Alkali residue detection

Residual components in surfactants are undesirable because of their toxicity or inadequacy for the finished product, the result of side and unfinished reactions, mainly from raw materials, and the process. Metals at low concentrations may be encountered in surfactants. Some metals such as iron, nickel, and chromium originate mainly from corrosion of process plant materials mercury comes from alkalis. Their detection is performed by three modes of AAS flame AAS for iron determination in detergents furnace AAS for chromium, nickel, and iron in powder... 

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

In calixarene-based compound M-8 (Figure 10.28), bearing four anthracene moieties on the lower rim, some changes in fluorescence intensity were observed on binding of alkali metal ions but no excimer emission was detected. Quenching of the fluorescence by Na+ may arise from interaction of four anthracene residues brought in closer proximity to one another enhancement of fluorescence by K+ is difficult to explain. 

L-Cysteic acid residues were produced within the peptide chain when submaxillary-gland glycoprotein from sheep was treated with alkali (pH 9.0), during 24 hours at room temperature in the presence of sulfite (0.1 M). The yield was —55% on the basis of the L-serine decomposed, and the corresponding derivative from L-threonine was not detected.167... 

Detection of Acetins.1—10 c.c. of the oil are shaken repeatedly with 40 c.c. of 10% alcohol, in which acetin is readily soluble and the oil practically insoluble after standing, the aqueous-alcoholic liquid is filtered through a filter moistened with the same alcohol. The oil and filter are washed with other small quantities of 10% alcohol, the alcoholic liquids being then evaporated on the water-bath to a small volume (5-10 c.c.). This residue is taken up in neutral alcohol, neutralised with N/10-potassium hydroxide (with phenolphthalein), and saponified with N/2-potasaum hydroxide, in the usual way, the volume of the alkali required for saponification being noted. 

Detection of other Esters of Fixed Acids [oxalates, tartrates, succinates, citrates).—A certain quantity of the oil (if possible 10-20 c.c. or more) is saponified in the usual way, the excess of alkali being neutralised with hydrochloric acid in presence of phenolphthalein and the alcohol expelled on a water-bath. The residue is diluted with water and extracted with ether, the aqueous solution being tested for oxalic, tartaric, succinic and citric acids by the ordinary analytical methods. 

Detection.—Metallic Iridium, like rhodium, is insoluble in all acids, save that in a very finely divided condition it is slowly attacked by aqua regia. Fusion with potassium hydrogen sulphate oxidises the metal but does not effect its solution (contrast ruthenium and rhodium). When fused with a mixture of potassium nitrate and hydroxide an insoluble residue containing the sesquioxide, lr203, with alkali is obtained. 

Detection and Estimation of Phosphites and Hypophosphites. —Solutions of hypophosphorous and phosphorous acids, as well as their salts, when evaporated to dryness and heated, give spontaneously inflammable phosphine and a residue of phosphoric acid or phosphate respectively. The reduction of salts of copper and silver, and of mercuric chloride, by these acids may also be used as tests. When the alkali salts are boiled -with concentrated alkali hydrogen is evolved and a phosphate is found in solution, thus... 

A dry sample which contains alkali hexacyanoferrate(II), decomposes on ignition to iron carbide, alkali cyanide, and nitrogen. By dissolving the residue in acid iron can be detected in the solution (all these operations must be carried out in a fume cupboard). 

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