Observations concerning… - EURL | Residues of Pesticides

Observations concerning…
a compound
EU Reference Laboratory for Pesticides Requiring Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
EURL@cvuas.bwl.de
a matrix a method other
Use of Analyte Protectants in GC-Analysis
a way to improve peak shape
and reduce decomposition of susceptible compounds
Reported by: EURL-SRM
Version 1 (last update: 22.04.2013)
Brief description of problem/observation/solution:
The GC-analysis of various pesticides is quite problematic due to unwanted tailing and decomposition
phenomena. Both phenomena are related to active sites on the surface of the
GC-system and become more pronounced the more contaminated the GC-system becomes.
Replacing the liner and cutting the first part of the column are only temporary measures as
new non-volatile components from the injected extracts are deposited forming new active
sites. Analyte protectants (APs) help to reduce analyte tailing and decomposition within the
GC-Inlet by masking these active sites. This effect is also called “matrix-induced signal enhancement”.
Most effective as APs are compounds entailing multiple hydroxyl-groups with
which they can effectively interact with the active sites via hydrogen bonds. To be effective
APs have to be added to solutions (e.g. extracts, standard solutions) at concentration by far
exceeding those of the analytes to be protected. In many cases the protective effect exhibited
by APs is stronger than that of matrix components. With this in mind APs are added to both
calibration solutions in solvent and sample extracts to equalize the protective potential, thus
obviating the need for matrix-matched calibrations. APs are often employed as a mixture of
compounds each covering a different volatility range.
Fig 1: Typical APs:
H O
H O
Ethyl glycerol
O H
Sorbitol
O H
O H
O H
O
O H
O H
O H
O
H O
Shikimic acid
O H
O H
O
O H
( E )
O
O H
O H
O H
d - Gluconolactone
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Fig 2: The AP-principle:
„Degree „Degree of of analyte analyte protection”
protection”
Analyte Protectants- Principle
Raw Extract
PSA
cleanup
Cleaned up
Extract
Standard in Pure Solvent
Cleaned-up Extract + AP
Addition of
„Analyte
Protectants“
(AP)
EU Reference Laboratory for Pesticides Requiring Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
EURL@cvuas.bwl.de
Standard
+ AP
APs reduce analyte
interactions with active
sites and thus errors
related to matrix-induced
peak enhancement
phenomena
Figure 3: Equalization of matrix effects between a standard in blank extract and a standard
in neat solvent by adding APs to both
Absolute Error [%]
100
90
80
70
60
50
40
30
20
10
0
Dichlorvos
Dichlobenil
Acephate
o-Phenylphenol
Phenmedipham
Carbofuran
HCH, gamma-
Chlorothalonil
Errors due to Matrix Effects
with and without Analyte Protectants
Vinclozolin
Parathion-m
Carbaryl
Methiocarb
Diclofluanid
Parathion-e
Chlozolinate
Tolyfluanid
Against Solvent w/o APs
Against solvent with AP
Procymidone
Captan
Folpet
Flubenzimine
Ditalimfos
Bupirimat
Binapacryl
Trifloxystrobin
Tetramethrin1
Dicofol
Acrinathrin
Bitertanol
Iprodione
Chinomethionat
TPP
MEAN ALL
Page 2- 3 -

Copies of slides illustrating the AP-principle
„Matrix-Induced Peak Enhancement Effect“
Active Sites (on Surface of GC-Liner & Column )
(Siloxanes & deposited non-volatile matrix-co-extractives)
Analytes (interact with Active Sites)
• Unwanted Retention/Tailing
• Quasi-catalysed degradation (susceptible compounds)
Matrix-Components (in Excess)
• Bloc active sites and protect analytes
Analyte: Atrazine ; Matrix: Strawberry
30000
25000
20000
15000
10000
5000
RT= 8,80 min
WITH Matrix co-extractives
(Strawberry-Extract)
RT= 8,92 min
EU Reference Laboratory for Pesticides Requiring Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
EURL@cvuas.bwl.de
GC-Liner
GC-Capillary
WITHOUT Matrix co-extractives
(in pure solvent)
e.g. Calibration standard
Stronger Tailing
Apex-Shift towards longer RTs!
0
8.70 8.75 8.80 8.85 8.90 8.95 9.00 9.05 9.10 9.15 9.20 9.25 9.30 9.35 9.40 9.45
Ratios:
• Peak-Areas: ~ 1,5:1
Matrix-Induced Peak Enhancement
• Peak-Heights: ~ 4:1
OVERESTIMATION OF RESULTS!!
• Peak-Width (at half height): ~ 1:3
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Instructions for the production and use of an AP-mixture:
a) Prepare the solvent:
Solvent A
Acetonitril content
[%-Vol.]
b) Prepare AP stock solutions (store at 4°C):
Sorbitol (CAS Number: 50-70-4)
Sorbitol
[mg]
EU Reference Laboratory for Pesticides Requiring Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
EURL@cvuas.bwl.de
Water content
[%-Vol.]
60 40
Solvent A
[mL]
Concentration of stock solution
[mg/mL]
500 10 50
D-(-)Gluconic acid-δ-lactone (CAS Number: 90-80-2)
D-(-)Gluconic acid-δ-lactone Solvent A Concentration of stock solution
[mg]
[mL]
[mg/mL]
500 10 50
Shikimic acid (CAS Number: 138-59-0)
Shikimic acid
Solvent A Concentration of stock solution
[mg]
[mL]
[mg/mL]
500 10 50
3-Ethoxy-1,2-propanediol (CAS Number: 1874-62-0)
Use pure substance without dilution.
c) Preparation of AP-Mixture (use volumetric flask)
1) Weigh 2 g of 3-Ethoxy-1,2-propanediol in a 10 mL volumetric flask
2) Add 2 mL D-(-) Gluconic acid-δ-lactone stock solution
3) Add 1 mL Sorbitol stock solution
4) Add 1 mL Shikimic acid stock solution
5) Fill the volumetric flask up to 10 mL with solvent A
d) Spike extracts or standard solutions with AP-mixture
Use 30 µL AP-Mix per mL of sample extract or solvent-based calibration solution (30 µL/mL).
Note: Different GC-Systems may require different amounts of APs.
Page 4- 5 -

AP-Related Publications:
Papers:
1. M. Anastassiades, K. Maštovská, and S.J. Lehotay J. Chromatogr. A, 1015 (2003) 163-184
2. K. Maštovska, S.J. Lehotay and M. Anastassiades, Anal Chem 77 (2005) 8129
Posters:
1. M. Anastassiades, S. Lehotay, 'Reduction of Analyte Degradation and Peak Tailing During GC Injection
by Addition of Protecting Agents'
4 th European Pesticide Residue Workshop in Rome/Italy, Awarded as best Poster
2. M. Anastassiades, E. Scherbaum, B. Tasdelen: „Investigations on the use of analyte protectants for
multiresidue GC analysis‘
6th European Pesticide Residue Workshop in Corfu/Greece
EU Reference Laboratory for Pesticides Requiring Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
EURL@cvuas.bwl.de
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