folate concentration in the human body may lead to the development of colorectal cancer and megaloblastic anaemia. However, its deficiency is easily compensated by taking an additional folic acid pill during regular therapy. At the moment, there are no studies that have examined the compatibility of folic acid with 5-aminosalicylate drugs used in the treatment of inflammatory bowel diseases. In this work, differential scanning calorimetry, forced degradation studies, isothermal stress testing and dissolution stability testing were used to determine the stability of folic acid and one of the most commonly used 5-aminosalicylates, mesalazine, when present in the same solution or blend. To monitor the assay of folic acid, mesalazine and nine of its related impurities, a single HPLC method was developed. Results of compatibility studies showed that no physicochemical interaction between mesalazine and folic acid occurs when combined, opening the path to the development of new formulations, such as a mesalazine/folic acid fixed-dose combination.

Simultaneous determination of tartrazine and allura red in commercial preparation by chemometric HPLC method

The concentrations of tartrazine (TAR) and allura red (ALL) in binary mixtures and commercial preparation were determined by the combined use of chemometric (or multivariate) calibrations and HPLC method. In this study, partial least squares (PLS), principal component regression (PCR) and classical least squares (CLS) based on multiwavelength HPLC data were refined as multivariate calibration techniques such as CPLS, CPCR, CCLS. The relation between multiwavelength peak area data (x-block) and concentration set (y-block) were used to obtain the chromatographic multivariate calibrations. Multiwavelength-chromatograms or multiwavelength peak area data were obtained by using photodiode array (PDA) detectors. Waters Symmetry® C18 Column 5 gm 4.6 × 250 mm and a combination of 0.2 M acetate buffer (pH = 5), acetonitrile, methanol and bidistilled water (55:20:10 v/v) at the flow rate of 1.9 mL/ min were used to obtain a good chromatographic separation between TAR and ALL in presence of sunset yellow (Internal Standard (IS)). These chromatographic multivariate techniques were validated by analyzing the different synthetic mixtures and by using standard addition technique. These methods were applied to the commercial soft drinking powder samples containing TAR and ALL. The results from these chromatographic multivariate techniques were compared with each other as well as obtained by alternative single HPLC method.

Development and validation of chiral HPLC method for quantitative determination of hydrazine analogue in Argatroban monohydrate

Abstract Argatroban is an anticoagulant which is used as direct thrombin inhibitor. It consists of hydrazine analogue, which is probably similar to Argatroban. The single HPLC method is already reported in to United States Pharmacopeia (USP). In that method, Argatroban peak eluted as R-Argatroban and S-Argatroban while hydrazine analogue eluted as P1 and P2 peaks. The P2 peak of Hydrazine analogue is eluted as retention time of R-Argatroban peak. Therefore it was difficult to determine the accurate concentration of Hydrazine analogue in to Argatroban. The existing method is longer run time up to 102 min. The present HPLC method shows appropriate resolution between hydrazine analogue and Argatroban. The total run time reduces up to 40 min, which is a ∼2.5 time lesser than reported in literature. In present method hydrazine analogue and Argatroban are eluted to be 9.0 min and 12.5 min respectively. The effective chromatographic separations are achieved on YMC chiralart cellulose-SC, 250×4.6 mm, 5μ column and normal phase with linear elution. The mobile phase was uniform mixture of methanol, acetonitrile, dichloromethane, trifluoroacetic acid, triethylamine with ratio of 30:50:920:3:4 and delivered flow rate 0.7 mL/min. Analysis is performed on UV/PDA detector with detection wavelength is adjusted at 259 nm. The injection volume is 5μL and column oven temperature is 35°C. The present method is accurate and precise as well as linear in the range of LOQ to 150 % level. The finalized concentration of hydrazine analogue for limit of detection and quantitation is 0.003 and 0.010%. The correlation coefficient of hydrazine analogue is 0.99947. The recovery for ranged between 100.00 to 103.29%. In robustness study for of mobile phase flow rate and column oven temperature, no significant changes are observed in system suitability parameters and result. This method has been developed and validated using the ICH guideline Q2(R1).The new method is sensitive, precise, accurate, and rapid; it also qualifies all the criteria of linearity, stability, as well as robustness.

