Off-Line and On-Line Preconcentration Techniques for the Determination of Phenylureas in Freshwaters

Comparison of on-line solid-phase disk extraction to liquid-liquid extraction for monitoring selected pesticides in environmental waters

“…From the results reported in Table I and from the figures it is obvious that still better recoveries are obtained following preconcentrating with C-18 bonded silica material than when SDB is used. These results disagree with previous preconcentration studies using PRP-1, one of the most used polymeric-type materials in on-line SPE LC studies (5,6,8). This type of polymeric material is recommended for medium polar compounds; e.g., a breakthrough volume of 100 mL was obtained for deethylatrazine in on-line studies using PRP 1 (23).…”

“…The CH2CI2 extracts are combined and analyzed simultaneously. 6 Coelution problem resolved by calculating chlortoluron recovery at 245 nm where MCPA does not absorb.0 Recovery calculated together. extraction of the most acidic pesticides, e.g., bentazone and MCPA, sulfuric acid (pH 2) and 50 mL of dichloromethane were added to the water sample, which was shaken again and extracted, thus following a previously described method from our laboratory (28).…”

“…As an alternative to LLE, solid-phase extraction (SPE) procedures have been implemented in the last few years. SPE methods can be easily converted into fully automated online systems coupled to LC (5)(6)(7)(8)(9)(10)(11). Coupling of various precolumns of different chemical composition, whether isolated or serially connected, packed usually with C-18 and styrene-divinylbenzene copolymer (PRP-1) have been demonstrated to exhibit a better performance than other types of precolumns for relatively polar compounds (5,6).…”

Modular Flow-Through Platform for Spectroelectrochemical Analysis

“…This easy to use and configure platform demonstrates the advantages of a flow system, such as the increase in the rate of mass transport that affects both the electrochemical and spectroscopic response, can be applied to various types of measurements, ranging from fundamental mechanistic studies to analytical measurements. Furthermore, by constructing a hyphenated system, for example, using Units ABC 1 and ABC 3 , a dual activation process followed by a UV–vis measurement could be envisioned, to sustain combined herbicide and pesticide studies. − Long-term use of this platform also could involve HPLC detection, taking advantage of the built in mass transport assembly and the linear flow pattern, which are already within the required HPLC flow rates (0.2–1 mL min –1 ) . Furthermore, the ability to also perform ECL (Unit ABC 2 ) can increase the overall sensitivity of analytical detection. , Finally, the ability to carry out ECL opens several future avenues for the detection of biomolecules and advantages over conventional fluorescence methods include enhanced S/N, increased sensitivity, reduced self-quenching, and simplified equipment. , …”

Quantification of Phenylurea Pesticides by HPLC/ECD and Photolysis

“…Coupling of the electrochemical detector to a UV-diode array detector enhances the selectivity and reinforces the identification of compounds [12][13][14][15][16]. Owing to the excellent sensitivity of electrochemical detection by itself, liquid chromatography in combination with amperometric detection and photolysis was chosen for the determination of the four phenylurea herbicides chlorotoluron [3-(3-chloro-p-tolyl)-1,1-dimethylurea], fenuron [1,1-dimethyl-3-phenylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and neburon [1-butyl-3-(3,4-dichlorophenyl)-1-methylurea] in ground and drinking water, although this method still has the unjustified reputation of being difficult to handle and having limited stability.…”