Alkaline Degradation Products Research Articles

Different Aspects in Partial Least Squares and Artificial Neural Network Models Used for the Analysis of Cefoperazone Sodium in Presence of its Alkaline Degradation Product

Several chemometric models were used for the determination of cefoperazone sodium in presence of its alkaline degradation product. The methods are either traditional (Partial Least Squares) or advanced (Artificial Neural Network). Partial Least Squares method was used with and without variable selection (Genetic Algorithm GA). Artificial Neural Network (ANN) was used with and without variable selection procedure (Genetic Algorithm GA) and data compression procedure (principal component analysis PCA). The chemometric methods used are PLS-1, GA-PLS-1, ANN, GA-ANN and PCA-ANN. The methods were used for the determination of cefoperazone sodium in bulk powder and pharmaceutical preparation. A 2-factor 5-level experimental design was built leading to 25 mixtures containing different ratios of cefoperazone sodium and its alkaline degradation product. Thirteen mixtures were used as a training set and the other twelve were used as a validation set.

Stability-Indicating RP-HPLC Methods for the Determination of Fluorometholone in Its Mixtures with Sodium Cromoglycate and Tetrahydrozoline Hydrochloride.

Two stability-indicating reversed-phase liquid chromatographic methods were developed and validated for the determination of fluorometholone (FLU) in its mixtures with sodium cromoglycate (SCG) and tetrahydrozoline hydrochloride (THZ). The first HPLC method (Method 1) was based on isocratic elution of FLU and SCG along with their alkaline degradation products on a reversed phase C18 column (250 × 4.6 mm id)-ACE Generix 5, using a mobile phase consisting of methanol-water (70 : 30, v/v), pH adjusted to 2.5 using orthophosphoric acid at a flow rate of 1.2 mL min(-1) Quantitation was achieved with UV detection at 240 nm. The second HPLC method (Method 2) was based on isocratic elution of FLU, its alkaline degradation product and THZ on a reversed phase C8 column (250 × 4.6 mm)-ACE Generix 5, using a mobile phase consisting of acetonitrile-50 mM potassium dihydrogen orthophosphate (40 : 60, v/v) at a flow rate of 2 mL min(-1) Quantitation was achieved by applying dual-wavelength detection, where FLU and its alkaline degradation product were detected at 240 nm and THZ was detected at 215 nm at ambient temperatures. Linearity, accuracy and precision were found to be acceptable over the concentration range of 5-50 and 10-500 μg mL(-1) for FLU and SCG (Method 1) and over the concentration range of 5-80 and 5-60 μg mL(-1) for FLU and THZ (Method 2), respectively. Besides, the FLU alkaline degradation product was verified using IR, NMR and LC-MS spectroscopy. The two proposed methods could be successfully applied for the routine analysis of the studied drugs either in their pure bulk powders or in their pharmaceutical preparations without any preliminary separation step.

Univariate spectrophotometry and multivariate calibration: Stability-indicating analytical tools for the quantification of pimozide in bulk and pharmaceutical dosage form

Simple, accurate sensitive and precise spectrophotometric and chemometric stability indicating techniques were adopted for the determination of Pimozide (PIM) in presence of its alkaline and acidic degradation products over a concentration range of 10–100μgmL−1. The proposed spectrophotometric technique includes first derivative (D1) spectrophotometric one at 252nm and 256.6nm in presence of its acidic and alkaline degradates, respectively, first-derivative of the ratio spectra spectrophotometry (DR1) at 292.5nm, the Q-analysis (absorption ratio) method, which involves the formation of absorbance equation at 242.2nm and 281.7nm, dual wave length method at 270.1nm and 284nm, the H-point standard addition method (HPSAM) and the mean centering of the ratio spectra method. The second technique is chemometric methods which include determination of PIM in presence of both its acidic and alkaline degradates using multivariate calibration methods [the classical least squares (CLS), principle component regression (PCR) and partial least squares (PLS)] using the information contained in the absorption spectra. The proposed methods have been successfully applied to the analysis of PIM in pharmaceutical dosage forms without interference from other dosage form additives and the results were statistically compared with the official method.

