Testing by immunoassay

Testing by immunoassay. Testing by GC/MS. Metabolite of marijuana. 8 Metabolite of cocaine. ... 

Many of the coagulation factors measured by global coagulation tests have limited stability, and the time and temperature of storage of sample will affect their measurements. Concepts of analyte stability and half-life in plasma extend to markers measured by immunoassay. Markers of platelet activation are affected by artifactual activation in vitro upon collection of the blood specimen. This section will highlight some of the nonanalytical variables that, if uncontrolled, can lead to spurious results and thus affect the interpretation of laboratory data. 

A number of different testing kits based on immunoassay technology are available for rapid field determination of certain groups of compounds, such as benzene-toluene-ethylbenzene-xylene (EPA 4030) or polynuclear aromatic hydrocarbons (EPA 4035, Polycyclic Aromatic Hydrocarbons by Immunoassay). The immunoassay screening kits are self-contained portable field kits that include components for sample preparation, instrumentation to read assay results, and immunoassay reagents. 

Detection limits in the range of low parts per billion (ppb) can be achieved by immunoassay testing for certain parameters in aqueous samples. For soil samples, detection limits of <10 ppm can be achieved for many contaminants... 

PCBs in soils and wastewaters can be rapidly screened on site or in the laboratory by immunoassay technique (Chapter 1.13). Immunoassay test kits are now commercially available from many suppliers. The samples can be tested at the calibration levels of 1 to 50 ppm. The kit primarily contains antibody-coated test tubes or magnetic particles, assay diluent, PCB-enzyme conjugate, a color-forming substance, and a solution to quench the reaction. The method does not distinguish accurately one Aroclor from another. PCBs can be measured semiquantitatively by comparing the optical density of the color formed in the sample against a set of calibration standards using a spectrophotometer. 

Ferguson, B.S., D.E. Kelsey, T.S. Fan, and R.J. Bushway (1993). Pesticide testing by enzyme immunoassay at trace levels in environmental and agricultural samples. Sci. Total Environ., 132 415 -28. 

Wittmann, C. and P.-Y. Schreiter (1999). Analysis of terbuthylazine in soil samples by two test strip immunoassay formats using reflectance and luminescence detection. J. Agric. Food Chem., 47 2733-2737. 

U.S. EPA (SW-846) (Environmental Protection Agency). 1995. (ed.). Method 4035, Soil Screening for Polynuclear Aromatic Hydrocarbons by Immunoassay, 3rd edition. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, Vols. I and II, pp. 1-10. Washington DC. 

Eichhorst JC, Etter ML, Rousseaux N, Lehotay DC (2009) Drugs of abuse testing by tandem mass spectrometry a rapid, simple method to replace immunoassays. Clin Biochem 42(15) 1531—1542. doi S0009-9120(09)00322-l [pii] 10.1016/j.clinbiochem.2009.07.019... 

The FSIS Test Review System was developed to encourage the development of new tests by making the testing requirements known to test developers, and by expediting and standardizing the review process. All methods designed to measure the same analyte will be evaluated by the same standard, e.g., HPIC methods, microbiological inhibition tests, and immunoassays for the same analyte would all be evaluated from the perspective of limit of detection, accuracy, and precision. 

Gas Chromatography-Mass Spectrometry. A positive screening result for amphetamine or methamphetamine (or MDA, MDEA, and MDMA) obtained by immunoassay is confirmed by GC-MS analysis of the urine specimen. A GC-MS method for amphetamine and methamphetamine that can be adapted to include MDA, MDMA, and MDEA is included in the Chapter 34 Appendix that is found on this book s accompanying Evolve site (http //evolve.elsevier.com/ Tietz/textbook/). With this method, it should be noted that specimens containing ephedrine or pseudoephedrine occasionally have been reported to test positive for methamphetamine when 4-carbethoxyhexafluorobutyryl chloride (4-CB) is used as a derivatizing reagent. ... 

In tins method, a urine specimen that tests positive for barbiturates by immunoassay is extracted (liquid-liquid). The extract is then dried and treated with N,N-dimethylformamide dimethyl acetal to form methyl derivatives of the barbiturates. Following addition of a buffer, the methylated barbiturates are extracted with hexane and analyzed by GC-MS. Pentobarbital-Dg and phenobarbital-Ds are used as internal standards for quantitation. 

Mule SJ, Lomax P, Gross SJ. Active and realistic passive marijuana exposure tested by three immunoassays and GC/MS in urine. J Anal Toxicol 1988 12 113-16. 

Validation of the Test Strip Immunoassay by Comparing with Instrumental Analysis... 

The reliability of the test strip immunoassay was determined by carrying out the test with the uncontaminated samples spiked with detected target at three levels and analyzed by strip test and instrumental analysis. The results obtained by strip test should be consistent with the results obtained by instrument. The correlation between the two methods should be good. An example of validation of gold-based lateral flow immunoassay and analysis of food samples for the detection of carbaryl was shown in the following. 

Elements in an immunoassay that could impact its robustness include incubation temperatures, light exposure (enzyme-linked immunosorbent assay, ELISA), and different lots of matrix (plasma, serum CSF). The ruggedness of the analytical method can be tested by implementing changes to the analysts, different instruments, batch size, and the day, time, or other environment factors otherwise should not greatly impact the consistency of the assay. 

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