Packing B gave satisfactory retention times and good separations; however, it proved t o be unstable. The retention times decreased with use until all peaks merged into one. Conditioning with helium a t 120'C. did not restore the column to its original condition. Packing C gave excellent separations and short retention times. Although with use the retention times of this packing decreased, it mas very readily regenerated by conditioning with helium for 16 hours at 120' C.
The difference in these three packings is believed to be due to the presence of excess NHIOH and/or NH4Cl. The procedure for making Packing A results in a large excess of iron and hydrochloric acid. Upon neutralization with N K O H , correspondingly large amounts of NH4Cl are formed which are absorbed by the gelatinous precipitate of Fe(OH)3. This conclusion is supported by the results obtained with Packing8 B and C, where reducing the amount of excess "4OH and NH4C1 improved the separation
and reduced the retention times. As shown in Figure 1, Packing C gave the best separation and the shortest retention times. This column has been in operation for six months and has undergone many regenerations. LITERATURE CITED
(1) Hunt, P., Smith, H., J . Phys. Chem.
6 8 7 (1961). R.7 J . A m . (2) Moore, w.R., Ward, Chem. Soc. 80, 2909 (19%). (3) Moore, W. R., Ward, H. R., J . Phys. Chem. 64, 832 (1960).
Determination of Carbonates by Infrared Measurement of Carbon Dioxide Harvey Pobiner, Analytical Research Division, Esso Research and Engineering Co., Linden, N.
spectrometric method carbonates, which offers a greater specificity than that in the usual absorptimetric or titrimetric techniques, has been developed. Carbonates are usually determined by acidification and measurement of the carbon dioxide generated by familiar finishing steps, such as the absorption of COZ in a suitable absorption tube (2) or the back-titration of a caustic solution containing absorbed COZ (1). Occasionally these standard procedures encounter interferences, such as the failure of absorption tubes in an absorption train to remove certain titratable acidic gases (HCI, H2S). The quantitative analysis for carbonate described herein is based on the infrared spectra of generated carbon dioxide. In a published catalog of the infrared spectra (3) of 66 gases, quantitative analysis of C 0 2 at 4.32 microns and 2.72 microns encounters minimal interferences from other gases. Further selectivity for this measurement is realized by the gaseous evolution technique to separate COz from possible interferences in solution. The infrared method utilizes simple apparatus and is rapid. An analysis is accomplished in 10 minutes, comparable to some absorption techniques. The method, as established, is sensitive to 100 p.p.m. of K2CO3 and can easily be extended to lower limits. N INFRARED
A for
X. J. The 4-necked, 500-ml. flask is fitted with a pressure gage and a pressure relief valve. The latter is a safety device which automatically vents the closed system when the pressure exceeds 5 p.s.i. The valve is obtainable from Circle Seal Products, Inc., Pasadena, Calif. Calibration. Prepare a series of standards of 0.01 t o 1.0 gram and 1.00 t o 5.00 grams of K2C03 in 50 ml. of solvent system. The solvent can be water or the diluents expected in routine samples. Place 180 ml. of 1 t o 1 HC1 in the reservoir of the cylindrical separatory funnel. Open valve E on the pressure equalizer arm of the separatory funnel. Close the valve between the reactor flask (valve A in Figure 1) and the remainder of the apparatus. Open valves B and C, and evacuate the system consisting of the infrared cell, manometer, and tubing connections beyond valve A. Valve D of the infrared cell is always closed. Deliver 20 ml. of 1 to 1 HCl from the separatory funnel into a standard 50ml. blend or sample in the reactor vessel and close valve E. Magnetically agitate for 5 minutes. Valve A remains closed during this time.
PROCEDURE
Carbonate in the sample is converted to COz by adding dilute HCl to the closed glass system shown in Figure 1. The COz thus generated is then delivered into an evacuated system consisting of mercury manometer, infrared gas cell, and associated vacuum stopcocks and delivery lines. COZis measured at 2.72 microns and 4.32 microns. By calibration with known blends of KzCO3 in solvent, the carbonate content of samples is calculated. The glass apparatus (Figure 1) utilizes standard S/J 35/25 ball joints and is available from Labglass Inc., Vineland, 878
ANALYTICAL CHEMISTRY
SSURE STOPCOCK ITH B A L L dOlNT
J.
