time, t,. This time does not vary usually during a day’s operation, but i t is good practice to run additional synthetic glucose or standard serum samples every 1 to 2 hours as a complete check on the instrument and reagents. If several beakers are used, they should be selected to give the same standardization meter reading *5% when containing the same solution. Blood Serum Measurement. T h e 2.00-ml. aliquots of t h e supernatants from blood serum deproteinization are run in the same way as t h e standa r d glucose solutions. T h e unknown time, t,, is recorded for each blood serum sample. Calculations. Equation 1 gives the unknown concentration, C, of glucose in blood serum samples in units of milligrams of glucose per 100 ml. of blood serum.
c,
=
loot.
tu
If only 1 or 0.5 ml. of the supernatant for the serum samples is used, the right side of Equation 1 is multiplied by 2 or 4, respectively, to obtain the correct concentration. This assumes the use of 2 ml. of standard solution supernatant. RESULTS AND DISCUSSION
The two series of results given in Table I were taken on different days and are typical of many such series.
I n general, the coefficient of variation and proportionality were about 27,. The results did not vary over several hours if room temperature remained constant within 11’ C. Therefore, one set of five standards can be run in a few minutes t o obtain a reference time, t,, and then unknowns can be run continuously for several hours with only an occasional check with a standard sample. For any given temperature the time interval can be adjusted by potentiometers R5 and R6 to be about 50 seconds for an average sample containing 100 mg. of glucose per 100 ml. of serum. If the mean temperature is not controlled to &lo C., the reproducibility will !x decreased and more frequent standardization required. The results for several blood serum samples (Table 11) were always about 15% lower than those given for the Benedict method. Therefore, the normal range should be corrected accordingly when the enzyme procedure is used. The per cent recovery for 100 y of added glucose to several of the serum standards is shown in the last column, as calculated from the difference between total glucose in serum with added glucose and glucose in serum only, both determined by the enzyme method. The instrument described can be
npplicd to other systems when a quantitatiw result for a specific constituent can be obtained from a rate measurement. The Spectro unit has a transmittance band between 340 and 350 mp for the nominal 525-mp interference filter in conjunction with the Corning 2950 cutoff filter. This could be used with the DPN-DPNH systsm. The instrument could be redesigned for further simplification but the setup presented here proved stable, sensitive, and reliable for the desired results. The only real difficulty in the instrument during its use came from a faulty locking-type reversing relay, KR, causing a n occasional loss of a result. LITERATURE CITED
(1) Hugget, A. St. G., Nixon, D. A., Biochem. J . 66, 12P (1957). (2) Malmstadt, H. V., Hicks, G. P., ANAL.CHEW32,445 (1960). (3) Saifer, A., Gerstenfeld, S , J . Lab. Clin. M e d . 51, 448 (1958). (4) Salomon, L. L., Johnson, J. E., AX.4L. CHEM. 31,453 (1959). (5) Sargent, E. H., and Co., Catalog 29700 for SE Titrator, 1959.
(6) Sargent, E. H., and Co., “Scientific Apparatus and Methods,” Vol. 10, 1958. ( 7 ) Worthington Enzymes Corp., Descriptive Manual 9 (1957). RECEIVED for review September 8, 1959. Accepted December 7, 1959.
Determination and Reactions of Some Acidic Oxy-Anions in Fused Chlorides and Nitrates J. D. VAN NORMAN and R. A. OSTERYOUNG Department o f Chemisfry, Rensselaer Polytechnic Institute, Troy, N. Y.
b A method has been developed for determining acidic oxy-anions, such as dichromate, metaphosphate, or metavanadate, in fused salts b y determining the number of moles of carbon dioxide evolved when excess sodium carbonate i s added to a fused salt containing one of these species. The method determines the acidic species in situ and i s reasonably accurate. The relationship of acid-base reactions to oxidation-reduction processes in fused salts i s discussed.
