Solvent extraction atomic absorption

COMPARISON OF FILTERED AND UNFILTERED SEAWATER SAMPLES ANALYSED BY THE SOLVENT EXTRACTION-ATOMIC ABSORPTION METHOD ... 

RECOVERY OF METALS FROM SPIKED SEAWATER OBTAINED BY SOLVENT EXTRACTION-ATOMIC ABSORPTION SPECTROMETRY [37 ]... 

MS. Mitchell, D. G., Ryan, F. J., and Aldous, K. M., The precise determination of lead in whole blood by solvent extraction-atomic absorption spectrometry. At. Absorption Neuislett. 11, 120-121 (1972). 

Rocks, minerals, nuclear fission products and biological material Solvent extraction as MHFA complex optional purification by back-extraction Atomic absorption spectrometry <0.08 mg/L No data Abassi 1989 m H I... 

Metal Extraction. As with other carboxyhc acids, neodecanoic acid can be used in the solvent extraction of metal ions from aqueous solutions. Recent appHcations include the extraction of zinc from river water for deterrnination by atomic absorption spectrophotometry (105), the coextraction of metals such as nickel, cobalt, and copper with iron (106), and the recovery of copper from ammoniacal leaching solutions (107). 

Metal impurities can be determined qualitatively and quantitatively by atomic absorption spectroscopy and the required purification procedures can be formulated. Metal impurities in organic compounds are usually in the form of ionic salts or complexes with organic compounds and very rarely in the form of free metal. If they are present in the latter form then they can be removed by crystallising the organic compound (whereby the insoluble metal can be removed by filtration), or by distillation in which case the metal remains behind with the residue in the distilling flask. If the impurities are in the ionic or complex forms, then extraction of the organic compound in a suitable organic solvent with aqueous acidic or alkaline solutions will reduce their concentration to acceptable levels. 

Further techniques which may be applied directly to the solvent extract are flame spectrophotometry and atomic absorption spectrophotometry (AAS).13 The direct use of the solvent extract in AAS may be advantageous since the presence of the organic solvent generally enhances the sensitivity of the method. However, the two main reasons for including a chemical separation in the preparation of a sample for AAS are ... 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

With flame emission spectroscopy, there is greater likelihood of spectral interferences when the line emission of the element to be determined and those due to interfering substances are of similar wavelength, than with atomic absorption spectroscopy. Obviously some of such interferences may be eliminated by improved resolution of the instrument, e.g. by use of a prism rather than a filter, but in certain cases it may be necessary to select other, non-interfering, lines for the determination. In some cases it may even be necessary to separate the element to be determined from interfering elements by a separation process such as ion exchange or solvent extraction (see Chapters 6, 7). 

Porra, R.J., Thompson, W.A., and Kriedemann, P.E., Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents verification of the concentration of chlorophyll standards by atomic absorption spectroscopy, Biochim. Biophys. Acta, 975,384, 1989. 

Munoz O, Velez D, Montoro R (1999) Optimization of the solubilization, extraction and determination of inorganic arsenic [As(III) i- As(V)] in seafood products by acid digestion, solvent extraction and hydride generation atomic absorption spectrometry. Analyst 124 601-607. 

Even with the simple laboratory equipment used in these experiments, the CESS procedure allowed quantitative recovery of the product free of solvent, and with rhodium contents ranging from 0.36-1.94 ppm (determined by atomic absorption measurements). Furthermore, using this approach removal of unreacted starting material or side products from the product is possible during extraction from the catalyst, since even small structural differences can result in significant differences in... 

Other methods reported for the determination of beryllium include UV-visible spectrophotometry [80,81,83], gas chromatography (GC) [82], flame atomic absorption spectrometry (AAS) [84-88] and graphite furnace (GF) AAS [89-96]. The ligand acetylacetone (acac) reacts with beryllium to form a beryllium-acac complex, and has been extensively used as an extracting reagent of beryllium. Indeed, the solvent extraction of beryllium as the acety-lacetonate complex in the presence of EDTA has been used as a pretreatment method prior to atomic absorption spectrometry [85-87]. Less than 1 p,g of beryllium can be separated from milligram levels of iron, aluminium, chromium, zinc, copper, manganese, silver, selenium, and uranium by this method. See also Sect. 5.74.9. 

Moffett [179] determined chromium in seawater by Zeeman corrected graphite tube atomisation atomic absorption spectrometry. The chromium is first complexed with a pentan-2,4 dione solution of ammonium 1 pyrrolidine carbodithioc acid, then this complex extracted from the water with a ketonic solvent such as methyl isobutyl ketone, 4-methylpentan-2-one or diisobutyl ketone. 