Comparative study of reversed-phase high-performance liquid chromatographyversusthin-layer chromatography—densitometry for determination of citicoline sodium in presence of its alkaline degradation products

Simple, sensitive, selective, and precise stability-indicating thin-layer chromatography (TLC)—densitometric and reversed-phase high-performance liquid chromatography (RP-HPLC) methods were developed and validated for the determination of citicoline sodium (CT) in the presence of its alkaline degradation products (CT Deg.) and in pharmaceutical oral solution. TLC—densitometry employs aluminum TLC plates precoated with silica gel 60 F254 as the stationary phase and ammonia—ethyl acetate—triethylamine (6:3.5:0.5, v/v) as the mobile phase to give compact spots for citicoline sodium (RF = 0.35) and its degradation product (RF = 0.1); the chromatogram was scanned at 272 nm. RP-HPLC utilizes a C18 column and a mobile phase consisting of methanol-water-acetic acid (60:40:0.1, v/v); the pH level was adjusted to 4 using 0.1% orthophosphoric acid, at a fow rate of 1 mL min−1 for the separation of citicoline sodium (tR = 1.801) and its degradation product (tR = 3.422). Quantitation was achieved by ultraviolet (UV) d...

Comparative Study of Multivariate and Univariate Determination of Zolmitriptan in the Presence of its Degradation products

This work describes comparative study of multivariate chemometric and univariate spectrophotometric determination of zolmitriptan (ZLM ) in the presence of its alkaline and oxidative degradation products. Both methods show high sensitivity and the same linearity range (1-6 µg/mL) while the chemometric method has the advantage of higher accuracy, higher specificity and better regression parameters. The study describes complete stability study on zolmitriptan and structure elucidation of the formed degradation products. The spectrophotometric method based on successive spectrophotometric resolution pattern namely; successive ratio subtraction (SRS) method using both degradation products as divisors successively followed by direct spectrophometric measurement of zolmitriptan at 222 nm while the chemometric method used PLS and PCR models. The proposed methods were successfully applied for the determination of zolmitriptan in pure powder as well as in its pharmaceutical formulation. Statistical comparison showed no significant difference between the developed methods and the reference method.

Isolation, LC–MS/MS and 2D-NMR characterization of alkaline degradants of tenofovir disoproxil fumarate

The present work describes the preparative isolation and characterization of two alkaline degradation products of tenofovir disoproxil fumarate (TDF). Tenofovir disoproxil is a prodrug of tenofovir (antiviral agent) and co-crystal form of this prodrug with fumaric acid is tenofovir disoproxil fumarate. The drug is subjected to alkaline degradation with 0.1N sodium hydroxide for 2min at room temperature. The two degradants were detected by high performance liquid chromatography (HPLC) at relative retention of 0.26 and 0.73 with respect to the drug. HPLC method involves gradient elution on Kromasil Eternity column (150mm×2.1mm, 2.5μm) using ammonium acetate (10mM) – acetonitrile as mobile phase at flow rate of 0.3mL/min and UV detection at 260nm. Two degradation products were isolated by preparative HPLC and further characterized by LC–MS, 1H NMR, 13C NMR and 2D-NMR. On the basis of this spectral data, the structure of two DPs are confirmed as methyl hydrogen ({[1-(6-amino-9H-purin-9-yl)propan-2-yl]oxy}methyl)phosphonate for DP-I and dimethyl ({[1-(6-amino-9H-purin-9-yl)propan-2-yl]oxy}methyl)phosphonate for DP-II.

Structural characterization of alkaline and oxidative stressed degradation products of lurasidone using LC/ESI/QTOF/MS/MS

A selective, accurate, precise and robust stability indicating liquid chromatography assay method was developed for the monitoring of a novel antipsychotic drug, lurasidone, in the presence of its degradation products (DPs). Also, we investigated degradation behavior of the drug under various stressed conditions such as hydrolytic (acidic, basic and neutral), oxidation, photolytic and thermal. The drug was found to be degraded under base hydrolytic and oxidative conditions, while it was stable in acid and neutral hydrolytic, photolytic and thermal conditions. The method showed adequate separation of lurasidone and its DPs on Xterra C18 (150mm×4.6mm i.d., 3.5μm) column using 20mM ammonium formate (pH 3.0): acetonitrile as a mobile phase in gradient elution mode at a flow rate of 0.6mL/min. This method was extended to liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI/QTOF/MS/MS) for structural characterization of DPs. A total of five DPs were characterized by LC/ESI/QTOF/MS/MS studies. Most probable mechanisms for the formation of DPs were proposed. The developed method was validated in terms of specificity, linearity, accuracy, precision, and robustness as per International Conference on Harmonization Guideline Q2 (R1).

