Negative Control Clause Samples

Negative Control. A model carbon black particulate sample (M120) was used as the negative control. It has been characterised to be 50 nm in diameter with an associated surface area of 32m2g-1 [277]. Electron-probe X-ray microanalysis studies have demonstrated that M120 is composed of carbon black, chloride and sulphur with no evidence of surface associated metals [302]. Therefore, potential confounding effects of the particle surface and size on antioxidant quantification due to absorbance were investigated through the use of the negative control concurrently to the PM testing. The preparation was the same as the positive control (see section on NIST), that is, a 500µg/ml stock was diluted to 55.56µg/ml solution for the exposures. Results demonstrated that the antioxidant depletion caused by M120 in the 2 hour exposure did not differ from the oxidation caused by the background controls (Figure 18). *** Concentration (µM) The diagram presents the overall ascorbate depletion mean + SD by the different controls, NIST caused the highest antioxidant depletion (p<0.001), while the remaining controls did not differ from the background oxidation control. Therefore, it can be concluded that the disc cut incubation and the related methods (carry over test) did not confound the results.