pensate for the relatively low phosphorus levels in gasoline. I t was possible to heat a large sample in a lowtemperature vacuum oven to volatilize most of the gasoline base. This concentrated the less-volatile phosphorus additive without loss and permitted the use of the oxygen-flask method. However, the fusion procedure proved more rapid. The combustion-decomposition of gasoline after absorption on zinc oxide usually requires lengthy heating to remove all of the carbon from the ignited sample; also, the zinc oxide cake dissolves only slowly in the acid solution. Sodium carbonate is free of these objections. Platinum crucibles speed the fusion and ignition of the organic residue because of their high rate of heat transfer. By the described technique, it is possible to complete the ignition and fusion in less than 10 minutes. Because only a small amount of phosphorus is present, the effect on the platinum is negligible. No effect has been observed on platinum crucibles used over 75 times each. Even if embrittlement does occur after much repeated use, the savings in time offered by the use of platinum should far outweigh the cost of replacement. The blank absorbance, equivalent t o approximately 0.0024 mg. of phosphorus, usually amounts to 5 or 10% of the total absorbance for average phosphorus levels. Most of this blank is attributable to the color given by the molybdate-hydrazine reagent. This color depends on the interval between the time that the ammonium molybdate and hydrazine sulfate solutions are combined and the time that the mixed reagent is used. The effect is small and reasonably constant for about 1 hour.
Table II.
Recovery of Volatile Additives from Gasoline Blends
P Taken, Mg./Kg.
Gasoline Sam le, Mf
NazCOt, Grams
36
2 2
Trimethyl phosphate
4 6 4
36
Tris(chloroethy1) phosphate Trimethyl thionophosphate
19 17
2 2 1 2 2 1
Additive Tris( chloroisopropyl) thionophosphate
1
The unmixed reagents appear to be stable indefinitely. It has been reported (4) that samples containing either tris(chloroisopropy1) thionophosphate or trimethyl phosphate, the two most volatile phosphorus additives in current use, give low results in the zinc oxide procedure when the ratio of sample to zinc oxide is too high, I n developing the proposed procedure, this effect was observed for tris(chloroisopropyl) thionophosphate, but not for trimethyl phosphate. Decreasing the ratio of sample to sodium carbonate gave acceptable results on gasolines containing tris(ch1oroisopropyl) thionophosphate (Table 11). The use of 6 grams of sodium carbonate and 2 ml. of sample was considered preferable to decreasing the sample volume and thereby losing sensitivity. At the conclusion of this work, two new phosphate esters, trimethyl thionophosphate and tris(chloroethy1) phosphate, were acquired and tested. Table I1 shows acceptable results for a blend of tris(chloroethy1) phosphate in gasoline by the proposed procedure. However, to obtain better recoveries on blends of trimethyl thionophosphate, it was necessary to reduce the sample size
P Found, Mg./Kg. 29, 36, 36, 36, 37, 36, 19, 10, 16,
4
6 4 6 6 6
30 37 38 36 37 36 19 12 18
to 1 ml. This effect points up the need to test new esters as they become available. If apparatus, reagents, etc. are ready, it is possible to complete a n analysis in 25 minutes after receipt of the sample. Proper scheduling of operations permits six samples to be analyzed in slightly less than 1 hour. LITERATURE CITED
(1) Boltz, D. F., “Colorimetric Deter-
mination of Nonmetals,” Interscience, Kew York, 1958. (2) Fett, E. R., Matsuyama, G., Chemist
Analyst 47,32 (1958). (3) Gedansky, S. J., Bowen, J. E., Milner. 0. I.. ANAL.CHEM.32. 1447 ( 1960) (4) Griffing, M. E., Leacock, C. T.,
.‘
O’Neill, W. R., Rozek, A. L., Smith, G. W., Ibid., 32,374 (1960). (5) Hoffman, F. F., Jones, L. C., Robbins, 0. E., Alsbera, -. F. L.. Ibid.,, 30.. 1334 (i958j. (6) Socony Mobil Oil Co.,
Research Department, Paulsboro Laboratory, Paulsboro, N. J.,Mobil Method 71,1956. S. J. GEDANSKY J. E. BOWEN 0. I. MILNER Research Department Paulsoboro Laboratory Socony Mobil Oil Co. Paulsboro, N. J.
Colorimetric Determination ot Neptunium with I horin SIR: The organic compound 2-(2hydroxy - 3,6 - disulfo - 1 -naphthylazo)benzenearsonic acid, referred to as thorin, is used for the colorime‘tric determination of plutonium ( 2 ) ,thorium Table
I.
Neptunium Recovery Thorin Method
Np Added, pg. 15.8 -_-.
127
Np Recovered, pg.
15.6 15.8 15.8 15.9 15.9 15.6 16.0 15.8
124 130 126 128 126 126 127 128
by
(4, zirconium (S), and uranium (1). We found that neptunium(1V) also formed a colored complex with thorin and had a molar absorptivity of 14,500 a t 540 mp as measured with a Beckman hlodel DU spectrophotometer. Ferrous sulfamate was used to reduce neptunium to the f 4 state. The color complex was sufficiently stable to permit the development of a colorimetric method for the determination of neptunium. The precision of the method a t the 95y0 confidence limits was 1.2.101, for 0.63 pg. of neptunium per ml. and *4.0% for 5.09 pg. of neptunium per ml. based on eight determinations at each concentration. Table I shows the data from which the precision values were calculated.