Smart Methods for Linezolid Determination in the Presence of Alkaline and Oxidative Degradation Products Utilizing Their Overlapped Spectral Bands

Linezolid (LIN) is considered the fi rst available oxazolidinone antibacterial agent. It is susceptible to hydrolysis and oxidation. Five simple, accurate, sensitive and validated UV spectrophotometric methods were developed for LIN determination in the presence of its alkaline (ALK) and oxidative (OXD) degradation products in bulk powder and pharmaceutical formulation. Method A is a second derivative one (D 2 ) in which LIN is determined at 240.9 nm. Method B is a pH-induced differential derivative one where LIN is determined using the fourth derivative (D 4 ) of the difference spectra (ΔA) at 285.3 nm. Methods C, D, and E are manipulating ratio spectra, where C is the double divisor-ratio difference spectrophotometric one (DD-RD) in which LIN was determined by calculating the amplitude difference at 243.7 and 267.6 nm of the ratio spectra. Method D is the double divisor-fi rst derivative of ratio spectra (DD-DD 1 ) in which LIN was determined at 270.2 nm. Method E is a mean centering of ratio spectra one (MCR) in which LIN was determined at 318.0 nm. The developed methods have been validated according to ICH guidelines. The results were statistically compared to that of a reported HPLC method and there was no signifi cant difference regarding both accuracy and precision.

Stability-indicating methods for the determination of olanzapine in presence of its degradation products

Simple, sensitive and precise spectrophotometric and chemometric stability indicating techniques were adopted for Olanzapine (OLA) determination in presence of its degradation products over a concentration range of 0.002-0.02 mg/mL. The spectrophotometric technique involves six methods; first method is first derivative (D1) spectrophotometric one, which allows the determination of OLA in presence of its acidic and alkaline degradation products at 261.2 and 260.6 nm with mean percentage recoveries of 99.90±0.48 and 99.95±0.67, respectively. While second derivative spectrophotometry (D2) was used for determination of drug in presence of alkaline degradation products. Second method is first-derivative of the ratio spectra (DR1) for determination of OLA in presence of its acidic and alkaline degradation products at 267.9 and 251.6 nm, respectively with mean percentage recoveries of 99.81±0.64 and 100.53±1.11, respectively. The third method is pH-induced difference method for determination of OLA in presence of its acidic and alkaline degradation products; with mean percentage recoveries 100.09±0.06 and 99.77±0.78, respectively. Fourth method is the Q-analysis (absorption ratio) method, which involves the formation of absorbance equation at 296.3 nm (isosbestic point) and 271 nm (λ max of OLA) for the determination of OLA in presence of its acidic degradation products. The mean percentage recovery is 100.07±1.51. Fifth method based on dual wavelength selection was developed for the determination of OLA in presence of its acidic degradation products with mean percentage recovery of 100.36±0.69. Sixth method based on simple mathematic algorithm by the bivariate calibration was also used for the determination of OLA with the mean percentage recovery of 101.72±1.10. The second technique is chemometrics, which includes determination of OLA in presence of its acidic degradation products using multivariate calibration methods (the classical least squares (CLS), principle component regression (PCR) and partial least squares (PLS)) using the information contained in the absorption spectra.

Kinetic study and mechanism of Niclosamide degradation

A spectrophotometric kinetic study of Niclosamide alkaline degradation as a function of drug concentration, alkaline concentration and temperature has been established utilizing double divisor-ratio spectra spectrophotometric method. The developed method allowed determination of Niclosamide in presence of its alkaline degradation products; namely; 2-chloro-4-nitro aniline (DEG I) and 5-chloro salicylic acid (DEG II) with characterization of its degradation mechanism. It was found that degradation kinetic of Niclosamide followed pseudo-first order under the established experimental conditions with a degradation rate constant (k) of 0.0829mol/h and half life (t1/2) of 8.35h. The overall degradation rate constant as a function of the temperature under the given conditions obeyed Arrhenius equation where the activation energy was calculated to be 3.41kcal/mol.

