Frozen Vitamin Standards OLOF E. STAMBERG A N D D. W. BOLIN Department of Agricultural Chemistry, University of Idaho, MOSCOW, ldaho
I
N VITAMIN analyses, the preparation of accurate standards is time-consuming and in most laboratories fresh standards are prepared every few days for some vitamins. Glick (5) shows the instability of standards and states “that it is unsafe to use a standard solution of thiamine in dilute acid after i t has been stored for more than a few days”. That ribohvin solutions undergo photolysis was especially shown by the recent work of De Merre and Brown ( d ) . The use of frozen vitamin standards is possible both for accuracy and as a time-saving method. Thiamine hydrochloride and riboflavin standards were prepared in 2y0 acetic acid containing 10 micrograms per ml. The salutions were made up and further handled in a dark room used for riboflavin studies. Five-milliliter aliquots were pipetted into 15-ml. vials and tightly stoppered with cork stoppers, which had previously been allowed to soak in 2% acetic acid and then in distilled water before drying. The vials were then immediately laced in a refrigerator a t about -15” C. and a t a 45” angle for freezing and storage. The ribo5vin vials were placed in a box to eliminate any light. Ordinary vials will not break on freezing if placed at an angle and if not filled completely. The frozen standards were tested at various intervals of time and compared with similarly prepared fresh standards. Frozen standards stored for 0 months or for shorter intervals were perfectly satisfactory. The Coleman photofluorometer was used for the measurements and the thiamine was oxidized by the
method of Conner and Straub (I). The frozen standards were thawed out in a beaker of water a t room temperature which required about 10 minutes. Immediately a 2-ml. aiiquot was pipetted out and diluted with 2% acetic acid to give the desired concentration. This was done in the dark room and is important in the case of riboflavin. At least two vials should be thawed each time for checks against improperly stoppered vials and hence moisture loss. Such frozen standards have proved very efficient, in that a large number of vials can be prepared and used over a long period of time, since the use of the microbalance and the accurate preparation of standards are time-consuming. The method is perhaps also applicable to other vitamins. The use of standard solutions stored at low temperatures is apparently unreliable, particularly in the case of thiamine. LITERATURE CITED
(1) Conner, R. T., and
Straub, G . T., IND.E m . CHEM.,ANAL.ED., 13,385 (1941). (2) De Merre, L. J., and Brown, W. S., Arch. Biochem., 5 , 181 (1944). (3) Glick, David, C e w d Chem., 21, 119 (1944). PUBLIBXED with the approval of the director of the ldaho Agricultural Experiment Station 88 Research Paper No. 237.
Apparatus For Small-Scale Vapor-Phase Treatment of
Solid
Compounds
MILTON ORCHIN Central Experiment Station, Bureau of Mines, Pittsburgh, Pa.
IN
T H E vapor-phase dehydrogenation studies being conducted in this laboratory (I, 8) it became desirable to examine the behavior of numerous solid compounds. For this purpose the apparatus shown in Figure 1 was constructed and found satisfactory. The preparation of the catalyst and a portion of the apparatus have been described (9). The solid compound to be treated is packed into the reservoir, d and the mercury leveling bulb lowered, so that the mercury in e’is just above the level of the nitrogen inlet tube. Dry hydrogen is admitted past the safety trap, f, through the capillary, g, and into the catalyst bed, b. A tube leading from receiver h to a bubble counter will indicate the rate of flow of hydrogen.
After the hydrogen pressure is once adjusted it should not be changed during the entire experiment. The catalyst tube is heated to the desired temperature by means of the furnace, a, which consists of an iron pipe wound with resistance wire. After the desired temperature is reached, the solid in d is melted by the heating coil, i, constructed of insulated resistance wire and controlled by a variable transformer. When the compound is liquid, the hydrogen entering through g will be observed bubbling up through d. A small stream of dry nitrogen is admitted and the mercury in e raised until the bubbling through d just stops. At this point the pressure on the liquid in d is just equal to the pressure in b. If the leveling bulb is now raised slightly, the increased pressure causes the melted compound to flow through the 1-mm. capillary, c, and into the hot catalyst bed. The head of mercury in e controls the rate of addition of the compound. With a little experience, as little aa 1.5 grams of material can be put through the furnace at a fairly uniform rate of about 0.7 gram per hour if desired. Solid compounds of any melting point can be conveniently handled. I n smaller furnaces the insertion and removal of catalyst are facilitated by attaching the receiver, h, by means of a cork and thus eliminating the cpnstriction in the catalysttube due to a T glass joint. Some kind of electrical heater should be placed below h to keep the product liquid and prevent clogging. The author is indebted to John J. Vidosh for the drawing.
Vent to~atmosphere
H ydr ogcn
LITERATURE CITED
(1) Orchin, J. Am. Chem. Soc., 67, 499 (1945). (2) Orchin and Woolfolk, Zbid., 67,. 122 (1946). PUBLIERED by permiesion of the Director, Bureau of Mined, U. 8. Department of the Interior.
Figure 1
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