Spectrophotometric determination of peptic ulcer sulfur-containing drugs in bulk form and in tablets.

Two spectrophotometric procedures are suggested for the determination of three irreversible proton pump inhibitors, rabeprazole (RAB), omeprazole (OMP) and pantoprazole (PAN) in pure form and in different pharmaceutical formulations. The first method is based on the oxidation of RAB and PAN with potassium iodate in an acidic medium followed by extracting the liberated iodine with cyclohexane and measurement at λ = 520 nm. Beer's law is valid in the concentration ranges from 10-400 and 5-400 µg ml(-1) for RAB and PAN, respectively. The apparent molar absorptivities of the resulting coloured product were found to be 1.34 × 10(3) and 1.64 × 10(3) l.mol(-1). cm(-1) for RAB and PAN, respectively. The second method is based on the interaction of the basic drugs, OMP, RAB and PAN, in 1,2-dichloroethane with bromophenol blue (BPB), bromocresol green (BCG) and bromocresol purple (BCP) in the same solvent to produce stable coloured ion pairs with maximum absorbance at 385-405 nm. Regression analysis of Beer's plots showed good correlation in the concentration ranges 10-60, 10-60 and 5-40 µg ml(-1) for OMP, 10-150, 10-150 and 10-60 µg ml(-1) for RAB and 10-250, 10-150 and 10-100 µg ml(-1) for PAN with BPB, BCG and BCP reagents, respectively. The limits of detection are 0.46-7.69 µg ml(-1) and limits of quantitation range between 1.52-8.53 µg ml(-1). The optimum assay conditions were investigated and the recovery of the drugs from their dosage forms ranged from 99.33% to 100.5%. Intraday relative standard deviations (RSD) were 0.029-1.397% and the correlation coefficients ranged from 0.9992 to 1. The two methods can be applied successfully for the determination of these drugs in tablets. The results of analysis were validated statistically through recovery studies.

Spectrophotometric study of the reaction mechanism between DDQ Pi- and iodine sigma-acceptors and chloroquine and pyrimethamine drugs and their determination in pure and in dosage forms.

Two simple and accurate spectrophotometric methods are presented for the determination of anti-malarial drugs, chloroquine phosphate (CQP) and pyrimethamine (PYM), in pure and in different pharmaceutical preparations. The charge transphere (CT) reactions between CQP and PYM as electron donors and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) pi-acceptor and iodine sigma-acceptor reagents to give highly coloured complex species have been spectrophotometrically studied. The optimum experimental conditions have been studied carefully. Beer' law is obeyed over the concentration range of 1.0-15 microg ml(-1) for CQP and 1.0-40 microg ml(-1) for PYM using I(2) and at 5.0-53 microg ml(-1) for CQP and 1.0-46 microg ml(-1) for PYM using DDQ reagents, respectively. For more accurate results, Ringbom optimum concentration range is calculated and found to be 10-53 and 8-46 microg ml(-1) for CQP and PYM using DDQ, respectively and 5-15 and 8-40 microg ml(-1) for CQP and PYM using iodine, respectively. The Sandell sensitivity is found to be 0.038 and 0.046 g cm(-2) for DDQ method and 0.0078 and 0.056 g cm(-2) for I(2) method for CQP and PYM, respectively which indicates the high sensitivity of both methods. Standard deviation (S.D.=0.012-0.014 and 0.013-0.015) and relative standard deviation (R.S.D.=0.09-1.4 and 1.3-1.5%) (n=5) for DDQ and I(2) methods respectively, refer to the high accuracy and precision of the proposed methods. These results are also confirmed by between day precision of percent recovery of 99-100.6%, and 98-101% for CQP and PYM by DDQ method and 99-102% and 99.2-101.4% for CQP and PYM by I(2) method respectively. These data are comparable to those obtained by British and American pharmacopoeias assay for the determination of CQP and PYM in raw materials and in pharmaceutical preparations.

2,6-Dichloroquinone chlorimide and 7,7,8,8-tetracyanoquinodimethane reagents for the spectrophotometric determination of salbutamol in pure and dosage forms.

A simple, rapid and sensitive spectrophotometric method for the determination of sulbutamol in pure form and in different pharmaceutical preparations has been developed. The charge transfer (CT) reaction between salbutamol as electron donor and 2,6-dichloroquinone chlorimide (DCQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor have been spectrophotometrically studied. The optimum experimental conditions for these CT reactions have been studied carefully. Beer's law is obeyed over the concentration range of 1.0-30.0 microg ml(-1) and 2.0-20.0 microg ml(-1) for salbutamol using DCQ and TCNQ, respectively. For more accurate results, Ringbom optimum concentration range is calculated and found to be 10.0 to 30.0 and 8.0 to 20 microg ml(-1) for salbutamol using DCQ and TCNQ, respectively. The Sandell sensitivity is found to be 0.011 and 0.010 g cm(-2) for salbutamol using DCQ and TCNQ, respectively, which indicate the high sensitivity of the proposed methods. Relative standard deviations (R.S.D.) of 0.27 to 0.68% and 0.20 to 1.40% (n=5) were obtained for five replicates of salbutamol using DCQ and TCNQ, respectively. The results obtained by the two reagents are comparable with those obtained by British pharmacopoeia assay for the determination of salbutamol in raw materials and in pharmaceutical preparations.