Ten measurements were taken with each instrument at each ethanol
reference vapor concentration, as well as ten measurements of each
potentially interfering substance concentration. Measurements were
alternated with the Pro, C8, and C6 at approximately 2-minute intervals.
The mean, percent coefficient of variation (%CV), percent bias,
R-squared, and ordinary least squares regression was calculated.
Apparent ethanol response to potential interfering substances was
recorded.
An evaluation of the potential
sources of uncertainty was evaluated using an Ishikawa diagram
(Ishikawa, 1989, pp. 229–232) seen in Figure 1 . Standard
uncertainties were combined using the root-sum-squares approach where,\(\mathrm{u}_{\mathrm{\text{combined}}}\mathrm{=}\sqrt{{{\mathrm{u}_{\mathrm{\text{reference}}}^{\mathrm{2}}\mathrm{+u}}_{\mathrm{\text{precision}}}^{\mathrm{2}}\mathrm{+u}}_{\mathrm{\text{bias}}}^{\mathrm{2}}}\), as detailed in the literature (Anghel, 2008; Archer, De Vos, &
Visser, 2007; Brockley-Drinkman & Barkholtz, 2019; Rod G. Gullberg,
2006; Hwang, Beltran, Rogers, Barlow, & Razatos, 2016; Hwang, Rogers,
Beltran, Razatos, & Avery, 2016; Philipp et al., 2010; Souza et al.,
2006). Bias was incorporated as a component in the estimate of
measurement uncertainty, expanding the coverage interval (Magnusson &
Ellison, 2008; Phillips, Eberhardt, & Parry, 1997). The combined
standard uncertainty was expanded to the 95% coverage interval
(\(U=2u_{\text{combined}}\)). Figure 2 shows the individual
uncertainty component’s percent contribution to the combined standard
uncertainty.