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V O L U M E 27, NO. 12, D E C E M B E R 1 9 5 5 of the values for the d spacings read on either side of zero degrees two theta is compared with the known values for the standard sample. If the agreement is not satisfactory, the Nies scale seleeted was incorrect. The magnitude of tbis disagreement will indicate which of the remaining six scales should be selected for the preparation of a new template. The difference between two readings for the 8&me d spacing in the front reflection region will indicate the length of film to he cut from the template, in order that the printed scale will be symmetrical with respect to zero degrees two theta. The dimensions of the template will change on standing unless it is stored in a desiccator. Hence, bhe dried template is equilibrated in a desiccator for a few days before calibratian. IMPRINTING TECHNIQUE
After the sample and film are placed in the camera, a photographic template (Figure 1, bottom) is fitted over the film with the calibrated end flush against the stationary film brace and the other end held firmly by the fingers, so that the template is pressed against the film. A two-part cover, made from any opaque material, is placed around the rim of the camera (Figure 2) to prevent blackening of the edge of the film. An overhead light (ZOO-watt bulb, 6 feet above the camera) is flashed for about 1 second. The template is removed and the usual x-ray and photographic procedures are carried out. Table I. Accepted (4) and Indicated d Spacings far Quartz Front Reflection, A. Read from male Calod.
Back Refleotion, A. Read from so& (.*I Calod.
A typical fihn with the imprinted scale is shown in Figure 1, tap, and Figure 3. The s m p l e is quartz, the d spacings of which are accurately known (4). Some of the accepted values me compared in Table I with those indicated by the scale.
from which can he obtained tho absolute intensity coefficient, D ~ A -=
1
- Aa.
Cl
where e = sample concentration 1 = cell length will be of value in the infrared for correlation of characteristic functional group bands ( 1 3 ) in addition to their preseut use for information on dipole moment (4). Their use for type compound analysis has been considered, and there Imve been two recent papers (5, 6 ) on type analysis where the use of A n . as :LIL oldinate function might have proved better thaii the m e elioseii. There has been little use of adu a8 the basic ordinate term For multicomponent quantitative analysis, yet herein miiy he L: major value. In comparison a i t h the present use of :horpl.,ivit,y,
a,
(:")
log,, Ymlr e n u would have the advantages of (1)better adherence tu Beer's law where a,fails for lack of monochromaticity of the o s i t radis, tiou beam, (2) higher accuracy and reproducibility, nod (3) with proper instrumentation, a directly readable number elimiuating operator errors of measurement and calculation, and the disadvantages of (1) lower ratio of diagonal to off-dingonsl terms in the analytical matrix, and (2) more difficult carrectiou for false radiation. There are many analyses where the advantages outweigh the disadvantages. Although the potential value of Ans 8s an ordinate function has been recognized for some time, its study has been deterred by the extreme tedium of accurate manual measurement and calculation. Therefore, &n %ttz+chmentto the Perkin-Elmer Model 21 doublebeam infrared spectrophotometer has been developed which %ill integrate the absorbance value continuously as the spectrum is being recorded over R. given wave-length or frequency range and present the integrated value on a counter. A pen system is attached, so that on the abscissa border of the spectrum unit =
ACKNOWLEDGMENT
H. P. Klug and L. E. Alexander, Department of Research in Chemical Physics, Mellan Institute, gave helpful advice and encouragement in this work. D. T. Pitman of this same department helped test the method. LITERATURE CITED
(1) Barrett, C. 8.. "Structure of Metals," 2nd ed., p. 143, McCrawHill, New York, 1952. (2) D e BretteviUe. A. P., and Levin, 5. B., Re". Sci. Instr., 19, 120 (1948).
(3) Higg, G., Ibid., 18, 371 (1947). (4) Wilson, A. . I . C., and Lipson, H., Proc. Pfius. Soe., 53,245 (1941).
Device for Automatic Measurement of Integrated Absorbance V. Z. Williomr, V. J. Cooler, and Frank Goarde, The Perkin-Elmer Corp., Norwalk. Conn.
is growing indication that the use of the integrated Tabsorbance, HERE
Figure 1. Absorbance integrator assembled on
where VI, y1
IO I
= limits in cm.-' = =
incident radiation transmitted radiation
spectrophotometer Four-digit reset counter reads integrated unite and marks nbsoissa
separate pen
ANALYTICAL CHEMISTRY
2018
integration multiplier is geared to the recording drum rotation. The resultant integrated absorbance is presented ,on a fourdigit high speed magnetic impulse counter actuated by a commutator. Electrical impulses from the counter actuate a marking pen on the margin of the recording paper a t the proper abscissa position. The accuracy of the device (over its absorbance range of 0 to 1) is somewhat better than that of the direct measurement of peak absorbance, as a range of absorbance is involved and variations in the instrument linearity are averaged. Multiplying the counter reading by a predetermined integration constant provides intensity values in terma of absorbance x om.? or absorbance mcron. The reproducibility is excellent. Tryelve readings over a 40em.? range of a band with absorbance about 0.9 over a 24-hour period showed a spread of 1 part in 250 or =t1 part in 500. The accuracy is within 1%. These figurea are based on absorbance. The accuracy and reproducibility of transmittance measurement would have to be roughly three times better to provide equivalent performmce.
100
Figure 2. Intenrator with cover removed to reveal mechanism
01
CMY'3200
Figure 4.
3100
3000
2900
21 )O
Effect of slit width on intensity
A b , in C-H stretching region Of polysturene. Although rpsolution and Deak absolption v+lues change appreclsbly. mtezrsted absorption remains cmrtant
A,
% ISOOCTANE
Figure 3.
"8.
% ISOOCTANE
Beer's law adherence
COUNTER
3
369.5
3
3.59.
4
371.
4
364
COUNTER 364.5
Absorbhnae A,, US. integrated sbsorbanoe. Abv. On a typical band as of iao-&taLle deviation of Ads IS about one fourth that of A ,
integrated values are marked by dashes. Thus, a ressonahly ttocwate absolute intensity value o m always be read from the standard spectrum. For most accurate work the difference in counter reading between V I and us is used. Far quantitative analysis a direct number for insertion in thecalculation is available. The possible operator error in spectrum measurement, division, and log conversion is eliminated. The device is npplicahle to either linear wave-number or linear wave-length instruments, as AA. can be converted to A n i by a known function. The accessory is shown in Figure 1 with cover on, mounted on the Model 21. In Figure 2, the cover is removed to show the mechanism. A logarithmic barrel cam is mounted on the pulley, connected to the optical wedge whose rotation determines the. transmittance position of the recording pen. A rider on this cam sets the radius position of a ball and disk integrator. The
RVN
RUN
Figure 5.
Reprodseibility i n presence of noise
Repeat run8 of ,a polystyrene band varying speed of 8can and signal-to-nome m$o. Although noise vanation in A, changes & ~ ~ r e e m bvariation ly, in AA" is small
Figures 3, 4, and 5 illustrate the first two advantages listed shove. LITERATURE CITED
(1) Bomstein, J., ANAL. CHEM.,25, 1770 (1953). (2) Jones, R. N., Ramsay. D. A,, Keir, D. S., and Dobrinei. K.3 .I. Am. C h a . Soc.. 74., 80 .. (19521. ,~ (3) R&& Y ., D.~A.,laid:, 74, 72 (1952). (4) Saier, E. L., Pouefsky, Abbot, and Coggeshall, N. D., ANAL. CHEM.,26, 1258 (1954). (5) Thompson, H. W.. and others, J . C h m . Soc. (to be published). (6) Wilson. E. B.. and Wells, A. J.. J . Chem. Phus.. 14, 578 (1946). ~~~~
