Reductic acids detection

Chemical methods for folic acid detection are not useful for unfractionated biologic materials (H16). Reduction of folic acid in acid yields a methylpteridine and N-(p-aminobenzoyl) glutamic acid. The latter is estimated by a method for aromatic amines (B33). Another assay method of historical interest is the growth of chicks as a measure of the folic acid content of crude biological mixtures. 

Although small proportions of other products are formed when D-xylose is exposed to rather high acid concentrations, arabinose, lyxose, and ribose form considerably more of alternative products (generally reductic acid) than of 2-furaldehyde under these conditions. Reductic acid (2,3-dihydroxy-2-cyclopenten-l-one, 47) has been detected as a product after acid exposure of D-xylose or its major dehydration product, 2-furalde-hyde. Further work performed with D-[l- C]xylose and [a- C]2-fural-dehyde showed that reductic acid having identical label distribution was obtained from both starting materials. This indicated that a common primary source was involved, probably 2-furaldehyde, as it is readily formed from D-xylose under acidic conditions. 

On treatment with aqueous mineral acid, L-ascorbic acid,90 hexu-ronic acids,91 and glycuronans92 undergo decarboxylation by which 1 mole of carbon dioxide per mole of acid is produced. For hexu-ronic acids, other detectable products include 2-furaldehyde (27) (Ref. 93), reductic acid (2,3-dihydroxy-2-cyclopenten-l-one, 75 see p. 207) (Refs. 53 and 94-96), and traces of 5-formyl-2-furoic acid... 

Electrochemical endpoint detection methods provide a number of advantages over classical visual indicators. These methods can be used when visual methods of endpoint detection cannot be employed because of the presence of colored or clouded solutions and in the case of detection of several components in the same solution. They are more precise and accurate. In particular, such methods provide increased sensitivity and are often amenable to automation. Electrochemical methods of endpoint detection are applicable to most oxidation-reduction, acid-base, and precipitation titrations, and to many complex-ation titrations. The only necessary condition is that either the titrant or the species being titrated must give some type of electrochemical response that is indicative of the concentration of the species. 

Figure 5-3. Electrocatalytic nucleic acids detection based on the reduction of FefCNjg mediated by RufNHj) . The Ru(III) complex is electrostatically bound to the anionic backbone of an immobilized DNA oligonucleotide and upon the hybridization of a complementary target sequence is present at a higher concentration at the electrode surface. This increases the surface concentration of the redox mediator and leads to an enhanced electrochemical signal tliat can be used to detect specific DNA sequences. The presence of Fe(CN)6 chemically regenerates electrochemically reduced Rufll), and thereby catalytically amplifies the signals. (Adapted from ref. 11).

Detection of Carbocydic Sugars of the Calotropis Glycosides.—In the investigation of members of this group, detection of the reductic acids has been achieved by the method of Hesse and associates. ... 

The determination of Ge by means of atomic absorption spectrometry (AAS) during the late 1960s was replaced by introduction of the hydride technique with sodium tetrahydroborate as a means of reduction. The detection limits indicated are 2xl0 g and 0.01 pg mL Abbasi et al. (2001) showed that there is a possibility of losing Ge in the presence of chloride when acid digestion procedures are carried out in open vessels. This is more pronounced if the Ge concentration is very low. In fact, 100 pg g can be considered as a critical value above which both open and closed vessels digestion methods can be used without any significant loss. 

One recent development that offers scope for direct injection of aqueous samples into an MS system is the high-field, asymmetric waveform ion mobility spectrometer (FAIMS). By interfacing the FAIMS technology to an ESI—MS instrument a significant reduction in detection limits has been achieved for molecules of <300 Da. Preconcentration is unnecessary and analytical times are significantly shortened. Recent appHcations of this technique include naphthenic and haloacetic acids in water and amphetamines, morphine and codeine... 

HPLC Post-column derivatisation e.g. Ellman s reagent) Non-specific pre-column derivatisation e.g. of amino acids to form chromophores or fluorophores) Pre-column derivatisation to form fluorophores e.g. with bimanes, maleimides) Oxidative and reductive electrochemical detection... 

