Table IV. Effect of Acid Concentration on Precipitation of Zirconium by Trimesic Acid
0.2 0.6
conditions such as acidity and digestion, the precipitate is not put in a direct weighable form on appropriate drying. The precipitates correspond to the following composition, excluding the water molecules associated:
0.0444 0.0445 0.0442
0.8 2.0
0.2 0.6 0.8 2.0
0,0440
0.0441
L
0.0444
where M
0.0443 0,0440
0.0435 0.0430 0.0385 0.0368
0.2 0.6 0.8 2.0
0.0443 gram of zirconium present in
each case.
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curves of the reagents. TMS starts decomposing slowly at around 300" C., whereas TML (anhydride) is fairly stable up to 325" C. PYM is the Ieast stable thermally and starts decomposing a t 165" C. However, all three
Table V. Decomposition Temperatures of Zirconium Carboxylate Precipitates for Conversion to Oxide
MiIl.
temp O C., to attain
oxide level
Precipitates Zirconium benzoate (3) Zirconium phthalate (3) Zirconium trimesitate Zirconium trimellitate Zirconium pyromellitate Hafnium trimesitate Hafnium trimellitate Hafnium pyromellitate
500 550 730 670 700 655 645 645
formation of complex sulfates of the type Hp[MO(SO&] (where M stands for Zr or Hf), Fhich are reported to undergo hydrolytic decomposition depending on experimental conditions (1). Figure 1 shows thermal decomposition
completely decompose between 430 " and 51.5" C. Any excess reagent, therefore, should not interfere with the analysis if the ignition is carried out above these temperatures. The first loss of weight with the zirconium and hafnium precipitates starts between 110" and 180' C., as shown in Figures 2 and 3. I n the case of hafnium-TMS and hafnium-TML precipitates anhydrous compounds form between 400" and 525" C. a t the 14% weight loss level. For the zirconium-TML and hafnium-PYM precipitates there is a similar plateau between 410"and 500°C. Zirconium-TMS and zirconium-PYM precipitates, however, show no evidence of any such intermediate compound formation. Decomposition temperatures necessary to attain the oxide level of different zirconium and hafnium carboxylates are compared in TabIe V. An increase in the number of carboxylate groups in the benzene ring has some influence on the decomposition temperature of the precipitates. The compositions of the zirconium and hafnium precipitates vary somewhat, probably because of the presence of various hydrolytic and adsorption products. Experiments indicated that even on changing
=
Zr or Hf.
From Tables I and I1 it is evident that the precision for the three reagents is about the same. Increase in the number of carboxylate groups seems generally to increase the minimum temperature required for obtaining the oxide level of the precipitates. Increase in the ortho positions of the carboxylate groups has a marked influence on the rate of appearance of the precipitates. ACKNOWLEDGMENT
Thanks are due to Michael J. Tarantino, Jr., for performing some of the experiments. LITERATURE CITED
(1) Blumenthal, W. B., "Chemical Behavior of Zirconium." Van Nostrand,
RECEIVED for review October 31, 1963. Accepted February 7, 1964. Financial support by the Petroleum Research Fund of the American Chemical Society is gratefully acknowledged.
Phosphorus Determination by Flame Photometry ABRAM DAVIS, F. J. DINAN,' E. J. LOBBETT, J. D. CHAZIN,2 and L. E. TUFTS Cenfraf Research laboratory, Hooker Chemical Corp., Niagara Falls, N. Y.
b A rapid method for the determination of phosphorus is based on the flame emission continuum centered at 540 mp. A wide range of both organic and inorganic phosphorus compounds has been analyzed in several solvents, and it has been found that the emissivity is the same for all structural types of phosphorus compounds. Many interfering cations are removed with ion exchange resin. Carbonate, nitrate, ammonium, halogen, and sulfate ions do not interfere at concentrations chemically equivalent to the phosphorus.