Two and three way spectrophotometric-assisted multivariate determination of linezolid in the presence of its alkaline and oxidative degradation products and application to pharmaceutical formulation

Linezolid (LIN) is determined in the presence of its alkaline (ALK) and oxidative (OXD) degradation products without preliminary separation based on ultraviolet spectrophotometry using two-way chemometric methods; principal component regression (PCR) and partial least-squares (PLS), and three-way chemometric methods; parallel factor analysis (PARAFAC) and multi-way partial least squares (N-PLS). A training set of mixtures containing LIN, ALK and OXD; was prepared in the concentration ranges of 12–18, 2.4–3.6 and 1.2–1.8μgmL−1, respectively according to a multilevel multifactor experimental design. The multivariate calibrations were obtained by measuring the zero-order absorbance from 220 to 320nm using the training set. The validation of the multivariate methods was realized by analyzing their synthetic mixtures. The capabilities of the chemometric analysis methods for the analysis of real samples were evaluated by determination of LIN in its pharmaceutical preparation with satisfactory results. The accuracy of the methods, evaluated through the root mean square error of prediction (RMSEP), was 0.058, 0.026, 0.101 and 0.026 for LIN using PCR, PLS, PARAFAC and N-PLS, respectively. Protolytic equilibria of LIN and its degradation products were evaluated using the corresponding absorption spectra-pH data obtained with PARAFAC. The obtained pKa values of LIN, ALK and OXD are 5.70, 8.90 and 6.15, respectively. The results obtained were statistically compared to that of a reported HPLC method, and there was no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

Validated Stability-indicating HPLC and Thin Layer Densitometric Methods for the Determination of Pazufloxacin: Application to Pharmaceutical Formulation and Degradation Kinetics

Two stability indicating methods were developed for the determination of pazufloxacin in presence of its acidic and alkaline degradation products, in pure form and in IV injection. The first method was based on RP-HPLC on X-terra C18 column (25 cm×4.6 mm×5 μm) using methanol and 0.5% phosphoric acid (15:85 (v/v)) with the addition of 1% Triethylamine (TEA) as a mobile phase over a concentration range 2-40 μg ml-1 and a mean percentage recovery of 100.467 ± 0.595. Quantification was achieved with UV detection at 249 nm. The second method was based on TLC separation of pazufloxacin from its degradation products followed by Densitometric measurement of the intact drug spot at 249 nm. The separation was carried out on silica gel 60 F254 aluminum sheets using chloroform, methanol and ammonia (10: 8: 2 v/v/v), as the mobile phase over a concentration range 0.1-2 μg per spot and mean percentage recovery of 99.694 ± 0.539. The two methods were simple, precise, and sensitive that could be successfully applied for the determination of pure and intravenous (IV) injection. The proposed HPLC method was used for the determination of acidic and alkaline degradation kinetics of pazufloxacin. The apparent first-order rate constants, half-life times, and activation energies of the degradation processes were calculated.

Validated Stability-Indicating UPLC and Derivative Synchronous Fluorescence Spectroscopy Methods for the Determination of Atomoxetine Hydrochloride in Pharmaceutical Preparation

HCl Two stability-indicating methods were developed for the determination of atomoxetine hydrochloride (ATM) and validated in the presence of its degradation products. Method I is based on (UPLC) separation of ATM from its alkaline, oxidative, and acidic degradation products on Zorbax SB C18 column using acetonitrile -aqueous 0.01M triethylamine, pH 4.2 (50:50, v/v) mobile phase. Photodiode array detection at 205 nm was used for quantitation of ATM over the range of 0.1-35 µg/ml. The run time was 2.5 min within which ATM and its degradation products were well separated. The method was also applied to the determination of ATM in spiked human plasma over the range of 0.1-4 µg/ml. Moreover, the produced acidic degradation products were isolated, and structural elucidation of the degradates was done by LC/MS spectrometry studies. A proposal of the acid hydrolysis pathway was presented. Method IIA describes direct measurement of the intrinsic fluorescence intensity of both ATM and its known acid degradates using sodium dodecyl sulfate as fluorescence enhancer in aqueous solutions. This method was extended to (Method IIB) to apply first derivative synchronous fluorescence spectroscopy for the simultaneous analysis of ATM and its acidic depredates. The proposed methods were successfully applied to quantify ATM in commercial capsules and the results were in good agreement with those obtained using a reference method.

Validated Stability Indicating RP-HPLC for Quantitation of Nitazoxanide in Presence of Its Alkaline Degradation Products and Their Characterization by HPLC-Tandem Mass Spectrometry

A simple and sensitive stability indicating HPLC method was developed and validated for quantitative determination of Nitazoxanide (NTZ), a new antiprotozoal drug, in presence of degradation products generated under forced alkaline hydrolysis. Chromatographic separation was achieved on Inertsil C8-3 column (150 × 4.6 mm i.d.) using a mobile phase composed of acetonitrile: 50 mM ammonium acetate buffer (50:50, v/v, pH 5.0 adjusted with acetic acid) at a flow rate of 1 mL/min. Quantification was achieved with UV detection at 298 nm based on relative peak area. The method was linear over the concentration range of 0.8-50 µg/mL (r = 0.9999) with a limit of detection and quantification 0.0410 and 0.1242 µg/mL, respectively. The developed method has the requisite accuracy, selectivity, sensitivity and precision to assay NTZ in presence of its degradation products either in bulk powder or in pharmaceutical formulations. The degradation products were then identified by HPLC-MS/MS analysis using an electrospray ionization source and an ion trap analyzer.

