Anilines detection limits

The optimization of the biorecognition layer by the modification of a transducer used. Nanostmctured poly aniline composite comprising Prussian Blue or poly-ionic polymers has been synthesized and successfully used in the assembly of cholinesterase sensors. In comparison with non-modified sensors, this improved signal selectivity toward electrochemically active species and decreased the detection limits of Chloropyrifos-Methyl and Methyl-Pai athion down to 10 and 3 ppb, respectively. 

To detect glycosides heat the chromatograms to 130—150°C for 15 min. Blue-grey zones are produced (detection limit prunasin 0.3—0.5 pg [18]). Flavonoids are better detected with a modified reagent of the following composition phosphoric acid (85%) — acetic acid — aniline — diphenylamine (20 ml - -100 ml + 5 ml + 5 g). 

The detection limits per chromatogram zone are 4-20 ng substance for aniline derivatives [52] and 3-KX) ng substance for indole derivatives [2, 4, 5, 32, 53].But some substances, e.g. dihydroergosine [11] and PR toxin and PR imine [44] can be detected in quantities smaller than 1 ng. 

SO) and 2,5-didiloioaniline (hRf 60-65) sqrpeared as pale blue-turquoise-colored chromatogram zones on a beige-colored badcground. The detection limits per chromatogram zone ranged from 2 ng (2,3-dimeth aniHne) to 10 ng (4-chlorD-2-metb -aniline). 

After a few minutes 2,4-diamino-6-methylphenol (hRf 5-10), 3-chloro-4-methoxy-aniline (hJ f 25-30), aniline (hRf 35-40), 4-bromoaniline (hRf 40-45), 3-chloroaniline (hJ f 50-55), 2,6-dimethylaniline (hi f 60-65), 2-methyl-6-ethylaniline (hi f 65-70) and 2-chloroaniline (hRj 70-75) yielded orange-colored chromatogram zones on a yellow background. The detection limits were between 5 ng (2,4-diamino-6-methylphenol) and 30 ng (2,6-dimethylaniline) substance per chromatogram zone. 

Aniline, methyl aniline, 1-naphthylamine, and diphenylamine at trace levels were determined using this technique and electrochemical detection. Two electrochemical detectors (a thin-layer, dual glassy-carbon electrode cell and a dual porous electrode system) were compared. The electrochemical behavior of the compounds was investigated using hydrodynamic and cyclic voltammetry. Detection limits of 15 and 1.5nmol/l were achieved using colourimetric and amperometric cells, respectively, when using an in-line preconcentration step. 

In potentiometric sensors, an electrical potential between the working electrode and a reference electrode is measured at zero current conditions in a solution containing ions that exchange with the surface. The first potentiometric MIP sensor was prepared in 1992 by Vinokurov (1992). The substrate-selective polyaniline electrode was electrosynthesized with polypyrrole, polyaniline, and aniline-p-aminophenol copolymers. The development of an MIP-based potentiometric sensor was reported in 1995 by Hutchins and Bachas (1995). This potentiometric sensor has high selectivity for nitrite with a low detection limit of (2 + l)x 10 M (Fig. 15.10). 

TABLE II. ESTIMATED HPLC DETECTION LIMITS FOR SELECTED ANILINES... 

Funazo et al. [812] have described a method for the determination of cyanide in water in which the cyanide ion is converted into benzonitrile by reaction with aniline, sodium nitrite and cupric sulphate. The benzonitrile is extracted into chloroform and determined by gas chromatography with a flame ionisation detector. The detection limit for potassium cyanide is 3 mg L 1. Lead, zinc and sulphide ion interfere at lOOmg L 1 but not at lOmgL-1. 

The Danish Veterinary and Food Administration determined the migration of PAAs from 33 samples of food packaging materials tested shortly after lamination. They used the food simulants distilled water or 3% acetic acid and a colorimetric method. PAA migration was detectable from only two of the samples. The detection limit of the accredited method was 1 pg/kg aniline/ food simulant. In all migration tests performed, any PAA migration was far below the limit of 20 pg/kg. 

Several authors have also reported the potential use of electropolyme-rized metalloporphyrin films as new electrode materials for anion detection and pH measurements. For example, Daunert et al reported that anion-selective membrane electrodes can be prepared by electropolymerizing aniline-substituted cobalt tetraphenylporphyrin complexes onto a glassy carbon surface. It was shown that the resulting electrodes are highly selective towards the detection of thiocyanate and nitrite anions. The mechanism by which these metalloporphyrin electrode sensors operate is probably related to the well-known axial complexation capability of the central metal cation of the porphyrin towards different kind of anions and bases. The same authors also reported a detection limit of 5 x 10 M for these ion-selective electrodes which have lifetimes of more than 2 months... 

Thirteen chloroanilines (two chloroaniline isomers, five chloromethylaniline isomers, five dichloroaniline isomers, and 5-chloro-2-hydroxyaniline) and aniline were extracted from river and drinking water samples [933]. They were baseline resolved on a Cig column (A = 245 nm or electrochemical detection at +0.95 V vs. Ag/AgCI) using a complex 60-min 26/74- 40/60 acetonitrile/water (SpmM acetate bufTo- at pH 4.9) gradient. Excellent resolution and peak shapes were obtained. Detection limits were rqwrted as 15-25ng/L (S/N = 5) with UV detection and 3-5 ng/L for electrochemical detection. A table of analyte and values was presented. 

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