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. Author manuscript; available in PMC: 2013 Dec 1.
Published in final edited form as: Drug Test Anal. 2012 Feb 24;4(12):912–922. doi: 10.1002/dta.394

Figure 4.

Figure 4

The three approaches to determining ion current ratios. A peak is detected on one of the ion current traces, and the start and stop defined. (a) Summation. The ion current is integrated for each ion trace. A trapezoidal background is subtracted by defining points on either side of the peak. (b) Curve-fit. The peak is parameterized as one of several functions for each ion trace, and the peak area extracted from the best fit parameters. (c) Linear regression. A plot of two ion currents is constructed. The slope of the least squares linear regression is taken as the ion current ratio.