Excel Integration Vs

Excel Integration vs. Manual Integrator II

Experiment 1.

I assessed the relative merits of these programs, using eight chromatograms like that shown in Figure 1.

Figure 1: Sample Chromatogram Program Methods: a. In Excel, peak areas were summed and background was corrected by subtracting baseline from either side of the peak. b. Manual Integrator II draws a line defining the slope of the baseline to correct for background. c. I measured the peaks three times by each method and averaged them.

Experimental Methods: The test solution was 0.3 M in each peak; the concentration was determined using the standard addition method, using a. the average of two runs of the test solution (“raw”), and b. the average of two runs of the test solution spiked 1:10 with a 30M stock (“spiked”). Results are in Table 1.

Table 1: Integrating the peaks in Solution 1 to solve for concentration

The standard deviations given for the concentrations are determined from propagation of error using error in the following parameters: a. pipetting the raw solution b. pipetting the stock solution c. the average of runs 1 and 3 d. the average of runs 2 and 4 The standard deviations do NOT include error in repeat measurements of a single peak (so the real standard deviation is slightly larger than that given).

Discussion: Though comparable in their accuracy, the manual integrator seems to overestimate values, while Excel seems to underestimate them. However, this is only one sample, and cannot therefore be called a trend. Experiment 2.

Solution 1 was filtered through a 30 kD cellulose acetate filter, then quantified as in Experiment 1. The purpose was to show that the filters do not change the concentration of the solution; therefore, the solution SHOULD still be 30 M, but the true concentration is unknown.

Results:

Discussion: Well, two solutions still isn’t a trend, but maybe the integrator really is overestimating and Excel really is underestimating. Shouldn’t matter; both are within experimental error of the ‘true’ value. And, the Integrator is so much faster than the Excel method—the Integrator should reduce my pain by at least half. 