Solvent extraction for analytical separation

Extraction chromatographic materials for analytical separations have been commercialized by Eichrom Technologies, Inc. (Darien, IL). These typically use extractants and solvents known in the field of liquid/liquid extraction for radiochemical separations. Some of the extractants and solvents used are shown in Scheme 9.1. 

Although PPE is the most efficient and inexpensive extraction technique, it is also the most nonspecific extraction procedure which is known to be susceptible to matrix effect for LC-MS/MS assay. In contrast, LLE provides a much cleaner extract. LLE, also known as solvent extraction and partitioning, separates analytes based on their relative solubility in two different immiscible solvents, usually water and an organic solvent. The most commonly used solvents for LLE are ethyl acetate (EtOAc), methyl ferf-butyl-ether (MtBE), methylene chloride (CH2C12), and hexane or the combination of the above solvents. In order to manipulate the polarity of the analytes, often a volatile acid or base such as FA or NH4OH respectively at 5-10 %... 

All of the sample preparation techniques that have been discussed may be used with solvent extraction and other separation procedures to concentrate the analyte and separate it from the matrix. Where such procedures are applicable they will be discussed together with the methods for determining the individual elements. 

Can FIA provide a solution to the automation of precipitation-dissolution and revitalize its function in modem analytical chemistiy The answer to this question came quite late, well after the application of FI techniques to solvent extraction and column separations. The reason for this delay obviously comes from the difficulties in on-line continuous manipulation of a heterogeneous system which could potentially create serious blockage problems in a standard FIA system. However, recent research efforts in this direction have been quite rewarding, and from the achievements described in this chapter the reader will see that the major difficulties in the automation of precipitation and even coprecipitation processes using FI techniques have been overcome. 

Method development for in-polymer additive analysis in the conventional sequence of sample collection, sample preparation, extraction (polymer-analyte separation), chromatography (analyte separation), spectroscopy or spectrometry (analyte identification) and data processing requires careful planning to minimise handling, starting with the initial solvent choice. Typically, a strategy for HPLC... 

Another line of analytical use is exemplified by the properties of l-(2-thiazolylazoi-2-naphthol (305), whose complexes with metals may be used for their spectrophotometric and titrimetric determination, as wel] as for their separation by solvent extraction (564, 568, 953-957, 1040). 

The importance of minimizing interferents is emphasized. Commonly used methods for separating interferents from analytes, such as distillation, masking, and solvent extraction, are gathered together in a single chapter. 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

To the acidic distillate in the 125-mL separatory funnel, add 5 mL of 50% sodium hydroxide and 15 mL of dichloromethane. Cap the separatory funnel tightly, and allow its contents to cool for 30 min. Heat created by the addition of caustic to the acidic distillate will cause some of the dichloromethane to volatilize, creating pressure in the funnel therefore, the cap must be secured tightly to the funnel. Escaping solvent will result in loss of analytes. Shake the funnel for 5 min on a mechanical shaker. Allow 15 min for phase separation after shaking the funnel. Drain the lower dichloromethane layer into a second 125-mL separatory funnel. Extract the aqueous layer a second time with 15 mL of dichloromethane. Following shaking of the funnel and phase separation, combine both dichloromethane layers in the same 125-mL separatory funnel. 

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