Forced Degradation Studies on Sodium Picosulfate and Separation of 15 Process Related Impurities/Degradants by HPLC

A selective, precise and stability-indicating, high performance liquid chromatographic method was developed for the analysis of active ingredient sodium Picosulfate and forced degradation behavior was studied. The current article describes forced degradation behavior of the Sodium Picosulfate drug substance in detail by analyzing 15 process related/degradants in a single HPLC method under ICH recommended stressed conditions. Mobile phase comprised of 0.01 M of Disodium hydrogen phosphate and 0.01 M of potassium phosphate monobasic buffer and 1 mL of triethyl amine in 1000 mL water adjusted to pH 7.5 with 10% phosphoric acid. Acetonitrile was used as Mobile Phase B. The separation was achieved on a gradient method. The reversed phase chromatography was performed in Hypersil BDS C18 5.0 μm, 4.6 × 250 mm column maintained at temperature 35°C. Injection volume was 60 μL. Milli-Q water used as diluent. The mobile phase was pumped at 0.9 mL/min-1. The eluted compounds were monitored at 220 nm. Secondary wavelength of the 263 nm was studied to check any further degradants during the forced degradation studies. New additional degradants Sodium Picosulfate Benzyl alcohol Impurity and N oxide degradations were discussed and studied during the forced degradation to understand the chemical stability of the drug substance.

HPLC Method for Determination of Aspirin, Rosuvastatin, Ezetimibe and Clopidogrel in Combination Drug Products

A single HPLC method for the determination of four active ingredients viz. aspirin, rosuvastatin, ezetimibe and clopidogrel in less run time is developed. HPLC method was developed and validated. X-terra C18 100 × 4.6 mm, 3.5 μ HPLC column, KH2PO4 buffer (mobile phase A) and acetonitrile (mobile phase B) were used. 20 μ injection volume, 1.0 mL/min flow rate, 230 nm and ambient column oven temperature were applied for separation. Gradient program: at 0 min mobile phase-B 13 %, at 4 min 13 %, at 8 min 44 %, 14 min 57 %, 17 min 57 %, 20 min 13 % and 25 min 13 %. Method validation was performed as per ICH guidance with precision, linearity, specificity, accuracy, ruggedness and robustness. Validation results were satisfactory and this method can be applied for regular drug product manufacturing

Optimization of a single HPLC-PDA method for quantifying Metformin, Gliclazide, Pioglitazone, Dapagliflozin, Empagliflozin, Saxagliptin, Linagliptin and Teneligliptin using central composite design

• Optimization of a single HPLC method using CCD for the assay of 8 antidiabetic drugs. • Validation of the method as per the ICH guidelines. • Application of the method for the assay of all the FDC’s of the 8 antidiabetic drugs.

HPLC methods for purity evaluation of man-made single-stranded RNAs

Synthetic RNA oligos exhibit purity decreasing as a function of length, because the efficiency of the total synthesis is the numerical product of the individual step efficiencies, typically below 98%. Analytical methods for RNAs up to the 60 nucleotides (nt) have been reported, but they fall short for purity evaluation of 100nt long, used as single guide RNA (sgRNA) in CRISPR technology, and promoted as pharmaceuticals. In an attempt to exploit a single HPLC method and obtain both identity as well as purity, ion-pair reversed-phase chromatography (IP-RP) at high temperature in the presence of an organic cosolvent is the current analytical strategy. Here we report that IP-RP is less suitable compared to the conventional ion-exchange (IEX) for analysis of 100nt RNAs. We demonstrate the relative stability of RNA in the denaturing/basic IEX mobile phase, lay out a protocol to determine the on-the-column stability of any RNA, and establish the applicability of this method for quality testing of sgRNA, tRNA, and mRNA. Unless well resolving HPLC methods are used for batch-to-batch evaluation of man-made RNAs, process development will remain shortsighted, and observed off-target effects in-vitro or in-vivo may be partially related to low purity and the presence of shorter sequences.

Advancing USP compendial methods for fixed dose combinations: A case study of metoprolol tartrate and hydrochlorothiazide tablets

The current United States Pharmacopeia–National Formulary (USP–NF) includes more than 250 monographs of fixed dose combinations (FDCs), and some of them need to be updated due to incompleteness of impurity profiles and obsolescence of analytical methodologies. A case study of metoprolol tartrate and hydrochlorothiazide tablets is presented to summarize challenges encountered during the USP monograph modernization initiative of FDCs and to highlight an “adoption and adaptation” approach employed for method development. To this end, a single stability-indicating HPLC method was developed to separate the two drug substances and eight related compounds with resolution 2.0 or higher between all critical pairs. Chromatographic separations were achieved on a Symmetry column (C18, 100 mm × 4.6 mm, 3.5 µm) using sodium phosphate buffer (pH 3.0; 34 mM) and acetonitrile as mobile phase in a gradient elution mode. The stability-indicating capability of this method has been demonstrated by analyzing stressed samples of the two drug substances. The developed HPLC method was validated for simultaneous determination of metoprolol tartrate and hydrochlorothiazide and relevant impurities in the tablets. Moreover, the developed method was successfully applied to the analysis of commercial tablet dosage forms and proved to be suitable for routine quality control use. The case study could be used to streamline USP's monograph modernization process of FDCs and strengthen compendial procedures.

