ANALYTICAL CHEMISTRY
144
Table 111.
Standard Deviation of Replicate Samples
Sample
h-0. of Observations
Av. Reid Vapor Pressure
Standard Deviation
deviations and replicate results are summarized in Table 111. The vapor pressures of the samples listed in these tables were determined in a random order by various operators over a period of about 2 weeks. The individual samples were identified only by numbers, and the relationship of the samples was unknown to the operators. The smaller samples permitted easier handling and storage than macro samples so that the small scale measurements require about one third less time than the standard measurements. ACKNOWLEDGMENT
Based on all gasoline samples measured. 76 degrees of freedom.
sample bottle, the sample can be transferred to the cup through a wash bottle top in place of the cork. If 10 to 12 ml. of sample are forced through the delivery tube before charging sample to the cup, the system will be cold enough for safe transfer of the sample. Heating the vapor space to 100" F. eliminates the need for correcting for change in air pressure on heating and for change in the vapor pressure of water. This technique also eliminates the necessity for measuring the temperature of the air chamber n.hen the apparatus is assembled. Performance. The repeatability of the method by different operators within one laboratory was evaluated by determining the Reid vapor pressure approximately 100 times. The standard
The authors are indebted to Robert Matteson and V. B. Waithman for the original design of this instrument. They nish to thank V. C. Davis for designing and constructing the bridge and R. K. Stone for his participation in many helpful discussions of this problem. LITERATURE CITED
(1) Am. Soc. Testing Materials, Philadelphia, Pa., "ASThI Standards
on Petroleum Products and Lubricants," Method D 323-53, November 1953. (2) Levin, H., Morrison, A. B., and Reed, C. R., ANAL.CHEM.,22, 188 (1950). (3)
Statham Laboratories, 12401 West Olympic Blvd., Los -4ngeles 64, Calif., Instmment S o t e s , S o . 4, (November 1949).
RECEIVED for review M a y 26, 19.54
Accepted September 9. 1954.
Determination of Boron in Silicates after Ion Exchange Separation HENRY KRAMER U. S. Geological Survey, Claremont, Calif. Existing methods for the determination of boron in silicates are not entirely satisfactory. Separation as the methyl ester is lengthy and frequently erratic. A n accurate and rapid method applicable to glass, mineral, ore, and water samples uses ion exchange to remove interfering cations, and boron is determined titrimetrically in the presence of mannitol, using a pH meter to indicate the end point.
R
E C E N T L T Martin and Hayes ( 3 ) have shown that boron can be separated from interfering cations by ion exchange. Their experimental data are restricted to the analysis of steel samples, although their basic data imply wider applications. This investigation confirms the earlier work and tests the method for the determination of boron in silicates. The conventional procedure for the isolation of boron is by distillation a3 the methyl ester. This method was investigated and, as others have found ( 3 , 4),incomplete volatilization was obtained from large amounts of aluminum, and frequently a double distillation was necessary in the presence of both iron and silicon. As such. the method is unwieldy and time-consuming. I n this investigation only minor modifications were made in the procedure described by JIartin and Hayes. Boron is brought into solution either by an acid extraction or by fusion, eluted through an ion exchange bed, and determined titrimetrically in the presence of mannitol, using a p H meter to indicate the end point. METHOD
Reagents. Methyl red indicator solution. Concentrated hydrochloric acid. Sodium carbonate, c.P., anhydrous. Sodium hydroxide, standardized 0.055. Sodium hydroxide, 20% weight per volume (carbonate free, prepared from 50% sodium hydroxide).
