Said A. Hassan

A comparative study was established between two signal processing techniques showing the theoretical
algorithm for each method and making a comparison between them to indicate the advantages and
limitations. The methods under study are Numerical Differentiation (ND) and Continuous Wavelet
Transform (CWT). These methods were studied as spectrophotometric resolution tools for simultaneous
analysis of binary and ternary mixtures. To present the comparison, the two methods were applied for
the resolution of Bisoprolol (BIS) and Hydrochlorothiazide (HCT) in their binary mixture and for the
analysis of Amlodipine (AML), Aliskiren (ALI) and Hydrochlorothiazide (HCT) as an example for ternary
mixtures. By comparing the results in laboratory prepared mixtures, it was proven that CWT technique
is more efficient and advantageous in analysis of mixtures with severe overlapped spectra than ND.
The CWT was applied for quantitative determination of the drugs in their pharmaceutical formulations
and validated according to the ICH guidelines where accuracy, precision, repeatability and robustness
were found to be within the acceptable limit.

Five signal processing techniques were applied to ratio spectra for quantitative determination of bisoprolol
(BIS) and hydrochlorothiazide (HCT) in their binary mixture. The proposed techniques are Numerical
Differentiation of Ratio Spectra (ND-RS), Savitsky–Golay of Ratio Spectra (SG-RS), Continuous Wavelet
Transform of Ratio Spectra (CWT-RS), Mean Centering of Ratio Spectra (MC-RS) and Discrete Fourier
Transform of Ratio Spectra (DFT-RS). The linearity of the proposed methods was investigated in the range
of 2–40 and 1–22 lg/mL for BIS and HCT, respectively. The proposed methods were applied successfully
for the determination of the drugs in laboratory prepared mixtures and in commercial pharmaceutical
preparations and standard deviation was less than 1.5. The five signal processing techniques were compared to each other and validated according to the ICH guidelines and accuracy, precision, repeatability
and robustness were found to be within the acceptable limit.

Different chemometric models were applied for the quantitative analysis of Amlodipine (AML), Valsartan (VAL) and Hydrochlorothiazide (HCT) in ternary mixture, namely, Partial Least Squares (PLS) as traditional chemometric model and Artificial Neural Networks (ANN) as advanced model. PLS and ANN were applied with and without variable selection procedure (Genetic Algorithm GA) and data compression procedure (Principal Component Analysis PCA). The chemometric methods applied are PLS-1, GA-PLS, ANN, GA-ANN and PCA-ANN. The methods were used for the quantitative analysis of the drugs in raw materials and pharmaceutical dosage form via handling the UV spectral data. A 3-factor 5-level experimental design was established resulting in 25 mixtures containing different ratios of the drugs. Fifteen mixtures were used as a calibration set and the other ten mixtures were used as validation set to validate the prediction ability of the suggested methods. The validity of the proposed methods was assessed using the standard addition technique.

Four simple, accurate and specific methods were developed and validated for the simultaneous estimation of Amlodipine (AML), Valsartan (VAL) and Hydrochlorothiazide (HCT) in commercial tablets. The derivative spectrophotometric methods include Derivative Ratio Zero Crossing (DRZC) and Double Divisor Ratio Spectra-Derivative Spectrophotometry (DDRS-DS) methods, while the multivariate calibrations used are Principal Component Regression (PCR) and Partial Least Squares (PLSs). The proposed methods were applied successfully in the determination of the drugs in laboratory-prepared mixtures and in commercial pharmaceutical preparations. The validity of the proposed methods was assessed using the standard addition technique. The linearity of the proposed methods is investigated in the range of 2–32, 4–44 and 2–20 μg/mL for AML, VAL and HCT, respectively.

Simple, specific, accurate and precise spectrophotometric method was developed for
the simultaneous determination of Amlodipine besylate (AML) and Atorvastatin calcium
(ATV) in tablet dosage forms. The proposed H-Point Standard Addition Method
(HPSAM) involves addition of the analyte of interest on the binary mixture, measuring
the absorbance at two wavelengths and then the calibration curves are used to estimate
the concentration of the main analyte and interfernt one. Two analytical wavelengths
selected were 241.0-252.4 nm and 278.0-305.6 nm for the estimation of AML and ATV;
respectively. The calibration curves were linear over the concentration range of 4-40
and 8-32 µg/mL for AML and ATV, respectively. This method was tested by analyzing
synthetic mixtures of the above drugs and they were applied to commercial
pharmaceutical preparation of the subjected drugs. The standard deviation was < 1.5 in
the assay of raw materials and tablets. Methods were validated as per ICH guidelines
and accuracy, precision, repeatability and robustness were found to be within the
acceptable limit.

