ANALYTICAL CHEMISTRY
164 marked on the cylinder along side the 20-cm. mark. I n use, it is desirable that all the cylinders in any one test have substantially the same dimrnsions-e.g., hold the same volume up to the 20-cm. mark. When calibrated, the cylinders generally held from 185 to I95 ml.; the greatest number held 185 ml. A pulley wheel is attached to the end of one of the axles, and also a handle for manual turning. Manual turning has been found to be quite sufficient for all ordinary comparisons; however in some cases it might be desirable to use a constant-speed motor attached to the pulley wheel. T E S T METHODS
Concentrated Emulsions, containing 10% or more of oil phape. EMULSIFIABLE COXCENTR.4TES HEAVIERTHASWATER. The emulsifiable concentrate is measured directly into the bottom of the glass cylinders, then the water used is added slowly down the side of each cylinder so as to leave the concentrate as a discrete layer beneath. A small amount of emulsion almost invariably forms a t the interface, but the two layers must. be clear. Keeping the frame slightly tilted aids in this operation. Afterward, the tubes are stoppered (No. 7 rubber stoppers or corks may be used) and the frame is closed and tightened. Rotation of the frame 10 to 20 times then forms all emulsions simultaneously, except for the traces of emulsion which formed during the previous operation. Comparisons are made a t convenient time intervals thereafter-for example, 1, 5, and 10 minutes, 1 hour, and 21 hours. If it is desired to take numerical readings of creaming or sedimentation rates, a thin strip of millimeter paper may be cemented to the side of each cylinder and readings taken from this. EMULSIFIABLE COSCENTR4TES LIGHTERTHANFvATER. The procedure is exactly as described above, except that the water is measured into the tubes first, then the emulsifiable concentrate(s) are measured carefully onto the surface of the water in each tube. DENSITYOF EMULSIFIABLE CONCESTRATE 1s EXACTLY 1.000. It is desirable to run a preliminary test a t room temperature to see whether sediment rises or falls. Either may occur through slight composition changes in the two phases. Thereafter bv raising or lowering the temperature a t which the test is run, it should be possible to carrv out the test as described for the two types above. Dilute Emulsions, containing 2% or less of oil phase. The emulsifiable concentrateis) are measured into 5-ml. Griffin beakers, which in turn are floated on the surface of the water used in the respective cylinderfi. The cylinders are stoppered, the rack is closed and tightened, and the frame turned through 10 to 20 rotations, as before. If the volume of the concentrate is less than about 1 ml., it is necessary to weight the bottom of each beaker to prevent tipping. This may be done by cementing a small disk or metal washer to the outside. I n use, the beaker almost invariably comes to rest in an upright position on the bottom of the emulsion tube. In the rare instance when one does not, i t can nearly always be righted by allowing all the beakers to fall through one more complete revolution. Turning the rack to an angle about 30” with the vertical, then allowing it to come to rest in vertical position, causes all the beakers to move to one side, after which sedimentation rates are observed from the other side. Since the vertical edge of each beaker occupies a relatively small, nearly constant area, it does not interfere seriously with reading of sedimentation rates, even though aome of the sediment falls inside the beaker. Wettable Spray Powders, suspension and foaming. The powders are weighed directly onto the surface of the water. It is desirable to weigh the powders first, then drop them all into the cylinders containing water, a t as nearly the same time as possible. The cylinders are stoppered and frame is closed, tightened, and rotated 20 to 30 times (more if necessary to break up agglomerates). If foaming is to be compared, it is desirable to fill the tubes only about half full and use vigorous agitation (rotate the frame quickly for about 30 seconds). Re-emulsification and Resuspension. These qualities may be determined after a suitable time interval by rotating the frame again and noting the number of complete revolutions necessary to resuspend or re-emulsify the sediment, in each case.
