Simultaneous determination of phenol and mononitrophenol isomers using PLS regression and conventional and derivative spectrophotometry

The partial least squares regression method (PLS) was tested as a calibration procedure for the simultaneous determination of phenol, o-nitrophenol, m-nitrophenol and p-nitrophenol by both conventional and first derivative UV/Vis spectrophotometry. The experiments were conducted in the acidic, neutral and basic media. The results obtained by the application of the PLS procedure on the conventional and first derivative spectra in two solvent media were compared. It was found that the results obtained in the basic medium have better performance characteristics than those obtained in the acidic or neutral media. Comparable results were obtained in the case of both conventional and first derivative absorbance data. The proposed method was applied to the determination of the four phenol derivatives in natural spiked water samples at concentration levels between 1.0 and 10.0 microg ml(-1) with average recoveries in the range 96% - 99%.     

Application of internal standard for derivative-spectrophotometric determination of azinphos-methyl in commercial formulations

The use of an internal standard is proposed in this work for first derivative spectrophotometric determination of azinphos in formulations. Generally, the spectrophotometric procedure is simpler and less expensive than chromatographic techniques recommended for the analysis of pesticides. However, while determining the pesticide in commercial formulations the, many-fold dilution required for such sensitive detection is a serious source of analytical error. It is known that an internal standard (IS), if properly chosen, can help eliminate this type of problem. A mixture of acetophenone (used as an IS in the high performance liquid chromatography (HPLC) procedure) and the blue dye Erioglaucine (A) was applied for the determination of azinphos-methyl in commercial formulations. To ensure the best conditions for the zero-crossing technique, the composition of the mixture was optimized to obtain the zero value of the first derivative absorbance of the IS at a minimum of the azinphos-methyl first derivative absorbance. Also, at the maximum of the first derivative spectrum of the IS, the differential absorption signal of the analyte was negligible. Analytical characteristics for the first derivative spectrophotometric procedure proposed were evaluated (r(2) = 0.9998, detection limit = 0.043 mg, quantification limit = 0.143 mg) and the analytical results obtained (35.02 +/- 0.20% of azinphos-methyl in the formulation) were in good agreement with the results obtained using the official HPLC method (35.44 +/- 0.32%).     

Kinetic-spectrophotometric determination of theophylline,dyphylline, and proxyphylline by use of partial least-squares regression

A kinetic-spectrophotometric method for the determination of theophylline, dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5-13 micro g mL(-1) dyphylline and proxyphylline, and 2-9 micro g mL(-1) theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.     

A Simple and Highly Sensitive Method for Quantitative Detection of Methyl Paraben and Phenol in Cosmetics Using Derivative Spectrophotometry and Multivariate Chemometric Techniques

This paper presents a simple and sensitive method for the simultaneous determination of methyl paraben (MP ) and phenol (PO ) based on the application of successive projections algorithm (SPA ) to the first derivative spectra (200–350 nm). SPA is used for variables selection in order to obtain multiple linear regression (MLR ) models using a small subset of wavelengths. The starting vector and the number of variables are optimized and the best variables are selected according to the sequence of projection operations on the spectral data matrix of the calibration set. Principal component regression and partial least squares models are also developed for comparison. The best models are found to be SPA‐MLR using seven wavelengths from the first‐derivative spectra with a root‐mean‐square error of prediction (RMSEP) of 0.08 for MP and eight wavelengths with RMSEP of 0.31 for the determination of PO . The accuracy of the proposed method is confirmed by spiked recovery test on cosmetic samples with satisfactory results (86–110%). Analysis results of the cosmetic samples are also statistically compared with those obtained from the HPLC method, showing no significant difference regarding accuracy and precision. The results indicate the potential of SPA‐MLR and derivative spectrophotometry for rapid and sensitive analysis of cosmetic samples.     

Determination of Ofloxacin in Pharmaceutical Forms by High - Performance Liquid Chromatography and Derivative Uvspectrophotometry

Abstract

A method for the determination of ofloxacin in pharmaceutical forms is described. The procedure is based on the use of the high-performance liquid chromatography, and of the second-derivative ultraviolet spectra, by utilizing the linear relationship between substance concentration and derivative peak amplitude. The minimum concentration detectable by derivative spectrophotometry was 20 ng/ml, and by HPLC 10 ng/ml. The proposed methods, which give thoroughly comparable data, are simple and rapid, and allow precise and accurate results.     