S
EVERAL
AUTHORS
(14,
6) have
determined phosphorus by flame phot,ometry. Often the suppression of 1066
ANALYTICAL CHEMISTRY
the emission from some cation is correlated with phosphorus content (1, S,5). Gilbert (4) used an air-hydrogen-alcohol flame to excite the chemiluminescence phosphorus spectrum. Brite (g) worked with the continuum centered at about 540 mp to obtain a direct measure of phosphorus in an organic compound. When excited in an oxygen-hydrogen flame, the 540-mp phosphorus emission is linear with concentration over the range from 0.0 to 1.0 gram per liter in all solvents tested. Elemental phosphorus, inorganic compounds, and organic compounds of various structural types all yield the same emissivity based on phosphorus content. I n order to gather sufficient energy for maximum accuracy from this continuum, a wide spectral
slit width is necessary. With wide slits almost all emissive metallic elements interfere strongly. This usually can be avoided by removing metallic cations from solution by adsorption on the acid form of a sulfonic acid ion exchange resin. Only solvents which do not give highly luminous flames may be used in the analysis. Ethanol and water with their steady, nonluminous flames are the most useful solvents. Acceptable solvents in order of decreasing desimbility 1
Present address, Film Department,
E. I. du Pont de Nemours and Co., Ton& Wanda, N. Y. 2
Present address, Starks Associates,
1280 Niagara St., Buffalo, N. Y.
are ethanol, water, or 1N hydrochloric acid, dimethylformamide, dioxane, butanol, ammonia water, acetone, 1:1 by volume acetone-water, ethyl acetate, ethyl benzoate, and deobase oil. Brite (2) employed kerotrine for solvent. Deobase oil has similar solvent properties, but gives a more satisfactory flame.
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EXPERIMENTAL
Apparatus. The analyses were made with a Beckman Model DU spectrophotometer equipped with a n AC power supply, a n RCA-1P-28 photomultiplier tube, and a n attachment for a n oxygen-hydrogen flame. The choice of burner is left t o the operator, as excellent results have been achieved with all three sizes of burner bore. Reagents. Amherlite-200 resin (Rohm and Haas ~Clo., Washington Square, Philadelphiri 5 , Pa.) is converted to the acid form by extraction in a column with l O g l , aqueous hydrochloric acid until sodium is completely removed. The column is then rinsed with distilled water until the efkluent is chloride free. The resin is stored as an aqueous slurry. Small but signiijcant adsorption of phosphorus occurs on columns made from &-dried rem. A 66.7% aqueous solution of phosphoric acid is the primary standard. Carefully analyzed triphenyl phosphite serves as standard for solvents in which phosphoric acid is insoluble. Procedure. Prepare an operating standard containing approximately 0.8 gram of phosphorus per liter and a sample containing 0.02 to 0.06 gram of phosphorus in 103 ml. If traces of metallic contaminsnts are present, discard about 30 ml, of sampIe, add approximately 0.4 gram of the airdried acid form of Amberlite-200 resin, shake for 2CI minutes, and decant the clear solution for the flame measurements. This treatment has prevented interference from trace metallic impurities in all 3f the nonacidic solvents recommended above. With samples of metallic salts, pass the solution through a column containing 15 ml. of settIed resin. Withdraw the effluent at 4 to 8 ml. per minute, discard the first 50 ml., and use the remainder. For the flame measurements the instrument sensitivity control is set approximately 1 / 2 turn from minimum, slits are set between 0.4 and 0.6 mm., and the wavelength it, set a t 540 mp. The solvent emission i s set a t 5er0 transmittance and the operating standard emission at 100% transmittance. DISCUSSION
The accuracy of the method has been tested b y analysis of a series of pure organic phosphorus coinpounds and by comparison with conventional analytical methods as shown in Table I.
Table 1.
Compound C~HspcIz ( CzHsOhPO (C6H6013P CH3POCl-OCH3 CHaPOCI-N( CnHr)i CH3POC12 PClS HaPOs POCI, PSClS PClS PBW
Analytical Results
Phosphorus, % Conventional analysis
Theory
Flame photometry 17.1
17.31 17.00 9.98 24.11 18.26 23.30
17.0
i0.i
17.0 37.3 17.6 17.3 12.5 27.81 16.6 11.81 8.37 16.3 15.7
e 0
4 0
a
23.8 18.0 23.3 17.0 37.4 17.6 17.4 12.5 27,85 16.7 11.8 8:34 16.2 15.7
These are unidentified research organic compounds for which the phosphorus analyses were obtained from Huffman Microanalytical Laboratories, 3830 High Court, Wheatridge, Colo.
