Aqueous extraction methods

Adjusting the Analyte s Concentration Analytes present at concentrations too small to give an adequate signal need to be concentrated before analyzing. A side benefit of many of the extraction methods outlined earlier is that they often concentrate the analytes. Volatile organic materials isolated from aqueous samples by a purge and trap, for example, can be concentrated by as much as 1000-fold. 

One patent (64) describes an extraction method to remove both trichloropropane and tetrachloropropyl ether from the dichi orohydrin solution by the use of carbon tetrachloride as a solvent. In this way the by-products are removed from the aqueous phase iato an organic phase from which they can be separated by distillation and disposed of ia a safe and proper manner. 

The method of detecting dimethylterephthalate (DMTP), dibuthyl-phthalate (DBP) and diocthylphthalate (DOP) in aqueous extract is based on their extraction with an organic solvent (hexane) and subsequent concentration using gas-liquid chromatography and an electron-absorbing detector. The detection limit is 0.05 mg/dirf for DMTP and DBP, and 0,01 mg/dm for DOP. 

Succinyl coenzyme A trisodium salt [108347-97-3] M 933.5. If it should be purified further then it should be dissolved in H2O (0.05g/mL) adjusted to pH 1 with 2M H2SO4 and extracted several times with Et20. Excess Et20 is removed from the aqueous layer by bubbling N2 through it and stored frozen at pH 1. When required the pH should be adjusted to 7 with dilute NaOH and used within 2 weeks (samples should be frozen). Succinyl coenzyme A is estimated by the hydroxamic acid method [J Biol Chem 242 3468 1967]. It is more stable in acidic than in neutral aqueous solutions. [Methods Enzymol 128 435 7956.]... 

Analysis of soils and sediments is typically performed with aqueous extraction followed by headspace analysis or the purge-and-trap methods described above. Comparison of these two methods has found them equally suited for on-site analysis of soils (Hewitt et al. 1992). The major limitation of headspace analysis has been incomplete desorption of trichloroethylene from the soil matrix, although this was shown to be alleviated by methanol extraction (Pavlostathis and Mathavan 1992). 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

The second acetamiprid extraction method uses aqueous methanol, and with alkaline methanol to extract acetamiprid and its degradation products which are converted to methyl 6-chloronicotinate (IC-O-Me) through alkaline hydrolysis, oxidation and esterification, prior to column cleanup and GC determination. 

The facilitated ion transfers of some alkaline earth metals have been also studied in the DCE systems by the cyclic voltammetry. These systems perhaps have not been studied by any solvent extraction methods yet. Typical voltammograms in the N15C5 diffusion-control systems are shown in Fig. 6. The aqueous supporting electrolyte was MgCl2 instead of MgS04 in these measurements because BaS04 precipitated. 

Raggi et al. [21] described a spectrophotometric analysis method with ammonium tetrachloropalladate for penicillamine in pharmaceutical formulations. An aqueous solution of penicillamine (298 pg/mL) was treated with 1.5 mL of 20 mM (NH4)2PdCl4 in 1 M HC1. The mixture was diluted to 10 mL, and the absorbance measured at 403 nm after 20 min. The method has a recovery of 98.8%, and was used to determine penicillamine in aqueous extracts of capsules. 

Sastry et al. [41] used a new spectrophotometric method for the estimation of primaquine, using 3-methylbenzothiazolin-2-one hydrazone. An aqueous extract of the sample of powdered tablets (containing 50 pg/mL of primaquine phosphate was mixed with 1 mL each of aqueous 8.5 mM 3-methylbenzothiazolin-2-one hydrazone and 11.84 mM CelV (in 0.72 M sulfuric acid), the mixture was diluted to 10 mL, and the absorbance was measured at 510 nm versus a reagent blank. Beer s law was obeyed for 0.7-12 pg/mL of the drug and for 50 pg, the coefficient of variation was 0.52%i (n = 8). Other antimalarials and pharmaceutical adjuvants did not interfere. 

Smith et al (84) determined hydralazine in tablets. An aqueous extract of the tablets was treated with 2,4-pentanedione, forming 1-(3,5-dimethylpyrazole) phthalazine. The method was applied to stability studies of tablets subjected to elevated temperatures, where tablets could not be analyzed by the USP method. 

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