Solid phase extraction environmental analysis

Two examples from the analysis of water samples illustrate how a separation and preconcentration can be accomplished simultaneously. In the gas chromatographic analysis for organophosphorous pesticides in environmental waters, the analytes in a 1000-mL sample may be separated from their aqueous matrix by a solid-phase extraction using 15 mb of ethyl acetate. After the extraction, the analytes are present in the ethyl acetate at a concentration that is 67 times greater than that in... 

Analytical methods for parent chloroacetanilide herbicides in soil typically involve extraction of the soil with solvent, followed by solid-phase extraction (SPE), and analysis by gas chromatography/electron capture detection (GC/ECD) or gas chromatog-raphy/mass spectrometry (GC/MS). Analytical methods for parent chloroacetanilides in water are similarly based on extraction followed by GC with various detection techniques. Many of the water methods, such as the Environmental Protection Agency (EPA) official methods, are multi-residue methods that include other compound classes in addition to chloroacetanilides. While liquid-liquid partitioning was used initially to extract acetanilides from water samples, SPE using... 

In environmental analytical applications where analyte concentrations, e.g. surfactants or their metabolites, are quite low, extraction and concentration steps become essential. Solid phase extraction (SPE) with cartridges, disks or SPME fibres (solid phase micro extraction) because of its good variety of SP materials available has become the method of choice for the analysis of surfactants in water samples in combination with FIA as well as LC—MS analysis. SPE followed by sequential selective elution provides far-reaching pre-separations if eluents with different polarities and their mixtures are applied. The compounds under these conditions are separated in the MS spectrometer by their m/z ratios providing an overview of the ionisable compounds contained in a sample. Identification in the sense it has been mentioned before, however, requires the generation of fragments. 

Table 4.2 summarises a selection of solvent pairs that are sufficiently immiscible to form biphasic mixtures suitable for LLE. Klick used LLE as one step in a method to measure an epoxide degradant of a pharmaceutical [12]. In an application of SEC to environmental analysis, LLE was found to give higher extraction efficiencies than solid-phase extraction (SPE - see below) [29]. 

Solid-phase extractions can reduce solvent consumption in analytical chemistry. For example, a standard procedure approved by the U.S. Environmental Protection Agency for the analysis of pesticides in wastewater requires 200 mL of dichloromethane for the liquid-liquid extraction of 1 L of water. The same analytes can be isolated by solid-phase extraction on C g-silica disks. The pesticides are recovered from the disks by supercritical fluid extraction with C02 that is finally vented into a small volume of hexane. This one kind of analysis can save 10s kg of CH2C12 per year.24... 

High-performance LC determination is also compatible with the extraction of environmental water with an organic solvent such as methylene chloride or ethyl acetate (31,32) and solid-phase extraction (SPE) (33,34). Solid-phase extraction and liquid-liquid extraction (LLE) have been compared with respect to their ability to preconcentrate pesticides prior to HPLC analysis. The reproducibility of the method is better when C,8 cartridges are used than with conventional LLE, but LLE sometimes gives better recoveries, for example, for dimethoate, chlor-pyriphos ethyl, and carbofenothion (35). 

Albanis, T.A. and D.G. Hela (1995). Multi-residue pesticide analysis in environmental water samples using solid-phase extraction discs and gas chromatography with flame thermionic and mass-selective detection. J. of Chromatogr. A, 707 283-292. 

Pichon, V., A.I. Krasnova, and M.C. Hennion. 2004. Development and characterization of an immunoaf-finity solid-phase-extraction sorbent for trace analysis of propanil and related phenylurea herbicides in environmental waters and in beverages. Chromatographia 60 S221-S226. 

J. R. Dean, Solid phase extraction, in Extraction Methods for Environmental Analysis, Wiley, Chichester, West Sussex, England, 1998, pp. 35-61. 

Martinez, D. Cugat, M.J. BorruU, E. CaluU, M. Solid phase extraction coupling to capillary electrophoresis with emphasis on environmental analysis. J. Chromatogr. A 2000, 902, 65-89. 

To further validate the assay for use with environmental samples, water samples spiked with molinate were extracted and analyzed by ELISA and GC. Recovery comparisons were made between ELISA and GC for both liquid-liquid and solid phase extraction methods. Recoveries were greater than 90 for levels as low as lppb for all analysis and extraction method comparisons (23.). This study also described the utility and compatibility between solid phase extraction and ELISA for measuring low concentrations of molinate. As much as 10 acetonitrile/propylene glycol (1 1) or 5 methanol had no effect on the molinate assay. Details of this study were reported by Li et al. (38). 

Sometimes the sample preparation is a difficult problem, especially in clinical and environmental chemistry. General procedures are filtration (perhaps by means of a dedicated membrane which retains compounds selectively), solid phase extraction with disposable cartridges (also with dedicated selectivity), protein precipitation and desalting. A special case is sample preparation for biopolymer analysis. 

Initially, SPE was based on the use of polymeric sorbents, such as XAD resins (polymeric adsorbents), which were packed in small disposable columns for use on drug analysis. The early environmental applications consisted of both XAD resins and bonded-phase sorbents, such as C-18 (McDonald and Bouvier, 1995). These precolumns were used for sample trace enrichment prior to liquid chromatography and were often done on-line, which means at the same time as liquid chromatography. However, these first, steel, on-line precolumns quickly were replaced with an off-line column made of plastic in order to be both inexpensive and disposable. Eventually, the term solid-phase extraction was coined for these low-pressure extraction columns (Zief et al., 1982). Thus, solid-phase extraction is an analogous term to liquid-liquid extraction, and in fact, solid-phase extraction might also be called liquid-solid extraction. However, it is the term solid-phase extraction or the acronym SPE that has become the common name for this procedure. 

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