Cadmium column

Physical and chemical measurements were made weekly at a central station in each side of the lake. Water samples were filtered through Whatman GF/C or Gelman A/E glass-fiber filters (1.0- xm pore size). N03 was measured by reduction to N02" in a cadmium column and formation of a pink azo dye, NH4+ was measured by using a phenol-hypochlorite method, and soluble reactive phosphate was measured by a molybdenum blue method. After 1990 nutrients were measured by using similar methods on a Technicon Auto Analyzer (83). 

Mix 25 mL sample with 75 mL of NH4C1-EDTA solution. The sample mixture is passed through the cadmium column at a rate of 5 to 10 mL/min. This reduces nitrate to nitrite. Discard the first 25 mL and collect the remaining solution. 

To 50 mL of solution passed through cadmium column, add 2 mL of color reagent and mix. Allow the solution to stand for 30 min Measure the absorbance at 543 nm against a distilled water-reagent blank. Read the concentration of N03 -N from the prepared standard curve. Standards should be reduced exactly like samples. 

Otsuki, A. (1978). A reactivation solution for a copperized cadmium column in the automatic determination of nitrate in natural waters. Anal. Chim. Acta 99, 375—377. 

Jones, M. N. (1978). Nitrate reduction by shaking with cadmium Alternative to cadmium columns. 

Anderson (11) was the first to report on the use of FIA for the analysis of seawater micronutrients. He developed a method for the simultaneous determination of nitrate and nitrite. The chemical reactions for the analysis of nitrate were based on the reduction of nitrate to nitrite by a copper-ized cadmium column placed in the flow path. The nitrite was then analyzed as an azo dye (11). This reaction sequence is conventionally used in both segmented CFA and manual analyses of nitrate and nitrite in seawater (2, 6, 7). The detection limits are 0.1 fxM for nitrate and 0.05 juM for nitrite. 

Figure 6. Manifold for the detertnination of nitrate and nitrite. A four-way valve (Rheodyne Model 50, 4V) is used to switch the cadmium column out of line for the determinatioii of nitrite only. (Reproduced with permission from Ref. 12. Copyright 1983, American Society of Limnology and Oceanography.)...

Vertical profiles were made to 70-m depths with a submersible pump at the anchor station. A thermistor, fluorometer, and the inlet for the rFIA system were placed in line with the effluent from the pump. The temperature and chlorophyll fluorescence were recorded continuously. The concentration of nitrate was determined 75 times per hour. The residence time of water in the pump was about 4 min. A typical vertical profile is shown in Figure 11. The cadmium column was switched out of line at each depth to... 

The eluent from the cadmium column was concentrated by transferring it directly to a rotary evaporator preloaded with NaOH. The base raised the pH to > 11 so that any from the target solution or from... 

The separation of zinc and cadmium occurs in the second processing step of the zinc refining process. Figure 2 describes a cadmium column by means of the geometric data of the cadmium column at Metaleurop Nord, Noyelles-Godault. 

The mathematical model was successfiilly used for the computation of the performance of the industrial cadmium column at Metaleurop Nord, Noyelles Godault and also for the trials on a laboratory scale. The Murphree efficiency and also the heat contribution along the height of the column are very sensitive parameters for the simulation program. 

Nitrate may also be determined by LC with an anion-exchange column. A comparison has been made between the traditional method of nitrate determination using a reducing cadmium column and spectrophotometric determination with a reversed-phase LC method with orthophosphoric acid adjusted to pH 3.5 with sodium hydroxide as the mobile phase. A high correlation was observed between the nitrate content determined by the two methods. However, LC was found to be more precise, reproducible, and appropriate for routine work. 

This has been implemented by making use of the MCFIA flow system shown in Figure 7.47 based on absorbance measurement of the azo dye obtained by the reaction of nitrite with iV-(l-naphthyl) ethylenediamine dihydrochloride and sulfanilamide. Nitrate was reduced to nitrite in a copperized cadmium column while the modified Berthelot s reaction (indophenol blue reaction) with salicylate... 

The determination of nitrite in mineral water and in cured meat samples was performed using a glassy carbon electrode modified with a film of tetraruthenated cobalt porphyrin [51], associated with an FIA configuration. With this modified electrode, the anodic process was anticipated (working potential maintained at -1-0.75 V rather than -1-1.0 V) and a 15-fold current enhancement was verified with respect to results observed with the unmodified working electrode. By incorporating a copper-cadmium column before the amperometric detector and in the FIA manifold, it was possible to succeed the quantification of nitrate in the same samples. 

Most spectrophotometric methods consist of colorimetric detection of nitrite at 520-540 nm, based on the classical reaction with N-(l-naphthyl)ethylenediamine and sulfanilamide (Griess reaction). Nitrate is determined colorimetrically in the same way after reduction to nitrite by means of a cadmium column (ISO Standard 14673-1 2004/ IDF Standard 189-1 2004). Different SIA systems based on the Griess reaction have been developed for the determination of nitrate and nitrite in infant formulas and milk powder, in dairy samples, in cured meat and infant formulas and milk powder (Oliveira et al., 2004, 2007 Reis Lima et al., 2006 Piston et al., 2011). 

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