1. Mann I, Brookman B (eds) (2011) Eurachem guide: selection, use and interpretation of proficiency testing schemes, 2nd edn.
www.eurachem.org
2. ISO/IEC 17043 (2010) Conformity assessment—general requirements for proficiency testing. ISO, Geneva
3. ISO/IEC 17025 (2017) General requirements for the competence of testing and calibration laboratories. ISO, Geneva
4. EA-4/18:2010 Guidance on the level and frequency of proficiency testing participation.
www.european-accreditation.org
. Accessed 17 Aug 2018
5. Örnemark U, Boley N, Saeed K et al (2001) Accred Qual Assur 6:140