Flame Photometric Determination of Calcium in Wet-Process Phosphoric Acid J. A. BRABSON and W. D. WlLHlDE Division o f Chemical Development, Tennessee Valley Authority, Wilson Dam, Ala.
E
CONOMY in the production of wet-process phosphoric acid
requires that the by-product calcium sulfate be easily filtered from the acid. Growth of the crystals of calcium sulfate to a readily filterable size is influenced greatly by the ratio of calcium ions to sulfate ions in the mother liquor (9). Control of this ratio is hampered when the time-consuming oxalate method (6) is used for the calcium determination. , Iron, aluminum, and phosphorus interfere and necessitate a double precipitation of calcium oxalate, with tedious filtrations. Flame photometric methods based upon the internal standard principle ( 2 , 4 ) have been used for the determination of calcium in complex materials ( f , 6, 10, 12 ). The direct intensity principle, with standards simulating the samples, also has been used for the determination of calcium (3,8). The internal standard technique has the advantage of simplicity in the preparation of standards. The flame photometric method described here-an internal standard method-cuts hours from the usual time required for the determination of calcium in wet-process phosphoric acid. APPARATUS AND REAGENTS
Flame Photometer. 'Perkin-Elmer, Model 52-C, with acetylene burner. Shaker. Equipped to hold 250-ml. flasks. Standard Calcium Solution. Dissolve 3.5696 grams of dried reagent calcium carbonate in 100 ml. of 1M hydrochloric acid and dilute to 1 liter. The calcium oxide content is 2 mg. per ml. Internal Standard-Strontium Chloride Solution. Dissolve 30.45 grams of the hexahydrate in distilled water and dilute to 1 liter. The strontium content is 10 mg. per ml. Cation Exchange Resin. Amberlite IR-120( H), analytical grade (Rohm & Haas Co.) or its equivalent. Treat 100 grams of resin with 5M hvdrochloric acid in an ion exchange column until flame photometGic tests of the eluate show an absence of sodium and calcium. Rinse the resin thoroughly and air-dry it. Ammonium Nitrate. Analytical grade. STANDARD1 ZATION
Prepare a series of eleven concentration standards containing 50 ml. of strontium chloride solution and from 0 to 50 ml. of the standard calcium solution in 5-ml. increments. Dilute to 500 ml. Warm up the electrical circuit of the photometer and adjust the burner to give a steady flame. Set the element selector a t about 5500 A. and adjust to maximum sensitivity while atomizing the calcium chloride solution. To calibrate the photometer, take readings on the two end concentration standards until the settings are reproducible. Then take three readings on each intermediate standard, with a recheck of the end standards after each series. Plot average readings against concentration. The standards correspond to from zero to 20 grams of calcium oxide per liter with the unknown in its specified dilution. ANALYSIS
Warm a 100-ml. sample of the unknown with 50 ml. of hydrochloric acid until suspended matter is dissolved. Dilute to volume in a 1-liter volumetric flask. Pipet a 10-ml. aliquot into a 250-ml. flask. Dilute. to 150 ml. with distilled water and add 1 gram of IR-12O(H) resin. Shake flask and contents in the shaking machine for 15 minutes. Collect the resin on a coarse filter paper and wash it ten times with distilled water. Dry the paper without charring and brush the resin into a platinum dish. Add 2.5 grams of solid ammonium nitmte. Heat on a hot plate until the reaction subsides, then over a Bunsen burner until organic matter is eliminated. Cool the residue, add 5 ml. of 72% perchloric acid, and evaporate just to dryness on a hot plate. Add 5 drops of concentrated hydrochloric acid and 30 ml. of distilled water. Warm to clarity, mix
with 10 ml. of the internal standard solution in a 100-ml. volumetric flask, and dilute to volume. Pour some of the unknown into the photometer and estimate the calcium content. Pour in some of the standard solution whose calcium content is nearest that of the unknown. Agreement of the scale reading with that obtained in the calibration indicates that the instrument is ready for the final measurements. Take three alternate readings for the unknown and for the nearest standard solution. Calculate the average reading for the unknown and read the calcium content from the calibration curve. EVALUATIOK OF METHOD
