Fully automated photocolorimetric method for dissolved silica in oil well water rich in sulfide and bicarbonate.
A fully automated photocolorimetric method for dissolved silica in oil well water rich in sulfide and bicarbonate is proposed; the method is based on yellow silicomolybdic heteropolyacid. To eliminate the interference of sulfide a treatment with bromate is utilized. The analytical range is 1-30 mg L(-1); with the automatically performed dilution it extends up to 300 mg L(-1), RSD 5.5%.
Inorganic interferences in the 2,4-xylenol spectro-photometric method for nitrate and their elimination
Abstract A study of inorganic interferences with the 2,4-xylenol spectrophotometric method for nitrate and their elimination is reported. Fifty-three substances do not interfere with the original method. Nitrite interferes somewhat by producing a faint yellow color. Certain reducing agents (Fe 2+ , S 2- , S 2 O 3 2- , and SCN - ) cause low results by reducing the nitrate in the strong sulfuric acid solution, while some oxidizing agents (Mn 7+ , Cr 6+ , V 5+ , and ClO 3 - ) cause low results by inactivating or destroying the 2,4-xylenol. Persulfate and small amounts of H 2 O 2 produce a slight deepening of the color; larger amounts of H 2 O 2 ; cause low results, as do Cl - , Br - , I - , and metals. The recommended maximum permissible limits (mg per 10-ml aliquot) for the original method are NO 2 - -N, Fe 2+ , S 2- , SCN - , V 5+ , ClO 3 - , Cl - , I - , 0.2; Mn 7+ , Cr 6+ , S 2 O 8 2- , 5; H 2 O 2 , 0.02; S 2 O 3 2- , Br - , 0.1; metals, none. Procedures for the elimination of most of the interferences are described. Nitrite is destroyed with sulfamic acid. The interferences of reductants (Fe 2+ , S 2- , S 2 O 3 2- , and SCN - ) and oxidants (Mn 7+ and Cr 6+ ) are eliminated with hydrogen peroxide, the excess of which (and S 2 O 8 2- ) is destroyed by boiling in the presence of Fe 3+ . The interference of Cl - , Br - , and I - is eliminated by precipitation with silver sulfate. An alternative to the sulfamic acid procedure is to oxidize nitrite to nitrate with peroxide and deduct NO 2 - -N from the total NO 3 - -N. After elimination of interferences, a 10-ml aliquot of sample solution is treated with 17.0 ml of sulfuric acid and 2,4-xylenol, the 6-nitro-2,4-xylenol is steam-distilled into an ammonia—water—isopropanol mixture, and the yellow color is measured.
Potential of modified reverse flow injection analysis for continuous monitoring and process control
SummaryModified reverse flow injection analysis is introduced as a novel means for monitoring purposes and online process control. The technique is based on the injection of standard solutions into the continuously flowing sample stream. The transient detector response occurring shortly after the injection reflects the deviation between the analyte concentration of the sample stream and the standard injected. Interpolative calibration and the check of nominal values are two interesting execution modes presented. The beneficial features of the novel approach are discussed and exemplarily demonstrated for practical problems. Experimental conditions are given for the photometric determination of chloride in tap water, phosphate in surface water and the potentiometric determination of fluoride. The respective advantages over common monitoring systems are outlined.