Constant Temperature Explosion-Proof Cabinet for Development of Two-Dimensional Chromatograms Hadd P. Cohen, Division of Neurology, University of Minnesota Medical School, Minneapolis, Minn.
J&n LogoihePb and
rate of migration of comB poundstheseparated by paper chomaEcAuaE
tographie techniques is, in part, tempemtureilependent (1, 8), fluctuations of a few degrees in ambient temperature within the cabinet during and between chromatographic runs may seriously inkfiere with separation of the spots and reproducibility of R, values. The available double-walled chromatographic cabinets, designed to keep such temperature changes a t a minimum, were found in preliminary studies to be unsatisfactory for chromatographic regroduri-
hiity. To improve results, separations were carried out a few degrees above ambient temperature by positioning two infrared lamps near the cabinet and adjusting their heat output with a rheostat. Although this improved temperature regulation within the cabinet and acceptable chromatograms were prepared (S), variations in temperature were still relatively wide. To provide a more constant temperature environment, an electrically heated, thermostatically controlled chromatographic cabinet was designed with the electrical
Figure 1, T h e m t e R caily cantdbcd chrome-
tographic cabinet
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TOP VIEW
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RUBBERCUSHION
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I2 ABOVE-AMBIENT TEMPERATURE CONTRQLING I N STALLITION
The stainless steel cabinet (Figure l ) , has an air-tight top cover and measures 16 x 16 X 30 inches. It was designed for use with a chromatographic rack holding 25 X 25 cm. filter paper squares. The double-walled construction, including the safety-glass window, provides for a free air space which surrounds the main compartment. Part of the air space is filled with a blanket of glass wool attached to the outer wall, allowing room for free circulation of warm air. The details of construction are shown in Figure 2. The small 1/n60-hp. fan, mounted between the double walls, receives power continuously when the unit is in operation. Two 250-watt herating elements are mounted at the bottom of the cabinet in the air space. Both elements are controlled by a relay (Honeywell RASSAlCG), mounted outside the cabinet, and activated by the sealed mercury switch of the thermostat (Honeywell T86A7X103), which is mounted inside the cabinet and is protected from the environment by a small borosilicate glass cover, 1 mm. thick. The cover is sealed to the cabinet wall with a replaceable rubber gasket relatively impervious to organic solvente used in the chromatographic s t u d i e e Le., phenol, lutidine, acetic acid, alcohols, etc. The interior of the cabinet thus contains only the thermostat and the lighting fixture, both corrosion- and explosion-proof. When in operation, circulation of warm air between the double walls. with the insulation on the outside wall. provides reasonably efficient radiation of heat to the inside of the cabinet. For a temperature setting of 10' above ambient, equilibration is reached within 2 hours. The only precaution with flammable organic solvents is to turn off all power before opening the cabinet after a chromatographic run. The cabinet can be modified in design to suit individual reauirements.
mom FAN PROTECTORELAY UNK LINE 115 V THERMOSTAT TOP LIGHT MANUAL LIGHT SWITCH DOUBLE GLASS WINDOW COMMUNICATING HOLES STAINLESS STEEL DOUBLE WALL AIR CIRCULATING SPACE BOTTOM OF TANK HEATERS DRAIN
3
Figure 2.
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S I D E VIEW-CROSS SEC,TON
system completely isolated from the solvent-vapor environment. Temperature control is excellent, and no danger of fire or explosion exists.
Essential parts of cabinet
Temperature regulation within thc cabinet proved excellent for above ambient settings. Cabinet temperature measurements were made over a 15day period and compared with laboratory temperatures and those of n double wall chromatographic cabinet purchased a few years ago (Figure 3). Temperature in the heated cabinet did not vary more than 0.32"C. as compared with temperature extremes of 9.2" C. VOL. 31, NO. 9 SEPTEMBER 1959
1601
in the laboratory and 8.5" C. inside the standard cabinet. Temperature inside the latter cabinet followed very closely that of the laboratory.
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ACKNOWLEDGMENT
(3
The authors express appreciation to Glen Grapp for valuable technical assistance.
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LITERATURE CITED
TEMPERANRE CHANGESINTHE LABM1ATORYlMAX VARAllON 9TC.j
28O
26' 25O
-
TEMPERANRE IN THERMOSTATIC CABINET [MAX VARIATION 0 32.C)
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TEMPERATURE CHANGES IN COMMERClAltY AVAILABLE CABINET [ M h X VAR 05'CJ
-
24O
23O
n 220
(1) Dent, C. E., Biochem. J . 43, 169 (1948). (2) Jirgensons, B., University of Texas, Publ. 5109, 56 (1951). (3) Logothetis,J., NeuroZogy8,299 (1958).
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DAYS OF EXPERIMENT
WORK supported by grant B-1183 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health.
Figure 3. Temperature fluctuation at various laboratory temperatures
Sodium Azide as an Internal Standard for Quantitative Infrared Analysis R. T. M. Fraser, Dominion Laboratory, Department of Scientific & Industrial Research, Wellington, New Zealand
A
to infrared quantitative analysis is the low solubility of some compounds in suitable organic solvents. The technique of mixing the sample with a known weight of an internal standard and incorporating the mixture in a mull or potassium bromide disk is designed to overcome this difficulty. Naphthalene (d), DL-alanine (f), lead thiocyanate (7), and calcium carbonate (3) have been suggested as internal standards, but the spectra of naphthalene and m-alanine are much too complex to be generally employed (6), and although calcium carbonate was added only in a 1 to 100 ratio, the carbonate peaks (1430,877, and 715 cm.-l) might interfere with the desired analytical peak. From the published spectra of inorganic compounds (5) potassium ferricyanide and then potassium thiocyanate were recommended as the internal standards for potassium bromide disks. Potassium thiocyanate was unsatisfactory because with the high proportion of standard to sample required (78: 100 to 540: loo), the 2020-cm.-l thiocyanate peak was very broad. These mulls showed a very high background, and water absorption was a problem. With quantitative running conditions (4, it is no longer necessary that the standard possess a reference peak close to that of the sample, and it is a distinct advantage if this peak is in the 2000- to 2800-cm.-l region where most organic compounds have little absorption. Sodium azide with a very strong peak a t 2140 crn.-' (Figure I) and a LIMITATION
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ANALYTICAL CHEMISTRY
weak peak a t 1309 cm.-' fulfills this requirement. In the determination of sodium fluoroacetate in dried residues from soil dispersion, sodium azide was used as an internal standard, but because' of the intense absorption of both the C-F peak (1338 cm.-l) and the azide peak it was necessary to use extremely thin mulls containing a large proportion of
Nujol. By adding a nonabsorbing compound such as potassium bromide as diluent, however, mulls of medium absorbance could be prepared in the usual way. The use of potassium bromide not only decreases the amount of Nujol required, thus increasing the transmission of the mulls, but also facilitates the grinding of the solids before mulling. Ratios of azide-so-
FREOUENCY Cm-1 4000
3000
2000
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E Figure 1. Infrared absorption spectrum of a Nujol mull of sodium azide 3 grams of ozide to i00 grams of potassium bromide CI
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Figure 2. Effect of grinding time on stand-ard to sample 'absorbance ratio
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Absorption of azide compared with absorption of free acid in a sodium salt
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