Development and validation of liquid chromatographic and UV derivative spectrophotometric methods for the determination of famciclovir in pharmaceutical dosage forms

A high-performance liquid chromatographic method and a UV derivative spectrophotometric method for the determination of famciclovir, a highly active antiviral agent, in tablets were developed in the present work. The various parameters, such as linearity, precision, accuracy, specificity, robustness, limit of detection and limit of quantitation were studied according to International Conference on Harmonization guidelines. HPLC was carried out by using the reversed-phase technique on an RP-18 column with a mobile phase composed of 50 mM monobasic phosphate buffer and methanol (50 : 50; v/v), adjusted to pH 3.05 with orthophosphoric acid. The mobile phase was pumped at a flow rate of 1 ml/min and detection was made at 242 nm with UV dual absorbance detector. The first derivative UV spectrophotometric method was performed at 226.5 nm. Statistical analysis was done by Student's t-test and F-test, which showed no significant difference between the results obtained by the two methods. The proposed methods are highly sensitive, precise and accurate and therefore can be used for its Intended purpose.     

Derivative spectrophotometric determination of sulphonamides by the Bratton-Marshall reaction

A modified method for the determination of sulphonamides, based on the Bratton-Marshall reaction with derivative spectrophotometry, is proposed. Diverse sulphonamides are determined with excellent precision by using first- to fourth-order derivative spectra. The method was applied for the determination of sulphonamides in urine, honey and pharmaceutical formulations without pretreatment of the samples.     

Simultaneous determination of norfloxacin and lomefloxacin in milk by first derivative synchronous fluorescence spectrometry using Al (III) as an enhancer

A novel method for the simultaneous determination of norfloxacin (NFLX) and lomefloxacin (LFLX) in milk samples was developed by using first derivative synchronous fluorimetry. The synchronous fluorescence (Δλ=160 nm) spectra and first derivative synchronous fluorescence spectra of NFLX, LFLX and their mixture were studied. The zero-crossing method was utilized to measure the first derivative value of the derivative spectrum. The zero-crossing points were located at 275.0 nm for NFLX and at 283.8 nm for LFLX, in first derivative synchronous fluorescence spectra. Therefore, 283.8 nm and 275.0 nm were selected for the determination of NFLX and LFLX. The first derivative values varied linearly with the concentrations in the range of 1.68×10(-8)-5.64×10(-6) mol L(-1) for NFLX and 1.89×10(-8)-6.19×10(-6) mol L(-1) for LFLX. The detection limits were 5.03×10(-9) mol L(-1) for NFLX and 7.58×10(-9) mol L(-1) for LFLX. The proposed method is reliable, selective and sensitive, and has been used successfully in the simultaneous determination of NFLX and LFLX in milk samples, whose results were in good agreement with those obtained by HPLC.     

Derivative spectrophotometric determination of nickel using Br-PADAP

A major problem with spectrophotometric methods for nickel is cobalt interference, because many of the reagents for nickel also react with cobalt. In this work, the interference of cobalt in the determination of nickel using 2-(5-bromo-2-pyridylaxo)-5-diethylaminophenol (Br-PADAP) was eliminated by the use of derivative spectrophotometry, using the zero-crossing method for evaluation of the derivative signal. Br-PADAP reacts with nickel(II) in the presence of Triton X-100 to form a red complex with absorption maxima at 530 and 562 nm. The reactions parameters and the conditions for the measurements of the first-derivative signal were studied and the results demonstrated that using the derivative technique, Br-PADAP can be used for nickel determination with a selectivity higher than that of ordinary spectrophotometry and with a limit of detection of 0.2 ng ml(-1). The pH should be in the range 5.0-6.0 using an acetate buffer. The determination of nickel in the presence of cobalt was performed with conventional and derivative procedures, and the results demonstrated that only the derivative method should be used and, of the methods used for evaluation of the derivative signal, the zero-crossing method is the best. The proposed procedure was used for nickel determination in steels standards. The results demonstrated that the procedure has satisfactory accuracy and precision. Cobalt interference can be also eliminated by using dual-wave-length spectroscopy.     

Simultaneous determination of caffeine and non-steroidal anti-inflammatory drugs in pharmaceutical formulations and blood plasma by reversed-phase HPLC from linear gradient elution

A reversed-phase HPLC procedure based on methanol-water gradient elution for determining caffeine and non-steroidal anti-inflammatory drugs with UV absorbance detection is proposed. Chromatographic operational conditions were selected by considering the peak resolution and the retention times of the first and last eluted compounds. The method was suitably validated and successfully applied to the determination of: caffeine, indoprofen, ketoprofen, naproxen, fenbufen and ibuprofen in blood plasma samples and several analgesic/antiphlogistic pharmaceutical formulations.     

