Applications and Accuracy. This method has been applied t o the determination of titanium in three Kational Bureau of Standards standard samples, t o demonstrate its accuracy and general applicability, and t o the determination of titanium in lithium metal and in filter paper ash (Table 1‘). This method is applicable t o a wide variety of samples and to a wide range of titanium concentrations. For example, it has been applied t o a sample which contained 5.0 mg. of titanium per ml. and somewhat smaller concentrations of several other metal ions. The results, after adequate dilution, were within 5y0 of the expected value and the entire determination was per-
formed in approximately 15 minutes. The precision, as demonstrated in the determination of titanium in the three NBS samples, is to 2% or less. The significant amount of titanium contained in filter paper ash should be considered if the dissolution of a particular sample involves an ignition of filter paper with subsequent addition of the dissolved ash to the final solution. Based on the amount of titanium found in filter paper ash, an absorbance correction of as much as 0.05 might be necessary if the entire quantity of the ash were equilibrated with tri-n-octylphosphine oxide. The titanium concentration in filter paper ash varies with the manufacturer and Riith different lots from the same manufacturer.
ACKNOWLEDGMENT
The authors acknowledge the assistance of J. R. French in carrying out some of the experimental details of this study. LITERATURE CITED
(1) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., p. 582,
Wiley, New York, 1953.
( 2 ) Stokes, H. N., Cain, J. R.,
J. Research Natl. Bur. Standards 3, 15’7,
(1907). (3) Young, J. P., White, J. C., Tulanta, 1, 263 (1958). RECEIVEDfor review June 26, 1958. Accepted October 15, 1958. Work carried out under contract No. W-7405-eng-26 a t Oak Ridge National Laboratory, operated by Union Carbide Nuclear Co., a division of Union Carbide Corp., for the U. S. Atomic Energy Commission.
Determination of Hydroxyl Concentration in PoIy propylene Glycols by infrared Spectroscopy EUGENE A. BURNS and R. F. MURACA Jet Propulsion laboratory, California Institute of Technology, Pasadena 3, Calif.
b A rapid method for determination of the hydroxyl concentration in polypropylene glycols by infrared spectroscopy has been developed. The -OH stretching vibration of 14 different polypropylene glycols follows the Lambert-Beer-Bouger law with a coefficient of variation (per cent The standard deviation) of 2.2%. “effective” molar absorptivity of the hydroxyl is calculated to be 6.74 grams per mmole-mm. at a slit width of 0.012 mm.
E
in this laboratory have demonstrated that the usual acetic anhydride acetylation procedure (6) for the determination of hydroxyl concentration is applicable to polypropylene glycols when the time for acetylation is increased to about 4 hours. Because of the amount of time required for this determination, it was considered desirable to investigate the possibility of supplanting the acetylation procedure by a rapid, simple, infrared technique such as has been used with great success for analysis of low molecular weight alcohols (8) and phenols XPERIRIEKTS
(‘J
4)’ EXPERIMENTAL PROCEDURE
The infrared work was performed with a Perkin-Elmer Model 21 doublebeam infrared spectrometer. All absorb-
ance measurements were made with a single, fixed-thickness sodium chloride cell, which was calibrated from its interference fringes (7) and found to have a path length of 0.0405 mm. The spectrometer was operated a t a scanning rate of 0.39 micron per minute, response 1, gain 5, suppression 10; the slit width a t the 2.84-micron -OH peak was calibrated and found to be 0.012 mm. The base-line technique (3, 9) was employed to evaluate Io (effective incident light intensity) , used in calculating the absorbance, A: A log ( l o / Z ) (1) where I is the transmittance a t the 2.84-micron absorbance peak. EXPERIMENTAL RESULTS
A typical transmittance curve of a polypropylene glycol having a molecular weight of about 2000 is shown in Figure 1. The -OH stretching vibration gives rise to a sharp peak a t 2.84 microns (3520 cm.-I) and thus should yield reproducible values for transmittance. The absorbance, A , of this peak, with a cell of constant optical path length, is a function of the amount of hydroxyl and water present in the sample : A = AOH A H ~ O = UOH COH U~OCH,O
+
+
(2)
where U O H arid u H 2 0 represent proportionality constants related to the molar
absorptivities of the species denoted by the respective subscripts, and COH and caz0 represent the concentrations. I n order to evaluate the true molar absorptivity of the hydroxyl group, it was necessary to establish the contribution of water to the 2.84-micron -OH peak, as preliminary experiments had shown that water exhibits some absorbance at 2.84 microns. The water content of a polypropylene glycol sample (sample I, Table I) mas determined by the Karl Fischer procedure, Samples containing different amounts of water were prepared by further additions of water, and the exact amounts were determined by a Karl Fischer titration. A graph of the absorbance of sample I as a function of the per cent water is a straight line. The absorbance value a t the intercept (0.273 absorbance unit) is a function of the hydroxyl content alone. The slope of the line, evaluated by least squares, is 0.075570‘0-1. Hence, for a 0.0405-mm. cell thickness, the following expression for the molar absorptivity of hydroxyl can be evaluated : aOB
AOH -= A
- (0.0755) ( % HzO)
COH
COB
(3) where uOH is obtained in gram per millimole of hydroxyl when cOH is expressed in millimoles of hydroxyl per gram. VOL 31, NO. 3,
MARCH 1959
0
397
Table 1.
