Colorimetric Screening Tests

These tests require little sample preparation and are usually performed directly on the specimen. This is a rapid procedure but requires confirmation. 

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Because a colorimetric screening test for urinary homocystine was positive, the doctor ordered several biochemical studies on Homer Sistine s serum, which included tests for methionine, homocyst(e)ine (both free and protein-bound), cystine, vitamin B12, and folate. The level of homocystine in a 24-hour urine collection was also measured. 

Syoyama and Nogima reported a colorimetric method for the detection of procaine in urine, where the drug and other phenethylamines were extracted [46]. The extraction involved ion association with Chrome Azurol S (C.I. Mordant blue 29), and was applied to a screening test for the drug and other related amines. 

Seven different bacterial sialidases, including six commercially available sialidases from Arthrobacter ureafaciens, Clostridium perfingens. Streptococcus sp. IID, Vibrio cholera. Salmonella typhimurium, and Streptococcus pneumoniae, as well as PmSTl which also possesses sialidase activity (20), were used as model systems to test the application of the sialoside library and the 96-well plate based high-throughput colorimetric screening method. 

The plasma level of paracetamol can be determined by gas-liquid chromatography, by its UV absorption spectrum following extraction, and by its colorimetric reaction with nitrous acid to form a yellow coloured nitrophenol (the Glynn and Kendal method). Paracetamol can be detected in urine by a screening test which consists of its hydrolysis to /7-aminophenol, followed by its reaction with o-cresol and ammonia to form a blue in-dophenol. 

To test our new signal reagent based on GZ-11 the detection system was applied to two competitive-format immunoassays. These two assays (for atrazine and clenbuterol) normally use chromogenic detection systems. While these colorimetric assays may be adequate for laboratory use, chemiluminescent detection offers potential advantages in sensitivity and on site screening applications [33],... 

Another sensitive colorimetric procedure is that of Mackenzie et al (1967), which utilizes the dye Rhodamine B to form benzene-soluble complexes with fatty acids. Nakai et al. (1970) developed a rapid, simple method for screening rancid milk based on the foregoing procedure. The test is said to detect rancid milk with an ADV above 1.2. Like the copper or cobalt soap method, the Rhodamine B reagent is also limited to the longer-chain fatty acids. Kason et al (1972) used the method employing Rhodamine 6G of Chakrabarty et al (1969) to investigate... 

In addition to test kits used in EPA-approved screening methods, a variety of other test kits are available from several manufacturers, for example, immunoassay test kits for BTEX in soil and water and for chlorinated solvents in water colorimetric kits for the detection of lead kits for a wide range of water quality parameter manufactured by Hach Company. 

In the selected example by Lam et al. [101] many peptide libraries were prepared using the mix and split technique and tested in different on-bead screens. Incomplete libraries were tested (the population of most of them was more than a million compounds), and the positive structures were exploited through focused libraries. Some libraries were screened against an anti-insulin monoclonal antibody tagged with alkaline phosphatase, which allowed an enzyme-linked colorimetric detection. Only the beads bound to the murine MAb showed a tourquoise color, while the vast majority remained colorless (details of the technical realization of the assay can be found elsewhere [101, 102]). The chemical structure linked to the positive beads was then easily determined via Edman degradation of the peptide sequences. 

Biotinidase deficiency met most of the criteria for inclusion in a neonatal screening program, such as ease and efficacy of treatment, frequency of the disorder, and the relatively low cost of testing. Therefore, a simple colorimetric method to determine biotinidase activity using the same soaked filter-paper blood... 

Biotinidase activity in newborn screening and in confirmational testing is usually determined by using the artificial substrate biotinyl-/>-aminobenzoate in the colorimetric assay. What are the ramifications of not using the natural substrate biocytin to... 

The basis for the standard method for determining blood (ChE) inhibition is the measurement of the enzymatic products derived when either acetylcholine or acetylthiocholine are used as substrates. The rate of formation of acetate is measured by changes in pH, while the formation of thiocholine is determined colorimetrically. A portable device utilizing this method, the Test-Mate OP Kit (EQM Research Incorporated, 2585 Montana Avenue, Cincinnati, OH 45211), provides a rapid, reasonably sensitive assay for ChE inhibition following OP exposure. The kit should be appropriate for emergency contingencies, and only very small blood samples are required. Military forces are viewing such a portable kit as a means to screen... 

There are many examples of the use of very small colorimetric devices for POC applications, such as urine dipsticks and test strips for blood sample screening. While not instruments as such, they are based on clever chemistries and reactions and are often single use, throwaway devices. The reagents required for the test are embedded and dried into a strip which is then dipped into the sample, e.g. urine or blood. The colour changes that result are compared to a colour chart, which is usually provided on the side of the container for the test strips. 

Another technique of single-bead, direct deconvolution is based on on-bead screening. When the biological assay can be run in this format, each library component is tested as resin bound in an assay medium where a soluble receptor is present and the receptor/ligand, or inhibitor, interaction takes place at the surface of the bead. After the biological assay a few positive beads are identified, usually through colorimetric, fluorescent, or radiolabeled detection. They are removed from the assay medium and characterized analytically after washing off the receptor. This technique was first described by Lam et al. [78], has since been... 

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