place by a clip, E , passcs through a perpendicularly adjusted stainless steel sleeve inch in internal diameter, F , which is push fitted intci a Lucite disk of inch thickness, H . The latter serves a t the same time as a cover. Lucite cover (fastened to the manifold, D)and tube holder K are, a t a working distancc of approximately 51/2 inches, both attached by a iTing screw, L, to a X 22 inch rod, A . This shaft rests in a 2-inch high c0ppf.r block, S,n ith a cylindrical
hole I / S ~ inch larger than the rod dianieter and freely rotating. The shaft seat. -i',is silver soldered onto thc pan, -11, in which the water is heated by a circular immersion heater and thermostatted at the desired temperature. If Erlenmeyer flasks are used, a wider pan is required or alternatively a bulge has to be nelded to the front of the pan. The advantages of this unit are obvious. For speedy operation a simple
attachment of the tubes is reqLiired, here brought about by the use of a spring. A facile n a y of adjusting the erld above the solvent surface has been achieved' rotary arrangement is convenient and 'pace saving* The general Principles of this construction can easily be adapted for similar purposes. (A similar unit is now available from Organomation Associates, Turnpike Sta., Shrewbury, Mass.).
Continuous-Feed Rotating Evaporator Gunter Zweig, Pesticide Residue Research laboratory, University of California, Davis, Calif. N
AN
a11-glass, continuous-feed ro-
ISAL. tating evaporator described b y Kohn CHEM. 28, 1061 (1956)] the evaporating flask was driven by a belt, made from a rubber band, connected to a pulley on a laboratory stirring motor. Because of difficulty due to slippage of the belt, another evaporator was assembled, which utilizes c.ommonly available equipment. This evaporator has been in use in this laboratory for sevwal months, concentrating large amounts of acetone and alcohol solutions of plant extracts.
The continuous-feed, rotating evaporator consists of a Rinco evaporator, 1; Rinco special condenser flask with $24'40 neck, 2; adapter with $24 '40 inner joint and SB28/15 outer joint, 3; adapter n i t h SB28/15 inner joint and $24140 outer joint, 4 ; condenser with $24140 joints, 5 ; vacuum adapter with $24,'40 joints, 6; round-bottomed flask with 24/40 joint (500-ml. size), 7 ; T12/30 inner joints, 8; and 3-liter separatory funnel, 9. Adapter 4 is clamped tightly to a ring stand, so that condenser flask 2 and adapter 3 are turning while the evaporator is in operation. The solution is fed
sa,paratol)l tunnel
n
to vacuum
1
from the sepamtory funnel a t a constant rate, which is regulated so that the level of the liquid is constant in the condenser flask, which is actually serving as the evaporating flask. The level of liquid is kept 2 inches be1oIv the opening, 10, to prevent splashing. The receiving flask, i , is kept a t room temperature, so that vapors do not collect and operation may be continuous. All glass connections are well greased with silicone stopcock grease. By using a u-ater aspirator a t about 25 to 30 mni. of mercury pressure, 2 liters of a n acetone eytract from potatoes or green leaves may be concentrated to dryness in less than 1 hour. The concentrate is then transferred from the condenser flask with several washings of acetone. Solutions containing mineral acids should not be concentrated, because the metal shaft of the Rinco evaporator nil1 corrode slightly. Substitution of a stainless steel shaft overconies this disadvantage, as the solution that passes through the metal shaft is a t ambient temperature. The relatively high cost (about $100) may discourage routine use of this evaporator in some laboratories.
Base-Line and Maximum Value Methods in Infrared Quantitative Analysis
H. L.
Cupples, Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md.
-4 STUDY of the susceptibility of infrared base-line methods to errors caused b y overlapping bands of unknown constituents not present in the calibrating solutions, base-line determinations were made of y-benzene hexachloride (BHC) in admixture with its isomers, which were considered for this purpose to be unknown impurities.
