Organic determination under alkaline conditions

A flow injection method based on the catalytic action of iodide on the colour-fading reaction of the FeSCN2+ complex was proposed and applied in order to determine iodine in milk. At pH 5.0, temperature 32°C and measurements at 460 nm, the decrease in absorbancy of Fe -SCN (0.10 and 0.0020 mol /I) in the presence of N02" (0.3 mol/ 1) is proportional to the concentration of iodide, with a linear response up to 100.0 pg/1. The detection limit was determined as 0.99 pg/1 and the system handles 48 samples per hour. Organic matter was destroyed by means of a dry procedure carried out under alkaline conditions. Alternatively, the use of a Schoninger combustion after the milk dehydration was evaluated. The residue was taken up in 0.12 mol/1 KOH solubilization. For typical samples, recoveries varied from 94.5 to 105%, based on the amounts of both organic matter destroyed. The accuracy of the method was established by using a certified reference material (IAEA A-11, milk powder) and a manual method. The proposed flow injection method is now applied as an indicator of milk quality on the Brazilian market (de Araujo Nogueira et al., 1998). 

ISO 2869 1973 (E) Surface active agents—Detergents— Anionic-active matter hydrolyzable under alkaline conditions— Determination of hydrolyzable and non-hydrolyzable anionic-active matter. International Organization for Standardization, Geneva. 

Description of Method. Creatine is an organic acid found in muscle tissue that supplies energy for muscle contractions. One of its metabolic products is creatinine, which is excreted in urine. Because the concentration of creatinine in urine and serum is an important indication of renal function, rapid methods for its analysis are clinically important. In this method the rate of reaction between creatinine and picrate in an alkaline medium is used to determine the concentration of creatinine in urine. Under the conditions of the analysis, the reaction is first-order in picrate, creatinine, and hydroxide. 

Important organic applications are to the determination of quinine and the vitamins riboflavin (vitamin B2) and thiamine (vitamin Bj). Riboflavin fluoresces in aqueous solution thiamine must first be oxidised with alkaline hexacyanoferrate(III) solution to thiochrome, which gives a blue fluorescence in butanol solution. Under standard conditions, the net fluorescence of the thiochrome produced by oxidation of the vitamin Bj is directly proportional to its concentration over a given range. The fluorescence can be measured either by reference to a standard quinine solution in a null-point instrument or directly in a spectrofluorimeter.27... 

Ioannou et al. [41] reported the use of terbium sensitized fluorescence to develop a sensitive and simple fluorimetric method for the determination of the anthranilic acid derivative, mefenamic acid. The method makes use of radiative energy transfer from anthranilate to Tb(III) in alkaline methanolic solutions. Optimum conditions for the formation of the anthranilate-Tb(III) complex were investigated. Under optimized conditions, the detection limit was 1.4 x 10-8 mol/L, and the range of application was 2.5 x 10 8 to 5.0 x 10 5 mol/L. The method was successfully applied to the determination of mefenamic acid in serum after extraction of the sample with ethyl acetate, evaporation of the organic layer under a stream of nitrogen at 40°C, and reconstitution of the residue with alkaline methanolic terbium solution prior to instrumental measurement. The mean recovery from serum samples spiked with mefenamic acid (3.0 x 10-6, 9.0 x 10-6, 3.0 x 10-5 mol/L) was 101 5%. The within-run precision (RSD) for the method for the two serum samples varied from 2 to 8%, and the day-to-day precision for two concentration levels varied from 2 to 13%. 

Phenylisothiocyanate combines with theN-terminusof a peptide under mildly alkaline conditions to form a phenylthiocarbamoyl substitution. (2) Upon treatment with TFA (trifluoroacetic acid), this cyclizes to release the N-terminal amino acid residue as a thiazolinone derivative, but the other peptide bonds are not hydrolyzed. (3) Organic extraction and treatment with aqueous acid yield the N-terminal amino acid as a phenylthiohydantoin (PTH) derivative. The process is repeated with the remainder of the peptide chain to determine the N-terminus exposed at each stage until the entire peptide is sequenced. Sign in at www.thomsonedu.com/iogin to see an animated version of this figure. 

Alternatively, direct analysis of nonfluorescent organic ligands by adding an excess of metal ion to form florescent compounds is also possible. Although this derivatization strategy has attractive analytical potential for the analysis of nonfluorescent aromatic compounds, it has received little attention. A typical example includes the fluorimetric determination of anthracyclines and tetracyclines as metal chelates with Mg " ", Ca " ", and Eu + under neutral or alkaline solutions, and with Al + or Zr", under acidic conditions. 

The first practical method developed for the simultaneous determination of heroin and its metabolites utilized a complex multistep liquid-liquid extraction scheme. Under mild alkaline conditions, analytes from plasma are isolated with a mixture of toluene-butanol. The analytes are back-extracted into dilute sulfuric acid and the acid phase is washed with n-hexane. After adjusting the pH, the aqueous phase is extracted with toluene-butanol. Following separation and evaporation of the organic phase, the extract is reconstituted in methanol and analyzed by LC. 

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