A
relationships in fused salts have recently become of increased interest. Probably the LUX concept ( 7 ) is the most useful as far as the present work is concerned, in conjunction with the concepts of Flood and Forland (4). Kinetic aspects of acid-base reactions in fused salts have CID-BASE
398
e
ANALYTICAL CHEMISTRY
recently been investigated by Duke and Iverson (2,s). T o the authors’ knowledge, no direct procedure for the determination of acids in situ in fused salts has been investigated, although certain proc e d u r e are suggested by the work of Flood and Forland. The present work describes the in situ determination of acids in fused salts by determining the amount of carbon dioxide evolved when sodium carbonate is added to a melt containing dissolved acidic species. Some experimental results pertaining to the relation of acid-base and oxidation-reduction reactions are also presented. PROCEDURE AND EQUIPMENT
Analytical reagent grade chemicals vacuum-dried at 100” C. were used throughout. An equimolar potassium nitrate-sodium nitrate mixture was
prepared by weighing the predried salts separately and mixing in a ball mill jar. The mixture was then fused and filtered through a fine glass frit and the solidified salts were crushed in a mortar. The potassium chloride-lithium chloride ’ lithium chloeutectic (38.56 mole % ride) was prepared by the procedure of Laitinen, Ferguson, and Osteryoung (6).
A 125-ml. round-bottomed borosilicate glass flask, with addition tubes attached at its top, was connected through a side arm to a vacuum line with the bulk of the flask in a furnace; reagents could be added from the addition tubes by swiveling them. Gas pressure in the system was measured with a cathetometer, capable of reading tenths of a millimeter, from a mercury manometer on the vacuum rack. The volume of the vacuum system was calibrated by expanding argon at a known pressure and volume into the static vacuum system, includ-
'np the reaction flask, which \vas in tlie
:tirnace a t t h r desired temperatu:.c. .i Consolidateti Elcctrotl!.iiainic's spectrometer with ;t modified amplifier circuit \vas availsbie for the anniTsi.; of evolvcd gnses. ,Standnril patterix w r e takcn for .,itrous oxide, ::itric oxide. nitrogen Llictxitle. :inti carbon i!iosiclc. --L ~ n o o\>-gen. \ v ~ iamounts of potassium tiichrornate aiid potassium chromate %;ere adtied to the prepurified, molten i-iimtes in the rcnction flask and sodium rhoiiate plncec! in an addition tube. e s!.sterii \vas evacuated and the :c.mperature of the flask held a t 300" = 5" 6 , The s;;stcm wv2s then closed off from the -\muurn pump and excess -;odium carbonate added. The y e s s i r e of the gns s o l v e d csas measured x w l the itleal gas Ian. used to calculate :iir moles of carbon dioxide evolved into :he previously caiibrated system. A c;'iwction was atuniieci for the volume ' f the melt. '?w ,x-ocediire used in the chloride ciitcctic tlii-Teretl somewhat from that 1 in the case cf the nitrate mixture. urified and filtered :KCl-LiCl eutwtic \vas placed in the reaction wssi-1 and anhydrous hyarogen chloride sed over the swface of the saits. lie Temperature of the reaction flask : w s slon.ly raiscti to 400" C. over a 2Ii!,iir period. Hvdrogen chloride was ed throug!i the molten eutectic for our after melting. T h e system was then evacuated for 1 hour to remove dissolved hydrogen chloride. Known amounts of potassium dichromate, sodium metaphosphate, or sodium metaTanadate were then added to the eutectic by quicklv opening the system t,o the atmosphere. 'The s'i-stem was then evacuated and closed off, and i x e s s sodium carbonate added from the addition tube. The gas pressure was measured a n a moles of carbon dioxide evoived were calculated as in:!kited above. M a s s spectral analysis 011 the evoived gases indicated only cirhon dioxide. In all cases, escept ,\-here indicated, yeactions were carried oat until no further change in pressure \vas noted. All reactions appeared to he complete in iess than 15 minutes. [The amount of Zhioride or nitrate eutectic used in the reaction flask was 50 grams.] ZESULTS AND DISCUSSION
Potassium diel-miniate and tlic dic!iromate in K2Cr20;-Ii2Cr01mixtures were determined i n the nitratc meit and some results are gresentcd in Ta!Jie I. The reaction is quantitative and goes t,o completion to tlic right. CrzO;2
+ COi2
--f
2 C r O i Z $- CO,
~ i t $he n melt to evc!\.e w d e s ot nitrogt n, probably from t:ic rracr on.
+ NO;
SO;
320, -+ ciecomposition products ( 3 j
The reaction
so, + crpo;2-+
2 C'rc;;~
-L
>:o; !4!
has been studied kine:icaily hy Duke and Iverson (3). ?'!>.e this reaction lies far x evidenced from the fact, that dichromate added to the nitrate :mlt ivys quantitaiively determined hy the evolution of carbon dioxide. Duke arid Iverson, however, added a met,ai ion which precipitated as an insolui ie chromate, driving Reaction 4 to t'hc right: 2 B a P I Crz0;2 T ,2 SO;-.-* :