Sample Designation PPG I PPG I1 PA-23a 4-A-23b 2025 4-A-1 Stock 2025 Sample I Sample I1 Sample I1 4-A-19a M-7-113-1 M-7-113-2 Stock 1025
Infrared Determination
COHseetyistbnt
Mmoles per
Gram 0.98 1.02 1.06 1.05 1.07 1.06
Water, % (Karl Fischer ) 0.17 0.16
Figure 1.
A series of 14 different polypropylene glycols was analyzed for hydroxyl concentration by the 4hour acetylation procedure and for water content by the Karl Fischer technique; the absorbance in the 2.84micron region was also measured. A summary of these results is presented in Table I. Values of AOR/COE for each glycol recorded in Table I show that the ratio is essentially constant. The average value of A o a l c o H is 0.273, with a standard deviation of 0.0059 gram per mmole. The coefficient of variation (per cent standard deviation) is 2.275, and the 99% confidence limits are 0.273 0.0047 gram per nimole. Also listed in Table I are the values of the hydroxyl concentration calculated using the 0.273gram per mmole average value. The “effective” molar absorptivity of the hydroxyl peak for any path length is thus calculated to be 6.74 grams per mmole-nim. These data, in the form of a Ringbom curve ( 5 ) (Figure 2), show that the method is applicable for the concentration limits investigated-Le., 0.98 to 2.70 mmoles of hydroxyl per gram. In samples of polypropylene glycol containing less than 0.25% water, the value of UOE obtained by omitting the water absorption correction is 0.283 a n d has a coefficient of variation of
*
398
ANALYTICAL CHEMISTRY
0.291 0.296 0.290
0.013 0.012 0.006 0.007 0.013 0.009 0.015
0.288
0.17 0.12 0.20 0.13 0.14 0.16 0.21 0.21 0.20 0.15
3.02 1.46 1.73 1.30 2.70 1.20 1.98
COHedod
Absorbance, A, 2.84 Mp Obsd. Water Hydroxyl
0.08 0.09
1.08
of Hydroxyl Concentration in Polypropylene Glycols
0.296 0.299 0.307 0.283 0.421 0.492 0.362 0.761 0.345 0.552
0.010
0.011 0.012 0.016 0.016 0.015 0.011
,
Mmoles/ Gram AOHICOH 0.284 1.02 0.279 1.04 0.268 1.04 0,268 1.03 0.265 1.04 0,274 1.06 0.266 1.07 ’ 1.00 0.268 1.50 0.281 0.277 1.76 1.27 0.266 2.73 0.276 1.21 0.275 1.98 0.273
0.278 0.284 0.284
0 .58i
0.283 0.290 0.292 0.273 0.410 0.480 0.346 0.745 0.330 0.541
Error,“ Mmole/ Gram 0.04 0.02 -0.02 -0.02 -0.03 0.00
-0.01 -0.02
0.04 0.03
-0.03
0.03 0.01
0.00
Typical infrared spectrum of polypropylene glycol
( I ) , intermolecular hydrogen bonding apparently does not take place. DISCUSSION
0.2
Il
’
~
l ,
0.8 1.0 2.0 HYDROXYL CONCENTRATION COH (MILLIMOLES/GM)
i -
4.0
figure 2. Ringbom curve of absorbance as function of hydroxyl concentration
2.3%. Hence, for samples containing less than 0.25% water, it is justifiable (within the error of the measurement) to omit the water correction and to use the corresponding effective molar absorptivity of 6.98 grams per mmole-mm. Polypropylene glycols appear to exhibit intramolecular hydrogen bonding through the -OH group and an ether oxygen, presumably forming a fivemembered ring. As the position of the hydroxyl band is unaltered by dilution with benzene or carbon tetrachloride
The possibility of eliminating a separate determination of water content by measurement of its absorbance in the 6.05-micron region was abandoned because of the low absorptivity of water a t these wave lengths. It is possible t o utilize absorption in this region for determination of water content if path lengths of the order of 0.20 mm. are used. hIost commercial samples of polypropylene glycol contain about 0.10 to 0.20% water. Thus, when the hydroxyl concentration is determined from the absorbance a t 2.84 microns, the character of the absorbance in the 6.05-micron region is also observed; if the latter absorbance value does not vary significantly from the value shown in Figure 1, the molar absorptivity of 6.98 grams per mmole-mm. is used for calculation. If a significant variation occurs in the 6.05micron region, or if extremely accurate hydroxyl determinations are required, the water content of the sample is determined by a Karl Fischer titration, and this value is used with Equation 4 for determining the actual molar absorptivity of the hydroxyl group :
where A b COH
observed absorbance path length in millimeters = hydroxyl concentration in millimoles per gram
= =
Recent work a t this laboratory has shown that polypropylene glycols of high molecular weights can be dried by evacuation for 0.5 hour at 0.1 mm. pressure and a temperature of 100’ C. The water content of samples can easily be reduced to 0.005% (the limit of the
Karl Fischer determination) by this procedure, and correction of --OH absorptivities for water content can thus be conveniently eliminated. LITERATURE CITED
(1) Bellamy, L. J., “In frared SDectra of Complex Molecules,” pp. 83-98, Wiley, New York, 1954. (2) Friedel, R. A., J . Am. Chem. SOC.73, 2881 (1951). (3) Heigl, J. J., Bell, M. F., White, J. U., ANAL.CHEM.19, 293 (1947). (4) Mecke, R., Discussions Faraday SOC. 9, 161 (1950). (5) Ringbom, A., 2. anal. Chem. 115, 332 (1939).