Table II. Tests for Interferences from Various Ions and Elements (Effectiveness of Ion Exchange Column)
Recovery of phosphorus,
74
Concn. of interfering component gram/liter 0 528F 0 400 Bi
Without ion exchange treatment
After elution through ion ex(-hange column
Solvent used Compound added in test Benzotrifluoride 100.0 i 0 . 3 . . . 2R ethanol . 1001, aqueous HCI Bismuth nitrate 0.428 Br .,. 2B ethanol Bromobenaene Hydrochloric acid 6 988C1Water 0 966NOs. . Water Nitric acid Sulfuric arid 3 85 504-2 .. . Water 0 716 Iz , . 2B ethanol Iodine Ammonia 0.%3 NHA+ . Water Interferences removed by the ion exchange column Lead nitrate 0.806 Pb +z 100 0 Water 106 2 Ammonia 1.917 NHI 101.o 100.0 Water Calcium chloride 100 0 Water 1.010 Ca+Z >200 Calcium chloride 0 200 Ce+2 99 8 Water >200 2 210 K + >200 99 4 Water Potassium chloride Potassium chloride 0 440 K + >200 99 4 Water 1 280Na+ >200 99.4 Water Sodium chloride 0 320Na+ Sodium rhloride >200 99 8 Water Ferrous chloride 0.398 Fe+2 >200 100 0 Water Ferric chloride 0.200 Fe +a >200 100 0 Rater Interferences not removed by the ion exchange column Ammonia 109 3 Water 117 5 19 1 7 m 3 Boric acid >ZOO >200 Water 0.406 B Xitric acid 9.66 KO?102 1 102 0 Water Aluminum nitrate 0 522 A1+3 85.5 85 9 Vater Arsenic trioxide 0 441 As 101 8 101.6 10% aqueous HCI Vanadium trioxide 0 407 V >200 >200 1007, aqueous HCl Dow Silicone Fluid" 0.885 Si 109.5 Dirnethylformamide 109.4 Dow Silicone 550 Fluid (phenylmethylpolysiloxane).
.. ... . ...
I
The average of 320 analyses of carefully purified dimethylmethyl phosphone is 24.943%, theory 24.963% phosphorus. The relative standard deviation is 1%. The importance of identical solvents for standard and samples was shown by an experiment wherein lOyoextra water in the ethanol sample solvent reduced the result for phosphorus from 0.4042 to
0.2464 gram per liter. Very large samples often give similar errors from nonidentical solvent matrices. I n such cases, the method of additions with constant sample concentration gives accurate results. The lower limit of detectability under routine operating conditions is 0.08% phosphorus for a 2.5-gram sample in 100 ml. This sample did not produce VOL. 36, NO. 6, MAY 1964
1067
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any matrix effect. By opening the slits to 2.0 mm. and readjusting operating conditions, it is possible to detect 8 p.p.m. of phosphorus in solution. The validity of such low results should be accepted only with considerable caution, since very low concentrations of many elements can cause interference equivalent to this amount of phosphorus. To study the effects of other elements, a series of standards containing 0.3- to 0.4-gram-per-liter phosphoric acid solutions was prepared, all with a different element in a concentration at least equivalent to the phosphorus. These solutions were each compared in the
flame photometer with a standard of the same phosphoric acid concentration, but without added impurities. From Table I1 it is evident that the ion exchange column greatly extends the range of samples for which the method can be used. ACKNOWLEDGMENT
The authors thank F. M. Hartinger and R. L. McCullough for their cooperation in furnishing analyses by classical methods of calibration standards and many of the samples in Table I.
LITERATURE CITED
fl) . , Bernhmt. D. N.. Chess. W. B.. Rnv. ---
