2.4- Dichlorophenoxyacetic acid detection limits

The detection limit was 0.1 pM 2,4-D, comparable to that of the radioassay, and the response range was 0.1-50 pM in buffer. Cross-reactivity of the polymer towards 2,4-dichlorophenoxyacetic acid methyl ester (2,4-D-OMe) was lower than that reported for immunoassays. 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

RELATIVE DETECTION LIMITS OF HALOETHYL ESTERS OF 4-CHLORO-2-METHYL-PHENOXYACETIC ACID (MCPA) AND 2,4-DICHLOROPHENOXYACETIC ACID (2,4-D) WITH THE USE OF ECD [500]... 

Electrochemical immunosensors have been widely used for environmental analysis in amperometric, potentiometric, and conductimetric configurations. Amperometric immunosensors measure the current generated by oxidation or reduction of redox substances at the electrode surface, which is held at an appropriate electrical potential. Wilmer et al. measured concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) in water by using an amperometric immunosensor with a limit of detection of 0.1 Jtg L-1 (Wilmer et al., 1997). Some examples of new developments are the disposable screen-printed electrodes for the detection of polycyclic aromatic hydrocarbons (PAHs)... 

Sorption of 2,4-dichlorophenoxyacetic acid (2,4-D) by Bentone 24 was rapid and occurred in considerable quantities, as shown in Figure 1. Although uncoated Wyoming bentonite had no sorption of 2,4-D within the detectable limits (less than about 0.3 mg/liter) of the analysis, the Bentone 24 sorbed about 13 mg of 2,4-D per gram of organo-clay when the equivalent of 20 mg of 2,4-D per 200 ml of aqueous solution was available. This sorption was nearly complete within 30 minutes and remained constant after 3 hours. Longer periods were used for equilibration because they were convenient. These longer periods also assured equilibrium at other temperatures used. 

Organic phase MIA has also been applied to the herbicide atrazine, the groups of Stanker [35] and Mosbach [36] publishing similar assays simultaneously. In both cases, selectivity was demonstrated over related substituted triazines. The former assay performed in acetonitrile had a detection limit of 4.6 pM, the latter performed in toluene 250 nM. Other analytes of environmental interest for which conventional radiolabel MIAs have been developed include 2,4-dichlorophenoxyacetic acid [23] and 4-nitrophenol [48], although in the latter case the influence of interferents was not studied. 

This is then concentrated in the polyanionic Nafion film coating the electrode and quantified by cyclic voltammetry as shown in Fig. 8.19. The feasibility of this immunoassay has been demonstrated for a herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) with a detection limit of 0.01 pg [89]. 

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