ANALYTICAL CHEMISTRY
1396
analysis of more than 150 samples with comparable reproducibility.
Table 111. Precision of RIoly-bdateMethod Sample Weight, Grams 5 5 8 Analyst A A A B
SUMMARY
The method as outlined is the only accurate method known for the determinaton of nordihydroM a x . Precision, 70 x a x P z= Deviation guaiaretic acid in creosote bush leaf. It is rapid, M a x . Yo Dev. N.D.G.A.. % of x 100) dr. S D.G:‘A. (Av. 7 N.D.G.A. easily mastered, and requires no special skills, and lb 9.13 8.95 9 . 1 0 9.36 9.13 0 41 2.2 is, therefore, suited for routine analytical determi1.8 8.20 8.28 8.11 0.30 2 7.98 8.00 nations. The method should be applicable t o 0.7 9.61 9.50 9.47 9.54 0.14 3 9.57 systems low in other o-dihydroxybenzene coma D a t e determined. X, Y ,2 refer t o different days. b 1 , 2 , 3are samples from different regions of Rio Grande Yalley. pounds and for the determination of added nordihvdroeuaiaretic acid in fats,. oils,. and various food products. The only disadvantage of the method Calculations. is the limited interference by structurally similar compounds. Approximate corrections can be made for these compounds y/mL (from curve) X 2000 (dilution factor) X 100 7 0 N.D.G. 4. = LITERATURE CITED 1,000,000(convert t o grams) X 5 (wt. of sample) Emmerie, A . , and Engel, C., Rec. tral;. chim., 58, 283 (1939). water-insoluble tannin (%) - 0.4% (interference of Gibbs, H. D., J . Bid. Chem., 72, 649 (1927). water-soluble compounds) Haworth, R. D., and Richardson, T., J . Chem. soc., 1935, 120. Horn, G. M., Ph.D. thesis, University of Minnesota, 1943. Or, condensed: Lundberg, IT.O., and Halvorson, H. O., Proc. Inst. Food Tech., 1945, 115. r / m l % S.D.G.X. = 25 - l/*water-insoluble tannin (%) -0.4% Martini, A., Mikrochemie, 12, 112 (1932). Mitchell, C. A . , Analyst, 48, 2 (1923). Schroeter, G., Lichtenstadt, L., and Irineu, Ber., 51, 1587 The precision of the method is about *2%, as is shown in Table (1918). 111. Snell, F. D., and Snell, C. T., “Colorimetric Methods of Analysis,” Vol. 2, New York, D. Van Nostrand Co., 1937. The determination of precision is based on checks run by the Waller, C. W., Ph.D. thesis, University of Minnesota, 1942. same analyst on the same and on different days and on compariRECEIVEDh’ovember 29, 1948. Presented before the Physical Science Secson with the results of another analyst who used a different tion of t h e 24th Annual Meeting of t h e American Association for t h e Adoriginal sample weight. The method has been used for routine vancement of Science, SouthFestern Division. ”
I
-
Automatic Distillation
has been applied to the design of the apparatus described below, in which the more fragile components are enclosed within a robust exterior and a device is incorporated whereby when a desired
J. G . REYNOLDS AND B. w. SWANSON “Shell” Rejining & Marketing Company, Ltd., Thornton Research Centre, Thornton-le-Moors, Cheshire, England
A steam-distillation apparatus particularly applicable to Kjeldahl estimations is described. Its value lies in freeing the analyst during the distillation. It should save time and labor w-hen large numbers of estimations are necessary.
N
D
URING recent years many modifications have been made in the standard Kjeldahl steam-distillation apparatus (1-4). Equipment designed to carry out the distillation directly from the digestion flask has eliminated the necessity for a quantitative transfer. Alternatively where an aliquot has been transferred to the distilling apparatus, the automatic emptying device has proved most useful. T o avoid an increase in the sample volume, arising from condensation during steam distillation, some investigators have surrounded the distillation vessel by a vacuum jacket or located i t in the steam trap or even in the boiler itself. Experience gained with such modified equipment
I
I
Figure
1.
I
Automatic Steam-Distillation Apparatus
1397
V O L U M E 21, NO. 11, N O V E M B E R 1 9 4 9 volume of distillate has been received, the heating circuit is automatically broken and an audible warning is given. DESCRIPTION OF APPARATUS
The apparatus is shown diagrammatically in Figure 1. The glass section is made up of four main portions, the distillation flask, -4,the steam boiler, B , the steam trap, C, and the condenser, D. A is situated inside the neck of B and the sample is introduced by means of the tap funnel, E, and passes through the tube, F. After test the distillation vessel empties itself through an open side arm of F into C. B can be charged with water through a t a p funnel, G . Steam enters A through F , distilling the sample into D. An aluminum clamp and stand, H , support the whole glass section of the apparatus.
