The determination of benzalkonium chloride in eye-drops by difference spectrophotometry.

A direct, extraction-free spectrophotometric method was developed for the determination of benzalkonium chloride (BAC) in various eye-drops. The procedure is based on ion-pair formation between BAC and 2',4',5',7'-tetrabromofluorescein (eosin-Y) which decreases the absorbance and induces a bathochromic shift of the maximum in the eosin-Y spectrum. The effects of pH, excess of reagent and ionic strength on the ion-pair formation have been studied in detail. At pH 4.40 and 9.62, the working curve is linear in the 1.98 x 10(-6) to 2.40 x 10(-5) M (0.7-8.5 microg cm[-3]) concentration range; however, the sensitivity drops to about one third in the basic solution. At pH 4.40, the analytical signal is stable for more than 60 min, while at pH 9.62 the signal changes in time and reaches the maximum value 3 min after mixing the reagent and the sample. When the active substance is beta-5-isopropyl-2'deoxyuridine and the sample contains typical additives, the reproducibility of the analytical signal at pH 4.40 is R.S.D. = 2.36% (n = 81). In the case of such samples, the linearity of the method is somewhat dependent on the composition, but generally acceptable at the 50-150% concentration levels. Eye-drops containing tobramycin, an aminoglycoside-type antibiotic, as the active substance were analyzed at pH 9.62. This was necessary to avoid strong interference from the analyte in acidic solution. In this case the linearity of the method is limited to a narrower concentration range; however, the recovery is still acceptable at the 100% level.

Determination of vitamin C in effervescent tablets containing other vitamins together with trace elements.

A simple, rapid method is reported for the determination of vitamin C in effervescent tablets containing other vitamins and several trace elements such as Mg(II), Zn(II), Fe(II), Mn(II), Cu(II) and Mo(VI). The procedure was developed on the basis of the bromate ion-iodide ion-ascorbic acid clock reaction (Landolt reaction). Interference effects of air oxygen and metal ions and the role of pH are discussed in detail.

Overpressured layer chromatographic study of retention behaviour of various benzodiazepine derivatives on layers impregnated with tricaprylmethylammonium chloride.

The retention behaviour of various benzodiazepine derivatives was investigated on silica gel layers impregnated with tricaprylmethylammonium chloride (TCMA). The chromatograms were developed by means of overpressured layer chromatography (OPLC). As for the case of amino- and nitrosalicylic acids, pyrimidine derivatives, barbiturates, penicillins, cephalosporins and tetracyclines, the retention of benzodiazepine derivatives increased with increasing layer TCMA concentration with eluents containing methanol and water, but not TCMA. On increase of the methanol content of the eluent, a retention-decreasing effect was observed. On layers impregnated with TCMA, a linear relationship existed between the RM values of the benzodiazepines and the methanol content of the eluent. A similar relationship held for silica gel layers impregnated with paraffin oil (traditional reversed-phase). There was no correlation between the results obtained on layers treated with TCMA or with paraffin oil. On TCMA-impregnated layers, the retention of compounds having different chemical structures showed no dependence on the pH of the eluent. There were two reasons for this. Firstly, as it was established, above a certain RF value, the pH of the layer in the presence of TCMA was almost identical irrespective of the original pH of the buffer. Secondly, below this RF value, the actual pH of the layer did not have a strong enough effect to cause appreciable differences between the retentions of the dissociated and undissociated species of the analytes. The conditions for optimum separation are given.

Chromatographic analysis of 1,3-bis(dimethylamino)isopropyl 4-chlorophenoxyacetate dihydrochloride, a new CNS stimulant.

A reversed-phase liquid chromatographic method is developed for the assay of the new CNS stimulant, 1,3-bis(dimethylamino)isopropyl 4-chlorophenoxyacetate dihydrochloride (BCE-001), and its main contaminant, 4-chlorophenoxyacetic acid (PCPA). In the first place the possible reactions of BCE-001 with mobile phase components are investigated and it is found that BCE-001 is readily hydrolysed in water and undergoes transesterification in methanol or ethanol. The methyl ester is formed rapidly and quantitatively so that BCE-001 can be assayed as methyl 4-chlorophenoxyacetate. PCPA is formed as a result of the hydrolysis of BCE-001 during the sample pretreatment and chromatographic separation and this causes an overestimate of the PCPA impurity in the bulk drug. An effective method is developed to prevent the hydrolysis of BCE-001 during sample pretreatment.

Reversed-phase chromatography of novel biologically effective aminoacridine-N-glycosides by OPLC.

The reversed-phase chromatographic behavior of novel biologically active aminoacridine-N-glycosides is studied. The chromatographic experiments are performed with overpressurized layer chromatography. Weak ion pairs are formed with methanesulfonic acid, but only at low concentrations of the ion-pairing reagent. The retention seems to involve a reversed-phase mechanism. The base compounds only slightly modify the retention, while the number and polarity of the substituents have larger effects. The pH dependence of the retention is very typical for the aminoacridine-N-glycosides, and it plays an important role in the separation. The monoglycosides are completely separated from the corresponding base compounds, as are the diglycosides from the monoglycosides, on RP-2, RP-8, and RP-18 layers with eluents containing 30 to 60% acetonitrile and at least 0.005 M ammonium carbonate at pH 4 to 6.

Determination of boron impurities in syrups containing lactulose.

An analytical method for the determination of boron content of crude and finished syrups containing lactulose has been described. A coloured complex of boron formed with azomethine-H is used for the determination. Conditions of the complex-forming reaction, and the effects of matrices containing mainly carbohydrates and flavouring and conserving agents too, have been studied. Boron content of the syrups has been measured as 95.4 to 104.6% with a standard deviation of +/- 3.7% (n = 20, p = 0.95).