A proficiency test scheme for the quality control of black tea and development of quality control material for internal quality control

• Published in: Accreditation and quality assurance 2011-10, Vol.16 (10), p.507-513
• Main Authors: Baltacı, Cemalettin, İlyasoğlu, Huri, Sarıkaya, Sevim Beyza Öztürk, Cavrar, Sevda, Yaylı, Nurettin
• Format: Article
• Language: English
• Subjects: Alkalinity; Analytical Chemistry; Ashes; Biochemistry; Black tea; Caffeine; Chemistry; Chemistry and Materials Science; Commercial Law; Ecotoxicology; Exact sciences and technology; Food; Food Science; Laboratories; Marketing; Practitioner's Report; Quality control; Reference materials; Sample variance; Standard deviation; Standard scores; Tea; Water chemistry
• ISSN: 0949-1775; 1432-0517
• DOI: 10.1007/s00769-011-0799-5

A proficiency test (PT) was organized for quality control analysis of black tea. Test materials for the analyses of total content of powder tea, moisture, total ash, acid-insoluble ash, water-soluble ash, alkalinity of water-soluble ash, water extract, crude fiber and caffeine were sent to the participant laboratories ( n:43 ) in 2009. The assigned value, standard deviation of the parameters and z -scores of the participant laboratories were calculated using the data reported by the participants. The percentage of the reported results for analytes was found to be ranged from 67.5 to 100%. Acceptable z -scores were achieved by 80.5–97.5% of the participant laboratories. More than 15% of unacceptable results were obtained for acid-insoluble ash and caffeine analyses. The quality control material for quality control analysis of black tea was developed from the remaining material.