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. 