DETERMINATION OF NITRITE, NITRATE AND TOTAL NITROGEN IN VEGETABLE SAMPLES

Yellow diazonium cation formed by reaction of nitrite with 6-amino-1-naphthol-3-sulphonic acid is coupled with β-naphthol in strong alkaline medium to yield a pink coloured azo dye. The azo-dyes shows absorption maximum at 510 nm with molar absorptivity of 2.5 ×104 M-1 cm-1. The dye product obeys Beer\'s law (correlation coefficient = 0.997), in terms of nitrite concentration, up to 2.7 μg NO2 mL-1. The above colour reaction system has been applied successfully for the determination of nitrite, nitrate and total nitrogen in vegetable samples. Unreduced samples give direct measure for nitrite whilst reduction of samples by copperized-cadmium column gives total nitrogen content and their difference shows nitrate content in the samples. Variety of vegetables have been tested for their N-content (NO2-/NO3-/total-N) with % RSD ranging between 1.5 to 2.5 % for nitrite determination. The effects of foreign ions in the determination of the nitrite, nitrate, and total nitrogen have been studied. Statistical comparison of the results with those of reported method shows good agreement and indicates no significant difference in precision. KEY WORDS: Yellow diazonium cation, 6-Amino-1-naphthol-3-sulphonic acid, Vegetables, Nitrite in vegetables, Nitrate in vegetables, Total nitrogen in vegetables Bull. Chem. Soc. Ethiop. 2007, 21(3), 445-450

Extraction of chloroplatinate(II)– 2-[(5-bromo-2-pyridylazo)]-5-diethylaminophenol-(TX-100)-<i style="">N</i>-hydroxy-<i style="">N,N’</i>- diphenylbenzamidine complex

138-143A sensitive and selective spectrophotometric method, developed for the determination of trace amounts of platinum, is based on the formation of platinum as a mixed complex with 2-[(5-bromo-2-pyridylazo)]-5-diethylaminophenol (5-Br-PADAP) and TX-100 or triton X-100 (Polyethylene-di-isobutyl-glycol-ether) from 0.1M SnCl2 in to HCl and extraction with N-hydroxy-N,N’-diphenylbenzamidine (HDPBA) in dichloromethane. The violet coloured Pt(II)- 5-Br-PADAP-(TX-100)–HDPBA complex in dichloromethane shows maximum absorbance at 575 nm with molar absorptivity value of 6.0x104 dm3/mol/cm. The repeatability of the method was checked by finding relative standard deviation (RSD, n=10) value for solutions each containing 1.5 g/cm2 Pt(II) and the RSD value of the method was found to be 1.5%. The system obeyed Beer’s law up to 2.1 mg/cm2 of platinum and the detection limit of the method is 20 ng/cm2 on a three times the standard deviation of the blank absorbance basis. High concentration of foreign ions, with the exception of palladium, does not interfere with the determination of platinum. The proposed method has been applied for determination of platinum in automobile exhaust sample, soil and vegetation samples