Mannitol, neutral, boron-free. Amberlite IR 120 (H), analytical grade (exchange capacity of the dry resin is approximately 5 meq. per gram). This material may be regenerated after use by transferring the accumulated resin from a number of determinations to a large glass tube and 9 ) hydrochloric acid until the issuing liquid washing with (1 gives a negative test for adsorbed ions. The hydrochloric acid is removed by washing with distilled water. Apparatus. Beckman, Model 2H, line-operated p H meter with saturated calomel and glass electrodes. Preparations of Ion Exchange Column. A borosilicate glass chromatograph tube, 20 X 400 mm., with sealed-in, coarse porosity, fritted disk provided with a small rubber tube extension and screw clamp is used. Fill the tube with water and add the resin slowly as a slurry until a column 10 inches in length is formed. The column should be free of air spaces. Before using, wash the column with 100 ml. of (1 9 ) hydrochloric acid and follow with 50-ml. portions of water until the effluent gives a negative test for chlorides. Solution of Borates. ACID-SOLUBLEBORATES. Keigh a sample containing 10 to 20 mg. of boron oxide into a 125-ml. 25) hydrochloric acid and Erlenmeyer flask. Add 30 ml. of ( 5 connect the flask to a reflus condenser. Heat the misture to boiling and reflux slowly for 20 to 25 minutes. After allowing the mixture to cool slightlv, pour 5 ml. of water through the top of the reflux condenser; disconnect the condenser and wash the tip of the condenser carefully with water. Filter the misture while hot through a 9-em. Whatman 41 H filter paper, and wash the residue with hot m.ter to a volume of about 50 ml. ACID-INSOLUBLE BORATES. Keigh a sample containing 10 to 20 mg. of boron oxide (not more than a 1-gram sample) into a platinum crucible, add six times the sample weight of anhydrous sodium carbonate, and, with a platinum stirring rod, mix the sample and flux intimately. Cover the crucible and heat gently for 5 to 10 minutes to expel moisture. Vow gradually increase the heat so that after 5 to 10 minutes more, a liquid melt is formed. When fusion is complete, grasp the crucible with tongs and give i t a rotary motion so as to spread the contents over the sides of the lower half of the crucible, thus expediting subsequent solution. Cool, and place the crucible in a 150-ml. beaker containing 20 ml. of water. Cover the beaker with a watch glass and add concentrated hydrochloric acid down the sides of the beaker until there is an eyress of 1 ml. over the theoretical amount
+
+
+
145
V O L U M E 2 7 , N O . 1, J A N U A R Y 1 9 5 5 calculated t o decompose the carbonate. After decomposition of the melt dissolve a n y carbonate adhering t o the crucible or cover with hot dilute hydrochloric acid; remove any adhering material with a rubber policeman, and rinse into the beaker with a stream of hot water. Filter the mixture through a 9-cm. Whatman 41 H paper, and wash with hot water to a volume of about 50 ml. PROCEDURE
Seutralize the solution obtained from t h e above treatment with 20y0 sodium hydroxide until aprecipitate just starts t o form; add concentrated hydrochloric acid dropwise until the precipitate just dissolves or until the solution is just acid to litmus paper. Pass the solution through the ion exchange column into a 400ml. beaker and follow with four 50-ml. portions of water, adding the wash water when there is 0.5 inch of supernatant solution above the resin. Adjust the rate of flow so t h a t the total elapsed time for the solution and the four washings is 15 minutes (flow rate of 16.7 ml. per minute). h t the conclusion of the last washing the effluent should be only slightly acid t o p H test paper. (If not, the amount of resin in the column should be increased t o ensure the complete removal of cations. No additional amount was ever necessary in this invest’igation.) .4dd 2 or 3 drops of methyl red indicator to the solution and make alkaline with 20% sodium hydroxide, and then barely acid with concentrated hydrochloric acid. Cover t,he beaker with a watch glass and boil gently for 3 t o 5 minutes t o rcmove carbon dioxide. Cool the solution to room temperature, preferably in a water bath. Introduce the p H meter electrode3 and stirrer into the beaker, and adjust the p H of the solution to 7.0 with 0.05N sodium hydroxide. The indicator needle of the pH meter should be steady and not drift from the reading of 7.0. .idd 40 grams of mannitol, and, using a microburet (calibrated 0.05 ml.), titrate rapidly with standardized 0.05N sodium hydroxide until the pH of the solution approaches a value of T and t,hen slowly near the end point t o allow for any slight lag i n re.sponse of the p H meter. When the indicator needle remains steady on 7.0 for a t least 10 seconds, record the volume of standard base used. -4 blank correction (usually less than 0.10 ml. of 0.05.V sodium hydroxide) for the reagents is subtracted from the sample titration and the boron oxide is calculated: 1 ml. of 0.05-V S a O H = 1.i41 mg. of B203
If the titer is small, repeat the determination, collecting the eluate in a 250-ml. volumetric flask, and determine the boron colorimetrically. Tin, rarely encountered in boron analysis, should be removed before the ion exchange separation is made. This is most easily done by plating out the tin ivith granular zinc after the borate is in acid solution. EXPERIMEYTAL DATA
A master solution was prepared containing a number of cations to test the effectiveness of the outlined procedure. I t contained: sodium chloride 1 2 . i l grams, potassium chloride 1.91 grams. calcium chloride 13.84 granw, magnesium chloride 20.90 grams, barium chloride 0.79 gram, ferric chloride 24.20 grams, aluminum
Table I. Boric Acid Taken, Mg. 4.96 4.96 19.83 19.83 39.66
Table 11.