Close valve B to the vacuum pump. Keep valve A on the reactor flask closed and valve C of the infrared cell open. Record the pressure in millimeters of Hg of the evacuated system. Open valve A to admit the gas sample at the maximum available pressure up to 760 mm. Close valve A . Record the increase of pressure of the manometer due to the sample. Close valve C of the infrared gas cell. Record the infrared spectrum from 2 to 6 microns vs. a NaCl compensation window. The reactor flask and the delivery end of the separatory funnel are washed and dried between runs. The accessory equipment beyond valve A is evacuated to 0 mm. This effectively removes CO2 contamination between samples. For the series of standards containing 0.01 to 1.0 gram of K2C03, determine the absorbance at 4.32 microns, relative to a base line drawn from 4.15 to 4.65 microns. For the series of standards containing 1.00 to 5.00 grams, determine the absorbance at 2.72 microns relative to a base line drawn from 2.60 to 3.15 microns. Investigate the effect of pressure us. absorbance. For a blend containing 0,3 gram of K2CO3per 50 ml. of solvent, determine the absorbance at 4.32 microns at pressures ranging from 50 to 760 mm. For a blend containing 4 grams of K2C03per 50 ml. of solvent, determine the absorbance a t 2.72 microns over a similar range of pressures. Plot pressure LIS. absorbance at each wavelength (Figure 2). Correct the absorbance to 760 mm. by multiplying the absorbance by a factor evident in the calibration investigation of absorbance us. pressure. For euample, if a blend is run at 502 mm., the correction factor at 4.30 microns from Figure 2, is A760 ,,,,J ASOO mm. = 0.620/0.440 = 1.41. Plot a calibration curve of absorbances at 4.32 -TO
ROUND BOTTOM, 500 ml. 4-NECK FLASK, S/J 35/2
MANOMETER
MAGNETIC STIRRER
Figure 1.
IR GAS C E L L
Apparatus f o r COz generation
TO VACUUM PUMP
microns and 2.72 microns, corrected to 760 mm. us. grams of KzC03 per 50 ml. These are smooth curves. Analysis of Samples. Pipet 50 ml. of sample into the reactor flask and proceed as in the calibration. If the pressure release valve is activated during a n analysis, a smaller sample is run. I n t h a t event, the volume is kept constant by adding additional solvent or water until 50 ml. is reached. Correct absorbances t o 760 mm. by using the pressure-absorbance curves and determine grams of K2CO3 per 50 ml. by the calibration curve. DISCUSSION
CO, Generation as Function of Time. As the d a t a of Table I indicate, the reaction reaches apparent maximum COZ formation in 5 minutes. Thus, a n interval of 5 minutes is the recommended minimal residence time in this procedure. G a s Flow Is Dependent on Proper Evacuation of Apparatus. It is important t o evacuate only t h a t part of the system beyond the reactor flask, namely, the manometer, infrared cell, and associated tubing and connections. Should the reactor and separatory funnel be evacuated, the generated COz will not flow readily when value A is then opened. As part of the system is not evacuated, a partial pressure in the reactor due to air, water, and hydrochloric acid is common to the calibration and analysis. This partial pressure is 676 to 678 mm. registered when 20 ml. of 1 to 1 HCl are delivered into a blank sample. I t is not subtracted from standard calibration blends or samples. Calibration of the apparatus for CO, analyses over a specific concentration range minimizes such errors as solubility of the gas in the c o n h i n g liquid and variations in molecular volume. Sample pressures are corrected to 760 mm.
Table 1.
COz Formation a s Function of Time Absorbances at 4.32 p in Minutes 7.5-cm. cell
i.*L/
m a S Q m
I
ob
1 200
1 400
.
