Non-specific reagents

The differentiation of analytical signal in the photometry enables one to use non-specific reagents for the sensitive, selective and express determination of metals in the form of their intensively coloured complexes. The typical representative of such reagents is 4-(2-pyridylazo)-resorcinol (PAR). We have developed the methodics for the determination of some metals in the drinking water which employ the PAR as the photometric reagent and the differentiation of optical density of the mixture of coloured complexes by means of combined multiwave photometry and the specific destmction of the complexes caused by the change of the reaction medium. 

K-hydroxyquLnolinr (mine) A non-specific reagent completing with over twenty metals. pH control can be exploited to aid selectivity. Prccipilates may t>c bromiuated to provide a volumetric finish (p. lift)... 

At present there is no known specific reagent for amino acids alone. Some non-specific reagents for nitrogen-contammg compounds and... 

Table 183. Amino acid detection mth predcminanUy non-specific reagents...

Solvent extraction is probably the separation technique which is most widely used in conjunction with AAS. It often allows the extraction of a number of elements in one operation and, because of the specific nature of AAS, non-selective reagents such as the thiocarbamate derivatives (e.g. APDC) may be used for the liquid-liquid extraction (see Section 6.18). 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

Apart from the mentioned advantages, the polymeric reagents covalently adsorbed by silica also diminish its inherent non-specific adsorptivity. One of the ways to synthesize a polymeric modifier of this type is a copolymerization of a vinylsilane with a compound of the desired functionality. The segments carrying silyl groups will condense with the surface silanols forming anchors or trains . 

NSB (non-specific binding) tubes These tubes contain all reagents except the binding protein. They will therefore show those counts that cause an error in that they are due to free label being counted as bound. 

While much care has to be used in performing competitive protein binding assays, most well-equipped and staffed clinical laboratories should have no serious problem in undertaking such assays. The biggest problem that may be encountered is the selection of a dependable and reliable manufacturer for reagents. Problems that may arise are non-purity of standards and label non-specificity of antibodies or the inability to maintain any of these characteristics from lot to lot. It therefore is a good practice to evaulate a few manufacturers before selecting one for routine use. 

Roth, J., Taatjes, D.J., and Warhol, M.J. (1989) Prevention of non-specific interactions of gold-labeled reagents on tissue sections. Histochemistry 92, 47-56. 

There are mainly three types of transducers used in immunosensors electrochemical, optical, and microgravimetric transducers. The immunosensors may operate either as direct immunosensors or as indirect ones. For direct immunosensors, the transducers directly detect the physical or chemical effects resulting from the immunocomplex formation at the interfaces, with no additional labels used. The direct immunosensors detect the analytes in real time. For indirect immunosensors, one or multiple labeled bio-reagents are commonly used during the detection processes, and the transducers should detect the signals from the labels. These indirect detections used to need several washing and separation steps and are sometimes called immunoassays. Compared with the direct immunosensors, the indirect immunosensors may have higher sensitivity and better ability to defend interference from non-specific adsorption. 

These uncertainties as to the location of ions such as OH- or F" cast doubt on the validity of the quantitative models which are used to treat micellar rate effects. The problem is less serious for reactions of less hydrophilic ions which bind strongly and specifically to micelles, and it should be relatively unimportant for bimolecular reactions of non-ionic reagents. It is probable also that the volume element of reaction decreases as the concentration of ionic reagent is increased, which would speed reaction. 

It is important to emphasize that the introduction of a spacer should never affect the binding characteristics of the support. The selected spacer must not introduce any charges and should not be sufficiently hydrophobic to cause any kind of non-specific interaction. Several molecules can fulfill this demand but only a few of them are regularly used. Most of these contain terminal amino or carboxylic groups. In particular these are diaminodipropyl amine, 6-aminocapronic acid, 1,6-diaminohexane, ethylenediamine, l,3-diamino-2-propanol, succinic acid, 1,4-butanediol diglycidyl ether, and others [96]. Extensive description of other bifunctional reagents can be found in the book of Wong [89]. 

Many of the earliest methods available for the measurement of carbohydrates were based on their chemical reactivity and involved the addition of a particular reagent with the subsequent formation of a coloured product. Although the cheapness and technical simplicity of these procedures contributed to their previous popularity, they are inherently non-specific and often involve the use of substances that are now recognized as hazardous. It is essential that the hazard assessment is undertaken before using such techniques. 

Another non-specific color reagent for RDX and HMX is a solution of thymol in concentrated sulfuric acid [3, 56, 59]. It produces a typical red color. Positive results are also obtained with non-explosive compounds such as sugars and aldehydes. 

ALIS reports only compounds that bind directly to the target of interest, preventing false positives that arise from off-target activity or interactions with substrates or other reagents. Since ALIS directly identifies bound components by MS, the incidence of false positives based on bulk effects and non-specific binding is lower than that of biochemical assays that yield a secondary readout of activity. 

The first step in immunochemical detection of proteins after electrotransfer is blocking the support with an inert material to inactivate further non-specific binding of protein. The blocking reagent should cover the membranes at those areas where no blotted protein is bound and should not react with any of the reactants of immunochemical detection cascade as indicated by no non-specific staining, i.e., resulting in blank background of the membrane. 

---