Recoveries of Boric Acid
S B S 93
Sample dried a t 500’ C
Table 111. BgOi Taken, Mg.
1 6 , 0 7 (colemanite) 2 0 , 3 2 (colemanite) 1 7 . 0 8 (howlite) 1 7 . 9.5 (howlite)
Analysis of Synthetic Alixtures Recoveries AI& 70 16.05 99.9 16.07 100.0 20.36 100.2 20.37 100.2 18.02 100.4 18.02 100.4 17.98 100.2 17.85 99.4
.
l f e t h o d of Solution Acid l e a d Acid leach Fusion Fusion rlcid leach Acid leach Fusion Fusion
Several “refractory borosilicates’’ were analyzed using the methanol distillation as described by Hillebrand et a!. ( 1 ) and the proposed procedure. The results are presented in Table IL-,
Table IV.
Analysis of Refractory Borosilicates
Mineral Black tourmaline (Kuevo, Calif.) Green tourmaline (Calif.) Dumortierite (impure) (Carpe l\Iucharcho Mts., Imperial Co., Calif.) Axinite (Sorth Hills Quarry, Riverside, Calif.)
Methanol Separation, % BzO3 9.79 10.51 1.93 8.80
Ion Exchange Separation, BzOa 10.03 1 0 . 70 2.02 5.98
The high iron, alumina, and silica contents of these minerals preclude complete volatilization of the boron in the first distillation. Only one distillation (collected in two fractions) per sample was made. CONCLUSIOYS
The proposed method has decided advantages over the methods currently used in that the accuracy and reproducibility are good; less manipulative skill is involved; blank corrections are very low; and time of analysis is greatly reduced.
Recoveries
;\Ig
%
ACKNOW LEDGMEh-T
4.97 4.97 19.83 19.83 39.78
100.2 100.2 100.0 100.0 100.3
The author gratefully acknowledges the mineral specimens supplied by W. C. Oke, Minerals Curator, California Institute of Technology, Pasadena, Calif., for use in this investigation.
Analysis of Sational Bureau of Standards Glasses
Glass S B S 92
chloride 23.49 grams, zinc chloride (metal dissolved in hydrochloric acid) 0.50 gram, water t o make 500 ml. The master solution was analyzed for boron, and none was found. Various amounts of boric acid were then added t o 10 ml. of the master solution. Results by the proposed procedure are given in Table I. National Bureau of Standards glass samples were fused and analyzed by the proposed procedure. The results are given in Table 11. Hollander and Riemann ( 2 ) report boron oxide values for NBS 92 as 0.65% and for NBS 93 as 12.5175, and conclude that their values are closer to the actual content. Synthetic mixtures of colemanite (CatBsOii.5HAO) and bentonite [(Mg, Ca) 0..41203 5SiOz n H 2 0 ] , and howlite [Ca2SiBjOp (0H)J and bentonite were also analyzed. T h e results are presented in Table 111.
BZOIReported, % 0.70 0.70 12.7 12.7 12.7
BpOz Found,
%
0.63 0.62 12,435 12.44 12.45
LITERATURE CITED
(1) Hillebrand, W. F., Lundell, G. E. F., Bright, bl. S.,and Hoffman, J. I., “A4ppliedInorganic rlnalysis,” p. 756, New York, John Wiley & Sons, 1953. ( 2 ) Hollander, M., and Riemann, W., 3d. Ax.4~.CHEM.,18, 7 8 9 (1946). (3) Martin, J . R., and Hayes, J. R., Ibid., 24, 182 ( 1 9 5 2 ) . (4) Rader, L. F., Jr., and Hill, W. L., J . A g r . Research, 57, 901 (1938).
RECEIVED for review May 1. 1954. Accepted October 13, 1954. Publication authorized by the Director, U. S. Geological Survey
