tcrial was measured in September 1960 and again in March 1961. The two spectra are identical, neither giving a hint of contamination with porphyrin nor “free chlorin.” Positive identification must remain in doubt until further study. 9. (Page 258, last paragraph.) The
black waxy pigment, insoluble in glacial acetic acid, has a very simple spectrum. Its blue-green solution in benzene may be so dilute that the weaker bands do not show up. It is not the intention of the report to say that this pigment is identical to pheophytin 8, But with what can it be compared, if not with pheophytin a?
LITERATURE CITED
(1) LUCM,John, Orten J. M., J. Biol. Chem. 191, 293 (1951). (2) Fischer, H;, Stern A., (‘Die Chernie des PYrroh VOl. 11, Part 2, Fig. 7 , p. 342, Akadernische yerlagsgesellschaft,
Leipzig.
W. WARRENHOWE
Colorado School of Mines Golden, Colo.
Qualitative Determination of Mercurous Ions with Potassium Antimono-Ta rtrate C. A mixture of the cations listed in section A was similarly tested and a black precipitate was observed. In the absence of mercurous ions, the test gave a white precipitate. The presence of mercurous ions resulted in a black precipitate also when sodium hydroxide or ammonium hydroxide were used, and a bright mirror when EXPERIMENTAL pyridine was used. When pyridine or A. A 2% aqueous solution of potasammonium hydroxide were used, the sium antimono-tartrate was prepared Au+3 solution did not turn red-purple. and 1% aqueous solutions of the folD. Potassium antimono-tartrate was lowing cations: Ag+, Al+31 Asf3, added to a very dilute solution of Au+3. Ba+2. Bi+3. Cat2. Cd+2. C O + ~ . mercuric ions and the mixture was Cu+2; Fe+a; Hgz42, K4, Li+,’ R.lgf2; made alkaline with pyridine. No black Mn+2, Na+, NHa+, Ni+2, Pb+2, Sn+‘, precipitate was observed. Sr+2, Th+‘, Ti+S.U02+2.and Zn+2. B.’ To 1 ml.’of each of the above RESULTS AND DISCUSSION solutions of cations was added 1 ml. of the potassium antimono-tartrate soluThe above facts indicate that the tion. Dilute potassium hydroxide was black precipitate is due to the presence added immediately to each misture of mercurous ions. On analysis this until it was alkaline. A black preprecipitate was found to be metallic cipitate appeared in the solution conmercury, and this indicates that the taining mercurous ions; the other reaction described in (1) was actually solutions either remained clear or white the reduction of mercuric ion to meror light yellow precipitates were obcurous ion and then to metallic merserved. The Au+3 solution became a cury. If pyridine is used as a base, it is deep red-purple.
SIR: The qualitative detection of mercuric ions with potassium antimonotartrate has been reported recently (1). Further information has indicated the possibility of the qualitative detection of mercurous ions as well.
possible to distinguish mercuric from mercurous ions, since the former are not sufficiently reduced in dilute solutions. Iodine interferes due to its reduction to iodide (8). We also found that bromine undergoes a similar reaction. Chromates and dichromates interfere since they form strongly colored basic salts. In the presence of strong oxidizing agents the reaction was inhibited, but the addition of cupric nitrate allows the reaction to proceed. The red-purple solution of Au+’ ions as formed in section B was highly staining on the human skin. This is a hydrosol of gold and this method appears to be a convenient way of preparing it. LITERATURE CITED
Chinoporos, Efthimios, ANAL.CHEM. 32,1364 (1960). (2) Hale, F., J. Am. Chem. SOC.24, 828 (1902). EFTHIMIOS CHINOPOROS (1)
NICHOLAS PAPATHANASOPOULOS
Suffolk University Boston. Mass.
