Chelex-100 column

Another relatively simple approach is that of Stolzberg and Rosin [419]. The sample is spiked with an excess of copper, then passed through a Chelex 100 column. The column retains the free copper ion, but passes the copper associated with strong ligands. The chelated copper eluted from the column is measured by plasma emission spectrometry. 

Olsen et al. (48, 20) have described an interesting method for the determination of lead in polluted seawater using FIA and flame atomic absorption spectroscopy. The system incorporates a Chelex-100 column for on-line preconcentration of the sample. The preconcentration and elution step improves the detection limit for lead by a factor of four (50 nM). Further increases in sensitivity are easily possible. The combination of this preconcentration step with a more sensitive detector, such as anodic stripping voltammetry, may make possible the determination of trace metals in seawater on a routine basis. 

FIA system employing the preliminary retention of Cu (and Zn) on a Chelex-100 column, elution of the metal ions with 0.1 M HNO3 and reaction with zincon was applied in analysis of brass and tap water [14]. PAR was used to the determination of Cu in industrial effluents [15]. The application of the complex with Michler s thioketone to the determination of Cu (the detection limit of 0.8 g 1 ) has been reported [16]. 

Zinc (and Cu) in brass and tap water were determined with the use of zincon after preliminary preconcentration on Chelex-100 column [3]. The application of V-hydroxy-AW-diphenylbenzamidine and diphenylcarbazone to the determination of zinc in airborne dust particulates has been described [4]. Trace amounts of zinc in standard alloys, environmental and pharmaceutical samples were determined by fourth derivative spectrophotometry using PAN as a reagent and ammonium tetraphenylborate supported on naphthalene as an adsorbent [5]. The detection limit was 9.5 ng ml Zn. Submicrogram amounts of zinc in water and rock samples were determined with 5-(2 -carbomethoxyphenyl)azo-8-quinolinol in the anionic micellar medium of sodium dodecyl sulfate [6]. 

For comparison with the previous FIA system. Figure 3.8 shows an MCFIA system also used to determine Fe(III) by preconcentration on a Chelex 100 column [28]. In the standby position, the solenoid valves are in Off mode in order to avoid overheating. Only carrier (distilled water) is thus aspirated, but not passed through the column, and the chromogenic reagent is returned to its reservoir. 

SIA system for the determination of Fe(lll) with preconcentration on a Chelex 100 column. HC holding coil SV ... 

Figure 5.17 shows an SIA system for the AAS determination of iron by preconcentration of the metal on a Chelex 100 column and elution with nitric acid [5]. The system uses a Crison Compact titrator to operate both burettes in such a way that the nebulizer will continuously receive liquid at a constant flow-rate. Another interesting example of coupling ASS detection and flow techniques is a multisyringe flow injection analysis (MSFIA) system with cold-vapor AAS developed to determine mercury [6]. 

Figura, EM. and McDuffie, B. (1980) Determination of labilities of soluble trace metal species in aqueous environmental samples by A.S.V and Chelex column and batch methods. Anal. Chem., 52, 1433-1439.

A large discrepancy between the two concentration techniques was found for the copper results. The average difference was 72 27 ngl-1. Bruland and Frank analysed the Chelex column effluent by the solvent extraction technique, and found 63 and 135ngl-1 as the copper content for the samples at 25 m and 2500 m, respectively. These values are almost equal to the difference between the Chelex and solvent extraction results. Therefore, they concluded that about 60% of the copper in seawater (unfiltered and unacidified) is not removed by the Chelex technique. As Riley et al. suggested, copper in seawater is not liberated by the Chelex resin because of association with colloids and fine particulates [62]. In order to avoid this error, acidification and heating of seawater is necessary prior to the Chelex treatment. According to the results of Bruland and Franks, acidification and storage followed by solvent extraction appears to be superior to the Chelex resin concentration for the quantitative determination of copper in seawater [15]. Similar problems have been pointed out by Eisner and Mark, Jr. [63] and Florence and Batley [64]. 

It was found that some Mn bleeds off the Mn02 resin column, hence the requirement for the Fe/Mn co-precipitation. This could be prevented by placing a Chelex column immediately below the Mn02 column, to remove any Mn from the column eluent. This would add to the cost of the analysis however, and the since the Fe precipitation needs to be carried out anyway the Chelex column may be redundant. 

Chelex-lOO also competes against the added chelators glycine, histidine, and ethylenediaminetetraacetic acid (EDTA) (Table II). In these experiments, various concentrations of chelators or phytoplankton cultures with cells removed were mixed in seawater with Cu, and the radioactivity was counted before and after the water was passed through Chelex columns. Since the only competition observed was with 10" M EDTA, the resin should be able to compete against natural complexes... 

The sample passes through a 0.4-/xm Nuclepore (Pleasanton, Calif.) filter bag placed in a tubulated polyethylene container. The filter bags are made from 142-mm filters or, if a larger surface area is needed, by heat-sealing rectangles cut from 8X 10-in. Nuclepore filter sheets. A small bead of silicone rubber is applied to the filter holder cap to make the filter assembly leak-tight. The first Chelex column removes the trace metals from the seawater. The second Chelex column is used as an analytical blank to correct for any salt matrix effects from the first column. 