Z.M. Zhou, J.C. Anders, H. Chung and A.D. Theoharides, Analysis of artesunic acid and dihydroqinghaosu in blood by high-performance liquid chromatography with reductive electrochemical detection, /. Chromatogr., mi, 414, 77-90. 

Effects on Abscisic Acid and Cytokinins. Lepage-Digivry (1973) reported an increase in bound ABA at the expense of free ABA in seeds of Taxus baccata during stratification. Enu-Kwesi and Dumbroff (1977) also reported a cold-induced reduction in detectable ABA in Acer fruits but, in most cases, changes in ABA levels have not shown a close correlation with thermodormancy (Berrie and Robertson 1976). 

Demonstration of the phenomenon employed an electrochemiluminescent reaction at the anodes and oxygen reduction at the cathodes, allowing photographic capture of signals, as shown in Fig. 6. This array design has subsequently been applied to nucleic acid detection and is discussed further in a following section of this chapter. 

The acetone test reagent consists of a 0 1 per cent, solution of 2 4-dinitro-phenylhydrazine and is prepared as follows Dissolve 0-25 g. of 2 4-dinitrophenyl-hydrazine in 60 ml. of water and 42 ml. of concentrated hydrochloric acid by warming on a water bath cool the clear yellow solution and dilute to 250 ml. with water. The acetone test is considered negative when 5 ml. of the reagent and 4-5 drops of the distillate give no cloudiness or precipitate of acetone 2 4-dinitro-phenylhydrazone within 30 seconds. After a negative test is obtained, it is stron y recommended that the mixture in the flask be refluxed for 5-10 minutes with complete condensation and then to collect a few drops of distillate for another test. If no acetone is now detected, the reduction is complete. 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

A flow-injection system with electrochemical hydride generation and atomic absorption detection for the determination of arsenic is described. This technique has been developed in order to avoid the use sodium tetrahydroborate, which is capable of introducing contamination. The sodium tetrahydroborate (NaBH ) - acid reduction technique has been widely used for hydride generation (HG) in atomic spectrometric analyses. However, this technique has certain disadvantages. The NaBH is capable of introducing contamination, is expensive and the aqueous solution is unstable and has to be prepared freshly each working day. In addition, the process is sensitive to interferences from coexisting ions. 

An enzymatic assay can also be used for detecting anatoxin-a(s). " This toxin inhibits acetylcholinesterase, which can be measured by a colorimetric reaction, i.e. reaction of the acetyl group, liberated enzymatically from acetylcholine, with dithiobisnitrobenzoic acid. The assay is performed in microtitre plates, and the presence of toxin detected by a reduction in absorbance at 410 nm when read in a plate reader in kinetic mode over a 5 minute period. The assay is not specific for anatoxin-a(s) since it responds to other acetylcholinesterase inhibitors, e.g. organophosphoriis pesticides, and would need to be followed by confirmatory tests for the cyanobacterial toxin. 

The Fcm derivative is prepared from amino acids on treatment with formylferro-cene and Pd-phthalocyanine by reductive alkylation (60-89% yield). It is cleaved with 2-thionaphthol/CF3COOH. Its primary advantage is its color, making it easily detected. ... 

Note The detection limit for aryl- and thioglucosides is 100 — 200 ng substance per chromatogram zone [2]. Reduction of the proportion of phosphoric acid in the reagent leads to loss of sensitivity [2]. 

Other secondary amines such as pyrrolidine, di- -butylamine, tetrahydro-quinoline, n-benzylamine, and piperidine were also found to be capable of effecting this reduction. Interestingly, morpholine does not reduce enamines as readily (47) and its acid-catalyzed reaction with norbornanone was reported (45) to give only the corresponding enamine (93), although trace amounts of the reduction product were detected when cyclohexanone was treated with morpholine under these conditions (47a). The yield of morpholine reduction product was increased by using higher temperatures. 

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