Detection of glucocorticoid residues in pig liver by high-performance liquid chromatography with on-line electrogenerated [Cu(HIO6)2](5-)--luminol chemiluminescence detection

A novel method was developed for the simultaneous determination of glucocorticoid residues such as triamcinolone (TR), prednisolone (PR), hydrocortisone (HC), cortisone (CO), methylprednisolone (MP), dexamethasone (DE) and triamcinolone acetonide (TA) by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the enhancement effect of glucocorticoids on the chemiluminescence reaction between luminol and the complex of trivalent copper and periodate ([Cu(HIO6)2]5-), which was on-line electrogenerated by constant current electrolysis. The HPLC separation used a Nucleosil RP-C18 column (250 mmx4.6 mm i.d., 5 microm, pore size, 100 A) with a mobile phase consisting of acetonitrile and 1.0 mmol L(-1) ammonium acetate (pH 6.8, 40:60,v/v) at a flow rate of 0.8 mL min(-1). The effects of several parameters on the HPLC resolution and CL emission were studied systematically. Liver samples were hydrolyzed with Helix pomatia juice followed by a solid-phase extraction procedure. Under optimum conditions, the limits of detection (LOD) at a signal-to-noise of 3 ranged from 0.08 to 1.0 ng g(-1) and the limits of quantification (LOQ) at a signal-to-noise of 10 ranged from 0.27 to 3.33 ng g(-1) for seven glucocorticoids. The relative standard deviations (RSD) of intra- and inter-day precision were below 6.8%. The average recoveries for glucocorticoids (spiked at the levels of 5-50 ng g(-1)) in pig liver ranged from 88 to 106%, and the relative standard deviations of the quantitative results were from 2.0 to 6.9%. The proposed method had been successfully applied to the determination of glucocorticoid residues in pig liver.     

High-performance liquid chromatographic determination of tocopherols in infant formulas

A method for the simultaneous determination of alpha-tocopherol acetate and alpha-, delta-, and gamma-tocopherols by normal-phase high-performance liquid chromatography (HPLC) with a fluorescent detector in infant formula is proposed. The values obtained in the determination of the analytical parameters: linearity, precision, limit of detection and accuracy (analysis of a standard reference material, SRM 1846), confirm the quality of the method. The proposed method is useful for the determination of alpha-, delta-, and gamma-tocopherols and alpha-tocopherol acetate in infant formulas at a low cost and in a total time of 2 h.     

Differential pulse polarographic determination of hydrocortisone in pharmaceutical preparations

Differential pulse polarograms of hydrocortisone recorded from acetate buffer pH 4.6 exhibit a well-defined peak at —1.25 V vs. SCE and the peak current is proportional to the concentration in the range 10^-5–8 × 10^-5 M. The electrode reaction involves one electron and one hydrogen ion. A simple rapid method is proposed for the determination of hydrocortisone in creams and ointments. The procedure does not involve time-consuming extractions, but it is not applicable to samples containing surfactants like polyethyleneglycol which are more strongly adsorbed on the electrode than hydrocortisone. Because degradation in the side chain of hydrocortisone is not detected polarographically, the method is suitable for production control but not for stability tests.     

Determination of 9-[(2-phosphonylmethoxy)ethyl]adenine in rat urine by high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic (HPLC) method for the determination of 9-[(2-phosphonylmethoxy)ethyl]adenine (PMEA) in urine is described. The procedure includes treatment of the urine sample with chloroacetaldehyde to form the fluorescent 1,N6-ethenoadenosine derivative, which was analyzed by reversed-phase HPLC with fluorometric detection. Validation of the method showed good sensitivity, precision and reproducibility. The method is useful for the study of urinary excretion of PMEA in the rat.     

Simultaneous kinetic-spectrophotometric determination of levodopa and benserazide by bi- and three-way partial least squares calibration

A procedure for the simultaneous kinetic-spectrophotometric determination of levodopa (I) and benserazide (II), from their oxidation reaction with KIO(4) in an acidic medium, is described. Both species instantly oxidize, giving rise to compounds which present maximum values of absorbance close to 400 nm. In the presence of an excess of the oxidizing agent, the levodopa derivative evolves to form the corresponding aminochrome (lambda(m)=480 nm), while the benserazide derivative decomposes to yield colorless compounds. The appearance of new compounds, with absorption bands in the region of 500-700 nm, is additionally seen upon adding the oxidizing agent to a mixture of I and II. These compounds also evolve decomposing and forming colorless products. In spite of the complexity of the system studied, the calibration by bi-linear partial least squares (PLS) as well as by three-way partial least squares (nPLS) permit the quantification of both analytes with a precision on the order of 0.7% for levodopa and of 1.5% for benserazide. nPLS also allows for the qualitative interpretation of the phenomena which occur. The proposed method is applied to the quantification of I and II in the commercial, pharmaceutical preparation Madopar, using high performance liquid chromatography (HPLC) as the analytical reference technique.     