Two RP-HPLC and TLC methods were developed and validated according to the
ICH guidelines for the simultaneous determination of Amlodipine, Valsartan and
Hydrochlorothiazide in tablet dosage form. The two methods are simple, rapid and
selective. Complete HPLC separation was achieved using Nucleosil C18 column and
acetonitrile/methanol/isopropyl alcohol (55:41:4 by volume) mixture as the mobile
phase, the pH was adjusted to 8 ± 0.1 with triethylamine and the flow rate was 1.2
mL/min. The detection wavelengths were chosen to be 238, 248 and 271 nm for
Amlodipine, Valsartan and Hydrochlorothiazide, respectively. The linearity of the
proposed method was established over the ranges, 2.0–28.0, 10.0–120.0 and 0.6–
32.0 µg/mL for Amlodipine, Valsartan and Hydrochlorothiazide, respectively. For the
densitometric TLC method, silica gel 60 F254 plates were used and ethyl
acetate/toluene/methanol/ammonia (50.5:23.5:23.5:2.5 by volume) mixture as the
developing solvent. Detection and quantification were performed densitometrically at
252 nm. The linearity of the proposed method was established over the ranges, 0.5-
9.0, 4.0-18.0 and 3.0-11.0 µg/band for Amlodipine, Valsartan and
Hydrochlorothiazide, respectively.

A new, simple and specific spectrophotometric method was developed and validated in accordance with ICH guidelines for the simultaneous estimation of Amlodipine (AML), Valsartan (VAL), and Hydrochlorothiazide (HCT) in their ternary mixture. In this method three techniques were used, namely, direct spectrophotometry, ratio subtraction, and isoabsorptive point. Amlodipine (AML) was first determined by direct spectrophotometry and then ratio subtraction was applied to remove the AML spectrum from the mixture spectrum. Hydrochlorothiazide (HCT) could then be determined directly without interference from Valsartan (VAL) which could be determined using the isoabsorptive point theory. The calibration curve is linear over the concentration ranges of 4–32, 4–44 and 6–20 μg/mL for AML, VAL, and HCT, respectively. This method was tested by analyzing synthetic mixtures of the above drugs and was successfully applied to commercial pharmaceutical preparation of the drugs, where the standard deviation is <2 in the assay of raw materials and tablets. The method was validated according to the ICH guidelines and accuracy, precision, repeatability, and robustness were found to be within the acceptable limits.

Three simple, specific, accurate and precise spectrophotometric methods depending on the proper selection of two wavelengths are developed for the simultaneous determination of Amlodipine besylate (AML) and Atorvastatin calcium (ATV) in tablet dosage forms. The first method is the new Ratio Difference method, the second method is the Bivariate method and the third one is the Absorbance Ratio method. The calibration curve is linear over the concentration range of 4–40 and 8–32 μg/mL for AML and ATV, respectively. These methods are tested by analyzing synthetic mixtures of the above drugs and they are applied to commercial pharmaceutical preparation of the subjected drugs. Methods are validated according to the ICH guidelines and accuracy, precision, repeatability and robustness are found to be within the acceptable limit. The mathematical explanation of the procedures is illustrated.

Three simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra are developed for the simultaneous determination of Amlodipine besylate (AM) and Atorvastatin calcium (AT) in tablet dosage forms. The first method is first derivative of the ratio spectra (1DD), the second is ratio subtraction and the third is the method of mean centering of ratio spectra. The calibration curve is linear over the concentration range of 3–40 and 8–32 μg/ml for AM and AT, respectively. These methods are tested by analyzing synthetic mixtures of the above drugs and they are applied to commercial pharmaceutical preparation of the subjected drugs. Standard deviation is <1.5 in the assay of raw materials and tablets. Methods are validated as per ICH guidelines and accuracy, precision, repeatability and robustness are found to be within the acceptable limit.