CTI provides water quality heavy metal chemical analysis services related to quality control samples, which are mainly used for method verification and confirmation, quality assurance of the test process, etc., and can be used for blind samples of regulatory agencies on-site review, supervisory review, reassessment, and unannounced inspections. Charge samples or blind samples used for laboratory internal audit, daily quality supervision, quality assessment, personnel assessment, method comparison, personnel comparison, equipment comparison, etc.