Acid-base partitioning

A gas liquid chromatographic (GLC) method was described for determining residues of Bayer 73 (2-aminoethanol salt of niclosamide) in fish muscle, aquatic invertebrates, mud, and water by analyzing for 2-chloro-4-nitroaniline, a hydrolysis product of Bayer 73 [83]. Residues were extracted with acetone-formic acid (98 + 2), and partitioned from water samples with chloroform. After sample cleanup by solvent and acid base partitioning, the concentrated extract was hydrolyzed with 2N NaOH and H202 for 10 min at 95°C. The 2-chloro-4-nitroaniline was then partitioned hexane ethyl ether (7 + 3) and determined by electron capture GLC. Average recoveries were 88% for fish, 82% for invertebrates, 82% for mud, and 98% for water at 3 or more fortification levels. 

Urine Adsorption onto XAD-2 resin, elution with acetone followed by clean up using acid-base partitioning and silica gel, formation of penta fluoropropyl derivative. GC/ECD 1 g/kg (ppb) 41 8 Bowman and Rushing 1981... 

PAHs were isolated from the crude extracts by a two-step procedure. The neutral fraction was separated by simple acid-base partitioning and then chromatographed on a silica gel column. The column was first eluted with TO ml of hexane. Subsequent elution with 200 ml of hexane containing 5 dichloromethane gave the PAH fraction. The solvent was carefully evaporated to produce the dry extract. The PAH fraction of SI and S2 were designated as S1-C2 and S2-C2, respectively. 

Low volatile, high molecular weight halogenated compounds can be extracted with hexane or iso-octane and determined by GC-ECD. Methylene chloride may be used for extraction if the analysis is done by GC/MS. Purge and trap efficiency will be poor for such compounds, especially those boiling over 200°C. Soils, sediments, and solid wastes may be extracted with methylene chloride by sonication or soxhlett extraction. Interferences from acidic compounds, such as chlorophenol, may be removed by acid-base partitioning cleanup. The extract is then concentrated and analyzed by GC/MS or exchanged to hexane and analyzed by GC-ECD. 

The hexane extract is shaken with 1 1 H2S04 in a small separatory funnel for 1 min and the bottom H2S04 layer is discarded. Such acid wash may be repeated two or three times. The extract is then repeatedly washed with 20% KOH solution. Contact time must be minimized because KOH could degrade certain chlorinated dioxins and dibenzofurans. If acid-base washing is performed, the sample extract should be washed with 5% NaCl solution each time after acid and base washes, respectively. Acid-base partitioning cleanup may, however, be omitted completely if the sample is expected to be clean. 

Soils, sediments, and solid samples mixed with anhydrous Na2S04 and then methylene chloride sonicated extract cleaned by acid-base partitioning and analyzed as above. 

Many chlorinated compounds and organic acids may interfere in GC-ECD analysis. Some basic and neutral interference can be removed by acid-base partitioning sample cleanup. 

A measured quantity of solid sample mixed with anhydrous Na2S04 the mixture sonicated or Soxhlett extracted with methylene chloride or chloroform solvent extract concentrated cleanup (if required) by acid-base partitioning analyzed as above by GC/MS using an appropriate column. 

Solid matrices mixed with anhydrous Na C/, followed by methylene chloride sonicated extract cleaned by acid-based partitioning and analyzed by GC-NPD, GC-F1D, or GC/MS. 

Taxine can be extracted from yew tissues using a conventional acid/base partition scheme. The following procedure has been used in the author s laboratory ... 

A survey of literature revealed that dinitrophenols (mostly 2,4-DNP) in environmental and biological samples are quantitated following extraction and sample clean-up steps. Acid-base partitioning is generally used for sample clean-up. This clean-up method takes advantage of the fact that DNPs are... 

U.S. Environmental Protection Agency Test Method 3650B, Acid-Base Partition Cleanup, U.S. Government Printing Office, Washington, pp. 1-7, 1996. 

Acid-base partition. This method is used to separate basic and acid compounds. 

Acid/base partition Acid/base partition Solid phase extraction Acid/base partition Acid/base partition Ion exchange Solid phase extraction... 

Acid-base partitioning separates acidic or basic organics from neutral organics (e.g., separates chlorophenoxy herbicides from phenols). 

The concept of acid-base partitioning has been introduced above in Section 15.6.1. This concept can be used as a cleanup technique to separate acidic or basic compounds from each other or from neutral organic compounds. In this... 

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