T a b l e VIII. Search Using Tri-n-butylphosphate Spectrum (Liquid Film, CsI Cell, and Grating Spectrometer (2.5-40 p ) ) as the “Unknown” Compounds
Spectra type
Tri-n-butylphosphate Tri-n-butyl. phosphate Tri-n-butylphosphate Di-n-butyln-butylphosphonate
Liquid film, CsI cell, grating (2.5-40 H) Liquid film, KBr cell, grating (2.5-25 p ) Liquid film, KBr cell, prisms (2-25 p ) Liquid film, KBr cell, grating (2.5-25 p )
Match result
100
Compared peaks
14
88.6
14
82.0
14
77.7
14
Table IX. Search Using Triphenylphosphate Spectrum (KBr Pellet and KBr Prism as the “Unknown”) Compounds
Spectra type
Triphenylphosphate Triphenylphosphate
KBr pellet, KBr prism KBr pellet, NaCl prism
Match result
Compared peaks
100
12
100
4
with a shift of this spectrum by -0.07 micron. The “known” in this case had a final match result of 70.5 and was dichlorophenylphosphine sulfide [liquid film, CsI cell, and grating (2.5-40 b ) ] . In the case of the above menond match utilizes a correction for linear wavelength distioned dichlorophenylphosphine “unknown”, there were placement obtained from the first attempted match if five match results above 50. A spectral shift for each of these resulted in an improved match result. The distances such a correction is required. The wavelength correction was calculated by replacing R Lin’Equation 1 by RL(Y,-XL) of these shifts were -0.07, -0.06, -0.06, -0.01, and and by dividing the resulting value obtained from the -0.03 microns. The consistency of these shifts, despite their small size, indicates that the particular “unknown” modified right side of Equation 1 by the absolute value of spectrum is probably slightly in error in the designation of Mo This displacement correction procedure was tested specific wavelengths. with spectra where the wavelengths of the peaks were deThe effectiveness of the system in aiding the user in deliberately shifted less than l micron. It worked satisfactotermining an unknown structure was demonstrated in a rily. number of cases. For example, the use of diethyl 4-nitroRESULTS AND DISCUSSION phenyl phosphate (CC14 solution, NaCl cell, and NaCl prism) as an “unknown” produced only one match result All of the spectra in a 57-spectrum file of organophosabove 50, diethyl 4-aminophenyl phosphate (liquid film, phorus compounds were run as “unknowns” against the KBr cell, and NaCl prism) which had a match result of total file. As would be expected, each produced a match 60.1. Thus, even though a compound may not be in the result with itself of 100. The first sample “search” is file, the highest match results generally correspond to shown in Table VII. In the sample searches, the number very similar compounds. of compared peaks is the number of peaks in the overlapCurrently the file has about 60 spectra of organophosping region of the two spectra being examined. For examphorus compounds and a search requires abou,t 1.3 secple, if an “unknown” spectrum has a range of 2 to 15 mionds. Therefore, a search of 10,800 spectra would take crons and the “known” a range of 10 to 25 microns, only about 4 minutes of Univac 1108 time. This time could those peaks in the 10- to 15-micron region can contribute probably be reduced if some effort were devoted to reproto the match result and are called the compared peaks. gramming for speed. In all of the searches, it was found that when a match result above 90 occurred, the compounds compared were ACKNOWLEDGMENT identical. Generally, all comparisons of different spectra of the same compounds yielded a match result of 80 or We thank John J. Callahan and Donald R. Bowie for more as illustrated in Table VIII. The differences between their helpful comments. spectra of the same compound from various types of spectrometers or cells result from actual variation in the specReceived for review January 26, 1973. Accepted January tra and not the search system. When compounds are run 22, 1974. This project was supported in part by the U. S . on different spectrometers; with unlike cells, using samArmy Materiel Command Computer-Aided Design and ples of varying purity, and by many spectroscopists; some Engineering Program. dissimilarities in spectra must be expected. Also, there may be some differences in the coding of the spectral data, but this should be minimized by the assigning of the lower weights to matches between weak peaks. CORRECTION High match results were often found for different spectra of the same compound even where only a few peaks Acquisition and Analysis of Cyclic Voltammetric Data could be compared as in Table IX. The “unknown” listed in Table IX yielded no other spectra with match results above 50 besides the ones listed in that Table. In this paper by P. E. Whitson, H. W. VandenBorn, Generally, there were very few linear shifts of one specand D. H. Evans [Anal. Chern., 45, 1298 (1973)], Equation trum with respect to another to improve matches. The 1, p 1301, should read largest observed improvement was with the “unknown” of dichlorophenylphosphine [liquid film. CsBr cell, and gratR‘ = ZT(1 +pcos a ) ing (2.5-40 p ) ] . The match result was improved by 9.3
[k $1
ANALYTIAL CHEMISTRY, VOL. 46, NO. 7 , JUNE 1974
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