A Simple Recorder of Ultraviolet Absorption in Column Effluents G. S. Begg, St. Vincent’s School of Medicdl Reseaxh, Melbourne, N. 6, Australia SIMPLE
and inexpensive unit for re-
A cording ultraviolet absorption in chromatography effluents allows the operator to follow directly the events during an elution and thus to modify the operation of the column-e.g., by introducing a gradient, a t the proper time. This does not require that the recording be quantitative, and consequent,ly the design can be rather simple. However, the unit can be modified to give a quantitative response, 12%
ANALYTICAL CHEMISTRY
if desired. The wave length used is the 2537-A. mercury line, a t which a very large numler af compounds show appreciable absorption. Our own interests have chiefly been :n proteins and phenylthiohydantoins. PRINCIPLE OF OPERATION
Light from a low pressure mercury lamp passes through a quartz flow cell containing the effluent and strikes Em ultraviolet-excitable fluorescent ma-
terial. The secondary, visible light output is then measured by a photoconductive cell. The same principle had been used earlier by P. Edman and J. Sjaquist [Acta Chem. Scand. 10, 1507 (1956)l for the visual assessment of paper chromatograms. Special precautions have to be taken in two respects. First, the visible output from the mercury lamp has to be prevented from reaching the photoconductive cell. For this purpose a fluorescent material with a secondary
3
0
Q b
0
Figure 1. system
Schematic view of optical Recorhr
1. Mercury lamp 2. Quartz flow cell 3. Photoconductive cells 4. Slit 5. Fluorescent layer 6. Red filter Right. Exploded view of photoconductive cell and loyerr
emission in the visible red was chosen, as the mercury lamp has only a neglible emission in this region. A red lter between the fluorescent material and the photoconductive cell prevents any visible light from the lamp reaching the cell (Figure 1,b). Secondly, the instability of the light source is compensated for by introducing a second photosensitive unit and placing the two units in a m e a t s t o n e bridge (Figure 2).
?!
OPTICAL SYSTEM
Mercury Lamp. Philips TUV 6W, which requires no ballast for connection to 220-volt mains. Approximately 65% of its emission is at 2537 A. None of the other limes will excite the activated cadmium borate of the fluorescent layer. The fluorescence excitation will be the same as if from a monochromatic light source. Quartz Flow Cell. A flattened cell made from clear quartz tubing with a path length of approximately 1 mm. was found most suitable. There is no optical focusing in the system and that leaves great freedom as regards shape and path lengths of the cell. Fluorescent Layer. Polyethylene film was dissolved in boiling heptane to make an approximately 0.25% solution, and, while hot, was thinly sprayed onto a microscope slide. This was sintered for 5 minutes in an oven at 110' C. Next, a suspension of activated cadmium borate (AB Lumalampan, Stockholm 20) in the same solution was sprayed on top of the first layer and then sintered as before. This procedure was repeated until an evenly opaque deposit was obtained. Finally, a protective coat of polyethylene was applied in the same manner. The resulting
0-lOOmV
Figure 2.
film (approximately 0.004 inch) was then peeled off the slide. Red Filter. Ordinary red cellophane was satisfactory. Our sample had the following transmittance characteristics: 3600 to 5800 A., 0; 6000 A,, 30%; 6200 A., 67%. This filter virtually cuts out the whole emission of the mercury lamp, but lets through a substantial portion of the secondary emission of the cadmium borate. Photoconductive Cells (Philips ORPSO). This cadmium sulfide cell has its maximum sensitivity in the visible red. Slits, fluorescent layers, and filters were mounted on the cells in the order shown in Figure 1,b. The cells were placed touching each other and parallel to the mercury lamp. This arrangement gave optimum cancellation for the flickering of the lamp. ELECTRICAL SYSTEM
The circuit diagram is presented in Figure 2, which is mostly self-explanatory. However, certain features need special mention. Sensitivity. The sensitivity of the photoconductive cells rises rapidly in the range above 100,000 ohms and they should therefore be made to operate in this region. The illumination corresponding t o 100,000 ohms was found by adjusting the slit size and the distance from the lamp. In our case the slits had the dimensions 30 x 3 mm., and the distance from the center of the lamp to the centers of the cells was 150 mm. Individual cells may show small differences in sensitivity but can be matched by shunting an appropriate resistance across the one with the higher sensitivity.
Circuit diagram
Absorption Range Selection. A range selector allows a choice of scales according to the expected absorption. It is preferable to make the selector stepwise with a factor of 2 between the steps. With the flow cell and the range selector, satisfactory recordings were obtained in the absorbance range of A';:. = 0.1 to 10. Balance. The balance control of the bridge allows adjustment for moderate degrees of absorption in the solvent system used. Once the unit is balanced, it is possible to switch from one absorption range to another without displacement of the base line. Stability. The output of the mercury lamp is rather unstable, with much flicker. However, thanks to the juxtaposition of the two photoconductive cells, and to the bridge circuit, this effect is not apparent, and i t is unnecessary to stabilize the lamp supply. Another cause of instability is a drift in the conductivity of the cells themselves. The drift observed on the recorder of course represents the difference in drift between the two cells, but a pair which is matched in this respect has not been found. However, after a warm-up period of about 30 minutes this drift becomes barely noticeable. Recording. The requirement on the recorder is that i t should be of the high impedance type, and we have used a Varian Recorder Model G10, 0 to 100 mv. The output of the bridge would then be too high and a voltage divider was therefore used (Figure 2). VOL 33,
NO. 9, AUGUST
1961
1291
