Application of SDE to the Analysis of Non Fatty Environmental Samples

Table 2 summarizes relevant data related to some reported SDE methods for the analysis of less volatile organic pollutants in non-fatty environmental samples. Most of the reported SDE applications referred to the analysis of OCPs and toxic aromatic compounds, e.g. PCBs, polychlorinated naphthalenes (PCNs), or polynuclear aromatic hydrocarbons (PNAs), in soils and sediments. Contrary to what might be expected from the high complexity of these samples, most of the methods did not include any further pre-treatment of the matrix but blending with the selected volume of water. Only a few procedures involving drastic treatments (e.g. blending of the sample with H2SO4 and K2Cr2O7) during the SDE to guarantee the destruction of the soil or sediment components in which the target compounds could be entrapped, can be found in the literature.

The efficiency (or need) of such a drastic treatment is difficult to evaluate from the data published. In general, high (quantitative) recoveries have been reported for freshly spiked analytes (globally in the range 78-102% for PCBs and OCPs at the 20-90 |gg~i level) with all the procedures (Table 2).

However, the efficiency of the proposed SDE methods for the extraction of endogenous pollutants from weathered samples has been scarcely evaluated. In these studies, Seidel et al. (1993) and Cooke et al. (1980) found concentrations very close or below the limit of detection have usually been reported for the endogenous contaminants, but the lack of comparison of the SDE results with those obtained by standard or more exhaustive methods, i.e. Soxhlet extraction, do not allow any discussion about the methods used.

Dunnivant et al. in 1988 reported recoveries ranging from 47 to 99% for SDE of certified sediments with PCBs at the 2.34-24.6 |igg~i. However, as quoted above, this SDE method involved a digestion of the sample under drastic conditions.

In a closely related study, Nash et al. compared the efficiency of steam distillation with subsequent organic solvent extraction to that of Soxhlet extraction for the analysis of pesticides in soil, plant tissues and air (polyurethane foam filters). Both procedures provided similar recoveries for the spiked samples (in the ranges 80-90%, 80-90% and 90-100%, respectively). However, the SDE levels determined for weathered soils blended with water were 40-50% lower than the concentrations found by the Soxhlet procedure. The study also showed that the efficiency

Table 2 SDE methods for the analysis of less volatile organic pollutants in non-fatty environmental samples (symbols as in Table 1)

Matrix

Compound Spiking level Pre-treatment

Solvent

Extraction Post-treatment Recovery RSD time (h) (%) (%)

Ref.

Sediment

Weathered sediment

Sediment Sediment Sediment

Certif. Sediment Sediment

Soil

Arochlor 1016 50

Chlorinated 100-1000 benzenes

Chlorinated 10-100 benzenes

Chlorinated 1-10 benzenes

PCBs PCBs

20.0

Weathered soil Endogenous OCP

Particulate

Fruits, vegetables Fruits, vegetables

Sediments

(homologues)

PCBs

Chiral PCBs

Sewage sludge Nonylphenol 100e polyethoxylates

Toothpaste

Fatty alcohol sulfates

Blended with 2.5 L water lsooct/tola(15) 1

Blended with 0.25 L water n-Hexane (10) 3

Blended with 0.25 L water n-Hexane (10) 3

Blended with 0.25 L water n-Hexane (10) 3

200 mL H2S04 + K2Cr207 200 mL H2S04 + K2Cr207

100 g soil + 20 mL water + 10 mL ethanol + ultrasonic, 1 min

100 g soil + 20 mL water + 10 mL ethanol + ultrasonic, 1 min

5-10 g sample blended with 0.25 L water 5-10 g sample blended with 0.25 L water

5 g sample blended with 4 g Cu + 50 mL water

1 g sample blended with 0.1 L water

30 g sample + 50 mL 4M H2S04 + LLE (diethyl ether, 10 mL) + concentrĂ¢t.

Petrolbenzine (?) 1

Petrolbenzine (?) 1

Cyclohexane (1 -2) 3

Ethyl acetate (2) 3

Elimination S 78 Concentration

Elimination S 76-91

Eliminations 71-88

Elimination S 66-89

Alumina Alumina

47-99 102

Basic alumina 85-116" ?

Derivatization

Veith et ai (1977) Cooke etat. (1979)

Onuska et ai (1985)

Dunnivant et ai. (1988) Seidel et ai (1993)

Townsend et ai. (1989) Hemmerling et ai (1991)

Glausch et al. (1996) Lee et al. (1997) Meissner et al. (1999)

alsooctane/toluene.

''Replace hexane layer after 1, 2, 4 and 8 h intervals. cRange for different homologues.

"Mass balance calculations for the whole SDE system by comparison with the initial amount. "Total concentration for all NPraEO (n = 1-17). fBy comparison with SFE, except for NP1EO.

of the SDE depends on the soil type and, in agreement with that mentioned for aqueous samples, on the volatility of the selected compounds. The less volatile the compound, the lower the recovery: SDE recoveries for DDT were only 21-60% of those found by Soxhlet extraction.

Onuska and Terry observed a similar trend when comparing the SDE and the Soxhlet efficiencies for the extraction of spiked chlorinated benzenes from a sediment. The concentrations found using SDE were 14-36% lower than those using the Soxhlet method, except for pentachlorobenzene and 1,3-dich-lorobenzene, which were not determined by the latter procedure. The authors also reported a decrease in the SDE recoveries of the target compounds as the investigated concentration level decreased (Table 2). The recoveries of the studied chlorinated benzenes decreased from 76-91% to 66-89% as the spiking level decreases from 100-1000 to 1-10

In a recent study, Meissner et al. used SDE for the determination of fatty alcohol sulfates in cosmetics (toothpaste) by combining this technique with a hydrolysis treatment. However, the application of SDE to the analysis of nonylphenol polyethoxylates in sewage sludge by Lee et al. failed when compared with the more efficient supercritical fluid extraction technique.

In general, the published SDE methods for the analysis of non-fatty environmental samples involve longer extraction times (1-8 h) than those reported for aqueous samples (1-1.3 h). In addition, and contrary to that proposed by the theoretical model of Rijks et al., the recoveries of less volatile compounds from non-fatty complex samples have been found to be independent of the vapour flow rates. However, it is important to note that in this study by Seidel ethanol was added to the water flask to improve the OCP recoveries, and that the possible effect of a co-distillation solvent was not included in the theoretical model.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment