~~
~~
Table I. Concn.,
Absorbance Values Individual
pg./4.5 111.
Glucose
100,3
Xylose
100.0
Conversion Factors
1,05 zk 0.03 19570 C.L.)
0,779 0.797 0.790 0.794 0,795 0.790 0.811 0.800 0.797
1.26 + 0.03 (557, C.L.)
Paper Chromatograms of Known Sugars Absorbance Values Individual
0.253 0.0i7
0.357 0.888
0.082
Conversion Factor, pg.lO.01 Absorbance
0.950 0,932 0,947 0,952 0.954
0.967 0.953 0.968 0.960
Table II.
Xylose Arabinose Mannose Glucose Galactose
AV.
0.273 0.067 0.364 0.914 0.083
0.271
0.079 0.361 0.872 0.087
Av.
0.277 0.070
0.337 0.883 0.085
0.276 0.073 0.355 0.889 0.084
ConverQuantity of sion Sugar, pg. Factor Found Theor. 1.26 1.26 1.05 1.05 1.05
31.9 9.2 37.2 93 3 8.8
36.0
the iudividual sugars vere separated (ethyl acetate-pyridine-water 8:2: 1, 19 hours. 26” C.) and eluted, using the method described by Sacman et a2. (3). The quantities of sugar were determined by using the procedure dcscribed above, with allowance made for paper blanks. Table I1 shon s that a deviation of 3y0 can be expected for the values of individual sugars. nhcn averaged from four independent determinations. This is highly satisfactory for determinations of this type, and in the majority of cases, duplicate determinations n o d d be adequate. ACKNOWLEDGMENT
9.0
36.2 53.5 9.1
The author is indebted to J . H. Cook, Mead Research Laboratoi-ies, for valuable assistance. LITERATURE CITED
T h e absorbance values are directly proportional t o the sugar concentrations, a n d t h e three hexoses form one group a n d t h e two pentoses another, with t h e proportionality constant (conversion factor) for the hexoses being appreciably smaller than that for the pentoses. These values were obtained during an earlier stage of work (“preliminary procedure”), and the reagent contained more water than the one used in the final procedure described above. Supplementary experiments were run with xylose and glucose, using this ‘[final” procedure, and these results are also shown in Figure 1. Again, straight lines are obtained, but the conversion
factors are, of course, higher and equal to those reported in Tables I and 11. Conversion Factors and Accuracy. T o establish conversion factors accurately, a number of replicates were run using known amounts of glucose and xylose. T h e results are given in Table I. These conversion factors are roughly half of the corresponding factors reported for the o-aminodiphenyl method (J)-i.e., the present method is approximately twice as sensitive. Determination of Sugars on Paper Chromatograms. As a final check, a known mixture of sugars was spotted on paper (quadruplicate runs), a n d
(1) Ek,J., Hultman, E., .l‘alure 181, 780 (1958). (2) Roy, J. K., Analyst 85, 294 (1960). (3) Saeman, J. F., Moore, W. E., LIitchell, R. L., Ullett, 11. A,, Tappz 37, 336 ( 1954). (4) Timell, T. E., Glaudemans, C. P. J., Currie, G., XXAL. CHEM. 28, 1916 (1956). Basic Research Section Mead Research Center Chillicothe, Ohio
BESCTLEOPOLD’
1 Present address, Empire State Paper Research Institute, State College of Forestrv, Syracuse 10, N. Y.
Reproducibility of Electronic Spectral Data in the Literature SIR: Although the precision attainable with commercial ultraviolet-visible spectrophotometers has been carefully evaluated under rigorously specified conditions in a number of studies, greater practical interest often attaches to the agreement that the experimenter may expect with spectra routinely reported in the literature under indeterminate conditions. The availability of a collection of 20,000 spectra taken from 90 journals published in 1958-59 (1) has permitted a study of the reproducibility achieved on replicates (usually duplicates) by different workers presumably operating without knowledge of each other. These replicates totaled 140 compounds having 257 absorption maxima comparable in both wavelength and log E . A11 data were taken from tablrs, not from graphs. Shoulders or inflections
were not compared; wavelengths in the collection were reported to the nearest millimicron, and absorbances were reported to the nearest 0.01 unit of log E . Of the 140 compounds, 40 were considered so common (acetone, aniline, phenol, pyridine, etc.) that results should have been influenced by knowledge of previously published spectra. However, separate analysis of these 40 did not give significant differences from the 100 supposedly novel compounds as reported below. For 4 out of 5 maxima, the wavelength range of replicates was 2 mp or less, and only 6.8% of the maxima had a range of 5 mp or more. This astonishingly good reproducibility may be partially attributed t o the fact that 90y0 of the maxima fell in the 220- t o 400-mp range where prism spectropho-
tometers are most accurate in wavelength setting. For molar absorbance data, reproducibility is poor. Thus, only two out of five maxima agreed within 0.02 of a unit of log E , only three out of five within 0.05, and fully 20y0 of the maxima differed by 0.10 or more. When it is considered that a log E difference of 0.10 corresponds to a 1.26 to 1.00 ratio of E ’ S , large variations in molar absorbances are clearly to be expected in published data. LITERATURE CITED
(1) Phillips, J. P., Xachod, F. C.!, “Organic Electronic Spectral Data, 1’01. IV, Interscience, Xew York, in press. J. P. PHILLIPS Department of Chemistry University of Louisville Louisville, Ky. VOL. 34, NO. 1, JANUARY 1962
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