J. J. Arias

Partial least-squares method in analysis by differential pulse polarography. Simultaneous determination of amiloride and hydrochlorothiazide in pharmaceutical preparations

A method is proposed for the simultaneous determination of amiloride and hydrochlorothiazide in pharmaceutical preparations using differential pulse polarography in the presence of oxygen and partial least-squares (PLS) for calibration. The experimental variables that influence the system (pulse height, pulse delay and pH) are optimized by using response surface methodology to relate the variables to be optimized to the mean relative square error of prediction (RSEP), which is minimized. The proposed method was used to determine the two drugs in synthetic mixtures and pharmaceutical preparations. The results were validated by comparison with HPLC, with errors less than 10% in all instances.

Application of PLS regression to fluorimetric data for the determination of furosemide and triamterene in pharmaceutical preparations and triamterene in urine

Multivariate calibration methods that use fluorescence data for the simultaneous determination of furosemide and triamterene were developed. One of the most salient advantages of them is that the vast amount of information provided by the whole spectrum of the sample is not required. This makes analyses simple and fast. The methods require selecting chemometric parameters such as the specific spectral region and number of factors to be used. Both spectral region and number of factors are selected, simultaneously, by minimising the prediction residual error sum of squares (PRESS). The proposed methods were used for the simultaneous determination of the two drugs in real samples (pharmaceutical preparations) with no excipient separation pre-treatment, with furosemide and triamterene contents of 1.68E-3 to 4.31E-2 and 1.03E-3 to 3.12E-2mugml(-1), respectively; as well as that of triamterene at concentrations of 5.00E-4 to 5.80E-3mugml(-1) in urine samples. The ability to construct the calibration validation sets directly from the urine samples itself avoids the need to consider matrix interferences or to pre-treat the sample and/or separate some analytes The results were quite good in all cases.

Simultaneous Spectrophotometric Determination of Hydrochlorothiazide and Pharmaceutical Preparations

Abstract We developed three methods for the simultaneous determination of amiloride (AMI) and hydrochlorothiazide (HCT): zero-crossing, derivative quotient spectra with normalized divisor and multiple linear regression (MULTIC) methods. The two first methods use the derivative spectrophotometry, and the last one uses the absorbance measurement. The three methods were used to determine both compounds in synthetic mixtures and pharmaceutical preparations with errors less than 5% and 15%, respectively.

Micellar electrokinetic capillary chromatography analysis of diuretics in pharmaceutical formulations

This paper describes the development of an electrophoretic method used to analyse diuretics, and its use in the analysis of pharmaceutical formulations. Chlorthalidone, furosemide, hydrochlorothiazide and triamterene were separated in 5 min by micellar electrokinetic capillary chromatography using a carrier containing sodium dodecylsulphate as surfactant, and were subsequently detected spectrophotometrically using a diode-array detector. The limits of detection (S/N=3) were in all cases less than 1.2 mugml(-1) for all compounds. Satisfactory repeatability was obtained for migration times (<1.6%) and corrected peak areas (<5.3%) in the analysis of pharmaceutical formulations. The reproducibility was less than 4% for all samples tested. The average recoveries obtained, which ranged between 97 and 100%, testify to the accuracy of the proposed method.

Simultaneous determination of diazepam and pyridoxine in synthetic mixtures and pharmaceutical formulations using graphical and multivariate calibration-prediction methods

Several methods are reported for the simultaneous determination of diazepam and pyridoxine: two graphical methods (zero-crossing and derivative quotient spectra); and two numerical methods (multiple linear regression and partial least-squares regression). The methods have been applied in the concentration ranges 1.4-4.0 micrograms ml-1 diazepam and 4.0-12.0 micrograms ml-1 pyridoxine. The accuracy and precision of the methods have been determined and they have been validated by analysing synthetic mixtures containing the two drugs in variable proportions. The methods were also applied to the determination of diazepam and pyridoxine in pharmaceutical preparations. The analytical results were quite good in all cases.

