were probably due to the larger amounts of benzene present. ;Is mentioned earlier, the relative response factors vary by an appreciable amount from sample to sample. I n the nine check samples, i,he pentane factor ranged from 0.85 to 0.98 and the sulfur dioxide factor from 1.14 to 1.29 relative to benzene. The effect of a relaidvely large change in some instrument component on the applicability of the calibration curves in Figure 1 was checked by running duplicate analyses with recorder battery voltages of 1.42 and 1.56 volts. This change was sufficient to shift the calibration curves a sizsble distance but the maximum differer ce in the duplicate analyses was 2i.45 us. 27.20 wt. 7,. for sulfur dioxide. The other two compounds had smaller differences in the opposite direction. The results discuss2d above, plus the work of 2Messner,Rosie, and drgabright (j),support the hypothesis that the relative response fackors at any given sample composition remain essentially constant despite shif s in the response area us. amount injected curves. This, together n-ith the iterative procedure described above, per nits accurate analysis of multicomponent mixtures with relatively little effort. It is important to note that the calibration curves must lie consistent with each other if accurate? results are to be obtained in the itwative procedure based on Equations 10-14. They must all be determined a t the same operating conditions and instrument condition. Also, the amounts injected and the areas obtained must be known quite accurately. I n this woik the Hamilton 7OlN microsyringes used to inject the liquid samples were calibrated with high purity mercury at t i e injection temperatures. The needle volume was included in the calibration because some vaporization of the needle contents a t the oven temperaturc? of 110’ C. was inevitable. To be cer :ain of the amount injected, the syringe was left in the sampling port until all the material was vaporized. The chart areas mere planimetered a sufficient number of times to get within 17; of the true area. AUso,multiple injections (at least three) were made at each veight. Variations in operating and instrument conditions between the various calibration curves we*e not so easy t o handle. The curves should all be
determined within a relatively short period of time and injections of the various compounds intermixed. Also, large and small sample injections should be intermixed. In short, all of the usual experimental techniques to avoid the effect of time on the variables should be employed. Once a set of accurate, consistent calibration curves are obtained most of the above precautions are not necessary in the routine analysis of unknown samples. The chart areas must, of course, always be measured accurately but the size of the injected sample need not be known with the precision described above-i.e., a calibrated syringe need not be used. This does not mean that the accurate measurement of the unknown sample volume is not important. Sample volumes greater than 5 filecan be measured easily within 2% with an uncalibrated Hamilton syringe. The possible additional 1% increase in accuracy obtained by calibrating the syringes will not affect any of the significant digits in the final set of relative response factors obtained and is therefore not worth the trouble. Incorrect volume readings, n-hich are off by, say, IO%, will of course affect the results and reasonable care in the measurements should be exercised. The recorder battery should not be alloa-ed to run down completely but a change in voltage from 1.5 to 1.4volts, for example, will not cause trouble. Similar remarks hold for other instrument components. The calibration curves will shift with such changes but the relative response factors evidently remain essentially invariant. The data and techniques described in this paper are given in complete detail in reference ( 1 ) .
p : Total system pressure. pi*: Vapor pressure of compound i. IT: Volume of totalinjectedsample. vf: Specific volume of compound i. wi: Weight fraction of compoundi. Q: Mole fraction of i in liquid. yi: Molefraction ofiin gas. LITERATURE CITED
Bowden. W. W.. Ph.D. Thesis. Purdue ~University, Lafaiette, Ind., 1964. (2) Kaufer, D. M., M. S Thesis, Purdue University, Lafayette, Ind., 1961. (3) Keulemans, A. I. M.,“Gas Chromatography,” 2nd ed., pp. 32-5, 83-91, Reinhold. New York. 1959. (4) Keulemans, A. I. ’M., Kwantes, A., Rijndens, G. A,, Anal. Chim.Acta. 16, 29 (1957). (5) Messner A. E., Rosie, D. M., Argabright, P. A., AN.~L.CHEM.31, 230 (1959). RECEIVEDfor review April 2, 1963. Accepted September 30, 1963. This work was made ossible by the support of the Humble Oiyand Refining Co. 1
\ -
Corrections Determination of Molecular Weights of Proteins by Gel Filtration on Sephadex In this article by John R. Whitaker [ANAL. CHEM.35, 1950 (1963)l on page 1952, in column 3, lines 25-30, the equations of the lines should read as follows: log molecular n-eight = -0.660 ZIC 0.054(vV - 1) f 4.785 rt 0.040 for Sephadex G-75 and log molecular weight = -0.973 0.012(v0 V - 1) f
*
5.190 i 0.010 for Fephadex G-100.
ACKNOWLEDGMENT
Jonathan Amy and William Baitinger of the Chemistry Department provided invaluable assistance during the course of this work. NOMENCLATURE
Ai: Response area of compound i. Response area is chart area in square inches multiplied by instrument attenuation setting. Ff-,:Relative response factor for compoundireferred t o compoundj. Defined by Equation 6. m,: RIasc, of compoundiin mg
Coulometric Efficiency of Anodic Deposition and Cathodic Stripping of Chloride at Silver Electrodes In this article by H. -1. Laitinen and Zui-Feng Lin [ d x a ~ .C H m . 35, 1405 (1963)l on pages 1407 and 1408, respectively, in Figures 3 and 5 the units of the abscissa should be cfa./cm.* rather than ma. /cm.’
VOL. 36, NO. 1, JANUARY 1964
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