Column packings chelating

Gamma, of a photographic emulsion 769 Gas chromatography 235 apparatus for, 235 column packing for, 238 derivatisation in, 236 detectors for, 240 elemental analysis by, 247 of metal chelates 237, 248 pyrolysis, 237... 

Chang et al. [952] used a miniature column packed with a chelating resin and an automatic online preconcentration system for electrothermal atomic absorption spectrometry to determine cadmium, cobalt, and nickel in seawater. Detection limits of 0.12,7 and 35 ng/1 were achieved for cadmium, cobalt, and nickel, respectively, with very small sample volume required (400-1800 xl). 

Determination of Pb(II) ion by classical or reversed FIA consists of a preconcentration step either on columns packed with a chelating sorbent (PC-FIA) or on a mercury film, followed by spectrophotometric determination of the complex with 4-(2-pyridylazo)resorcinol (11, kmax 518 nm) in borate buffer solution RSD 3-6% at 0.01-1 pM. End analysis by ASV was also applied99. 

Elimination of coextracted materials and concentration of tetracyclines have also been accomplished using mixed-phase extraction membranes with both re-versed-phase and cation-exchange properties (294,295), or solid-phase extraction columns packed with cation-exchange materials such as CM-Sephadex C-25 (301), aromatic sulfonic acid (310), and carboxylic acid (283, 300). For the same purpose, metal chelate affinity chromatography has also been employed. In this technique, the tetracyclines are specifically absorbed on the column sorbent by chelation with copper ions bound to small chelating Sepharose fast flow column (278-281, 294-296). 

Sakamoto et al. [626] demonstrated the application of the microwave plasma detector to the analysis of trace amounts of aluminium and copper in zinc by GC in the form of their volatile chelates. A column packed with 0.5% of SE-30 on glass beads was used at 140°C. With the same chelates as above, the detection limit was 1 ng for copper and 0.5 ng for aluminium. 

Foreman et al. [631] compared the direct method of the chelate formation with the preliminary ashing method for the analysis of beryllium in rat urine. A detailed study showed that both of the methods are satisfactory, whereas testing of column material and packings showed the best results for a PTFE column packed with SE-52. Down to 1 ng/ml of the element could be detected in urine with the use of an ECD and EDTA as a masking reagent and a 0.05 M benzene solution of trifluoroacetylacetone. 

Chromium was measured in steels with high and low contents of carbon by Ross and Sievers [633]. A small amount of the sample (2 —4 mg) was allowed to react directly with trifluoroacetylacetone in the presence of nitric acid. If an undissolved residue occurred, it was dissolved in 70% nitric acid, evaporated to dryness and the procedure was repeated. The resulting red solution was extracted with benzene and excess of the chelating agent was removed by extraction with dilute sodium hydroxide solution. A PTFE column packed with 15% of SE-52 on Anakrom ABS and an ECD were used. The results showed a relative error of 1.4-1.7%. 

Lead has been determined chromatographically in the form of its chelates with different j3-diketones [642]. A column packed with 15% of Apiezon L at temperatures around 200°C appeared to be the most suitable, but even with its use adsorption and peak tailing of chelates occurred. In combination with MS and using integrated ion-current curves the detection limit was about 10 14 g of lead. 

Iron was determined in ores by Sievers et al. [644] with the use of the same chelating agent. Less than 1 mg of the sample was treated with the reagent in a sealed capillary, which was then crushed in a modified injection port of a gas chromatograph. A PTFE column packed with 10% of SE-30 on Gas-Chrom Z and a TCD were used. Quantitative data obtained by GC accorded well with those obtained by other methods. 

An advantage of this sampling configuration is that particulate matter can be trapped on the column packing or removed by filtration prior to chelation. This allows analysis of either the total trace element concentration or the dissolved trace metal concentration. 

Preconcentration of selected metal ions is probably the main use of chelating resins in chemical analysis. Trace amounts of complexed metal ions may be concentrated from a large sample onto a very short column. Subsequent elution by acid breaks up the metal chelates and gives a much more concentrated solution of the metal ions for further analysis. However, a column packed with a chelating resin may also be used to separate sample metal ions based on differences in the strength of their chelates. 

An alternative method for oxygen removal is catalytic reduction over a platinum-on-alumina catalyst in the presence of methanol [22,23]. A short column packed with the catalyst is inserted between the pump and injector. Provided that the mobile phase contains about 1% methanol (or more) oxygen is very efficiently reduced producing formaldehyde and formic acid. It is necessary to ensure that these products do not react with or degrade the sample. An in-line chelation column placed between the pump and injection valve was suitable for the removal of metal impurities from the mobile phase [24]. 

Fig.4.7a-c a, b, schematic diagram of a dual column FI on-line preconcentiation manifold for flame AAS with parallel sample loading and sequential elution using two pumps, a, loading sequence b, elution sequence for column Ca. Pi, Pn, peristaltic pumps Sa, Sb, samples Ea, Eb eluent (2 M HNO3) Ra, Rb, ammonium acetate buffer, T, timer for pump control V, 8-channel multifunctional valve Ca> Cb columns packed with chelating ion-exchangers W, Wa, Wb, waste flows Wa same waste line as Wa and AAS, flame AA detector [12]. 

Figure 2 Isocratic separation of standard mixture of 14 lanthanides and yttrium on a 250 mm x 4 mm column, packed with 5 pm silica IDA. Eluent 1.6x 10" moll" HNO3 with 0.5moll KNO3 flow rate 1.0 ml min " k column temperature 65°C, sample volume 20 pi, sample concentration of each metal was 4 ppm in 0.2% HNO3. Detection, Arsenazo III postcolumn reaction at 658 nm. (Reprinted with permission from Nesterenko PN and Jones P (1998) Isocratic separation of lanthanides and yttrium by high performance chelation ion chromatography. Journal of Chromatography A 804 223-231 Elsevier.)...

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