Alone, chelating resins such as Chelex-100 in columns have been used to separate weak metal complexes, but have not been widely applied in speciation studies. More recently success has been obtained with the use of tuned Chelex columns, where the column volume is minimized and solution flow rate is maximized, while still giving quantitative recovery of ionic metals. Lability is influenced by... 

Heavy metal contamination of pH buffers can be removed by passage of the solutions through a Chelex X-100 column. For example when a solution of 0.02M HEPES [4-(2-HydroxyEthyl)Piperazine-l-Ethanesulfonic acid] containing 0.2M KCl (IL, pH 7.5) alone or with calmodulin, is passed through a column of Chelex X-100 (60g) in the K" " form, the level of Ca ions falls to less than 2 x 10" M as shown by atomic absorption spectroscopy. Such solutions should be stored in polyethylene containers that have been washed with boiling deionised water (5min) and rinsed several times with deionised water. TES [, N,N, -Tetraethylsulfamide] and TRIS [Tris-(hydroxymethyl)aminomethane] have been similarly decontaminated from metal ions. 

Ion exchange column. Prepare the Chelex-100 resin (100- 500 mesh) by digesting it with excess (about 2-3 bed-volumes) of 2M nitric acid at room temperature. Repeat this process twice and then transfer sufficient resin to fill a 1.0 cm diameter column to a depth of 8 cm. Wash the resin column with several bed-volumes of de-ionised water. 

The concentration of copper in the column eluent was determined by flame atomic absorption spectroscopy of samples which were preconcentrated with ammonium pyrrolidine dithiocarbamate (APDC) and methyl isobutyl ketone. The pH of the acidified sample was adjusted to pH 2.5-3.5 using 400 pi 8 M ammonium acetate (Chelex cleaned). 

When the samples were returned to the laboratory the pH was adjusted to approximately pH 8 using concentrated ammonia (Ultrapure, G. Frederick Smith). Chelating cation exchange resin in the ammonia form (20 ml Chelex 100,100 - 200 mesh, Bio-Rad) was added to the samples and they were batch extracted on a shaker table for 36 hours. The resin was decanted into columns, and the manganese eluted using 2N nitric acid [129]. The eluant was then analysed by graphite furnace atomic absorption spectrophotometry. Replicate analyses of samples indicate a precision of about 5%. 

Cerium was included in a list of 14 elements determined by Lee et al. [627] in seawater using neutron activation analysis. The metals were first precon-centraed on a mixture of Chelex 100 and glass powder. The elements were desorbed from the column by 4 M nitric acid, and aqueous solution was irradiated for 3 days and subjected to y-ray spectrometry method with a Ge(Ii) detector coupled to a 4000-channel analyser. Cerium was found to be present to the extent of 16.7 xg/l in water taken from the Kwangyang Bay (South Korea). 

A method described by Hirata and Honda [618] uses a flow injection analysis manifold for pH adjustment of a seawater sample, followed by concentration of zinc on a column packed with Chelex 100 resin. The zinc was eluted with nitric acid and determined by atomic absorption spectrometry. The detection limit is 0.5 p,g/l and the relative standard deviation is 2.7% at the 10 ig/l level. 

In a procedure [627] employing preconcentration of the metals on a column containing a mixture of Chelex 100 and Pyrex glass powder, the problems associated with swelling of the Chelex 100 were overcome and constant flow rates of sample down the column achieved. The water samples were passed through the resin column and eluted with 100 ml 0.01 M nitric acid, and the eluate was discarded. Trace elements were collected from the column by eluting with 50 ml 4 M nitric acid. The eluate was heated to reduce its volume, transferred to a volumetric flask, and diluted to 10 ml. 

Analytical Procedure We followed the OECD guidance document [United Nations 2007, p. 548] for the preparation of a standardized marine test medium. The document states that trace metals should be removed from the test medium before T/D tests are performed. For this step we used a Chelex-100 resin in a column set-up with a flow rate of 5 ml/min. 

The major anions and cations in seawater have a significant influence on most analytical protocols used to determine trace metals at low concentrations, so production of reference materials in seawater is absolutely essential. The major ions interfere strongly with metal analysis using graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma mass spectroscopy (ICP-MS) and must be eliminated. Consequently, preconcentration techniques used to lower detection limits must also exclude these elements. Techniques based on solvent extraction of hydrophobic chelates and column preconcentration using Chelex 100 achieve these objectives and have been widely used with GFAAS. 

Figure 28-18 The pH dependence of the recovery of trace metals from seawater by Chelex-100. The graph shows the pH of the seawater when it was passed through the column. [From S.-C. Pal, Anal. Chlm. Acta 1988, 211.271.]... 

Christensen and Lun [57] developed a speciation procedure using a cation-exchange resin (Chelex 100) in a sequential batch/column/batch system for determining free divalent cadmium and cadmium complexes of various stabilities at the cadmium concentrations typically found in landfill leachates... 

An ion exchange chromatographic method has been described [16] for the determination of the various forms of vanadium in fresh water. These include tetravalent cationic, pentavalent anionic and neutral complexed forms of vanadium. Separation is achieved on two columns in series involving the absorption of the sample on Chelex 100 and Dowex 1x8 columns followed by the selective elution of the different vanadium species and their assay by neutron activation analysis. Experiments were carried out using vanadium-48... 

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