1. % € $ Multiresidue analysis of 25 pesticide residues in wines
comparative study of SPE and QuEChERS methods
Maja Pelajić Plant Protection Institute, Croatian Centre for Agriculture, Food and Rural Affairs Dubravka Vitali Čepo Faculty of Pharmacy and Biochemistry, University of Zagreb
Abstract
Pesticide residues monitoring in wines is of great importance due to a large number of active substances that are often used to protect grape vine. Although the process of vinification involves many different technologies that alter the concentration of pesticide residues in different ways, as a rule, the concentration of residues decreases during wine making process. Consequently, methods to detect and quantify pesticide residues in wine must be very sensitive as well as selective [1]. Due to the complexity of the wine matrix, sample preparation is the key step in the analytical process of pesticide determination. Traditional procedures are time-consuming, labour-intensive, complicated and expensive. It is also quite common occurrence that many physically and chemically different compound have to be determined rather than only one analyte or single class of compound [2]. A number of techniques have been employed for the extraction and purification of pesticides from food product. Probably the most popular extraction procedure is standard solid-phase extraction (SPE). Recently, the QuEChERS (Quick, easy, cheap, effective, rugged and safe) method has been developed for the multiresidues analysis of pesticides from different food matrices with high water content. This method is particularly popular due to its simplicity, low cost, amenability to high throughput and relatively high efficiency results [3]. In this work, 25 pesticides are chosen for residues analysis in wine. Pesticides are analyzed with gas chromatography-mass spectrometry (GC-MS). Analytical procedure involved two extraction procedures: SPE and QuEChERS. Optimization of extraction procedure has been applied on both methods. Results for SPE and QuEChERS have been compared considering theirs analytical recoveries. Based on the results, it is shown which extraction procedure is method of choice for the analysis of pesticides residues in wine.
Introduction
GC or LC techniques sample preparation method for analysis of broad number of analytes.
Key points
Cartridges (stationary phase)
Polarity
Elution solvent
Solid
Phase
Extraction
Quick
Easy
Cheap
Effective
Rugged
Safe
Sample preparation method for analysis of multiple pesticide residues in food via GC or LC techniques.
Key points
Salts (NaCl, MgSO4, Na acetate & citrate)
Agitating, shaking, centrifuging
SPE
QuEChERS
Sample dilution (optional) | 10 mL wine with 10 mL water
Cartridges conditioned | Oasis HLB with 3 mL acetonitrile & 3 mL water
Loading the sample | Analyte retained on sorbent
Washing cartidges (optional) | Methanol:water, 50:50 v:v (antocyanins)
Elution of the fraction | 2 mL n-hexane & 8 mL acetonitrile
Original QuEChERS | Proposed optimization
10 g sample & 10 mL acetonitrile | 10 mL wine & 10 mL acetonitrile
Extraction | 4 g MgSO4 & 1.5 g NaCl
6 g MgSO4 | 3 g Na citrate & 2 g Na acetate
1.5 g Na acetate | g disodium citrate sesquihydrate
Shaking 1 min & centrifuge 5 min | Shaking 10 min & centrifuge 15 min
Aliquote 8 mL & cleaning | Aliquote 8 mL & cleaning %
0.4 g PSA | 0.2 g PSA
1.2 g MgSO4 | 1 g MgSO4
Shaking 1 min & centrifuge 5 min | Shaking 5 min & centrifuge 15 min
Comparison
Recovery values of 25 target pesticides in wine on the left graph
Satisfactory recovery interval % (extended interval 60 – 140 %)
SPE – satisfactory recoveries for most pesticides
Original QuEChERS – failed to produce satisfactory recoveries
Optimized QuEChERS (proposed) – satisfactory recoveries for most pesticides
Time of sample preparation for SPE and QuEChERS is about the same. € $
Due to relatively high price of sorbens used in SPE, QuEChERS methods, both original and optimized, are significantly less expensive.
Conclusion
At the present time, it seems that original QuEChERS method is not applicable for pesticide determination in wine, at last using GC-MS technique. It is possible to optimize QuEChERS (for example by applying procedure described here) to produce satisfactory recoveries for selected pesticides in wine. This optimization procedure however, is in contradiction with the spirit of the QuEChERS method that is supposed to be Quick and Easy. Moreover, optimization could lead to additional expanses in terms of total laboratory spending for chemicals. Regardless of the optimization process, it seems that optimized QuEChERS will require more preparation time. Compared to SPE QuEChERS downsides could be traced to inefficient extraction of target pesticides from aqueous to organic phase, that is salts used in original QuEChERS do not have ionic-strength sufficient for this transition to occur. It could be argued that benefits in SPE method (defined as better recoveries compared to QuEChERS) are due to differences in nature of extraction of pesticides; SPE extraction is performed in solid phase where pesticides are bonded to sorbens and afterwords eluted with appropriate solvent. If this holds true, there is a question of intrisic limitation of QuEChERS in pesticide extraction from wine. This should be investigated further.
Need for optimization!
[1] A. Economou, H. Botitsi, S. Antoniou, D. Tsipi, J. Chromatogr. A 1216 (2009)
[2] A. Wilkowska, M. Biziuk, Food Chem. 125 (2011)
[3] S. N. Sinha, K. Vasudev, M. V. Vardhana Rao, Food Chem. 132 (2012)
Literature
21st International symposium on separation sciences June 30th - July 3rd 2015 Ljubljana Slovenia