Table 11.
Boron Analyses by Meeker and Muffle Ashing Ashed Over Meeker Ashed in Muffle
Porcelain evaporating dish (uncovered)
Porcelain high-form (uncovered)
Porcelain high-form (covered)
25.2 25.6 25.3 25.6 25.4
25.6 25.4 25.4 25.6 25.2
24.4 24.4 24.4 25.0 24.4
obtained with porcelain and platinum crucibles, heated in the muffle furnace, and with duplicate samples heated over a Meeker burner in open air. The data show close agreement between plant material ashed over a Meeker burner and that ashed in covered highform porcelain and platinum crucibles in the muffle furnace. Evidently the use of these crucibles with covers eliminated the error previously obtained when samples were ashed in porcelain evaporating dishes in electric furnaces.
Platinum (covered) 24.4 24.4 24.4
Boron values reported in the literature show good reproducibility of values even when ashed in electric muffle furnacese.g., the data of Hatcher (3). He compares boron analyses by wet and dry combustion, with much higher values obtained for dry than for wet combustion. The conclusion is drawn that the samples prepared by wet combustion are lower and more variable as a result of loss of boron during the acid digestion, and that boron analysis by dry combustion gives good reproduc-
ibility, and implies that dry ashing is more reliable. However, the fact that dry combustion figures are higher and more constant than wet digestion values does not obviate the possibility of a constant hidden error in dry combustion values. This constant error can come from a procedure standardized in time and temperature of ashing. I n the light of this work, boron analysis on plant or soil material following dry combustion in a muffle furnace should be re-examined. LITERATURE CITED
(1) Calif. Agr. Expt. Sta. Bull. 766, 64 (1959). (2) Dible, W. T., Truog, E., Berger, K. C., ANAL.CHEM.26, 418-21 (1954). (3) Hatcher, J. T., Ibid., 32,726 (1960). (4) U. S. Salinity Laboratory Staff, U. S. Dept. Agr. Handbook, pp. 60, 129, 135 (1954). D. EMERTON WILLIAMS ' JAMES VLAMIS University of California Berkeley 4, Calif.
Rapid Fusion Determination of Phosphorus in Gasoline SIR: Motor gasolines commonly incorporate organophosphorus compounds to reduce spark plug fouling and preignition or to combat rumble in high compression engines. To permit rapid analyses for phosphorus content, a colorimetric method was devised bmed on use of the reduced phosphomolybdate complex (1). The color system mas used previously for determining higher concentrations of phosphorus in lubricating oils (3). Phosphorus in gasoline has been determined by emission spectroscopy ( 4 ) . It has also been determined colorimetrically following conversion of the organophosphorus compounds to inorganic phosphate, either by evaporating the gasoline and wet oxidizing (6) or by ashing in zinc oxide (2, 4, 6). By the more rapid method described below a single sample can be analyzed in less than 30 minutes. Under routine conditions, 30 to 35 samples can be analyzed in a n 8-hour day. The method is applicable to phosphorus concentrations as low as 1 mg. per kg. (p.p.m.).
add 2.00 ml. of gasoline sample a t room temperature. (For samples containing more than 60 p.p.m. of phosphorus, use 1.00 ml. of sample.) Cover the sample with another measure of sodium carbonate. Ignite the gasoline by passing a flame over the top of the crucible. After burning has ceased, heat the crucible strongly in a Meker burner flame until a clear melt is obtained. Allow the crucible to cool for several minutes, and then place it in a 400-ml. beaker containing 50 ml. of 1 to 11 sulfuric acid. [This amount of acid is
RESULTS
Table I.
The apparatus and reagents are similar to those used earlier (3). I n addition, a 15-ml. centrifuge tube was marked to contain 3 5 0.1 grams of sodium carbonate, anhydrous powder. Standard form 15-ml. platinum crucibles were found suitable for the fusion. Place one measure (3 i 0.1 gram) of sodium carbonate in a 15-ml. platinum crucible. By means of a pipet 968
ANALYTICAL CHEMISTRY
Determination of Phosphorus in Gasoline
Phosphorus, Mg./Kg. zinc oxide method Proposed Additive Present (2, 4, 6) method Tris( chloroisopropyl) thiono36, 35 35, 35 phosphate Tris( chloroethvl) - . phosphate 19, 19 19, 19 Trimethyl phosDhate
EXPERIMENTAL
sufficient to react completely with the sodium carbonate and provide the standard excess required for the colorimetric method ( J ) . ] After several minutes, when most of the sodium carbonate has dissolved, rinse down the walls of the beaker with 50 ml. of molybdatehydrazine reagent, and develop and measure the color as described previously. Measure the specific gravity of the gasoline and calculate the weight of sample. In most cases a n average density of 0.74 gram per ml. may be assumed.
Alkylamine phosphate Tri-n-propyl phosphate hfethyldiphenyl phosphate Mixed methylphenyl phosphates
42. 43
42. 43
30, 30
29, 29
32, 32
33, 33
33, 33
33, 33
34, 18, Tricresyl phosphate 33, Cresyldiphenyl 10, phosphate 26,
35 18 35 10 27
34, 17, 33, 10, 26,
34 17 35 11
27
To test the proposed method, a series of representative gasoline samples was analyzed by both the conventional zinc oxide (2, 4, 6') and proposed procedures, Table I. The standard deviations of the zinc oxide and proposed methods are 0.60 and 0.56 p.p.m., respectively. This represents no significant statistical difference. Table I1 shows phosphorus recoveries obtained, under various conditions, for gasoline blends of the more volatile additives being used currently. Except for the results on a blend using trimethyl thionophosphate, recoveries mere acceptable for these additives using the recommended procedure. DISCUSSION
In preliminary experiments, attempts were made to adapt the oxygen-flask method ( S ) , but it was not possible t o burn sufficiently large samples to com-
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