Application of the partial least-squares calibration method to the simultaneous kinetic determination of propoxur, carbaryl, ethiofencarb and formetanate

A method based on the application of partial least-squares analysis to bilinear data was used for the simultaneous determination of propoxur, carbaryl, ethiofencarb and formetanate by a kinetic–spectrophotometric method. The procedure is based on the different rate constants of the reactions between p-aminophenol, in the presence of potassium metaperiodate, and the phenolic and naphtholic compounds obtained from the alkaline hydrolysis of the pesticides using a stopped-flow injection procedure. Mixtures containing 2–10 µg ml–1 of propoxur, 2–8 µg ml–1 of carbaryl, 2–10 µg ml–1 of ethiofencarb and 2–10 µg ml–1 of formetanate were successfully resolved with errors of less than 5%.

Simultaneous spectrophotometric determination of diuretics by using multivariate calibration methods.

The wavelength range and number of factors used in partial least-squares (PLS) calibration for the resolution of the dihydralazine (DHZ)-hydrochlorothiazide (HCT) binary mixture and the dihydralazine-hydrochlorothiazide-reserpine ternary mixture were optimized in terms of the relative standard error (R.S.E.) and relative mean standard error (R.M.S.E.). Under the optimum conditions thus established, synthetic mixtures of the analytes can be resolved with errors and relative standard deviations (R.S.D) less than 4.5 and 1.0%, respectively. The ensuing method, which was validated by comparison with high performance liquid chromatography (HPLC), also gives good results with real samples (pharmaceutical preparations).

Multicomponent analysis: Comparison of various graphical and numerical methods

The performance of several graphical (zero-crossing and derivative quotient spectra with standardized divisor) and numerical methods (MULTIC and PLS) for the resolution of binary and ternary mixtures of species is compared. Numerical methods were found to be specially suited to multicomponent analysis, particularly for mixtures containing more than two analytes with highly overlapped spectra. The results obtained by using the compared methods to analyse various synthetic mixtures of acetylsalicylic acid, caffeine and thiamine were quite consistent and errors in the simultaneous quantification of the analytes amounted to less than 5% in all instances.

Simultaneous kinetic spectrophotometric determination of five phenolic compounds by reaction with p-aminophenol, using partial least squares data treatment

A fast and accurate procedure has been developed for the simultaneous determination of resorcinol, m-aminophenol, o-cresol, phenol and m-cresol in waters. The method is based on the reaction between the aforementioned phenolic compounds, at concentration levels of ppm, and 300 ppm of p-aminophenol in 0.05 mol l–1 NaOH and in the presence of 0.004 mol l–1 KIO4. The treatment of absorbance data, between 400 and 700 nm, obtained at interval times of 20 s between 40 and 120 s and 40 s between 120 and 600 s, by means of the use of Partial Least Squares 2 (PLS-2), using the UNSCRAMBLER program, suggested that the use of 7 factors can explain more than 99.5% of the residual variance. The method has been applied to the analysis of synthetic samples, not employed for calibration, and average errors lower than 4% were found.

SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF FOLIC ACID, PYRIDOXINE, RIBOFLAVIN, AND THIAMINE BY PARTIAL LEAST-SQUARES REGRESSION

ABSTRACT A new method for the simultaneous spectrophotometric determination of folic acid, pyridoxine, riboflavin and thiamine based on total absorbance measurements and their processing by partial least square regression is proposed. The concentration ranges used to construct the calibration matrix were 1.02–14.3 µg mL−1, 1.01–16.2 µg mL−1, 1.02– 10.2 µg mL−1 and 6.00–20.0 µg mL−1 for folic acid, pyridoxine, riboflavin and thiamine, respectively. Estimated limits of detection were: folic acid 0.08 µg mL−1, pyridoxine 0.45 µg mL−1, riboflavin 0.09 µg mL−1 and thiamine 0.17 µg mL−1. The proposed methodology was checked by applying it to the analysis of a set of laboratory-made samples. It was shown that is possible to resolve complex mixtures of compounds even when they have strongly overlapped signals. The analytical results obtained were good in all cases.