-4typical example is shown in Figure 1; the emulsifiable concentrate in tube 1 was added slowly down the side of the tube into the water 3 minutes before agitation, while the same concentrate in tube 2 was added to the floating beaker; thus, introduction of concentrate into the water was simultaneous with agitation. Otherwise the two emulsions received identical treatment (experimental details appear in Table I ) . This does not appear to be a problem with emulsions containing IO’% or more of oil phase, when evaluated as described above, and may not be a problem with all emulsifier-solvent systems. The range between 1% oit phase and 10% oil phase is doubtful.
Table I. Tube S o 1
Details of a.Typical Comparisonn
Water Used Tap
Hardness (as CaCOd. P.P. M , 40 (approx.)
Method of Adding Concentrate .Idded down side of tube 3 minutes before agitation Added t o floating beaker Added t o floating beaker Added t o Boating beaker Added t o floating beaker Added t o floating beaker
40 (approx.) Tap 0 Distilled 250 Artificial hardb 500 5 Artificial hardb 6 .Irtificial hardb 1000 a Results shown in Figure 1. b Equal moles of calcium chloride and magnesium chloride
2 3 4
LITERATURE C I T E D
Griffin, W. C., and Behrens, R. W,, . \ N ~ L . CHEY..24, 1076-8 (1952). Kelly, J. A., J . A g r . Food Chem., 1, 254-7 (1953). Sela, E., Ibid., 1, 381-6 (1953). Suggitt, J. W., “Procedures for Evaluating Herbicides,” presented before Agricultural Pesticide Technical Society, Xacdonald College, Quebec, Canada, June 23, 1954.
Trap for Attenuating Mercury Vapors in the Mass Spectrometer B. 1. Tuffly and W. J. Lambdin, Carbide & Carbon Chemicals CO., Division of Union Carbide & Carbon Corp., South Charleston, W. Va. HE
presence of mercury parent peaks a t m/e 198 to 204 and of
Ttheir half-peaks a t m / e 99 to 102 has caused difficulty in the interpretation of some mass spectra. Mercury in the ionization chamber of the Consolidated mass spectrometer Model 21-103 arises from three different sources: the manometer in the gas inlet system, the diffusion pumps in the exhaust vacuum unit, and the mercury orifice (liquid inlet). Mercury vapors from the manometer of the gas-inlet system are
n-
-32 X 90 mm VESSEL
DISCUSSION
Where dilute emulsions containing 1% or less of oil phase are evaluated, it has been the experience of the author that variable and erratic results are obtained when there is a delay between the introduction of the emulsifiable concentrate into the water and agitation of the mixture While believed to be due to extraction of part of the emulsifying agent by the water before agitation, this effect has not been investigated beyond establishing that it exists.
Figure 1. Diagram of Trap
165
V O L U M E 2 7 , N O . 1, J A N U A R Y 1 9 5 5 of little importance because this portion of the spectrometer is usually closed to the metal valve block; a trap of solid carbon dioxide and another of oxygen (or nitrogen) prevents mercury vapors in the diffusion pumps from entering the ionization chamber to any great extent. Mercury vapors most often arise from the sample inlet region. The entire inlet system becomes saturated with mercury; passage of the vapors into the ionization chamber is, therefore, unavoidable, particularly with the introduction of higher boiling liquids. Many of the metals readily form amalgams with mercury; however, the material selected to attenuate the vapors must be sufficiently inert to organic vapors. Although gold foil is commonly used to check mercury in vacuum systems, the expense of the metal makes the use of such a trap less attractive, especially if the trap must be changed periodically. While zinc is known to be active toward the more polar materials, it was selected in this investigation because of ready availability. In order to test the efficiencyof zinc as an attenuator, mercury vapors a t a pressure of a few microns were pulled through a trap filled with 10-mesh (Bakpr’s analyzed) zinc, followed by a liquid oxygen trap. There was no evidence of mercury in the cold trap even after 48 hours. The installed trap is illustrated in Figure 1. The trap is between the mercury orifice and the metal valve block. The gas inlet line has not been modified, and therefore, mercury may still enter the chamber from this region. To facilitate removal of the trap for cleaning and refilling, ball joints were used. Platinum gauze n’ae placed over the two openings, thus preventing migration of zinc to otherparts of the spectrometer. Because of thelarge increake in surface area of the inlet system, considerable background effectsfrom absorbed materials will be noticed. This can be avoided by heating the trap with resistance wire. The temperaturp chould be held below 100” C. to prevent damage to the wax joints. Numerous runs a t 50’ C. using air, water, or methanol a? fluehing agent indicated that background effects were not increased, if the pump-out time waq a t least 5 minutes. The height of the mercury half-peak ( m / e 101) is shown in Table I for different compounds expanded in the inlet system before and after installation of the trap.