The collection behaviour of chromium species was examined as follows. Seawater (400 ml) spiked with 10-8 M Crm, CrVI, and Crm organic complexes labelled with 51Cr was adjusted to the desired pH by hydrochloric acid or sodium hydroxide. An appropriate amount of hydrated iron (III) or bismuth oxide was added the oxide precipitates were prepared separately and washed thoroughly with distilled water before use [200]. After about 24 h, the samples were filtered on 0.4 pm nucleopore filters. The separated precipitates were dissolved with hydrochloric acid, and the solutions thus obtained were used for /-activity measurements. In the examination of solvent extraction, chromium was measured by using 51Cr, while iron and bismuth were measured by electrothermal atomic absorption spectrometry. The decomposition of organic complexes and other procedures were also examined by electrothermal atomic absorption spectrometry. 

A conventional analytical method, like solvent extraction-graphite furnace atomic absorption spectrometric detection, requires a contamination-free technique. Moreover, it is time-consuming and troublesome, as litres of the sample solution must be treated because the dissolved concentration of iron in oceanic waters is extremely low (lnmol/1 = 56ng/l). Martin et al. [341] recently found that the dissolved concentration of iron was less. 

Atomic absorption spectrometry coupled with solvent extraction of iron complexes has been used to determine down to 0.5 pg/1 iron in seawater [354, 355]. Hiire [354] extracted iron as its 8-hydroxyquinoline complex. The sample is buffered to pH 3-6 and extracted with a 0.1 % methyl isobutyl ketone solution of 8-hydroxyquinoline. The extraction is aspirated into an air-acetylene flame and evaluated at 248.3 nm. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

The concentration of nickel in natural waters is so low that one or two enrichment steps are necessary before instrumental analysis. The most common method is graphite furnace atomic absorption after preconcentration by solvent extraction [122] or coprecipitation [518]. Even though this technique has been used successfully for the nickel analyses of seawater [519,520] it is vulnerable to contamination as a consequence of the several manipulation steps and of the many reagents used during preconcentration. 

Orren [663] used atomic absorption spectrometry to determine these elements in seawater in both their soluble and insoluble forms. The alkali metals are determined directly, but the other elements are first concentrated by solvent extraction. The particulate matter content is derived by dissolving the membranes used to filter the sample and determine the metals in the resulting solution. For organic standards of known metal content, the efficiency of the technique was almost 100%. 

Amankwah and Fasching [4] have discussed the determination of arsenic (V) and arsenic (III) in estuary water by solvent extraction and atomic absorption spectrometry using the hydride generation technique. 

Yamamoto et al. [33] have studied the differential determination of heavy metals according to their oxidation states by flameless atomic absorption spectrometry combined with solvent extraction with ammonium pyrrolidinedithio-carbamate or sodium diethyldithio-carbamate. 

A rough estimate of the total amount of anionic surfactant present can be obtained by reacting the surfactant with a metal-containing material such as bis(ethylenene diamine) copper (II) [199,200,203], or o-phenanthroline-CuS04, extracting the complex into an organic solvent (209 MIBK), and determining the metal by atomic absorption. 

Aliphatic amines have been determined by a number of methods. Batley et al. [290] extracted the amines into chloroform as ion-association complexes with chromate, then determined the chromium in the complex colorimetri-cally with diphenylcarbazide. The chromium might also be determined, with fewer steps, by atomic absorption. With the colorimetric method, the limit of detection of a commercial tertiary amine mixture was 15ppb. The sensitivity was extended to 0.2 ppb by extracting into organic solvent the complex formed by the amine and Eosin Yellow. The concentration of the complex was measured fluorometrically. Gas chromatography, with the separations taking place on a modified carbon black column, was used by Di Corcia and Samperi [291] to measure aliphatic amines. 

Over thirty different elements have been determined in medical and biological materials by atomic absorption spectroscopy. The popularity of the technique is due to a number of factors, including sensitivity, selectivity, and ease of sample preparation. With biological fluids, often no preparation at all is required. The techniques employed usually involve simple dilution of the sample with water or with an appropriate reagent to eliminate interference. Alternatively, the element to be determined is separated by solvent extraction. Either an untreated sample, a protein free filtrate, or an ashed sample is extracted. 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

Butylation of methyl tin species before solvent extraction and the use of atomic absorption spectrometry shortens the extraction procedure and reduces detection limits to about O.lng [102],... 

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. 

---