Purines colorimetric methods

Several techniques have been developed for the determination of purine and pyrimidine derivatives in food sample and in particular for hypoxanthine quantification biosensors (220-223) and electrochemical methods making use of immobilized enzyme electrode (224 -227), electrochemical enzymatic-based HA methods (228,229), enzyme reaction with fluorimetric detection (230), radioimmunoassay (231), colorimetric methods (232), capillary electrophoresis (233), and TLC (234). Many HPLC methods have also been developed and are reported in Table 4 (235-247) the most recent ones are described next. 

In addition to analyzing compounds, enzyme sensor has been used to determine the freshness of meats. Xanthine oxidase has been used to determine the levels of xanthine and hypoxanthine that are accumulated from purine degradation during muscle aging so as to monitor fish freshness for a long time. Traditional methods including the automated colorimetric method (54) were time consuming. Jahn et al (55) developed a dipstick test by... 

Colorimetric methods The determination of magnesium is carried out by complexation with coloring agents such as eriochrome black T [23], titan yellow [24], 5,7-diiodo-8-quinolinol and rhodamine S [25], beryllon II [26], quinolin-8-olate [27,28] leucoquinizarin [29], emodin [30,31], pur-purin [32], or bromopyrogallol red [33]. 

These three methods are commonly used the detection of radioactive phosphate containing [24], the colorimetric detection of a complex of phosphomolybdate and malachite green [25], and the colorimetric detection of a phosphorylated product obtained by a secondary enzymatic phosphate transfer using purine ribonucleoside phosphorylase (PNP) [26] (Figure 2). 

Two methods, the one based on the alkali lability of RNA and the other on the acid lability of both RNA and DNA, appeared simultaneously in 1945 and have provided the analytical foundation for much of the recent research activity revolving about nucleic acids. The former of these methods is that of Schmidt and Thannhauser (abbreviated here as ST) (91) which depends upon the selective conversion of RNA phosphorus to organic acid-soluble phosphorus (mononucleotides) by alkali after removal of acid-soluble phosphates and of phospholipid phosphorus (16 et ante). The method of Schneider (S) (93) extracts the same lipid-free protein precipitate with hot trichloroacetic or perchloric (95) acid which solubilizes both RNA and DNA the estimation of each in the mixture utilizes specific colorimetric reactions for the (purine) ribose and desoxyribose moieties. These two methods will be discussed in connection with the combined method which follows. 

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