Comparative Study on Preparation Technology of Evaporation Samples in Pesticide Analysis

Dr. Felix Massat, Benoît Planel*, Antoine Venezia

Laboratoire départemental d'analyses de la Drôme biological laboratory in Valence, France

Introduction

When a highly controlled environment, such as an environmental analysis laboratory, needs to introduce any new instruments or equipment, these new instruments are often rigorously verified to ensure they are equivalent to existing equipment in the laboratory or Better operational performance. This will give you a good idea of ​​any influencing factors in the test method and revalidate the test method if necessary. The recovery of samples (especially very volatile analytes) is the most critical factor in terms of sample concentration and evaporation techniques. In addition to evaluating the operational performance of the Genevac EZ-2 evaporator, the Laboratoire départemental d'analyses de la Drôme (LDA26) laboratory compared the existing two experimental methods in the new equipment evaluation process. This report summarizes the relevant experimental data.

Left: Genevac EZ-2 evaporator

Genevac EZ-2 Performance Benchmark

A pesticide sample (20 mg/l) was added to a mixture of 50 ml of dichloromethane (DCM) and acetone (50:50 by volume of the two substances). An additional drop of pentanol (as solvent) was added to each sample. The sample was evaporated by Genevac EZ-2 (Figure 1) at 35 ° C and concentrated in a drop of pentanol. The experimental procedure uses a special environmental test evaporation method developed by the Tuscan Environmental Protection Agency ^{1 to} selectively evaporate volatile solvents from the analyte to obtain a less volatile solvent component. In a subsequent evaporation experiment, a 1 ml sample dose was made by adding ethyl acetate, and it was injected into a gas chromatograph for analysis using an electron capture detector (GC-ECD). Figure 2 shows the corresponding sample recovery.

Comparative study of Genevac EZ-2 and existing equipment

The Zymark TurboVap Concentration Method and the Simple Fume Hood Air Evaporation Method are two evaporation methods commonly used in the LDA26 laboratory. The EZ-2 preliminary assessment is based on these two conventional experimental methods.

The experimental sample is a volatile environmental analyte. A sample (50 mg/l) was added to a mixture of 50 ml of dichloromethane (DCM) and acetone (volume ratio of the two materials was 50:50). An additional drop of pentanol (as solvent) was added to each sample. Follow the procedure above to evaporate the sample by Genevac EZ-2 or use a Zymark TurboVap concentrator to evaporate the sample and obtain a pentanol drop at 35 °C. In a subsequent evaporation experiment, a 1 ml sample dose was made by adding ethyl acetate and allowed to evaporate to dryness. For samples that have been previously evaporated in Genevac EZ-2, they are again dried in EZ-2 at 35 °C, while samples that have been previously dried in a TurboVap concentrator are required to be in a fume hood. Ventilate and dry again. Water and acetonitrile were then added to the sample and the pH was adjusted to pH 2. Samples were injected into a gradient HPLC system for analysis using a multi-wavelength fluorescence detector (HPLC-Fluor). Figure 3 shows the corresponding sample recovery.

Figure 2 – Multiple analyte recovery rates prepared in Genevac EZ-2

% = recovery SD = standard deviation

Figure 3 – Volatile analyte recovery prepared by two-stage evaporation operation by different methods

Another set of 1 ml samples of ethyl acetate used in the experiments contained different volatile analytes (50 mg/l). An additional drop of pentanol (as solvent) was added to each sample. These samples were placed in Genevac EZ-2 to evaporate at 35 ° C or placed in a fume hood for venting and drying. In a subsequent evaporation test, a 1 ml sample dose was made by adding water and acetonitrile, and its pH was adjusted to pH 2. The sample was injected into the HPLC-Fluor system for analysis. Figure 4 shows the corresponding experimental results.

Figure 4 – Volatile analyte recovery by evaporation in different ways

in conclusion

The new evaporation method using the Genevac EZ-2 vaporizer enables excellent sample recovery, even for highly volatile environmental analytes, yields better sample recovery than previous evaporation methods. The EZ-2 vacuum evaporation method causes the solvent to boil under low temperature conditions to maintain the sample at the boiling point of the solvent. In contrast, when the experiment was carried out using other methods, the sample was always at a high temperature of 35 ° C during the evaporation process. This higher operating temperature increases the rate of evaporation of solvent and volatile components in the sample. By strictly controlling the evaporation conditions in the EZ-2 unit, the solvent can be preferentially removed and the analyte and pentanol are left behind.

references

1. Marsico, Anna Maria, 2006. Improving Analysis of Pesticides – a new method development protocol to increase recovery of volatile compounds. First published in Lab Asia (August 2006 issue), please visit http://www. genevac.org/en/ArticleDetail.asp?S=6&V=1&ProductDownload=81  

About the Author

Dr. Felix Massat is the head of the laboratory; Benoît Planel is a chemist; Antoine Venezia is the head of the R&D department; all three work at the Laboratoire départemental d'analyses de la Drôme biological laboratory, Valence BP118, France ,26904F-91

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Comparative study on evaporation sample preparation techniques in pesticide analysis (Chinese) Comparative Study on Evaporation Sample Preparation Techniques in Pesticide Analysis (English)