EXPERIMENTAL
A Beckman Model DU spectrophotometer equipped with 5-cm. Corex absorption cells was used. Table 11. Absorbance of NeptuniumThorin Complex as a Function of Time and Final Neptunium Concentration
Time, Np Present, pg./Ml. Min. 0 . 6 3 1.27 2.56 5.09 10 20 30
40 50 60 90
0.211 0.211 0.212 0.212 0.212 0.212 0.212
Absorbance 0.362 0.700 0.370 0.715 0.374 0.722 0.376 0.730 0.378 0.737 0.378 0.738 0.378 0.740 ~~
1.37 1.38 1.38 1.38 1.39 1.39 1.39
~
VOL. 33, NO. 7, JUNE 1961
969
\
0.2
’\
\ \
‘\
\
0
500
525
550
---
575
600
Wave Lenqth, mp
Figure 1. A. 6.
Absorbance of thorin and neptunium-thorin complex
Reagents, distilled wafer reference Neptunium-thorin complex, (5.78 pg./ml. Np), reagent reference 1-cm. cells
0.1
0.2 0.3 0.4 0.5 HN03, molarity
0.6
Figure 2. Absorbance of neptuniumthorin complex as a function of nitric acid concentrations a t various neptunium concentrations LITERATURE CITED
Procedure. Known amounts of neptunium covering the range 15.8 to 127 pg. were added to 25-ml. volumetric flasks that contained 0.5 ml. of 2M ferrous sulfamate and sufficient nitric acid to yield a final acid concentration of 0.4M after dilution. The contents were mixed and allowed to stand 15 minutes. Finally 2.5 ml. of 0.1% aqueous solution of thorin was added and the contents were diluted to volume and allowed to stand 30 minutes (Table 11). The blank was treated in the same manner as the standards. Figure 1 shows the absorbance spectra of the neptunium-thorin com-
plex and thorin. Figure 2 shows the effect of the concentration of nitric acid on the absorbance of solutions containing 0.63, 2.56, and 5.09 pg. of neptunium per ml. The data in Table I1 show that the complex was stable enough to make the readings after 1 hour. Beer’s law was obeyed over the entire range. A discussion of the interferences in the plutonium-thorin procedure and methods of removing them, given by Healy and Brown (W), applies equally well to the neptunium-thorin procedure.
(1) Foreman, J. K., Riley, C. J., Smith,
T. D., Analyst 82,89 (1959). (2) Healy, T. V., Brown, P. E., Atomic
Energy Research Establishment (Gt. 1287 (Kovember 1957, unclassified). (3) Horton, A. D., ANAL.CHEW25, 1331 (1953). (4) Thomason, P. F., Perry, M. A., Byerly, it7.M., Zbid., 2 1 , 1239 (1949). R. D. BRITT,JR. Savannah River Laboratory E. I. du Pont de Nemours & Co. Aiken, S. C. WORK supported by the United States Atomic Energy Commission under Contract ilT-(07-2)-1. Brit. j, Rept. A E F C/R
Quartz Flow Cells for Continuous Spectrophotometric Analysis of Column Effluents
N. G. Anderson,
Biology Division, O a k Ridge National Laboratory, O a k Ridge, Tenn.’
spectrophotometric analysis of liquid chromatographic column effluents containing ultravioletabsorbing materials (proteins, peptides, nucleotides, etc.) has generally been done manually on collected fractions. With controlled flow rates, however, the absorption may be recorded continuously with increased resolution, accuracy, and convenience. The major difficulty has been lack of a flow cell of good optical quality that contains a minimum volume of fluid, has no liquid-retaining corners, and connects UANTITdTIVE
1 Operated by Union Carbide Corp. for the U. S. Atomic Energy Commission.
970
ANALYTICAL CHEMISTRY
to small-bore plastic tubing. This paper describes suitable quartz cells and a two-cell holder for the Beckman DU spectrophotometer. Two cells of different optical path length (1.00- and 0.20-cm.) may be used in series to record a greater range of densities. Another method is to connect two identical cells in parallel, with the input to the chromatographic column flowing through one cell and the column effluent through the other. The blank cell may then be moved into position at intervals to check the zero absorbance settings. To match the light transmittance through the two cells, movable masks are provided, which may be ad-
justed when the cell holder is in the spectrophotometer. With minor changes this system may be used for double-beam recording.
-4drawing of the apparatus is shon-n in Figure 1. The cell holder, 1, is constructed from a standard Beckman DU aluminum cuvette holder (Beckman Catalog No. 5010). The 1.00-cm. path quartz cell, 2, and the 0.20-cm. path cell, 15, (Oak Ridge quartz flow cells, Quaracell Products Co., New York 13, N. Y . ) are both 22 mm. long, 12 mni. deep, and 13 nim. Tide. Round connecting holes 4 nun. in diameter and 3 mm. deep are provided a t both top and bottom. The 0.20-em. path cell contains 0.064 ml. in a chamber 0.2
