Comparison of various liquid chromatographic methods involving UV and atmospheric pressure chemical ionization mass spectrometric detection for the efficient trace analysis of phenylurea herbicides in various types of water samples

The performance of mass spectrometric (MS) detection and UV detection in combination with reversed-phase liquid chromatography without and with the use of coupled column RPLC (LC-LC) has been compared for the trace analysis of phenylurea herbicides in environmental waters. The selected samples of this comparative study originated from an inter-laboratory study. For both detection modes, a 50 mm x 4.6 mm I.D. column and a 100 mm x 4.6 mm LD. column packed with 3 mu m C-18 were used as the first (C-1) and second (C-2) column, respectively. Atmospheric pressure chemical ionization mass spectrometry was performed on a magnetic sector instrument. The LC-LC-MS analysis was carried out on-line by means of direct large volume (11.7 mi) injection (LVI). The performance of both on-line (LVI, 4 mi of sample) and off-line LC-LC-UV (244 nm) analysis was investigated. The latter procedure consisted of a solid-phase extraction (SPE) of 250 mi of water sample on a 500 mg C-18 cartridge. The comparative study showed that LC-LC-MS is more selective then LC-LC-UV and, in most cases, more sensitive. The LVI-LC-LC-MS approach combines direct quantification and confirmation of most of the analytes down to a level of 0.01 mu g/l in water samples in less then 30 min. As regards LC-LC-UV, the off-line method appeared to be a more viable approach in comparison with the on-line procedure. This method allows the screening of phenylurea's in various types of water samples down to a level of at least 0.05 mu g/l. On-line analysis with LVI provided marginal sensitivity (limits of detection of about 0.1 mu g/l) and selectivity was sometimes less in case of surface water samples. Both the on-line LVI-LC-LC-MS method and the LC-LC-UV method using off-line SPE were validated by analysing a series of real-life reference samples. These samples were part of an inter-laboratory test and contained residues of herbicides ranging from 0.02 to 0.8 mu g/l. Beside good correlation between the methods the data agreed very well with the true values of the samples. (C) 2000 Elsevier Science B.V. All rights reserved.