Determination of a novel ACE inhibitor in the presence of alkaline and oxidative degradation products using smart spectrophotometric and chemometric methods

Simple, accurate, sensitive and validated UV spectrophotometric and chemometric methods were developed for the determination of imidapril hydrochloride (IMD) in the presence of both its alkaline (AKN) and oxidative (OXI) degradation products and in its pharmaceutical formulation. Method A is the fourth derivative spectra (D4) which allows the determination of IMD in the presence of both AKN and OXD, in pure form and in tablets by measuring the peak amplitude at 243.0nm. Methods B, C and D, manipulating ratio spectra, were also developed. Method B is the double divisor–ratio difference spectrophotometric one (DD–RD) by computing the difference between the amplitudes of IMD ratio spectra at 232 and 256.3nm. Method C is the double divisor-first derivative of ratio spectra method (DD–DR1) at 243.2nm, while method D is the mean centering of ratio spectra (MCR) at 288.0nm. Methods A, B, C and D could successfully determine IMD in a concentration range of 4.0–32.0µg/mL. Methods E and F are principal component regression (PCR) and partial least-squares (PLS), respectively, for the simultaneous determination of IMD in the presence of both AKN and OXI, in pure form and in its tablets. The developed methods have the advantage of simultaneous determination of the cited components without any pre-treatment. The accuracy, precision and linearity ranges of the developed methods were determined. The results obtained were statistically compared with those of a reported HPLC method, and there was no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

Stability-Indicating HPLC and RP-TLC Determination of Cefpirome Sulfate with Kinetic Study

Two sensitive and selective stability-indicating methods were developed for the determination of the antibiotic cefpirome sulfate in bulk powder, pharmaceutical formulation and in presence of its acid, alkaline, photo- and oxidative degradation products. Method A was based on HPLC separation of cefpirome sulfate in the presence of its degradation products on a reversed phase column C18, 250 × 4.6 mm, 5-μm particle size and mobile phase consisting of 0.1 M disodium hydrogen phosphate dihydrate pH 3.9 adjusted with phosphoric acid–acetonitrile (85:15, v/v). Quantitation was achieved with UV detection at 270 nm. The linear calibration curve was in the range 5.0–50.0 μg mL−1. Method B was based on reversed phase TLC separation of the cited drug in the presence of its degradation products followed by densitometric measurement of the intact drug at 270 nm. The separation was carried out using disodium hydrogen phosphate dihydrate 2.0 g %w/v, at pH 3.5 adjusted with phosphoric acid–acetone (15:10, v/v) as a developing system. The calibration curve was in the range of 1.0–10.0 μg/spot. The HPLC method was used to study the kinetic of cefpirome sulfate acid degradation. The results obtained were statistically analyzed and compared with those obtained by applying the official Japanese method.

Riluzole: Validation of Stability-Indicating HPLC, D1 and DD1 Spectrophotometric Assays

A stability-indicating reversed-phase high-performance liquid chromatographic assay procedure has been developed and validated for riluzole in the presence of alkaline and oxidative degradation products. The liquid chromatographic separation was achieved and compared isocratically on C18 Zorbax ODS and Poroshell 120 EC-C18 columns by using a mobile phase containing methanol-water, pH = 3.10 (70:30, v/v), at a flow rate of 1 mL/min and ultraviolet detection at 264 nm. The method was linear over the concentration ranges of 20-200 µg/mL (r = 0.9997) and 10-200 µg/mL (r = 0.9995). The limit of detection and quantitation for the two columns were 2 and 6 µg/mL and 1 and 3 µg/mL, respectively. Moreover, spectrophotometric methods were applied for the determination of riluzole in the presence of its oxidative degradation products by using first derivative spectrophotometry at 252.5 and 275.0 nm. The method was linear over the concentration range of 1-20 µg/mL (r = 0.9995 and 0.9996) at the studied wavelengths, with limits of detection and quantitation of 0.1 and 0.3 µg/mL. In addition, the first derivative ratio spectrophotometry (DD1) method was applied for the determination of riluzole in the presence of its alkaline degradation product at 252.0, 278.5 and 306.3 nm by using 100 µg/mL of alkaline degraded riluzole as a divisor; riluzole was additionally determined in the presence of its hydrogen peroxide oxidative degradation products at 252.5, 275.0 and 305.0 nm by using 200 µg/mL of oxidative degraded riluzole as a divisor. The DD1 method was linear over the concentration range of 1-20 µg/mL (r = 0.9996, 0.9995 and 0.9996 for the alkaline degradation product at the three studied wavelengths, respectively; and r = 0.9995, 0.9996 and 0.9995 for the oxidative degradation product at the three studied wavelengths, respectively), with limits of detection and quantitation of 0.1 and 0.3 µg/mL for both alkaline and oxidative degradation products. The two studied chromatographic and spectrophotometric methods were comparable and display the required accuracy, selectivity, sensitivity and precision to assay riluzole in bulk and pharmaceutical dosage forms. Degradation products resulting from the stress studies did not interfere with the detection of riluzole, which indicates that these are stability-indicating assays.

