Correction Anal. Chem. 1996, 68, 3703
Macromolecule Analysis Based on Electrophoretic Mobility In Air: Globular Proteins Stanley L. Kaufman,* Jeffrey W. Skogen, Frank D. Dorman, Fahimeh Zarrin, and Kenneth C. Lewis (Anal. Chem. 1996, 68, 1895-1904).
We have discovered an analog voltage error in the high-voltage supply of the differential mobility analyzer. This error affects the electrical mobility diameters (EMDs) reported in the paper, especially for smaller molecules. Correcting for the error, and using protein density of 0.80 g/cm3, significantly improves the match between our results and the simple spherical model relating EMD to molecular weight (Figure 3 in the paper). To measure the voltage error, we set the voltage through software commands and then measured it using a Keithley 191 digital voltmeter for 30 values across the experimental range. The result was fitted by least squares to AV ) A + B(SV), where AV is the actual voltage and SV is the voltage set by the software. The correlation coefficient was r2 ) 1 - (2 × 10-7), and the coefficients are A ) 30.91 ( 0.22 V and B ) 0.99845 ( 0.00008. To perform the correction, we used the relation between EMD and mobility (eq 1 in the paper) and the relation between analyzer voltage and mobility given in ref 17. After applying the voltage correction to the voltages corresponding to a given EMD value, we solved numerically for the EMDs of particles passing through the analyzer at the actual applied voltage. To make it easy to apply this correction to any measured EMD, the procedure was applied to each discrete diameter value used by the data acquisition system and fitted to an interpolation formula:
AEMD ) [a + b(MEMD) + c(MEMD)2 + d(MEMD)3 + e(MEMD)4]1/2 where AEMD is the actual EMD and MEMD is the “measured” EMD determined by the original fitting process, both in nanometers. The coefficients for 1.6 nm e MEMD e 40 nm are
a ) 5.1286
d ) 1.780 × 10-5
b ) 1.2577 × 10-2
e ) 1.82 × 10-7
c ) 0.99895 The maximum error in AEMD using this formula in place of the numerical solutions is 2.2 × 10-4 nm, which is negligible compared with the remaining uncertainties. AC961398D
S0003-2700(96)01398-4 CCC: $12.00
© 1996 American Chemical Society
Analytical Chemistry, Vol. 68, No. 20, October 15, 1996 3703
