NEMI Method Summary

Method Summary Information

Method Number: A00147 Media: WATER
Revision: Rev. 02-04-98
Method Source: Strategic Diagnostics, Inc.
Subcategory: ORGANIC Analytes in this method
Official Name: Paraquat (BTO) RaPID Assay A00147
Descriptive Name Paraquat Immunoassay
Source Info: Strategic Diagnostics, Inc.
111 Pencader Dr.
Newark, DE 19702
phone: 302-456-6789
www.sdix.com
Citation: Strategic Diagnostics, Inc.
25780 Byte file
Brief Method
Summary:
 A sample and an enzyme conjugate (enzyme labeled paraquat) are added to a sample tube, followed by addition of paramagnetic particles coated with paraquat-specific antibodies. Both the paraquat and enzyme conjugate compete for antibody binding sites on the particles, and bind in proportion to their concentrations. At the end of an incubation period, a magnetic field is applied to hold the paramagnetic particles. The unbound reagents are decanted and the particles are washed.

The presence of paraquat is detected by adding the enzyme substrate (hydrogen peroxide) and chromogen (3,3',5,5'-tetramethylbenzidene). The enzyme conjugate catalyzes the conversion of the substrate/chromogen mixture to a colored product. After an incubation period, the reaction is stopped and stabilized by the addition of acid. Since the enzyme conjugate was in competition with the paraquat for the antibody sites, the color change (which is measured with a spectrophotometer) is inversely proportional to the concentration of paraquat in the sample. The system is calibrated with paraquat.

Requirements: A clean water supply to prepare dilutions of water samples; filtration equipment to remove particulate from water samples; an SDI magnetic bead separator, required for the SDI RaPID assay kit; a spectrophotometer which accepts sample tubes (SDI RaPID Assay) for analyses at visible wavelengths (450 nm primary; 600 or 650 nm reference); equipment to automate sample preparation for large numbers of samples (pre-filtration, measurement of uL volumes, rinsing, agitation), so that contact times with reagents are controlled as required; and a computerized data acquisition and processing system.
Scope And
Application:
 This method determines paraquat in water (groundwater, surface water, well water) using immunoassay (enzyme linked immunoabsorbent assay -- ELISA).
Applicable
Conc Range:
 0.02 - 0.5 ug/L as paraquat cation
Interferences: Sensitivity > paraquat: methylbipyridinyl methyl sulphonium salt; diethyl paraquat. Sensitivity < paraquat: monoquat. Sensitivity << paraquat: morphamquat. Sensitivity <<< paraquat: diquat; 4,4-bipyridyl; chlormequat; 1-methyl-4-carboxy-pyridinum.
QC Requirements: Recommended for a kit allowing 100 quantitative determinations:

A. Calibration with 3 standards and 1 blank, all analyzed in duplicate

B. Precision: All 46 samples analyzed in duplicate (repeats)

C. Accuracy: 3 matrix samples, spiked with the target analyte at different levels in the range for quantitative analysis.

D. Validation: Analysis of 4 positive and 4 negative samples by an independent method, for confirmation.
Sample Handling: Samples are typically collected in glass containers with Teflon-lined caps. Drinking water samples are typically dechlorinated with 0.008% sodium thiosulfate, which does not interfere with the immunoassay. Samples are held in a refrigerator at 4oC. Immunoassay reagents and kits are stored in the dark at 4 to 8oC until use.

Water samples generally need to be centrifuged or prefiltered to 0.2 um. Quantitative analysis requires dilution of highly concentrated samples, until they are bracketed by standards in the linear response range. Aliquots of samples and reagents are accurately measured (uL) and mixed for required times, following manufacturer's instructions for use of the materials purchased.
Max Holding Time:
 5 days at 4oC until extraction and analysis
 
Relative Cost: Less than $50
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