1798
ANALYTICAL CHEMISTRY
for a detormination is set by the magnitude of the blank. The unexpectedly large value of this blank has heen shown t,o result from lithium impurity in the quartz tubing used in this investigation. The concentration of lithium found in the quartz by flame photometric analysis of the residue from hydrofluoric acid treatment was 5.9 p.p.m.; that calculated from the tritium recovered by heating an irradiated tube at 600" C. was 5.5 13.p.m. Fortunately, only a very small fraction of this tritium passes into the sample a t room temperature; the measured blank is equivalent to ahout 0.02 y of lithium-6. The large absorption ( T O S S section (about sq. cm.) of lithium4 sets an upper limit. to the amount of sample that can he tolrratcd without the introduction of significant error h y "selfs1i:tdowing." For a mean path length of 0.5 cm., a solution 0.03.1.' in lithium-6 would cause a 1% attenuation in the neutron flus. That this effect is not serious under the conditions of the esperiment for solutions less than 0.01S in lithium4 is demonstrittrd by the propxtionality between tritium production and lithium concentratbn. The irradiation exposure could be considerably lcss th:tn that used in these experiments. The more dilute solut,ioris listed in Table I yielded about 0.3 microcurie of tritium from :L IO-mg. aliquot; a hundredth of this quantity can be measured with :L precision within 1% ( 1 2 ) . Any method of determination of total lithium may I)c used i n conjunction with the tritium measurement in order to compare the isotopic content of lithium samples. The data in Table I are based on v-eighing ?he sulfate; satisfactory results have it130 I)ren obtained by flame photometry. For absolute determinations, separated lithium-6 of high isotopic purity, available from Oak Ridge, may be used as a standard.
In principle, the lit,hium-6content of a saniplc can I)e culculated from the tritium production and the neutron exposure. The neutron flux is, however, seldom known with sufficient accuracy for this purpose. In fact, the production of tritium from lithium has been used to measure the neut,ron flus in determining the iieutro~i:tl~sorptioncross section of deuterium ( 6 , 7 ) . ACKNOWLEDGMENT
The authors are indebted to J. K. Rrodj. for the lithium sulfate standards, and to R. W, Bane, J . P. Fnria, and J. A. Goleb for lithium determinations. LITERATURE CITED
Hrody, J. K., Fred. >I.. and Tompkins, F. S., J . O p / . SOC.A m e r . , 42, 870(A) (1952) : paper presented at Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. >larch 1 to 5 , 1954. Cornog, R., and Libby, W. F..Piiys. Rei'., 59, 1046 (19411. Fireman, E. L., Ibid., 91, 922 (1933). Herr. W.,2. .Yaticrforsciz.. a8, 305 ( I 9 3 ) . Hutchiaon, D. A , . Phgs. Ret.. in press. Kaplaii. L., Ringo, G . R..and Wilzbnch. IICSally, J. It., Jr., J . O p t . SOC.Au7er., 42, 883 (1952). Wilzbach, K. E., Kaplan, L., and Brown. If'. G., Science. 118, 522 (1953). Wilabach, K. E., Van Dyken, -1.R., and Kaplan, I. .. AX.AL. CHEM., 26, 880 (1954). RECEIVED for rei l e x May 27, 19.54, .iccepted:.iugrist
20, 19d4.
Determination of Hypophosphite in the Presence of Phosphite D. N. BERNHART Research Laboratory, Victor Chemical
Works, Chicago Heights, 111.
Hypophosphite can be oxidized quantitatively to phosphite by cerium(1V) in sulfuric acid solution. The excess cerium(1V) is determined by titration with iron(I1) solution using ferroin as an indicator. The reaction is complete in 1.5 hours at room temperature or in 30 minutes at 60" C. Although the reaction as prescribed stops at the phosphite stage, further oxidation to phosphate is achieved by raising the temperature to 80" or 100" C. Either phosphite or hipophosphite is oxidized quantitatively to phosphate when boiled for 15 minutes in an excess of reagent. This new ceriometric method may therefore be used for the determination of hypophosphite ion in the presence of phosphite and phosphate, of phosphite ion in the presence of phosphate, or of both hypophosphite and phosphite if total lower valent phosphorus must be determined.
B
ECAUSE hypophosphites and hypophosphorus acid have become more and more useful for a number of commercial
applications and most commercial grades contain small amounts of phosphite, an analytical procedure is needed for ?he quantitative determination of hypophosphite in the presence of phosphite. Jones and Swift ( I ) have shown that hypophosphite does not interfere in the quantitative determination of phosphite, which can be oxidized quantitatively with iodine under proper conditions. Such a titration must be carried out in neutral solution;
this requirement represents a disadvantage, as the calcium and barium phosphites, both commercially available at the present time, are insoluble. The iodometric procedure is rather specific for phosphite and is satisfactory if only small quantities of hypophosphite are present. The accuracy of the method falls off, however, when small amounts of phosphite are present, especially in compositions ahich consist essentially of hjpophosphite. Considering that the iodometric procedure, even under the best conditions, is more or less specific for phosphite, the purity of a sample of hypophosphite can then be determined only by difference Other osidizing agent leagents such as hot permanganate, mercuric chloride, and potassium bromate oxidize both phosphite and hypophosphite to phosphate. Although these reagents can be used to determine either or both constituents, indirect methods
Table I.
Determination of Hypophosphite by Procedure A RaPOz
HIPO1
Taken,
Mg
Taken, hlg.
61.10
1 .oo
81.10
3.00
61.10
5.00
HaPOz F o u n d , AIg 61 06 61.04 61,lO 61.03 61.08 61.05 61.06 61.09 61.09
V O L U M E 2 6 , NO. 1 1 , N O V E M B E R 1 9 5 4
1799 hours two equivalents of cerium(1V) were used for every mole of sodium hypophosphite present and this value remained constant up to 48 hours. A qualitative test for phosphate after the 48-hour period proved to be negative.
il comparative series of experiments was carried out using sodium phosphite instead of sodium hypophosphite. KO cerium(1V) was expended during the same time interval and this value remained unchanged and constant up to c 5 3c 6C ss 20 48 hours. I t may therefore be con1. cluded that at room temperature and a reaction time of 1.5 to 2 hours hypoFigure 1. Oxidation of Hypophosphite to Phosphite can be determined in the -phosphite presence of phosphite by treatment must he used. These procedures, therefore, are neither desirable with an excess of standard cerium(1V) solution in sulfuric acid. nor precise. lloeller and Quinty ( 3 )have shown that hypophosThe procedure was then repeated on 0.1-gram samples of sophate can be quantitatively oxidized to phosphate by using a dium hypophosphite and sodium phosphite a t 40°, 60". 80", and boiling 'solution of cerium(1V) in nitric acid. They found, 100" C. The data are plotted in Figure 1 and show that a t however, that both hypophosphite and phosphite Tvere also oxi40" C. oxidation sf hypophosphite to phosphite t'akes place within dized under these same conditions and the method could not he an hour, but that phosphite itself does not interfere. At 60" used for mixtures. oxidation of hypophosphite takes place in 30 minutes and again I n the current work it has been found that cerium(1V) will phosphite does not interfere. At 80" and 100" C. phosphite is oxidize hypophosphite quantitatively to phosphite in sulfuric acid oxidized along with the hypophosphite; phosphate v a s found solution. Osidation is complete a t room temperature within 1.5 to be present in these latter mixtures. hours, or 30 minutes a t 60" C. Under the prescribed conditions, OXIDATION OF PHOSPHITE AND HYPOPHOSPHITE phosphite undergoes no oxidation. TO PHOSPHATE __i
I,.
2Ce+-++
