Real-time polymerase chain reaction (PCR) is the gold standard for DNA detection in many fields, including food analysis. An EURL and NRL network for physical hazards is strongly recommended. Part 2 presents the actual validation procedures with experimental designs and equations for calculating the relevant parameters, and can be used as blueprint for a SOP in a quality management system. Part 1 of the Guidance includes the general background, theory and principles. The general framework of the Guidance is adopted from ISO standards (17023, 17043, 13528). In the view of these specific circumstances, a Guidance for quality assurance and control of visual methods has been developed, which are being presented and discussed in this paper. Identification of legal ingredients and composition analysis in the domain of visual examination relies on the expertise of the laboratory staff, therefore validation of a method usually includes the validation of the expert. A series of examples from publications show inconsistent or not correct implementations of these validation procedures, which stress the need for dedicated validation procedures. In most cases procedures for validation of visual methods are based on principles adopted from other domains, such as chemical analysis. As for other domains, examination methods for visual monitoring need to be properly validated and quality control during actual application is needed. These parameters do not follow a normal distribution but Poisson (counts), lognormal (weights) or binomial (Booleans) distributions, with effect on the interpretation of validation parameters. The level of detection equals at least the size of one unit, usually with a weight exceeding 1 mg, which is in the range of parts per million (ppm). The two principal results are counts (numbers) and weights for macroscopic methods, or presence/absence for microscopic methods. Visual examination of visually recognisable substances, including microscopy, focus on targets or contaminants such as particles of animal origin, plant seeds, spore bodies of moulds, sclerotia, packaging material, microplastic and 'Besatz' (everything that differs from the norm).
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