IN
Spectra were taken in carbon disulfide solution on a single-beam recording spectrophotometer, and the relevant points converted to per cent transmittance. All base lines were drawn from the curve intersection with the ordinate a t the selected wave length, parallel to
the zero energy line. A t 15 selected wave lengths in the 7.5- to 15.0-micron range, 27 base lines I\ ere established (tm-o each a t 12 of the wave lengths), and, using purified y-BHC, graphical calibrations were determined for each base line. All these calibrations, therefore, were valid for a y-BHC-carbon disulfide system; the base lines were drawn in a uniform manner, none being specially chosen for use in the presence of the isomers or a n y other specific impurities. Then y-BHC was determined in a carbon disulfide solution containing 15.0 grams per liter of 7-BHC in admixture with 15.0 grams per liter of its isomers, the isomers being present in
proportions approximately that of technical BHC. Figure 1 sho\vs determined amounts as percentages of the true amount. Of the 27 determinations only nine are within + l o % of the true amount, and many are seriously in error. It is evident that a n indiscriminate application of baseline methods to mixtures of unknown qualitative composition may result in large errors. If, however, the spectra of the sample and known components are compared, and the analytical wave lengths and base lines chosen with reference to them, better results will be obVOL. 3 1, NO. 5 , M A Y 1959
e
967
tained. The arrows in Figure 1indicate wave lengths which might be so selected.
Maximum Value. At the same wave lengths, determinations were made of t h e absorbance of t h e solute, log loil,in which lo is the intensity of t h e beam when t h e cell is filled with solvent and I is t h e corresponding intensity with t h e cell filled with sample or calibrating solution. At each wave length, y B H C was estimated by referring the absorbance of the sample to a corresponding y-BHC Calibration curve, with no correction for overlapping bands. The lowest of these estimations is the "maximum value," in this instance 101.2% of actual. This maximum value is not merely an uncorrected value, or approximation. It is also a value which, within experimental error of the absorbances, will equal or exceed the actual value, except for the very unusual situation (in the 7.5- to 15.0-micron
Figure 1. Determination of T-BHC in BHC isomers b y baseline-density methods
range) where the analytical mode is weakened by molecular complexing of substances not present in the calibrating solutions. The maximum value technique has been applied with good results to the
determination of dieldrin and aldrin (insecticides) in emulsifiable concentrates. It may be of substantial value in regulatory and control work which requires only evidence that the amount present is below a stated value.
Improved Method of Heating Chromatographic Columns L. R. Bunney, Randall Phillips, and E. C. Freiling, U. S. Naval Radiological Defense Laboratory, San Francisco 24, Calif. N INVESTIGATIOKS involving ion ex-
1 change column
chromatography it \vas desired to operate columns above room temperature to increase the rate a t which ion exchange equilibrium is approached. The range of 80" to 90" C. includes most usual operating temperatures, but some experience has been obtained a t higher temperatures. Three methods of heating hare been used b y numerous investigators: refluxing vapors of a suitable liquid, such as trichloroethylene (boiling point 87 ' C.),
nN,/
ION FXCHANGE
I
I I I
II
circulating rvater from a constant temperature bath, and flexible heating tapes wrapped around a liquid-filled jacket. These methods all have drawbacks.
I
TOP CONTACT
ELUENT [ZONE PWHEATING (-
(
ION EXCHANGE COLUMN
A 48-inch length of tubing 30 mm. in outside diameter, divided into three sections wired in parallel, is used as a heating jacket for an ion exchange column, 13 mm. in outside diameter, as shown in Figure 1. Water is used as a heat transfer agent between the two columns for temperatures below 90' C. For operating temperatures in the range of 90' to 220' C., Dow Corning 550 fluid has given the most satisfactory performance. The temperature is controlled by a Variac. The maximum service temperature of the tubing is 350' C.
7' VARIAC
U Figure 1. Schematic diagram of chromatographic column jacket
968
ANALYTICAL CHEMISTRY
A method that has been in use in this laboratory for over a year utilizes a column heating jacket of electrically conducting Pyrex tubing (Corning Glass Co., Corning, N. Y., Catalog Xo. 9340). The electrically conductive film, which acts as a resistance element, is on the outside surface of the tubing. This film is chemically inert, very hard, and transparent. Using this technique reduces the complexity of the equipment necessary for heated column chromatography and increases the reliability of the experimental setup. The shock hazard from the equipment is small, if care is taken with the polarity of the Variacs.
TEMPERATURE 1%)
Figure 2. Temperature variation in column jacket at 85', 173", and 216" C.
The temperature variation along the length of the column under steadystate conditions is shown in Figure 2 for operating temperatures of 85" I-t Z', 173' f 3". and 216" ==I 6" C.
