Nanju Lee

Immunochemical Approaches to the Detection of Sulfathiazole in Animal Tissues

A series of ELISAs based on anti-sulfathiazole (STZ) monoclonal antibodies (MAbs) were developed that can detect STZ below the tolerance level in tissues. The IC50 values (concentrations of STZ inhibiting 50% of binding in a competitive ELISA) for each MAb ranged from 6 to 21 ng ml−1 of STZ. Immunoassays based upon two MAbs, STZ-23 and SDM44, were evaluated for their assay performance using swine liver samples spiked with STZ. Swine liver tissue was analyzed without a complex sample preparation step, with only a simple dilution of swine liver extract being necessary. A good correlation between immunoassay results and spike levels in swine liver (R2 >0.98) was obtained, demonstrating that the immunoassays are capable of quantifying STZ in swine liver. The cross-reactivities of other sulfonamide drugs and STZ metabolites in these immunoassays were also examined.

Quantification of the urea herbicide, diuron, in water by enzyme immunoassay.

Urea herbicides are widely applied to soil for total vegeta t ion control, or for preor postemergence treatment in crops. Uses include pre-plant treatment of fields in cotton, sugar cane, and vegetables; removal of annual weeds in citrus orchards; and for treatment of irrigation canal, road, and railroad rights of way. Several of the compounds are highly persistent in the environment; this can lead to damage to crops if contaminated water is used for irrigation and increase the possibility of unacceptable residues in drinking water. Diuron and related urea herbicides have rather simple chemical structures, being characterised by a substituted aryl moiety on one of the nitrogen atoms of urea, while two methyl groups are attached to the other urea nitrogen. Diuron has been one of the major urea herbicides in use since the 1950s. After simazine, it is the second most persistent herbicide in common agricultural practice (Hassall 1990). Its persistence in soil is due to a combination of three properties chemical stability, low aqueous solubility (EI-Dib and Aly 1976) and strong adsorption to soil (Kozak and Weber 1983; Alva and Singh 1990)o Urea herbicides can be difficult to detect instrumentally at low part-perbillion levels. HPLC of water extracts following concentration can typically detect down to only 0.5-1 ppb in water. While more sensitive gas-liquid chromatography (GC) methods have been developed, the low volatility of these compounds can lead to decomposition by use of high column temperatures before separation (Bowmer and Adeney 1978; Peterson and Batley 1991). A number of ELISAs for phenylurea herbicides, differing in the sensitivity and specificity for diuron, have been developed. These used either rabbit antisera (Newsome and Collins 1990, Liegeois et al. 1992; Schneider et al. 1994) or mouse monoclonal antibodies (Karu et al. 1994a). With the exception of analyses of groundwater samples using the monoclonal antibody assay (Karu et al. 1994b) these antibodies have only had limited application to water. We describe here an immunoassay for diuron based on use of sheep polyclonal antibodies to chlortoluron (Aherne 1991), and report the specificity and sensitivity properties of this assay and its application to detection of diuron in surface and sub-surface water.

A rapid ELISA for screening aflatoxin B1 in animal feed and feed ingredients in Indonesia

Abstract To facilitate a sustainable aflatoxin management system in Indonesia, a simple, rapid and effective Enzyme Linked Immunosorbent Assay (ELISA) test for screening aflatoxin B1 (AFB1) in animal feed and feed ingredients was developed. Anti-AFB1 polyclonal antibodies were produced against AFB1-BSA and AFB1-KLH immunogens. Using AFB1 conjugated to horseradish peroxidase (HRP) as an enzyme marker in a direct competitive ELISA, an IC50 of 0.85±0.15 µg/kg and a detection limit (IC15) of 0.18±0.06 µg/kg of AFB1 were achieved. The assay was highly specific to AFB1 with very little cross reaction with other aflatoxin congeners (AFB2 0.9%, AFG1 3.1% and AFG2 1.2%) and metabolites. The ELISA was tolerant to methanol (up to 60%) and pH (pH 7.2–9.6) without significantly affecting the overall performance and was not affected by interferences from the animal feed and corn samples. Satisfactory recovery results were obtained from the spike and recovery study (77–97% recovery for 10–252 µg/kg). A pilot survey conducted on corn and animal feed samples collected from the local feed factories and poultry shops indicated that significant amounts of corn and animal feeds were contaminated by aflatoxin B1 greater than the MRL (50 µg/kg).

Immunoanalysis and separation of dissolved from particle‐bound pesticide residues

A small‐volume filtration method was developed for use in the analysis of total, bound and dissolved residues of four agrochemicals which differed in physico‐chemical properties, in turbid water. Low immunoassay recoveries of molinate, chlorpyrifos and endosulfan (but not diuron) in highly turbid water samples suggested that the antibodies were unable to recognize particle‐bound residues. However, in samples of moderate or low turbidity, the results indicated that the data obtained by immunoassay s may approximate the total residue load in samples, especially if the samples are filtered through a non‐absorptive membrane. The adsorption pattern of each membrane was different for each pesticide, and related to their water solubilities and partition coefficients. A syringe filter with an aluminium oxide membrane was more suitable than one with cellulose acetate, polyvinylidene difluoride or polytetrafluoroethylene for filtration of small volumes of water for separation of the dissolved residues, and removal ...