(6) Siggia, S., “Quantitative Organic Analysis via Functional Groups,” Wiley, New York, 1949. (7) Smith, D. C., Miller, F. C., J . Opt. SOC.Am.. 34. 130 (1944). . ~~ , , ~ . . ~ ~ , . (8) Smith, F. A., Creitz, E. C., J. Research Natl. Bur. Standards 46, 145 (1951). (9) Wright. N., IND.ENQ.CHEM.,ANAL. . E D . 15, 1x1941). ~~
RECEIVED for review December 5, 1957. Accepted October 2, 1958. This paper presents one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. DA-04495-0rd 18, sponsored by the Department of the Army, Ordnance Corps.
Determination of Total Gaseous Pollutants in Atmosphere PHILIP W. WEST, BUDDHADEV SEN, and BHARAT
R. SANT
Coates Chemical laboratories, Louisiana State University, Baton Rouge 3, l a .
b A rapid method based on measurement of thermal conductivity is described for determination of total gaseous pollutants in atmosphere. When small quantities of organic solutes or inorganic gases are introduced into a flowing helium stream in an empty column, a symmetrical distribution of concentration of the solutes takes place because of their diffusion. The times of emergence and the areas under the curves are reasonably the same for the same quantities of a single solute or mixtures in spite of possible differences in their physical properties. The total error rarely exceeds 20y0 which would b e acceptable for an air pollution index, alarm system, or certain survey studies. The sample can b e used eventually for further identification b y gas chromatographic analysis. EST and coworkers have described a method of sampling air pollutants for separation and estimation by gas chromatography (4). Very frequently the analyst is interested in an immediate measure of total gaseous contaminants in the air. The present paper describes a method in which a single measurement will provide a nondiscriminatory estimate of all major gaseous contaminants. Taylor (9,s) has shown that a soluble substance introduced into a fluid flowing slowly through a small-bore tube spreads out under the combined action of molecular diffusion and the variation of velocity over the cross section.
He has shown both theoretically and experimentally that the distribution of concentration is centered around a point which moves with the mean speed of the flow and is symmetrical about it in spite of the asymmetry of the flow. The dispersion along the tube is governed by a virtual coefficient of difFusivity which can be calculated from the observed distribution of concentration. It was expected that a similar symmetrical distribution would be exhibited when both the solute and the flowing carrier were gaseous. A series of experiments was carried out to study the distribution patterns of volatile organic liquids and inorganic gases and their mixtures as solutes in flowing helium. The time of emergence and the distribution of concentration of the solute bands were determined by means of a thermal conductivity cell placed in the path of the helium flow. I n a number of studies, the solutes were collected on a sampling tube and transferred into the helium stream ( 4 ) , thus simulating field sampling techniques applicable in air pollution and industrial hygiene studies.
wise s ecified, all the experiments were Carrie$ out a t a carrier gas (helium) flow rate of 10 ml. per minute and flow tube temperature of 80” C. Liquid samples were injected into the helium stream with an Agla micrometer syringe, and gas samples were introduced from a gas pipet. I n sampling experiments, the solutes were adsorbed on a standard sampling tube (4)a t temperatures near or below the
EXPERIMENTAL
The detector and recorder units of a Burrell Kromo-Tog were used to monitor and record the arrival and distribution of solute bands. A 1-meter U-shaped tube of uniform bore ( 5 mm.), wound with a Xichrome wire for heating purposes, was used as the flow tube. It was inserted on the instrument in place of a conventional packed chromatographic column. Unless other-
Figure 1 . Distribution of six-component organic sample obtained b y desorption from sampling tube Helium flow, 10 ml. per minute Length of flow tube, 1 meter Temperature of flow tube, 80’ C. Sample volume, 2 PI. Inset. Sample trapped a t outlet of flow tube and chromotographed on pocked column VOL. 31, NO. 3, MARCH 1959
399