The preponderance of phosphorus pentoxide over calcium oxide in wet-process phosphoric acid is as much as a hundredfold. The acid also contains iron, aluminum, fluorine, and sulfur as impurities. Preliminary tests of the effects of phosphorus and of these impurities on the calcium determination were made with reagent chemicals. Lithium was the internal standard. The photometer was tuned to the diatomic band emission that occurs a t about 5500 A. and which gives much greater sensitivity than the primary calcium line emission at 4226 .I Iron, fluorine, and sulfur in their usual proportions were without effect. Aluminum depressed the calcium readings, the depression becoming more scvere as the ratio of aluminum to calcium was increased. Phosphorus also interfered. Moreover, the action of aluminum and phosphoius together was synergistic. Mitchell and Robertson ( 7 ) found that strontium lessens the interference of aluminum in the determination of calcium by the Lundeghrdh flame spectrographic method. The materials with which they worked, however, apparently did not entail the combined effect of aluminum and phosphorus. Since aluminum affects the spectral emissions of strontium and calcium in the same way, strontium was viewed as a potential internal standard in the present problem. Strontium chloride equivalcnt to 100 grams of strontium per liter was added to a series of five solutions containing 300 grams of phosphorus pentoxide, 4 grams of calcium oxide, and from 10 to 50 grams of aluminum oLide per liter. The emission intensities then were compared with those of similar phosphorusfree solutions. Since the factory setting of the fixed slit to transmit the lithium line emission at 6708 A. corresponds to a band t,mission of strontium chloride, adjustment of the slit was unnecessary. The calcium found in thv phosphorus-free solutions was uniformly 100% of that present. The calcium found in the phosphorus-containing solutions r a n g d from 98% of that present at 10 grams of aluminum oxide per liter to 80% at 50 grams of aluminum oxide per liter. To take advantage of the strontium standard as a means of eliminating the interference of aluminum, the phosphorus would have to he removed. A separation by means of an ion exchange resin often proves practical for eliminating the interference of one ion in thr determination of another of opposlte charge. The commonly used column tcchnlque of ion cwharlge-with Iegeneration of the resin-requires an aggregate time, however, that was viewed as objectional in the present work. An alternative was sought through a batch separation of cations with a small amount of resin that then could bc considered as expendable. Calcium was separated from solution quantitatively when an aliquot equivalent to 1 ml. of net-process acid was diluted to
1060
V O L U M E 2 6 , NO. 6, J U N E 1 9 5 4
1061
Table I. Comparison of Photometric and Chemical Determination of Calcium in Wet-Process Phosphoric Acid CaO, Grams Photometric Method Av. Max. Min. 4.1 4.1 4.0 2.7 2.7 2.6 4.1 4.1 4.0 8.3 8.4 8.0 22 .. 48 22 .. 47 22 .. 36 3.7 3.7 3.5 3.0 3.1 2.9 3.0 3.1 2.9 2.2 2.3 2.1
per Liter Chemical Method Av. Max. Min. 4.2 4.3 4.0 2.6 2.7 2.6 4.0 4.0 4.0 8.5 8.5 8.4 22 .. 74 22 .. 85 22 .. 64 3.8 3.8 3.7 2.8 2.9 2.8 3.1 3.2 3.1 2.1 2.2 2.1
150 ml. and shaken for 15 minutes with 1 gram of Amberlite IR-lSO(H) resin. The resin was collected on a paper filter, transferred to a dish, and ignited with ammonium nitrate a t a low temperature. The ash was digested with Perchloric acid. Strontium chloride was added as an internal standard and calcium was determined photometrically. Triplicate analyses of ten samples of wet-process acid by this method are compared with analyses by the conventional chemical method in Table I. Some commercial wet-process acids contain sodium that was added to precipitate This 'Odium enhances the photometric reading for calcium. Tests on synthetic samples showed that the effect of sodium on the calcium determination is linear a t concentrations of sodium oxide from 0 to 4 grams per liter. if%en the sodium oxide content higher, Part of it must be removed. About half of it can be removed without loss of calcium by washing the resin acid' Further loss Of twenty times with through in the ashing step lowers the 'Odium 'Odium to less than 20% of that present in the original acid.