Stability indicating spectrophotometric methods for determination of bumadizone in the presence of its alkaline degradation product

ObjectivesSimple, selective and precise stability indicating spectrophotometric methods were adopted and validated for the quantitative determination of Bumadizone calcium semihydrate (BUM) in presence of its alkaline degradation product (DEG I). MethodsMethod A is based on the application of first derivative (1D) spectrophotometry, then measuring the amplitude of BUM at 245.4 nm. Method B depends on measuring the peak amplitude of the first derivative of the ratio spectra (1DD) at 242.6, 260 and 274 nm over a concentration range of 6–20 μg mL−1. Method C is isoabsorptive point spectrophotometry where total concentration of BUM and DEG I was calculated at their isoabsorptive point at 242.2 nm (Aiso) while DEG I concentration alone can be determined at λmax 320 nm, and then BUM concentration can be determined by subtraction. In Method D ratio subtraction spectrophotometry is applied. ResultsThe four methods were found to be specific for determination BUM in presence of different concentrations of DEG I and were successfully applied for the determination of BUM in Octomotol® tablets. ConclusionStatistical comparison between the results obtained by applying the proposed methods and that obtained by the manufacturer one for the determination of the drug was done, and it was found that there is no significant difference between them.

Micelle‐enhanced spectrofluorimetric method for determination of sitagliptin and identification of potential alkaline degradation products using LC‐MS

A novel, quick, simple and highly sensitive spectrofluorimetric method was developed and validated for the determination of sitagliptin (SG) in its pharmaceutical formulations. The proposed method is based on investigation of the fluorescence spectral behavior of sitagliptin in an SDS micellar system. In an aqueous solution of phosphate buffer pH 4.0, the fluorescence intensity of SG in the presence of SDS was greatly enhanced, by 200%, i.e. twofold enhancement. The fluorescence intensity of SG was measured at 300 nm after excitation at 270 nm. The method showed good linearity in the range 0.03-10.0 µg/mL with a good correlation coefficient (r = 0.9998). The limits of detection and quantitation values were 5.31 and 16.1 ng/mL, respectively. The proposed method was successfully applied to the analysis of SG in its single and co-formulated commercial tablets; the results were in good agreement with those obtained using a reference method. Application of the proposed method was extended to stability studies of SG after exposure to different forced degradation conditions according to the ICH guidelines, such as acidic, alkaline, thermal, photo- and oxidative stress. The chemical structure of certain potential degradation products (DPs) were investigated using LC-MS.

D-Galacturonic Acid as a Highly Reactive Compound in Nonenzymatic Browning. 1. Formation of Browning Active Degradation Products

Thermal treatment of an aqueous solution of D-galacturonic acid at pH 3, 5, and 8 led to rapid browning of the solution and to the formation of carbocyclic compounds such as reductic acid (2,3-dihydroxy-2-cyclopenten-1-one), DHCP (4,5-dihydroxy-2-cyclopenten-1-one), and furan-2-carbaldehyde, as degradation products in weak acidic solution. Studies on their formation revealed 2-ketoglutaraldehyde as their common key intermediate. Norfuraneol (4-hydroxy-5-methyl-3-(2H)-furanone) is a typical alkaline degradation product and formed after isomerization. Further model studies revealed reductic acid as an important and more browning active compound than furan-2-carbaldehyde, which led to a red color of the model solution. This red-brown color is also characteristic of thermally treated uronic acid solutions.