Provision of proficiency test (PT) scheme on proximate and mineral analyses: Philippine experience

Based on ISO Guide 43-1: 1997 and ILAC G-13: 2000 guidelines three (3) proficiency test (PT) Rounds were organized for moisture, fat, protein, ash, iron, calcium and sodium analyses using wheat flour (Round 1), powdered tonic food drink (Round 2) and dried paste shrimp (Round 3) as PT materials. Fifty-three (53), fifty-two (52) and forty-six (46) local and foreign laboratories participated in PT Rounds 1, 2 and 3, respectively. Results were evaluated using the appropriate statistical procedures based on ISO 13528: 2005 and/or IUPAC Technical Report, 2006. The z-scores used to evaluate the performance of participant laboratories were computed, applying the standard deviation for proficiency test assessment (σp) derived from the CVs/RSDs of previous PTs and the general expression of Horwitz, while the assigned values (robust mean or mode with uncertainty) were obtained from the consensus of PT participants' results. For proximate analyses, 65-90% of PT participant laboratories achieved “satisfactory” (|z-score| ≤ 2) performance for the three (3) PT Rounds. For iron and calcium analyses, only 50-70% achieved “satisfactory” performance. The PT test materials' given assigned values (X) and range (X ± 2σp) were used in method validation and as quality control test materials by the local laboratories. The three (3) PT Rounds provided an effective tool in assessing the laboratory performance of proximate and mineral analyses and in conducting the necessary investigative and corrective action on “questionable” (“Q”) and “unsatisfactory” (“U”) results.