Proficiency testing (PT) for the determination of dithiocarbamate pesticides in mango matrix



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Proficiency Testing (PT) for the Determination of Dithiocarbamate Pesticides in Mango Matrix
Armi W.Nóbrega1, Damares S. Santos2, Heloísa C. A Góes1, Paulo R. F. Santos2,

Vanderléa de Souza2

Adherlene V. Gouvêa1, Adriana S. de São José1, Denise de P. Dias1, Fernando G. M. Violante2, Janaína M. R. Caixeiro2, Lucia Helena P. Bastos1, Maria Helena W. M. Cardoso1, Raquel D. C. C. Bandeira2,

Renato R. R. de Almeida1, Tânia M. Monteiro2
1 Fundação Oswaldo Cruz- FIOCRUZ/INCQS, Rio de Janeiro – RJ - Brazil

E-.mail: armi@incqs.fiocruz.br

2 Instituto Nacional de Metrologia, Normalização e Qualidade Industrial, INMETRO/PEP-DIMCI/DQUIM, Rio de Janeiro – RJ - Brazil

E-mail: prsantos@inmetro.gov.br / dquim@inmetro.gov.br
In order to enhance the confiability of results of complex pesticide determinations, participation in Proficiency Tests is a fundamental tool in any laboratory as prerequisite of the Quality System Program based on the ISO/IEC 17025.

Although there is a large offer of assays by international PT providers, many factors limit the participation of Brazilian laboratories: difficulties on importing, which frequently result in receiving samples in inadequate integrity or temperature conditions, and the high cost of the participation. INCQS is the only Brazilian PT provider of samples for the determination of pesticide residue in foods.

This work presents the results of twelve Brazilian and one Dutch (VWA/KWV) Laboratories in a PT organized by INCQS and INMETRO, with samples of dithiocabamate thiram in mango pulp.

The mangos were bought in a market of Rio de Janeiro, tested to be dithiocarbamate-free, blended and the resulting pulp transferred to plastic recipients. 100mL of a 13.15 mg/mL solution of thiram (Thiram, Dr. Ehrenstorfer, Germany) in ethylic alcohol was prepared and distributed in 5mL ampoules. The reference material used was certified and had a declared purity of 97.5%. The samples consisted of two sets of 1 ampoule of thiram and one recipient of mango pulp. Each set was to be mixed right before the performing of the assay, according to the instructions. The homogeneity of the samples was tested in 20 ampoules and 20 mango pulp recipients and the stability in 10 ampoules and 10 mango pulp recipients. These analyses were performed in INCQS, using Keppel methodology. According to ISO GUIDE 35 analysis of variance (ANOVA) was used for homogeneity statistical evaluation and confirmed the homogeneity of the samples provided. The stability study lasted 5 weeks, the result was evaluated through residue analysis and the results demonstrated the stability of the samples.

The reproducibility of the result sent by the participant laboratories was evaluated by calculating the respective relative standard deviation (RSD). According to the Codex Alimentarius (Alinorm03/24A) for pesticide residue analysis, the RSD must be 15%. The designated value calculated by using the ISO 13528 Supplement to ISO/IEC Guide 43 was 0.3771 mg/kg of CS2, with a standard deviation of 0.0931. Of the twelve participating laboratories, two presented an unsatisfactory-score and between them only one presented a RSD greater than 15%. Two laboratories presented questionable-scores, despite the fact that they have presented acceptable RSD.

The results now presented could suggest that a better recovery was obtained by using the photometric method. However, it has been demonstrated previously that the photometric and the chromatographic methods are equivalent even though the chromatographic method seems to be more sensitive.


ABNT ISO/IEC GUIA 43-1:1999: Ensaio de proficiência por comparações interlaboratoriais – Parte 1. Desenvolvimento e operação de programas de ensaios de proficiência. Traduction to portuguese of ISO/IEC Guide 43-1:1997.
ISO GUIDE 35: Reference Materials – General and statistical principles for certification. Third Edition. 2006.

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