acetic anhydride, and acetic acid, were also examined. Comparison of the spectra obtained with and without the trap revealed no apparent differences in peak ratios or intensities. This indicates that there is no discrimination of the more polar molecules while passing through the trap. Sensitivity values were not affected in any way; indeed, there should be no change in base peak height per micron because the trap does not alter the calibrated volume. The micromanometer measures the pressure within the3-literpreleak bulb, and the trap is in the line prior to the metal valve block. The authors do not use calibrated volumes for sensitivity measurements, but instead use a micromanometer for measuring the pressure in the expansion volume. If calibrated dippers are used, there will obviously be a volume change, and, consequently, a pressure change; therefore the volume of the system must be determined after installation of the trap. The zinc in the trap was changed after 6 months (1500 complex nonroutine samples) of continuous use. Mercury peaks are obtained only after prolonged pumping of the orifice system and operating the instrument with five times the normal sensitivity (50 pa.).
Versatile Polarographic Cell Robert 1. Pecrok and Richard S. Juvet, Jr., University of California, Lor Angeler 24, Calif.
\
POLAROGRAPHIC “dilution” cell of conventional design - (Kolthoff, I. M., and Lingane, J. J., “Polarography,” Vol. I, p. 364, S e w York, Interscience Publishers, 1952) fails when strongly acidic or basic test solutions are to be analyzed. In these cases, the test solution slowly dissolves the agar plug, resulting in contamination of both the test solution and the reference electrode. Carritt (Carritt, D. E., Ph.D. thesis, Harvard University, 1947) recommended a modified H-cell which prevented the diffusion of chloride ion from the reference electrode into the test solution. However, his cell was somewhat fragile, and did not prevent the eventual contamination of the reference electrode.
Table 1. Effect of Zinc Trap Compound Examined llethanol E t h y l alcohol 2,4-Hexadienal -4cetic acid Isopropyl alcohol Dodecene
a
Height of m/e 101 Arbitrary Units Before installation After installation 4.0 2.1 4 6
15 1 6.3 5.0 4.1
18.3 76.1 3Iethanol 0.3 E t h y l alcohol 1.1 Examined shortly a f t e r installing t r a p .
2.50
2.1” 0.2 0 0 0.0 0.0 0.0 0.1 0.3 0.1 0.0
Samples admitted through the gas inlet are obviously not affected by the trap, whereas those admitted through the mercury orifice show a marked decrease in peak height a t m / e 101. These data were taken several months after installation of the trap; mercury peaks were detcctable a t normal ionizing current (10 pa.) for about 2 weeks after installation because of adsorbed mercury in the metal valve block; after this period, however, the device functioned satisfactorily for several months without service In order to determine the effect of zinc on organic samples, the following compounds were examined mass spectrometrically hefore and after fabrication of the trap: ethylene dichloride, methanol, n-butyl alcohol, 2,4-hexadienal, acetic acid, water, propylenediamine, acrolein, ethyl acetate, and benzene. Mixtures containing ethylene chlorohydrin, ethylene dichloride, and ethylene oxide--20 hydrocarbons, saturated, unsaturated. and aromatic-
T
3 cm I i B cell of rugged construction has been designed to eliminate these problems. Volumes of solution from 2 to 55 ml. may be analyzed, and the opening is large enough so that a glass electrode may be permanently mounted in the stopper, if desirable. Compartment A contains the saturated calomel electrode. B is an agar plug saturated with potassium chloride. A sintered-
