Reductor column

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

The flow injection technique is based on three main principles sample injection, reproducible timing, and controlled dispersion [128]. The dispersion can be described as limited, medium, or large in a colorimetric system based on a reaction between the sample and a suitable reagent, a medium dispersion is preferred. Thus in the flow injection determination of nitrate, the reductor column should not excessively increase the dispersion. In a copperised cadmium reductor, more than 90% of the total nitrate is reduced within 1 - 2 s with minimum risk of further reduction of nitrite [167]. Consequently, the reductor can be made very small, which results in a minimal increase of dispersion. 

The concentrates were subsequently analysed for arsenic using Varian-Techtron AAS atomic absorption spectrophotometer fitted with a Perkin-Elmer HGA 72 carbon furnace, linked to a zinc reductor column for the generation of arsine (Fig. 5.3). A continuous stream of argon was allowed to flow with the column connected into the inert gas line between the HGA 72 control unit and the inlet to the furnace. Calcium sulfate (10-20 mesh) was used as an adsorbent to prevent water vapour entering the carbon furnace. The carbon tube was of 10 mm id and had a single centrally located inlet hole. 

Maher [130] has described a procedure for the determination of total arsenic in sediments. Arsenic is converted into arsine using a zinc reductor column, as shown in Fig. 12.8. The evolved arsine is trapped in a potassium iodide-iodine solution and other arsenic determined spectrophotometrically as an arsenomolybdenum blue complex. The detection limit is 0.024pg and the coefficient of variation is 5.1% at the 0.1 pg level. The method is free from interferences by other elements at levels normally encountered in sediments. In this method the sediments were freeze-dried and ground (to less than 200pm) before analysis. 

The arsenic in each fraction was determined by reduction to the corresponding arsine in the zinc reductor column, decomposition of the... 

The nitrite value can be determined by eliminating the reductor column and standardizing with an appropriate nitrite value. In order to determine the nitrate values, the nitrite alone must be subtracted from the total (nitrate and nitrite). 

Henrickson and Selmer-Olson [18] applied an autoanalyser to the determination of nitrate and nitrite in soil extracts. In an autoanalyser, the water sample, buffered to pH 8.6 with aqueous ammonia-ammonium chloride, is passed through a copperised cadmium reductor column. The nitrite formed is reacted with sulfuric acid and N-l-naphthylethylenediamine, and the extinction of the azo dye is measured at 520 nm. For soil extracts, the range and standard deviation are 0.5-1.0 and 0.007mg/1, respectively. 

Reductor columns have been prepared from zinc, silver, lead, cadmium, bismuth, antimony, nickel, copper, tin, and iron. 

The method for nitrite determination based on the diazotization-coupling reaction by column preconcentration and on the reduction of nitrate to nitrite using the Cd-Cu reductor column has been proposed for the determination of nitrate and nitrite in water and some fruit samples [6]. On-line monitoring of nitrite in fertilizer process streams, natural and waste water effluents based on the diazotization of nitrite in the sequential injection system with N-(l-naphthyl)etylenediammonium dichloride and the formation of a highly coloured dye has been described [7]. 

Ninety grams of chromium (III) chloride 6-hydrate is dissolved in 120 ml. of water and 30 ml. oi 2 N sulfuric acid. The solution is poured into the reductor column and... 

Flow-through methods are also used for sample treatment prior to coulometric titration, for the purpose of cleanup or preconcentration on an ion-exchange column or for reduction to a desired oxidation state in reductor columns. Preadjustment of redox states or removal of interferents may also be carried out by an auxiliary electrochemical flowthrough cell located ahead of the analytical cell. 

Naphthol Green B-i-BrOs" (NOi") Simultaneous determination of nitrate and nitrite using a reductor column and flow-injection... 

In the case of nitrate, the majority of applications for its determination are based on copperized-cad-mium or cadmium-coated zinc reductor columns, which are generally used for reducing nitrate to nitrite. After formation of color, specific reagents are added and nitrate is determined from the difference between the total nitrite and nitrate concentrations. 

The mercury(l) chloride is unaffected by oxidants during the subsequent titration. Sulfite (or SO2) and hydrogen sulfide are alternative reductants. Metals may also be used. Small pieces of metal (zinc - a Jones reductor, silver - a Walden reductor) are used to fill a column, through which the analyte solution is passed. The effluent is titrated with oxidant. A comparison of the reduction products of the two reductor columns is given in Table 3. 

The reductor column is a glass tube of 10-25 cm length and 3-S nun inner diameter. It can be either straight, U-shaped or formed otherwise (Fig. 10-8) depending on the mechanical mounting and flow requirements. 

Measure the nitrate content of the irradiated and untreated samples as described in II.6,F.l-4 using tfie same reductor column for both solutions (Note e). 

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