T h e nonglass section of the apparatus consists essentially of a wooden box, S , fitted at one end with vertical metal runners down which a second smaller box, X, can slide when a release, R, is operated. A platform, L, supported by four springs carries an aluminum pan, K . L can be depressed to close the contact switch, M , which operates a relay breaking the current to the electrical heater, J , and operating the buzzer, 0. The aluminum clamp embracing B has been omitted from Figure 1 to allow the details of the distillation vessel to be more clearly noted. The details of the electrical circuit are shown in Figure 2. Receiver. The capacity of the receiver should be suited to the volume of distillate required. The present apparatus, designed mainly for routine Kjeldahl distillations, has been constructed for distillate volumes of about 50 ml. and the standard carbon dioxide flask of 150-ml. capacity with a wide neck has been found suitable. Only flasks of approximately equal weight have been selected as receivers and the lighter the flask, consistent with capacity, the greater the volume of distillate which can be received. PROCEDURE
Figure 2.
Electrical Circuit
B is half-filled with distilled water which is brought to the boil. With G and C open, the sample is introduced into A through E. I n the case of Kjeldahl distillations excess sodium hydroxide
Table I.
Reference Letter A
Designation Distilling vessel
B
Steam boiler
C
Steam trap
D
Condenser
E
Sample funnel
F
Sample and steam tube
G
Boiler funnel
H
Clamp and stand
J
Heating unit
Specifications for Apparatus Reference Designation Description and Dimensions Letter Pyrex, 5.75 cm. internal diameter K Sprung pan X 17cm. Pyrex, 7.6 cm. internal diameter X 17 cm. sealed to 1-liter round-bottomed flask. Heater Sprung platform well 3.2 X 3.2 cm. is made in L boiler Pyrex, 3.2 X 16.5 cm. drawn out at bottom to 0.95 X 3.8 cm. tube fitted with rubber tube and screw clip Contact switch Pyrex, double surface 3.2 cm. inM ternal diameter X 16.5 cm., drawn out at bottom to 0.95 X 10 cm. tube ground obliquely Pyrex tap funnel, capacity about 30 ml. Pyrex, 0.6 X 11.4cm. Forkedsections, one attached to E and one Platform box entering distillation vessel from N C Pb-rex tap funnel, capacity about Buzzer 30 ml. 0 Aluminum clamp 0.16 cm. thickness X 3.8 cm. width embracing Lamp condenser steam trap and neck P Switch of steam boiler. The stand, Q Platform box made from 1.25 X 20 cm. brass R release rod, is screwed to clamp between steam trap and boiler, and fits Box into an adjustable collar on top S of s 2.5-cm. diameter Sindanyo (hard asbestos cement) bored rod grooved at top into a spiral, carrying heating element which consists of 8.2 meters of 30 standard wire gage Nichrome wire having a resistance of 150 ohms suitable for 240 volts a.0. Rod of heating unit enters S through metal collar and its height is adjustable
Description and Dimensions Aluminum, 0.16 cm. thickness X 5.75 cm. diameter bored to reduce weight and mounted on aluminum rod 0.64 cm. diameter X 10.1 cm. Tufnol, 0.16 X 5.1 X 7 cm. suspended at each corner by springs made from 28-gage spring piano wire. Springs are made to extend 5 cm. when a weight of 110 grams is placed on K Closed by pressure of L. Switch can be raised or lowered abou 2.5 cm. in Tufnol slide and locked into place by grub screw. A small metal rod is located under actual contact points to prevent L going beyond switch after making contact Tufnol, 8.3 om. deep X 13.3 X 13.3 cm. Box slides up and down runners fixed t o end of S Normal bell type operated by stepdown transformer froin the mains Panel operating lamp Double-pole toggle switch Brass. When operated A- can be held fast or allowed t o slide as required Plywood, 12.7 cm. deep, 27.3 om. long, 26.7 cm. high. Base 1.26 X 22.9 X 45.7 cm. One end wall is made of Sindanz-o and carries runners for N . A slot in the Sindanyo wall allows wiring from M to travel up and down vith N
1398
ANALYTICAL
solution is introduced into the distillation vessel, followed by aqueous washings of the funnel. With a t the bottom of its runners, the receiving flask containing 10 ml. of 4% boric acid and 3 drops of indicator is placed on K . Ai is then slid up its runners until R engages and holds it in position. The bottom of the condenser tube should now be just ])elow the surface of the liquid in the receiver. If necessary both H and the rod of J can be adjusted in their base collars until the correct height is attained. The taps on E and G and the screi? clip on C are closed. Dry steam enters the sample liquid through the branch of F and distillation ensues. Because A is surrounded by a steam jacket, very little increase in volume occurs. I s the volume of distillate increases, K is depressed until 1.I closes, operating 0 and switching off J . In the construction, the ratio of spring extension of L to the height which the distillate will rise in the receiver (allowing adequate volume for complete distillation) can be so arranged that at least the last 5 ml. of the distillate enter the receiver after the bottom of the condenser tube has come above the surface of the distillate. Larger volumes of distillate can be received by lowering d l in its adjustable slot. R allows iV to slide down its runners and the receiver can then be removed from the pan and its contents titrated. Steam distillations, not requiring the interception of gases as in the Kjeldahl distillation, may be carried out with A: a t the bottom of its runners. Any desired volume of distillate, within limits, can be collected. The salient features in the design and use of the apparatus may be summarized as follows: The glass section of the apparatus can be made in one piece if desired. The ground joint between the distillation head and the condenser is provided merelv for convenience.
