A rapid and sensitive colorimetric method for the determination of thiamine propyl disulphide and thiamine disulphide, as pure drugs and in their respective dosage forms, has been developed, which is based on a colour reaction with 2,6-dichloro-p-benzoquinone-4-chlorimine in the presence of methanolic hydrobromic acid in a chloroform medium. The colours produced from thiamine propyl disulphide and thiamine disulphide have absorbance maxima at 445 and 460 nm, respectively. The concentration range for Beer's law compliance is 0–5.75 µg ml–1 for thiamine propyl disulphide and 0–12 µg ml–1 for thiamine disulphide. The method can be applied to the analytical control of thiamine propyl disulphide and thiamine disulphide in dosage forms with simple matrices, but when other compounds carrying an amino group are present a separation is necessary as the proposed colour reaction is a general one for all such compounds. The removal of riboflavine and analgin, present in some of the currently available commercial formulations of thiamine propyl disulphide and thiamine disulphide, was found to be necessary and is described.
Abstract A solution of piperazine or its salts is heated with 2,6-dichloroquinonechlorimide, and the color produced is measured at 525 nm to obtain the concentration of piperazine. The color developed obeys Beer’s law in the concentration range of 6.4–51.2 μg piperazine/ml. The results of the proposed method agree with those of the official methods within ± 1.0% for piperazine and its salts and ± 2.0% for formulations. The method is rapid and precise and gives reproducible results. It is suitable for the analytical control of piperazine or its salts and their formulations.
A colorimetric method is presented for the estimation of diazepam as the pure drug and in formulations. Diazepam is hydrolyzed with 6N HCl to 2-methylamino-5-chlorobenzophenone, which is extracted with chloroform to give a yellow solution whose absorbance is measured at 410 nm against a solvent blank. The color obeys Beer's law in the concentration range of 0-30 mug/ml. In 5 determinations, recovery was 99.0 +/- 1.9%. The method is applicable to pure diazepam and its formulations for oral and parenteral use. No interferences were observed from pyridoxine hydrochloride and commonly used preservatives, vehicles, and colors.
A new colorimetric method has been developed for estimating folic acid. The British Pharmacopoeial method has been modified to reduce folic acid to 2,4,5-triamino-6-hydroxy-pyrimidine (TAHP), which is treated with ninhydrin to yield a stable purple complex. Participation of 5-amino and 6-hydroxy groups of TAHP in the color reaction with ninhydrin is suggested on the basis of experimental evidence. The color obtained has an absorbance maximum at 555 nm and obeys Beer's law in the concentration range of 4.5 to 45 microng folic acid/ml. The method has been successfully used for assaying folic acid, its tablets, and injections.
Abstract A colorimetric method is presented for the estimation of diazepam as the pure drug and in formulations. Diazepam is hydrolyzcd with 6N HC1 to 2-methyIamino-5-chlorobenzophenone, which is extracted with chloroform to give a yellow solution whose absorbance is measured at 410 nm against a solvent blank. The color obeys Beer's law in the concentration range of 0–30 μg/ml. In 5 determinations, recovery was 99.0±1.9%. The method is applicable to pure diazepam and its formulations for oral and parenteral use. No interferences were observed from pyridoxine hydrochloride and commonly used preservatives, vehicles, and colors.
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