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(A) Left row bottom to top: urine blank and 5 different spiked concentrations (25, 50, 100, 250 and 500 µmol/L). Right row top three vials: three clinical samples, which show a positive test result for PPD. (B) Concentration dependent transmittance (%) from 25–250 µmol/L on a spectrophotometer at 450 nm.
