A Simple Micro-Kjeldahl Apparatus Taiichi Asami,’ 406th Medical General Laboratory, Camp ;!.ama,Japan the introduction of Rjeldahl’s S original apparatus (6)in 1883 many changes and modifications have been INCE
presented. Scandrett ( 7 ) constructed an all-glass micro-Rjeldahl apparatus, consisting of four sections: IZjeldahl flask, still head, steam inlet tube, and air condenser. Each section could be replaced by the use of ground-glass joints. The IZjeldahl flask mas held in position by a spring clip. Part of the steni which delivered the steam into the Kjeldahl flask passed through a Claisenlike still head. Hayazu (3) constructed an apparatus having a similar still head and consisting of the traditional trap attached to a water condenser. He used air in place of steam for the distillation.
DlSTl LLATION, M L
Figure 2. Recovery of nitrogen from standard ammonium sulfate solution
APPARATUS
Construction and Function. The proposed apparatus is made of borosilicate glass. Figure 1 shows the main component, C and D,of the apparatus, which consists of two parts: the inner jacket through which the steam delivery tube passes and the outer jacket through which condensed steam containing alkali returns to Kjeldahl flask E, through a circular capillary opening around the end of the inner tube a t D. A desirable size for the capillary opening was found to be 0.2 to 0.5 mm. If smaller, a liquid seal might result, and, if larger, steam might pass through it in preference to going through the inner jacket or it inight enter siniultaneously the inner and outer jackets. The alkaline solution is introduced into E through A . The incoming steam passes through B, carries out steam distillation a t E, and rises through the inner jacket to pass through a small spherical opening in the inner mall a t C, and finally to the receiving Erlenmeyer flask, G, after passing through the outer jacket and condenser, 8‘. Plastic or rubber stoppers were used for the joints of the glassware. The rate of distillation should be adjusted so that bubbles do not pass through the surface of the boric acid solution. Under ideal conditions the bubbles move back and forth near the end of the stem, F , extended into G. A slightly larger glass cylinder is used a t A and the upper part of F t o prevent any serious backing up of the solutions. It is advisable to heat strongly near the end of the distillation. Upon completion, G is lowered in order to remove the tip of F from the surface of the boric Present address, Daiki Engineering Co , Ltd., 2, 2-chome, Siba-Tamurdcho, Minato-ku, Tokyo, Japan. 1
630
ANALYTICAL CHEMISTRY
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Figure 1 .
Micro- Cjeldahl apparatus
A. 8.
Upper part of steam delivery tube Steam intake C. Inner port of steam jacket D. Copillary opetiing of the end of C E. Micro-Kjeldahl flask F. Condenser G. Receiving flask
acid solution and E ic; heated with a microburner. The stopper a t A is removed, soon after tk v tube carrying the incoming steam is climped a t B, to prevent sucking back the solution from G into E. Advantages. The steam can be fractionated by p a s i n g it through the long vertical column, which has been continuously heated by the incoming steam, and through the small opening a t C where it iuddenly teiids t o change its pressure and temperature. m7hen a traditional Kjeldahl apparatus is used, there is a tendency to distill oyer alkali with rat1 rr strong heating. However, in this near apparatus, alkali contamination was nrver observed unh opening a t less foam passed thro ~ g the C. If foam is produced during the distillation, it tends to bt’ destroyed before passing through this o xning. A micro-Kjeldahl A tuk containing the digested specimen mxy be directly attached to this appaxtus. The main
portion of the apparatus, C and D,can be used for a macro-IZjeldahl setup by changing parts E, F , and G. TKOsets of apparatus, to carry out the distillation of two specimens siinultaneously, may be used with one steam generator placed on a stand, because the apparatus is constructed rather simply and occupies vertical space. This feature also facilitates the easy moving of the apparatus. I n place of the standard sulfuric acid, boric acid is used frequently for the absorption of ammonia (1, 2,5,6, S, 9). In this experiment, 47, boric acid \\.as used. Distillation of Standard Ammonium Sulfate Solution. The distillation curve given in Figure 2 indicates that 15 inl. of distillate was sufficient when a standard ammonium sulfate solution containing 0.84 mg. of nitrogen was used. In this distillation, a definite volume of distillate was collected, rather than distilling for a definite time as Wagner (8)has recommended. ACKNOWLEDGMENT
The author is indebted t o John 111. Armistends for the experimental work. LITERATURE CITED
(1) Assoc. Ofic. Agr. Chemists, JVasliiiigton, I). C., “Official Methods of hnalysis,” 8th ed., pp. 805-7, 1955. ( 2 ) Fukukawa, l., Nngase, 0. IC., J . Phann. Sac. Japan 70, 590-1 (1950). (3) H ? ~ ~ zIt., u ,Ibid., 70, 357-8 (1950). (4) Rjeldahl, J., 2. anal. (Iheut. 22, 366 (1883). ( 5 ) McICenzie, H. A., Wall:tce, €I. S., Busfraliun J . Chem. 7 , 55 (1954). ( 6 ) Ogg, C. L., Willits, C. O., ,I. ilssac. Ogic. A y r Chemists 33, 100-3 (1950). ( i )‘Scandrett, F. J., A n a l y s t 78, 734-7 (903). ( 8 ) IT-agner, E. 1x1). ESG. CrlEnI., AXAL.ED. 12, 771 (1940). (9) Yuen, S. H., Pollard, A. G., J . Sei. Food Ayr. 4, 490-6 (1953).
c.,
