Pre-column conversion of ammonia and a number of aliphatic amines into phenylthiourea or its derivatives by reaction with phenyl isothiocyanate, followed by HPLC, has been used for their determination in environmental waters. Optimum conversion was found when the reaction was carried out in sodium hydrogencarbonatecarbonate medium at 40 °C for 15 min. Well separated peaks were obtained on a C 18 column with an acetonitrile-water gradient (1 ml min 21 ) of 30% acetonitrile for an initial 5 min which was increased linearly to 100% over 15 min and then maintained isocratic for 5 min, the acetonitrile ratio finally being returned to 30% in 5 min. The derivatized analytes were subjected to off-line solid phase extraction on C 18 sorbent. A linear calibration graph was obtained for 0.01-10 mg l 21 analytes with a correlation coefficient of 0.9954 for ammonia and in the range 0.9982-0.9996 for amines. The limit of detection for ammonia was 0.2 mg l 21 and for amines in the range 0.3-0.6 mg l 21 . The method was applied to tap, underground, river and aquarium waters, the recovery being in the range 97-106% (RSD 1.8-4.5%). Many of the samples were found to contain more than the permissible limit of ammonia. Phenyl isothiocyanate is stable for long periods in aqueous medium over wide ranges of pH and temperature, and the resulting phenylthioureas have adequate retention on C 18 sorbent and strong UV absorption, making this reagent suitable for the determination of amines in water.
Low concentrations of phenols and amines in environmental waters and their low breakthrough volume during solid-phase extraction (SPE) hinder the detection of phenols and aromatic amines, whereas ammonia and aliphatic amines are not suitable for SPE. Pre-column derivatization to arylbenzoates and N-alkyl-or N-arylbenzamides and their GC-MS is proposed to separate and determine phenols and amines in aqueous samples in the range 0.1-100
A real-time determination of iodide is proposed which involves the oxidation of iodide with 2-iodosobenzoate in the presence of N,N-dimethylaniline. The reaction is completed within 1 min to yield 4-iodo-N,N-dimethylaniline, which is extracted in cyclohexane and determined by GC-MS. It was also possible to determine iodine by derivatization in the absence of 2-iodosobenzoate, and iodate by its reduction with ascorbic acid to iodide and subsequent derivatization. A rectilinear calibration graph was obtained for 0.02-50 micrograms l-1 iodide with a correlation coefficient of 0.9998. The limit of detection was 8 ng l-1 iodide. The method was applied to the determination of iodate in iodized table salt and free iodide and total iodine in sea-water, and to spiked samples when the recovery was in the range 96.8-104.3% (RSD 1.9-3.6%). A sample clean-up by solid-phase extraction with a LiChrolut EN cartridge is proposed.
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