Paper Strip Holder for Absorption Spectroscopy Robert M. Horowitz and Lawrence F. Atkinson, Fruit and Vegetable Chemistry Laboratory, Western Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Pasadena, Calif.
RADFICLD
and Flood ( J . Chem. SOC.
1952, 4740) recently published a
method for measuring the ultraviolet absorption spectra of substances directly on paper chromatograms. A holder for 'paper strips, designed specifically for use in a Model DU spectrophotometer, is extremely convenient for routine use. The area of paper containing the spot can be centered accurately a t the position of maximum concentration. The paper is held firmly in a fixed position while the spectrum is heing measured; this is essential if reproducihle readings are to be obtained. The paper may be removed after the initial determination of the spectrum, sprayed with a reagent n-hich effects a characteristic change in the spectrum, and replaced in the holder in almost emctly the same position t h a t it occupied originally. This device is used in measuring the entire spectrum of a particular spot on a chroniatogram and is not suitable for scanning an entire chromatogram a t one m-aye length. Aluminum was used in construction, although other materials would serve equally nell. The holder consists of tn-o halves hinged a t the bottom which,
when closed and fastened with a clasp, become a unit having the same over-all dimensions as the cell holder furnished with the Model DU instrument. With the unit held in the closed position, four openings are cut n-hich have the shape, size, and spacing of the regular cell holder. In practice, the holder is opened and one side is placed flat on a table. An area of paper, about 1 X 2.5 cm., encompassing the spot in question, is
centered over the secoiiil, third, or fourth space. (The first space is reserved for a blank strip of paper.) The holder is then closed and the spectrum is determined in the usual manner. For readings below -255 nip the instrument is operated n i t h the selector switch set a t 0.1. The precise location of spots on the chromatogram may be determined by examining it in ultraviolet light or by spraying a parallel guide strip n i t h an appropriate reagent.
Polarographic Cell for Continuous Monitoring of Ion Exchange Effluents Charles
K. Mann,
Department of Chemistry, University of Texas, Austin 12, Tex.
w
HLS the elution characteristics of ion exchange columns are studied much labor can be saved if the effluent solution can be analyzed continuously and automatically. The polarographic cell described permits continuous analysis when the ion being studied is subject t o polarographic determination.
The cell, shown in Figure 1, coiisists of a 1-mm. thick-walled borosilicate glass tube connected to the column by a standard-taper joint. The tube is fitted with a port to admit the dropping mercury capillary and, directly opposite, a side arm to hold the mercury pool anode. -4glass flange around the electrode opening acts as a seat for a rubber gasket used to obtain a temporary water-tight seal. The body of the cell
Figure 1.
Polarographic cell
must be reamed out to accommodate the end of the capillary. Polarographic equipment and techniques are essentially the same as for amperometric titration. A potential from the plateau beyond the polarographic wave of the ion in question is
imposed across the ccdl electrodes. Elution of reducible material from the column is indicated by a n increase in current flow. Figure 2 shows the curve obtained for the elution of 0.010 mmole of lead with 1.05N nitric acid from a column of D o w r 50 resin operated a t a flow rate of S.3 cm. per minute. This flow rate corrcsponds to 1.00 ml. per minute. A Sargent Model XYI pen recording polarograph was used to record the curve. The polarograpli was adjusted to furnish a const,ant potential of -0.92 volt, us. the mercury pool and current iyas measured a t a sensitivity of 0.06 Fa. per inin. With a constant flow through the column, the volume of effluent can he estimated directly from the chart. When the reduction current at a dropping mercury electrode is nieasured VOL. 2 9 , NO. 9, SEPTEMBER 1957
1385