SEPARATION AND ASSAY OF FOUR ANTIHISTAMINE DRUGS DIPHENHYDRAMINE, CHLORPHENIRAMINE, CYPROHEPTADINE AND FEXOFENADINE IN PHARMACEUTICAL FORMS BY A SINGLE HPLC METHOD

Objective: The objective of this study was to develop and validate a single HPLC method, in order to separate and assay four antihistamine drugs diphenhydramine, chlorpheniramine, cyproheptadine and fexofenadine in pharmaceutical forms. This method was a practical additional choice in quality control laboratories.Methods: The chromatographic conditions comprised of a classical C18-type stationary phase (150 × 4.6 mm, 5μ), with a mobile phase consisting of, 2.5g of sodium octane sulfonic acid in a mixture of 500 ml of deionized water and 500 ml of acetonitrile, and apparent pH of 2.0 was adjusted with phosphoric acid. The flow rate was 1 ml/min; the detection wavelengths were at 220 nm, 230 nm, 265 nm and 254 nm for diphenhydramine, chlorpheniramine, cyproheptadine and fexofenadine respectively. The temperature was ambient temperature.Results: The method was validated for linearity with correlation coefficients very close to one, the accuracy with mean recovery values between 95.0-105.0%, precision with relative standard deviations of the calculated concentrations less than 5.0% and specificity in the presence of degradation products. Then it was used successfully to separate a mixture of them and to assay these drugs in pharmaceutical forms purchased from Syria.Conclusion: The results presented in this paper showed that the developed method was simple and applicable, for the separation and determination of the four drugs in their pharmaceutical forms.

Development and validation of stability indicating HPLC methods for related substances and assay analyses of amoxicillin and potassium clavulanate mixtures

Antibacterial combinations consisting of the semisynthetic antibiotic amoxicillin (amox) and the β-lactamase inhibitor potassium clavulanate (clav) are commonly used and several chromatographic methods were reported for their quantification in mixtures. In the present work, single HPLC method for related substances analyses of amoxicillin and potassium clavulanate mixtures was developed and validated according to international conference on harmonization (ICH) guidelines. Eighteen amoxicillin and six potassium clavulanate impurities were successfully separated from each other by using triple gradient elution using a Thermo Hypersil Zorbax BDS C18 (250 mm×4.6mm, 3μm) column with 50μL injection volumes at a wavelength of 215nm. Commercially unavailable impurities were formed by degradation of amoxicillin and potassium clavulanate, identified by LC–MS studies and used during analytical method development and validation studies. Also, process related amoxicillin impurity-P was synthesized and characterized by using nuclear magnetic resonance (NMR) and mass spectroscopy (MS) for the first time. As complementary of this work, an assay method for amoxicillin and potassium clavulanate mixtures was developed and validated; stress-testing and stability studies of amox/clav mixtures was carried out under specified conditions according to ICH and analyzed by using validated stability-indicating assay and related substances methods.

A novel reversed-phase liquid chromatographic method for the simultaneous determination of potential impurities of bisoprolol fumarate and hydrochlorothiazide in a fixed dosage form

ABSTRACTIn the present study 12 impurities of bisoprolol fumarate (BISO) and hydrochlorothiazide (HCTZ) were separated simultaneously in a single HPLC method. Out of these 12 impurities, five are potential degradants, which are validated as per The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines. As the two active drug substances BISO and HCTZ have different solubilities and polarities, the most critical parameters in resolving the components from each other are pH, temperature, and solvents. The method is precise (RSD < 1.0%), accurate, linear (r2 > 0.999), robust, and stability indicating in the range of limit of quantification (LOQ) to 150%. The HPLC method is then migrated to ultra-performance liquid chromatography (UPLC) to further reduce the run time and solvent consumption, and increase the sample throughput.

Development and validation of a single HPLC method for determination of α-tocopherol in cell culture and in human or mouse biological samples.

A straightforward and common analytical method for α-tocopherol (αT) determination in various biological samples, including plasma, red blood cells (RBC), tissues and cultured cell lines, was developed and validated, using a reverse phase-chromatographic method (RP-HPLC). Even though many chromatographic methods for αT determination have been reported, most of them require readjustment when applied to different types of samples. Thus, an effective and simple method for αT determination in different biological matrices is still necessary, specifically for translational research. This method was applied using a C18 column (250 × 4.6 mm, 5 µm particle size) under isocratic elution with MeOH:ACN:H2 O (90:9:1 v/v/v) at a flow rate of 1 mL/min and detected using photodiode array at 293 nm. Linearity (r >0.9997) was observed for standard calibration with inter- and intraday variation of standard <4%. Lower limits of detection and quantification for αT in this assay were 0.091 and 0.305 µg/mL respectively. Validation proved the method to be selective, linear, accurate and precise. The method was successfully applied in great variety of biological samples, that is, human and mouse plasma, RBCs, murine tissues and human/mouse/rat cultured cell lines. More importantly, a single protocol of extraction and detection can be applied, making this method very convenient for standardization of different types of samples.