CHEMISTRY
Increase in volume due to condensation of steam within the distillation vessel is reduced to a minimum. The steam boiler is heated rapidly and effectively by electricity with very little heat loss. When, however, the circuit is automatically broken on receipt of the desired volume of distillate, the cooling of the element is rapid and the distillation vessel empties itself in about 20 seconds. The single rod stand and clamp are neat and permit rapid adadjustment. The apparatus can be adjusted to receive, within limits, any desired volume of distillate. The operator is free to carry out other duties, knowing that the receiver cannot overflow if neglected and that audible warning will be given a t the end of the experiment. The apparatus is best suited t o employment in banks of four or six units when large numbers of distillations are required. The device for controlling the volume of distillate and time of distillation may well suggest to the reader similar laborsaving devices in his own laboratory. ACKNOWLEDGJIENT
The authors wish to acknowledge the assistance provided in the design and construction of the apparatus by J. C. Button, E. Mears, and J. Nicholson and to thank “Shell” Refining & Marketing Company, Ltd., for permission to publish this paper. LITERATURE CITED (1) Cox, Chemistry & Industry, 56, 913 (1937). (2) Hoskins, J. L., Analyst, 69, 271 (1944). (3) Kirk, P. L., IND.ENG.CHEM.,BXAL. ED.,8, 223 (1936). (4) Parnas-Wagner (Pregl-Roth) , Mikrochemie, 23, 218 (1937).
Calcium in High=Purity Sodium Salts Determination of Microgram Amounts by the Oxine-Oxalate Method JOSEPH RYNASIEWICZ AND MURIEL E. POLLEY Knolls Atomic Power Laboratory, General Electric Company, Schenectady, N . Y . As little as 0.1 mg. of calcium can be determined in high-purity sodium chloride and sodium nitrate by separating the calcium with 8-hydroxyquinoline (8quinolinol), followed by an oxalate precipitation and titration with 0.01 N potassium permanganate.
0
KLY two chemical methods for calcium in sodium salts could
be found by the authors in the literature ( 1 , d ) . Both methods depend upon the precipitation of calcium oxalate from concentrated salt solutions. The Association of Official Agricultural Chemists (1)describes a method for calcium in sodium chloride of “average” purity. Shuman and Berry ( 4 ) modified this procedure and “calibrated” it by using empirical corrections for varying amounts of calcium in high-purity sodium chloride (above 99.90%). For example, correction factors of $0.006 to -0.003% were added in the case of samples containing 0.02 t o 0.2% calcium. As a 50-gram salt sample is usually taken for analysis, this means corrections of $3 mg. to -1.5 mg. of calcium for 10 to 100 mg. of calcium analyzed. However, Shuman and Berry reported good accuracy for calcium above 0.02% using these correction factors. Tanne (6) found that low results were obtained for calcium and magnesium in proportion to the amount of salt taken for analysis and ascribed this fact to “something which complexed with calcium and magnesium, but did not react with the oxalate and phosphateions.” In another paper (e)he attributed the low recoveries of magnesium to water-insoluble magnesium hydroxide which was formed on hydrolysis. The low results are more understandable in view of the work of Rlaljaroff and Gluschakoff (Z), \Tho deter-
mined the solubilities of calciuin oxalate in the concentrated salt solutions of ammonium, sodium, and magnesium. They found that 36 mg. of calcium oxalate would dissolve in 1 liter of 10% sodium chloride a t 18”to 20” C. The method described below eliminates the undesirable effect of concentrated sodium salt solutions on the solubility of calcium oxalate. As little as 0.1 mg. of calcium can be separated from the sodium salt by precipitation as 8-hydroxyquinolate (calcium oxinate) a t pH 9.5 to 10 along x i t h %hydroxyquinoline (8quinolinol, oxine). After the oxine-calcium oxinate is ashed, calcium is precipitated as oxalate in the absence of high salt concentrations, and measured by titrating with 0.01 iV potassium permanganate. The method assumes the absence of large amounts of cations which would be separated as oxinates and included in the calcium oxalate precipitation. PROCEDURE
Solutions Required. 8-Hydroxyquinoline solution, 2.5% in 5% acetic acid. Ammonium oxalate solution, 0.5 N . Potassium permanganate solution, 0.01 S. Method. Dissolve enough sodium salt in water (up to 50 grams) to give 0.1 to 5 mg. of calcium and make the solution slightly acid with hydrochloric acid. Adjust the volume to a t
