Concentration by extraction

Ammonium pyrrolidine dithiocarbamate (APDC), for example, is suitable for group extraction in water. It is added as a 2 % aqueous solution to the water sample, which should be set to pH 2 (5 ml to 1 litre of water sample). Repeat extraction with about 13 ml of chloroform each time until 

Add a quantity of a 10 % aqueous diammonium citrate solution sufficient to prevent the precipitation of calcium and magnesium ions, set the pH to 8, treat with 3 ml of APDC solution and extract again with chloroform. One extraction generally suffices. 

Evaporate the chloroform extracts almost to dryness over a water bath, wash over to a porcelain crucible, bring to dryness on a sand bath and incinerate in a muffle furnace at 330 C. Proceed with spectrographic analysis as described under Concentration by trace precipitation . 

In order to make the circle of trace elements detectable by group extraction as wide as possible, F. A. Pohl has described a method in which the 

The extraction of 1 - 3 litres of the water sample is usually sufficient for a spectrographic survey analysis. The water sample must be completely 

---

In typical processes, the gaseous effluent from the second-stage oxidation is cooled and fed to an absorber to isolate the MAA as a 20—40% aqueous solution. The MAA may then be concentrated by extraction into a suitable organic solvent such as butyl acetate, toluene, or dibutyl ketone. Azeotropic dehydration and solvent recovery, followed by fractional distillation, is used to obtain the pure product. Water, solvent, and low boiling by-products are removed in a first-stage column. The column bottoms are then fed to a second column where MAA is taken overhead. Esterification to MMA or other esters is readily achieved using acid catalysis. 

Solvent Recovery. A mixture of methanol and methyl acetate is obtained after saponification. The methyl acetate can be sold as a solvent or converted back into acetic acid and methanol using a cationic-exchange resin such as a cross-linked styrene—sulfonic acid gel (273—276). The methyl acetate and methanol mixture is separated by extractive distillation using water or ethylene glycol (277—281). Water is preferred if the methyl acetate is to be hydroly2ed to acetic acid. The resulting acetic acid solution is concentrated by extraction or a2eotropic distillation. 

This study evaluated the impurity profile of untreated water from a textile plant in Portugal [35]. The organic material was concentrated by extraction from 11 of water into dichloromethane and HPLC-NMR and HPLC-MS experiments were carried out using a reverse-phase separation with an acetonitrile/ D2O gradient elution with H NMR spectroscopic observation at 600 MHz. For the HPLC-NMR studies, the samples were further fractionated into two pools according to their HPLC retention times. The HPLC-NMR studies were carried out in the stop-flow mode and the combination of NMR and MS results yielded the identification or tentative identification of 14 compounds, comprising mainly surfactants, anthraquinone dyes and nonylphenol-related molecules. 

Difficulties have been observed in the preservation of samples for speciation of chromium. Chromium speciation in seawater was determined on board ship shortly after samples had been collected (Abollino et at., 1991). Some samples were frozen, and analysed later in a laboratory. However, significantly lower concentrations of Crvl were observed in these latter samples. Thus, sea-going analytical methods for the determination of Crm and total chromium are of particular importance (Mugo and Orians, 1993). The volatile trifluoroacetyl-acetone derivative of Crm was formed and then concentrated by extraction into toluene. Chromium was determined by means of a gas chromatograph equipped with an electron capture detector. Total chromium was determined as Cr111 after reduction. The detection limits were 0.062 and 0.255 nmol dm 3 total chromium. A useful method was described for sampling natural water in the field, and for the preservation of Crm and Crvl species for subsequent analyses in a laboratory (Cox and McLeod, 1992). Water samples were drawn through small columns packed with activated alumina, which had been prepared previously. Chromium species were retained on the columns. 

To increase the sensitivity of the analysis, it is recommended that a 5 or 10 cm path length cell be used. The detection Hmit using a 10 cm cell is approximately 0.05 pM, with an upper limit of 40 pM without dilution. Use of a long-path liquid waveguide capillary cell (2 m) lowered the detection hmit to 5 nM with a precision of 5% in the 10—100 nM range (Li et al., 2005). Another approach used to decrease the limit of detection is to preconcentrate the NH4+ prior to analysis. In one technique, the indophenol is concentrated by extraction into n-hexanol this method has a precision of 1.9 nM at concentrations <50 nM (Brzezinski, 1987). The indophenol can also be concentrated onto soHd phase extraction (SPE) octade-cylshane (C18) columns (Selmer and Sorensson, 1986), with the final concentration determined as outlined in Brzezinski (1987). 