A validated stability-indicating RP-HPLC method for paracetamol and lornoxicam: Application to pharmaceutical dosage forms

A new method for the simultaneous determination of paracetamol (PR) and lornoxicam (LR) has been developed by reversed phase HPLC from the combination drug product. The separation achieved on C18 column using acetonitrile and 0.02 M potassium dihydrogen phosphate was in the ratio of 35:65 (v/v) as mobile phase at a flow rate of 1.0 mL/min. Both the components were monitored at a single wavelength at 260 nm and the column temperature was maintained at 30?C throughout the analysis. A linear response was found in the concentration range of 125-375 ?g/mL for PR and 2-6 ?g/mL for LR, with the correlation coefficient of more than 0.999. Although the tablet contained a high dose of PR (500 mg) and a low dose of LR (8 mg), the single HPLC method was developed and the intra as well as inter day precision was obtained at less than 2% of RSD. The accuracy results obtained were between 98% and 102%. The drug was intentionally degraded under acidic, basic, peroxide, thermal, and photolytic conditions. The major degradation observed for both PR and LR under peroxide condition indicated that the drug product is susceptible to oxidation. The degraded peaks were properly resolved from PR and LR. Hence, the method is stability indicating.

Development and Validation of a Precise, Single HPLC Method for the Determination of Tolperisone Impurities in API and Pharmaceutical Dosage Forms.

A novel, sensitive, stability-indicating HPLC method has been developed for the quantitative estimation of Tolperisone-related impurities in both bulk drugs and pharmaceutical dosage forms. Effective chromatographic separation was achieved on a C18 stationary phase with a simple mobile phase combination delivered in a simple gradient programme, and quantitation was by ultraviolet detection at 254 nm. The mobile phase consisted of a buffer and acetonitrile delivered at a flow rate 1.0 ml/min. The buffer consisted of 0.01 M potassium dihydrogen phosphate with the pH adjusted to 8.0 by using diethylamine. In the developed HPLC method, the resolution between Tolperisone and its four potential impurities was found to be greater than 2.0. Regression analysis showed an R value (correlation coefficient) of greater than 0.999 for the Tolperisone impurities. This method was capable of detecting all four impurities of Tolperisone at a level of 0.19 μg/mL with respect to the test concentration of 1000 μg/mL for a 10 µl injection volume. The tablets were subjected to the stress conditions of hydrolysis, oxidation, photolysis, and thermal degradation. Considerable degradation was found to occur in base hydrolysis, water hydrolysis, and oxidation. The stress samples were assayed against a qualified reference standard and the mass balance was found to be close to 100%. The established method was validated and found to be linear, accurate, precise, specific, robust, and rugged.

Development of a Reversed-Phase HPLC Impurity Method for a UV Variable Isomeric Mixture of a CRF Drug Substance Intermediate with the Assistance of Corona CAD

The compound studied, an antagonist of corticotropin-releasing factor (CRF) receptor 1, was under development for the treatment of major depressive disorder and generalized anxiety disorder. To control the quality of intermediate compounds in the synthetic pathway, the preference is to develop a single HPLC method that could determine impurities of the sequential and structurally similar intermediates. However, the chemical nature of one of those intermediates, Compound C, posed a number of challenges to the development of a suitably rugged impurity method for this isolated intermediate. In the solid state, Compound C is a stable mixture of its trans-isomer and semicarbazone forms. In most solution states, Compound C interchanges between the trans and semicarbazone forms as well as degrades rapidly to impurity X, resulting in sample solution instability. Furthermore, the trans-isomers and semicarbazone exhibited different UV response factors, but reference standards of the two forms were not available to determine the relative response factor. Consequently, irreproducibility was observed during the HPLC analysis when conventional UV detection was applied directly. This article describes the following approaches that were employed to meet these challenges: (1) diluent screening was performed to select a \solvent that afforded adequate sample solution stability; (2) appropriate chromatographic conditions were selected to eliminate or minimize any on-column degradation; (3) alternate HPLC detection, Corona charged aerosol detection, in conjunction with UV analysis, was used to determine relative amounts of the isomeric forms which subsequently permitted the use of conventional UV detection for routine analysis. The validation data of this reversed-phase liquid chromatographic method are also discussed.