Determination of Retinal

Abstract

A procedure employing absorbance or fluorescence is described for the determination of retinal after it is converted to an intensely colored, fluorescent derivative of 2-diphenyl-acetyl-1, 3-indandione-1 -hydrazone. β-Carotene and retinyl acetate are eliminated as potential interferences. The procedure was applied to microgram levels of retinal.     

Simultaneous Determination of Caffeine and Meclizine Dihydrochloride in Sugar-Coated Tablets

Abstract

In this study, simultaneous determination of caffeine and meclizine dihydrochloride in their binary mixture was conducted by two spectrophotometric methods. In the first method, derivative spectrophotometry, the quantification of caffeine and meclizine dihydrochloride was performed by reading the dA/dλ values at 286.2 nm and 243.4 nm respectively in the first derivative spectra of their mixture in methanol. The relative standard deviation of the method was 0.54% for caffeine and 0.67% for meclizine dihydrochloride. In the second, selective precipitation + derivative spectrophotometry, determination of meclizine dihydrochloride was carried out by precipitation with potassium ferricyanide at pH 2 selectively, then measuring the absorbance of its solution in methanol at 420.8 nm, and determination of caffeine was succeeded by reading the dA/dλ values at 260.6 nm in the first derivative spectra of the remaining solution after precipitation. Relative standard deviation of the method was found to be 0.56% for caffeine and 1.85% for meclizine dihydrochloride. These two methods were applied successfully to a sugar-coated tablet containing these drugs.     

Spectrophotometric Methods for the Determination of Acediasulfone in Mixture with Cinchocaine

Abstract

Derivative spectrophotometry techniques (ratio‐spectra first derivative and zero‐crossing first derivative) were described for simultaneous determination of acediasulfone and cinchocaine. Acediasulfone was also determined via the formation of a colored product as a result of its reaction with p‐dimethylaminobenzaldehyde. In the ratio‐spectra first derivative method, the measurements were taken at 310 and 233.9 nm for acediasulfone and cinchocaine, respectively. By the zero‐crossing first derivative method, lines of regression were taken at 318 and 233 nm for acediasulfone and cinchocaine, respectively. In the colorimetric method, absorbance measurements were obtained at 452 nm. Acediasulfone showed linearity over concentration ranges 2–14 µg/ml, 2–16 µg/ml, and 12–60 µg/ml for ratio‐spectra first derivative, zero‐crossing first derivative, and colorimetric methods, whereas cinchocaine showed linearity over concentration ranges 1–10 µg/ml and 2.28–16 µg/ml for ratio‐spectra first derivative and zero‐crossing first derivative techniques. The proposed methods proved to be specific and accurate for the analysis of the cited drugs in laboratory‐prepared mixtures and dosage form. The obtained results agree statistically with those obtained by reference methods.     

Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne

An integrated solid-phase spectrophotometry/ FIA method is proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at lambda = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L(-1); 0.013 mg L(-1); and 0.6%; and for QYSS, between 10 and 1.000 microg L(-1); 2 microg L(-1); and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically.     

Quantitative analysis of the cholesterol-lowering drugs ezetimibe and simvastatin in pure powder, binary mixtures, and a combined dosage form by spectrophotometry, chemometry, and high-performance column liquid chromatography

Simple, accurate, sensitive, and precise UV spectrophotometric, chemometric, and HPLC methods were developed for simultaneous determination of a two-component drug mixture of ezetimibe (EZ) and simvastatin (SM) in laboratory-prepared mixtures and a combined tablet dosage form. Four spectrophotometric methods were developed, namely, ratio spectra derivative, ratio subtraction, isosbestic point, and mean centering of ratio spectra. The developed chemometric-assisted spectrophotometric method was the concentration residual augmented classical least-squares method; its prediction ability was assessed and compared to the conventional partial least-squares method. The developed HPLC method used an RP ZORBAX C18 column (5 microm particle size, 250 x 4.6 mm id) with isocratic elution. The mobile phase was acetonitrile-pH 3.5 phosphate buffer (40 + 60, v/v) at a flow rate of 1.0 mL/min, with UV detection at 230 nm. The accuracy, precision, and linearity ranges of the developed methods were determined. The developed methods were successfully applied for determination of EZ and SM in bulk powder, laboratory-prepared mixtures, and a combined dosage form. The results obtained were compared statistically with each other and to those of a reported HPLC method; there was no significant difference between the proposed methods and the reported method regarding both accuracy and precision.