Single extraction ammonium acetate

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. 

There are two aspects to the use of single extractants. Firstly they are used for the prediction of plant availability, plant uptake or plant growth in an agricultural context. Selective single extractants for most essential nutrient trace elements have been identified and validated for these purposes for different crops and soil types by field experiments relating plant, uptake, growth or health over several years. Of these, the most successful and widely used are EDTA, acetic acid and ammonium acetate. Similar validated extractants are also available for a few toxic elements such as molybdenum (to animals) or nickel at excess soil contents that can occur as a result of natural, geological, soil parent material contents. 

The diversity and complexity of the available approaches has identified the major difficulties associated with producing suitable guidelines that would allow comparisons between different laboratories and different countries in assessing metal mobility in the soil environment. This led to the development of single and sequential extraction procedures by the Standards, Materials and Testing (SM T - formerly the (European) Community Bureau of Reference (BCR) Programme of the European Union (1987)). Single extractants evaluated included 0.05 moll-1 EDTA, 0.43 moll-1 acetic acid, and 1 moll-1 ammonium acetate at pH 7. 

Take a look at the results of this study in Table 5.9 below. As a result of these findings, the use of ammonium acetate was excluded as a suitable single extraction method. Why do you think this was ... 

Several tests were run to determine the eflBciency and precision of extraction of metal complexes with sodium diethyldithiocarbamate and methyl isobutyl ketone by the following procedure. A single liter solution was prepared to contain 0.25 p.p.m. of the following ferric iron, copper, zinc, cadmium, and lead in 1% hydrochloric acid (V/V). The solution was split into four 250-ml. portions. The concentration of each metal was determined in the normal manner prescribed for aqueous solutions on one portion. The remaining three portions were adjusted to pH 2.5 with an ammonium acetate-acetic acid buffer solution and transferred to 500-ml. separatory funnels. Twenty ml. of a 5% sodium diethyldithiocarbamate solution was added to each sample and shaken. Each solution was then extracted with two 20-ml. portions of methyl isobutyl ketone. The extracts were combined for each sample and diluted to 50 ml. with methyl alcohol. The absorbance of each metal was determined in the three 50-ml. organic solutions. 

The project was started in 1987 by a consultation of Emopean experts examining the possibility of harmonizing single and/or sequential extraction schemes for soil and sediment analysis [60]. This inquiry was followed by the design of single extraction schemes (EDTA, acetic acid and ammonium acetate) and a sequential extraction protocol which were proposed to a group of ca. 30 laboratories for possible harmonization in 1989 [193]. Interlaboratory studies (two on soils and two on sediment) were carried out between 1989 and 1993 [194-196] and were followed by certification campaigns conducted between 1994 and 1996 [197-199]. 

A test of the stability of the extractable contents of a single soil was carried out for EDTA, acetic acid, ammonium acetate and calcium chloride extracts. With the exception of chromium, the EDTA extractable contents were shown to be stable over 3 year intervals within about 10% for the elements Cd, Cu, Fe, Mn, Ni, Pb and Zn [193]. For acetic acid extracts, one-year changes for Cr, Fe, Mn and Zn were poorer than for EDTA, but for Cd, Cu, Ni and Pb the extracts were reasonably stable. For ammonium acetate and calcium chloride extracts, however, the results, apart from Cd and Ni in ammonium acetate, were useless. These failures in ammonium acetate and calcium chloride were probably related to the fact that the solution concentrations measured were too low for reliable determination by the FAAS and ICP-AES methods used. 

Since both the temperature of extraction and the vigour of the mechanical shaking could be expected to affect the amount of metal extracted, limits for both of these parameters were prescribed in the detailed protocol for extraction and analysis issued to the participating laboratories along with the solid sample [193]. As a check on each laboratory s calibration, reference solutions containing the trace metals of concern (Cd, Cr, Cu, Ni, Pb and Zn) were prepared. Three types of single extractant were used EDTA (0.05 mol L" ), acetic acid (0.43 mol L ) and ammonium acetate (1 mol L ). 

Seventeen hydroperoxy polyunsaturated fatty acids (e.g., 5-(5)-hydroperoxyeico-satetraenoic acid, 5-(S)-hydroperoxyeicosatetraenoic acid) were extracted from brain tissue and derivatized with acetic anhydride [1058]. The resulting solution was injected onto a Cjg column X = 235 nm) and eluted with a 15/8/2 acetonitrile/ water (0.1 M ammonium formate)/0.1 M formic acid mobile phase. The internal standard (12-hydroxyoctadecadienoic acid-rfg) was made up at the 600pmol level and stored in a solution containing BHT to prevent its oxidation. Thermospray MS was also used as a detector and was most sensitive when a 15/6/4 acetonitrile/0.1 M acetic acid/O.lM ammonium acetate mobile phase was used. In this example, detection limits of 0.1-0.5 pmol were obtained by single ion monitoring (SIM). 

The SPE assay was further modified by Cone et al. by combining the assay for heroin and its metabolites with cocaine and its metabolites into a single procedure. Hair wash and incubation fractions were added to a conditioned Clean Screen SPE cartridge. The cartridges were washed with deionized water, pH 4 acetate buffer, and acetonitrile. The cartridges were aspirated to dryness and the analytes were eluted with a solution of methylene chloride 2-propanol (80 20) with 2% ammonium hydroxide. The solvent extract was evaporated and derivatized. 

---