A.I. Jiménez

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.

Simultaneous spectrophotometric determination of drugs in pharmaceutical preparations using multiple linear regression and partial least-squares regression, calibration and prediction methods

Two new methods for the simultaneous determination of acetylsalicylic acid, acetaminophen and caffeine based on total absorbance measurements and their processing by multiple linear regession and partial least-squares regression are proposed. The concentration ranges used to construct the calibration matrix were 4.0-12.0, 2.0-10.0 and 0.9-6.0 mug ml(-1) for acetylsalicylic acid, acetaminophen and caffeine respectively. The proposed methods were validated by using a set of synthetic sample mixtures and subsequently applied to the determination of the three active principles in three different pharmaceutical preparations.

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.

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.

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 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.

Evaluation of multicomponent flow-injection analysis data by use of a partial least squares calibration method

Abstract This paper reports on the use of a flow-injection analysis technique for the simultaneous spectrophotometric resolution of binary and ternary mixtures with the aid of a multivariate calibration method, and its application to the simultaneous determination of Co(II), Cu(II) and Zn(II) with 2-carboxyl-2-hydroxy-5-sulfoformazylbenzene (Zincon) over the concentration range 0.397–1.590, 0.268–1.879 and 0.240–1.612 μg/ml, respectively. Multicomponent analysis was implemented by using a modified version of the partial least squares program. The influence of various chemical and FIA variables affecting the reaction was evaluated. The proposed method was successfully applied to the determination of cobalt, copper and zinc in synthetic mixtures; copper and zinc in blood serum; and cobalt, copper and zinc in veterinary formulations.

Simultaneous second-order analogue derivative spectrophotometric determination of vanadium and cobalt in steels

A method is proposed for the simultaneous determination of vanadium and cobalt by second-derivative spectrophotometry based on their reactions with 4-(1′H-1′,2′,4′-triazol-3′-ylazo)-2-methylresorcinol. The method allows the determination of 0.10–1.02 p.p.m. of vanadium and 0.12–1.18 p.p.m. of cobalt in mixtures for which 10 ⩽CV/CCo⩽ 0.2 and it has been applied to their determination in alloy steels.