Aliquots of a standard sodium solution equivalent to from 5 to 25 grams of sodium oxide per liter were added to a practicdly sodium-free sample of wet-process phosphoric acid. The solutions then were analyzed photometrically for calcium and sodium, the resin being washed as described. The calcium results, when corrected for sodium interference, agreed closely with those obtained in the analysis of the original sodium-free phosphoric acid. The flame photometric method is practically as precise as the chehical method and is faster. A single determination of calcium in wet-process phosphoric acid can be made in 1 hour, whereas the chemical method requires 5 hours. Multiple analyses by the photometric method require about one third the time required by the chemical method. LITERATTJRE CITED
(1) Barnes, R. Berry, J. W., and Hill, W. B., EW. MininU J., 149, No. 9,924(1948). (2) Berry, J. W., Chappell, D. G., and Barnes, R. B., Im.ENQ. CHEM., ANAL.ED., 18,19-24 (1946). (3) Brown, J. G., Lilleland, O., and Jackson, R. K., Proc. Am. SOC. Hort. Sei., 52, 1-6 (1948). (4) Gerlach, W., 2.anorg. u.allgem. Chem., 142, 383-98 (1925). (5) Hiliebrand, w, F., Lundell, G. E, F., "Applied ~ ~ Analysis," pp. 500-1, New York, John Wiley & Sons, 1929. (6) Knight, S.B., Mathis, W. C., and Graham, d. R., ANAL.CHEM., 23,1704-6 (1951). (7) Mitchell, R. L., and Robertson, 1, M.,J , So,.. Chem. I&. (London), 55,269-72T (1936). (8) Mosher, R. E.,Bird, E. J., and Boyle, A. J., ANAL.CHEM.,22, 715-17 (1950). (9) SokolovskiC A. A*, Zhur. Khim. Prom., 13992-102 (1936). (10) Toth, S. J., and Prince, A. L., Soil Sci., 67,43945 (1949). (11) Toth, S. J., Prince, A. L., Wallace, A., and Mikkelsen, D. S., Ibid., 66,459-66(1948). RECEIVED for review December 21, 1953. Accepted February 23, 1954. Presented at the Southwide Chemical Conference, Auburn, Ala., October 1952.
Isolation and Purification of Semimicro Quantities of Morphine LEONARD
B. ACHOR
and
E. M. K. GElLlNG
Department o f Pharmacology, University o f Chicago, Chicago
M
ETHODS for the isolation of morphine from the opium poppy are numerous (3) but not satisfactory for the recovery of quantities of thc order of 1 to 10 mg. The cost of production of carbon-14-labeled morphine (at least 20 mc. of carbon-14 as barium carbonate are required a t a cost of $36 per mc.) by biosynthesis (6) in amounts sufficient for tracer and metabolic studies requires a method which will give maximum yields from the limited amounts of radioactive Papaver somnife r u m available. It has been shoun that certain of the ion exchange resins can be applied successfully to the separation and purification of substances containing the basic nitrogen group (4). The fact that morphine contains both an N-methyl and a phenolic hydroxyl group somewhat simplifies the problem and, accordingly, several ion exchange resins were evaluated. Of the resins studied, optimum performance and maximum recoveries were obtained with Nalcik SAR (anion, polyamine) and Amberlite IRC-50 (cation, carboxylic acid). The procedure for the extraction, purification, and crystallization of morphine is given below. REAGENTS AND SOLUTIONS
Aqueous sodium carbonate, 10%. A ueous ammonium chloride, 20%. 1-c8utanol-benzene, 1 to 1. Aqueous sodium bicarbonate, 5%.
37, 111.
Sulfuric acid, 0.525N. Potassium hydroxide, 2%, saturated with barium hydroxide. Aqueous methanol, 50%. Hydrochloric acid, 0 . W . Aqueous sodium hydroxide, 10%. Dihydrogen potassium-phosphate-disodium monohydrogen phosphate buffer, p H 7.0, 0.5M. Chloroform-ethyl alcohol, 3 to'l. rlbsolute ethyl alcohol. Concentrated aqueous ammonia ISOLATION AND PURIFICATION PROCEDURES
Two grams of oven-dried (80' C.) P. s o m n i erum capsules are ground to 40 mesh in a Wiley mill, transferre to a 40-ml. glassstoppered centrifuge tube, and mixed intimately with 10 ml. of a 10% aqueous sodium carbonate solution. After 1 hour of quiet standing, the mixture is brought to p H 8.6 f 0.1 by the addition of 20% aqueous ammonium chloride (approximately 5 ml. being required) and extracted to 15 ml. of 1 to 1 l-butanolbenzene solution. The mixture is centrifuged to separate the organic layer, which is drawn off. The extraction is repeated twice using 10 ml. of 1-butanol-benzene solution in each case. The organic layers are combined, and shaken in succession with two 15-ml. portions of 5% aqueous sodium bicarbonate to remove igments, many of which are present in the organic layer ollowing the original extraction. The 1-butanol-benzene fraction is then shaken with 15 ml. of 0.525N sulfuric acid and washed with two 10-ml. portions of water, so as to remove the morphine and certain impurities to the aqueous phase. The procedure described permits recoveries of the alkaloid on the order of 92 to 95%; these values were checked by carrying out extrac-
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