Substitution of dichloromethane in the analysis of pesticide residue
In analysis of pesticide resisdues cyclohexane, ethylacetate, tert. butyl methyl ether, diethylether and light petroleum are tried as alternatives. Conclusively cyclohexane, light petroleum or tert. butyl methyl ether is recommended in the article . Of these three recommended substances, light petroleum and tert. butyl methyl ether is included in the database of hazardous substances according to Subsports screening criteria (SDSC).
There is limited evidence of carconogenic effect of dichloromethane (R40). Dichloromethane is included in the database of hazardous substances according to Subsports screening criteria (SDSC).
The alternative, cyclohexane, is highly flammable, irritating to skin, may cause lung damage if swallowed and vapours may cause drowsiness or dizziness.
Light petroleum ( CAS No. 64741-84-0) and tert. butyl methyl ether (CAS No. 1634-04-4) are also recommended as alternatives in the article. They are both hazardous according to Subsports screening criteria (SDSC). Light petroleum may cause cancer and tert. butyl methyl is an endocrine disruptor ether.
In pesticide multiresidue analysis the most common applied method (S19) involves liquid/liquid partition with dichloromethane. Dichloromethane is used because of its ability to transfer both non-polar and polar analytes from the aqueous into the organic phase. This document reports the investigation of substituting dichloromethane by several non-chlorinated solvents (ethyl acetate, tert. butyl methyl ether, diethyl ether, light petroleum, cyclohexane/ethyl acetate (1:1), cyclohexane). S19 is used as a reference method. In S19 the following solvents are used in different parts of the analysis: acetone, water, dichloromethane, ethylacetate and cyclohexane/ethylacetate (1:1). With the aim of reducing the amount of chlorinated solvent in waste water a substitute for dichloromethane was investigated while the rest of the analysis was kept the same.
Replacing the extraction procedure with so-called “on-line” methods was also tried out in order to omit the liquid/liquid partition with dichloromethane. One methodology consists of an application of ethyl acetate for the extraction step in combination with sodium sulphate as the drying agent. In another “on-line” method an extraction with a hexane/acetone mixture (8:2) directly includes a transfer of pesticides into the non-polar organic phase.
The results show comparable high recoveries for each methodical approach. Only the ethyl acetate yields a lower recovery both in the liquid/liquid partition and in the “on-line” method. Cyclohexane showed to be a suitable substitute because it is used as a solvent in the following procedures.
The repeatability is also an important parameter of an analytical method. Especially the “on-line” methods lead to comparable results. The other variants show higher relative standard deviations up to 27% for light petroleum.
The final conclusion of this study is “it is recommended to replace this chlorinated solvent with cyclohexane, light petroleum or tertiary butyl methyl ether. For special applications, “on-line” methods are possible alternatives”.
This article does not contain any CAS- numbers. Light petroleum can have many CAS -numbers, but the one listed in this SUBSPORT description fits the boiling point of the described solvent.
The risk of flammability has to be taken into account in organizing the working procedures.
Only three of the tested alternatives were recommended. Two of these recommended alternatives – light petroleum and tert. butyl methyl ether – are included in the database of hazardous substances according to Subsports screening criteria (SDSC). Of the recommended alternatives only cyclohexane is not included in SDSC. This substance is on several others lists of not-wanted substances, and the risks have to be taken into account in organizing the working procedures.
A. Koinecke, R. Kreuzig, M. Bahadir, J. Siebers, H.G.Nolting :Investigation on the substitution of dichloromethane in pesticide residue analysis of plant materials. Fresenius J Anal Chem (1994) 349:301-305Further languages available
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A. Koinecke, R. Kreuzig, M. Bahadir, J. Siebers, H.G.Nolting :Investigation on the substitution of dichloromethane in pesticide residue analysis of plant materials. Fresenius J Anal Chem (1994) 349:301-305Type of publication and availability
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