1
600
800
1000
PRESSURE, mm. Hp
Figure 2. Pressure-absorbance curves of generated C o t Curve A, at 4.32 p Curve B, at 2.72 I.(
by reference to the standard pressureabsorbance curves established in the calibration. Under normal laboratory conditions, temperature corrections are ignored. Accuracy a n d Repeatability. Carbonate analyses by the infrared method agree with those obtained by the gas evolution-absorption tube method (Table 11). At the 0.4yG KzC03 level in solvent, the one sigma repeatability figure is 0.04YG. This is based on 11 replicate analyses from one sample. The generation of COZ over a n aqueous acid solution does not produce significant etching of the NaCl windows of the gas cells. After 250 analyses in the IR gas cell, the slight etching of the NaCl windows does not warrant any polishing of the plates. Applicability. This procedure has been developed for soluble carbonates. It has not been applied to those carbonates in natural mineral deposits, such as magnesite and dolomite, which are decomposed slowly by cold dilute acid (4). The apparatus will be used for measuring
a
0.25 0.292 2 0.532 5 0.620 10 0.620 15 0.629 20 0.639 30 0.623 0.302 g. of KzC03 per 50 ml.
Table II. Comparison of IR Method with Absorption Method for Carbonates KZCOI, Wt. % Theory Infrared Absorption 0.16
Unknown 0.80 1.06
0.22 0.81 0.90 1.10
0.22 0.78 0.91 1 06
gases generated in other chemical reactions. ACKNOWLEDGMENT
The author acknowledges the technical assistance of Francis T. FitzSimmons. LITERATURE CITED \
1) Loveland. J. IT..Adams. R. ,
W..Kine.
H. H., Sowak, F.’A., Cali, L. J.,’ANAI:
CHEM. 31, 1008 (1959). (2) Lundell, G. E. F., Bright, H. A.,
Hofmann, J. I., “Applied Inorganic Analysis,” Chap. 50, %ley, New York,
1953. (3) Pierson, R. H., Fletcher, A. N., Gante, E. S t . Clair, ANAL. CHEM.28, 1218 (1956). (4) Treadwell, F. B., Hall, W. T., “-4na-
lytical Chemistry,” Vol. 11, Chap. VIII, Wiley, New York, 1947.
Room Temperature Oxidation of Silicone High Vacuum Grease Robert H. Linnell, Harold J. Wimette, and Frederic W. Gross, Scott Research Laboratories, Inc., P. 0. Box 66, Perkasie, Pa. gas samples containing Ipounds low concentrations of organic comwe use a 40-meter pathlength N ANALYZING
absorption cell and a Perkin-Elmer Model 21 infrared spectrometer. Our 40-meter cell has a volume of 57 liters. We frequently find it convenient to sweep gas samples into this evacuated cell with either prepurified nitrogen or dry, COz-free air. Gas samples are collected in borosilicate glass flasks of 600- to 1500-mi. volume with a stopcock at each end. We have been using Dow Corning high vacuum grease on the stopcocks. It is stated that this grease is oxidation resistant and t h a t the grease can be removed by rinsing with
kerosene and then cleaning with warm chromic acid solution. We have run into trouble with contamination of our gas samples and it has been definitely established that this is due to the reaction of chromic acid with the silicone grease. It had been our practice to clean our borosilicate glass sampling flasks by filling them with chromic acid cleaning solution (at room temperature), letting them stand a few minutes, flushing out the residual chromic acid with tap water, cleaning with Alconox, flushing with tap water, and finally rinsing several times with distilled water. Prior to use, each sample flask is evacuated to 50 microns
and filled with either dry, COz-free air or prepurified Nz and this procedure is repeated three times. After collecting a gas sample, the sample is flushed into the long-path infrared cell and the spectrum recorded. Bands appearing a t 3.32, 7.90, 9.15, 9.63, and 12.27 microns made us suspect contamination from the sample flask. A flask was cleaned as described and flushed with our dry, Coz-free air into the long-path cell and the same unknown bands appeared. The bands are tentatively identified as follows: 3.32 microns, C-H stretch; 7.90 microns, Si-CH8, deformation; 9.15 microns, Si-0 stretch (cyclic tetramer) ; 9.65 microns, Si-0 stretch VOL. 34, NO. 7, JUNE 1962
879
