Question

24. may produce false negatives in presumptive assays. a. Reductants b. Plant peroxidases c. Oxidizing agents d. Bleach 25. In this confirmatory assay for the identification of blood, the anti-human hemoglobi antibodies are utilized: a. Chromatographic method b. Electrophoreic method c. Immunological method d. Spectrophotometric method

Answer 1

24) a.Reductants
The presumptive tests are done to identify the presence of blood stain which are commonly done in crime scenes. It involves the catalytic activity of haemoglobin to oxidise a compond. Thus chemicals which change colour when undergoing oxidation is used in presumptive tests.
But certain reductants or reducing agents act as antioxidants which present in the surface along with blood, will obstruct the reaction and oxidation is not happening. So eventhough the stain is blood, the result becomes negative. That is called false negative result.

25) a.Chromatographic immunoassay method
It is an immonoassay method where human anti haemoglobin antibody is made reaxt with the antigens in the blood and this reaction causes change in colour. It is used as a conformational test.