A thorough analysis of chaotic oscillations for the NH3/O2 reaction over Pt has been performed by Sheintuch and Schmidt (2//). Bifurcation diagrams were presented in great detail, as well as phase plane maps and Fourier spectra. Figure 18 shows a series of oscillation traces obtained for various oxygen concentrations. By extracting a next return map from trace g in Fig. 18, evidence for intermittency could be obtained. 

A further example is the detection of iron in the combustion residue of a textile sample or directly on the fibre material. For example, after adding a few drops of 1 N hydrochloric acid p.a. and 1 N ammonium thiocyanate a red iron complex is formed which can be concentrated by extraction with ether so that the detection limits are very low (more detailed description in Section 8.5.1). 

Partial Resolution of Optical Isomers. Co(admh)(acac)2 was resolved partially on a previously described 230 x 3.9 cm o.d. column of D-(+)-lactose (10). In two separate chromatograms, 130 mg of sample dissolved in 1.5 ml of benzene was placed on the column and eluted with l.-l benzene-hexane. The entire eluted solution was collected in two parts. The first fractions from each chromatogram were combined and evaporated to dryness. The enantiomer in excess was then concentrated by extracting the residue with 1 ml of hexane. 

Partial Resolution and Absolute Configurations. Partial resolution of the Co(admh)n(acac)g n complexes was effected by column chromatography on D-(+)-lactose. Co(admh)(acac)2 was resolved partially at room temperature using a 230-cm column that we have employed previously for partial resolution of metal g-diketonates (10). However, this procedure did not work for the bis- and tris-admh complexes. The bis and tris complexes were resolved partially, with much greater difficulty, by a low-temperature procedure that employed D-(+)-lactose on alumina as the adsorbent, isopentane-ether as the eluent, and temperatures of-95 to-125°C. After chromatography, the eluent was evaporated and the enantiomer in excess was concentrated by extracting the solid with chlorodifluoromethane at -120°C. The values of - er for the Co(admh)n(acac)3 n complexes (Table IV) are very small compared with - er for partially resolved Co(acac)g (17), indicating that resolution was incomplete in all cases. 

Extraction. A completely different approach is that in which the element is removed and concentrated by extraction from the matrix. Large sample-to-extractant ratios can be utilized, thus reducing contamination. Because of the complex nature of petroleum, total recovery on samples containing naturally occurring elements should be confirmed before using an extraction technique. This can be done by comparing the extraction results with those obtained by independent techniques utilizing total decomposition. 

Concentration" Compounds at low concentrations in relatively large volumes can be concentrated by extraction onto a solid phase extraction medium and then eluted m a small volume of a strong eluent. This is typically used for concentrating analytes that are present in only trace amounts, such as drug metabolites in serum samples, or environmental contaminants in seawater. 

Metal Concentration by Extraction Caused by Organic Solvent Overall Aqueous By Proposed Method... 

Pay particular attention to the safety regulations for the use of chloroform. When testing for heavy elements, X-ray fluorescence may also be used for identification. A method which has proved valuable for the detection of Ag, Bi, Cd, Co, Cu, Ni, Pb, Tl and Zn following concentration by extraction is described in DIN 38 06, Part 21, September 1980. 

Direct atomization of the aqueous solution (flame absorption), if necessary with concentration by extraction... 

The fermentation, which is carried out batch-wise at 25 °C, lasts some 200 hours in total. In subsequent washing, the cell mass (mycelium) formed is filtered off on rotating dmm filters, and the filtrate is acidified to pH 2 with sulfuric or phosphoric acid. Penicillin G is concentrated by extraction with solvents such as butanol or amyl acetate. When the acid has been converted to the potassium salt, penicillin G is recovered by filtration and drying as a 99.5% pure product. The mycelium can be used as an animal feedstuff. 

Reliable results usually afford also in urine the complete destruction of the biological matrix. Separation and concentration by extraction or volatilization are necessary at low levels of arsenic and from solutions with interfering substances. Further techniques are required to detect the different valencies or organic arsenics. 

Silicomolybdic acid can be concentrated by extraction with /i-butyl alcohol followed by reduction to molybdenum blue with ascorbic acid. The method is said to be useful for determining silica in aluminum oxide (323). 

Anionic surfactants can be determined at low concentrations by extraction of the ion pair with a cationic fluorescent molecule, such as Rhodamine B or Safranine-T (121-123). This method is entirely analogous to the ion-pair extractions, such as the methylene blue method, discussed in Chapter 12. The fluorescent method has no greater selectivity, but is somewhat more sensitive. Because of fluorescence quenching effects, this approach can be... 

---