About this Testing
The current study protocol has been designed to support routine analytical laboratories testing pesticide residues in agricultural commodities. The PT will be used to assess the various matrices represented in the AOAC food composition triangle
(Figure 1) over the course of five years. For the 2018/2019 financial year PTs will focus on pesticides in fruit, a high carbohydrate, low protein and fat matrix. These are Class A commodities, primarily of plant origin
(Figure 2). The matrices selected for this year are oranges, apples and apricots.
Specific attention has been paid to tailoring the scheme to current export limits as well as maximum residue levels for the South African market. The target pesticide and commodities were selected to match the growth season within South Africa. Pesticides selected for analysis in this PT represents various chemical classes associated with the specific commodity selected. Thereby accommodating the routine analysis performed by the majority of laboratories at the time the proficiency test material is circulated.
Proficiency testing program scheme Provider
Private Bag X34
Dr Laura Quinn
Organic Analysis Section
Phone + 27 12 841 3359
Participation Fees and Charges
The cost of participation in one round of the PT scheme is R 6000.00 (0% VAT, please note that we are not a VAT registered company). This fee includes two test samples and a blank sample of 50 g each. Two participants may submit a result per laboratory using the sample provided. For more than two participants per laboratory an additional fee will be levied and additional material supplied. A discount will be offered for laboratories participating in all four of the PT rounds, please refer to Table 1. After conclusion of the PT round, a report will be issued. Upon registration for participation an official quotation will be provided. Please find registration form attached as an addendum to this document. Transport costs are not included in these fees please refer to the section “Test sample transport” below.
Table 1: Summary of participation fees
All three rounds
R5 000.00 (R15 000 in total)
Reports provided to participants
A report will be issued to each participant detailing their performance in the PT. The report will contain the following information: description of the material used and how it was prepared; verification of target values, a summary of participating laboratories analytical techniques and data evaluation. The PT value for the studies will be determined using participant consensus or a reference value issued by the NMISA depending on the number of participating laboratories. The NMISA reference value will be calculated using gravimetrically spiked values. A report detailing a participant's z-score will be issued within one week and a full PT report will be issued to each participating laboratory within one month of the submission deadline.
The participant data will be processed according to ISO 13528:2005 (Statistical methods for use in proficiency testing by interlaboratory comparisons). A z-score will be used to determine the individual laboratories performance based on the following equation:
The target standard deviation used to calculate the z-score will be based on the Horwitz performance model, where the maximum measurement result variation expected between laboratories is 22%.
The agricultural commodities and pesticide residues selected for this proficiency testing scheme have been selected based on routinely tested seasonal commodities and their regulated pesticide residue limits respectively. Concentration levels range from below the regulated export limits to above the maximum residue limit for South Africa.
The test samples will consist of a homogenised raw fruit sludge that has been spiked with a known concentration of selected pesticides from the pesticide list described in Table 2. For each round a participant will be provided with 50 g of test sample. A portion of the un-spiked commodity will also be provided to be used as a blank control.
Table 2: List of possible matrix specific pesticides included within the 2018/2019 proficiency testing scheme.
Test sample transport
Samples will be packaged and transported in a manner to minimise deterioration of the sample in transit. Transport costs are calculated depending on the location of the participating laboratory and are therefore not included in the PT cost price. Upon registration, a quotation will be issued including transport costs. Local laboratories may collect the sample directly from the NMISA premises. For international laboratories, please note that any import or quarantine permits remains the responsibility of the participating laboratory, and must be submitted to the NMISA prior to the shipment date. Participants are accountable for all customs and import duties.
All PT material shall be delivered and collected at the participant’s own risk. The NMISA will not take responsibility for samples damaged during transport, although all due care will be exercised during packing to prevent this from occurring.
Methods of Analysis
Participants are requested to use the methods/ procedures used during routine sample analysis.
Information requested for reporting
An electronic result submission form will be sent to participants when samples are delivered/ collected. For each participant two results per pesticide per sample may be submitted.
The following information will be requested from participating laboratories:
- Method validation information
- Quality control measures implemented
- Method of extraction used
- Sample size analysed
- Instrumentation specification
- Analytical method information
- Recoveries for method and if a correction for recoveries is applied
- The method limit of detection and limit of quantification
Table 3: Pesticide in fruit PT scheme important dates
02 July 2018
30 July 2018
30 August 2018
08 October 2018
08 November 2018
08 December 2018
10 December 2018
14 January 2019
15 February 2019
Please note that the registration closing date is three(3) weeks before sample distribution.
- F. Cordeiro. Statistical methods for use in proficiency testing (2009). Institute for Reference Materials and Measurements. JRC –EC
- M.M. Phillips, K.E. Sharpless and S.A. Wise. Standard reference materials for food analysis (2013). Analytical and Bioanalytical Chemistry, 405: 4325 – 4335
- Codex Alimentarius International Food Standards: Codex pesticides residues in food online database (July 2016).