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.C ~ M .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
AIR
AIR
a
.
b 0
0 N
Figure 2. Distribution of mixture of sulfur dioxide and two organics (carbon tetrachloride and trichloroethylene) obtained by desorption from sampling tube Helium flow, 10 ml. per minute Length of flow tube, 1 meter Temperature of flow tube, 80' C. Volume of organic mixture ( 1 : 11, 2 pt. Volume of SO*,1 ml. a t 50' C. and 1 atm. Inset. Sample trapped a t outlet of flow tube and chromatogrophed on packed column
boiling points of the material under investigation. The organic liquids were sampled at 0" C. (ice), sulfur dioxide a t -20" C. (ice-sodium chloride), and ammonia, chlorine, and hydrogen sulfide at -70" C. (acetone-solid carbon dioxide). Prior to desorption by heat,ing to 200" C. and tiansferince of samples into the helium stream, the air in the sampling tube was displaced by helium. During this displacement, the sampling tube was kept at the temperature of sampling and the flow rate was raised momentarily to 50 ml.
Table 1.
Figure 3. Distribution of concentration of different helium flow rates
a. b.
Length of flow tube, 1 meter Temperature of flow tube, 80' C. Volume of organic samples, 2 pl. Volume of inorganic sample, 1 ml. a t 50' C. and 1 atm. Carbon tetrachloride Sulfur dioxide
per minute. Immediately after the air peak was recorded, the original flow rate (10 ml. per minute) was reestablished and sample desorption accomplished by placing the sampling unit in a heating bath. The emergence times, peak heights, widths, and areas under the curves for different solutes introduced into the empty tube by injection are given in Table I, as well as the pertinent physical properties of the solutes. Distrihution
Characteristics of Distribution Curves and Relevant Physical Properties of Solutes
Massa X
EmerArea, Sq. Cm. Thermal gence Peak, Cm. Conduc- TimeIcHeight, Width, '/z plat,ivityb Cm. H W HW nimeter
10-8, B,. P., Mol. Compound Grams C. Wt. Carbon 0,807 1.50 10.5 0 . 8 4.20 4 . 6 0 tetrachloride 3 . 2 7 6 . 8 153 1.50 10.0 0 . 9 4.50 4.60 Chloroform 3.0 61.26 119.39 0.608 n,--4mvl .. 5 . 6 1.1 3 . 1 0 3.50 1 .55 chl&de 1.8 108 88.15 Acetone 0.8 56.5 58.08 0.906 1.50 1 0 . 5 1 . 0 5.30 5.90 155 7 3 1 3 5 5 1 0 590 Methanol 1.6 64.65 32.04 1.32 8 6 1 0 430 460 155 Diethyl ether 1 . 4 34.6 74.12 1 . 2 1 150 7 2 1 1 370 390 Mixtured Chlorine 2 . 8 -34.6 70.91 0 . 7 8 150 1 4 5 0 9 650 680 Sulfur dioxide 2 . 6 -10.0 64.07 0.768 1 4 5 1 5 5 0 9 7 0 0 7 1 0 Hydrogen 1.40 1 0 . 7 0 . 9 4.90 5.20 sulfide 1 . 4 -61.8 34.08 1.20 6 . 5 1.0 3.25 3.25 1.50 Ammonia 0 . 7 -33.35 17.03 2.00 a Volume of liquid samples, 2 pl.; gaseous samples, 1 ml. at 50" C. and 1-atm. pressure. b Values taken from International Critical Tables. c 1 em. on chart paper is equivalent to 70 seconds. d Equal volumes of allyl chloride, acetone, sec-butyl chloride, n-amyl chloride, carbon tetrachloride, and chloroform. ~
solutes at
of concentration in helium streams of a mixture of six organic compounds obtained by desorption from a sampling tube is shown by the lower curve in Figure 1. This mixture was collected from 20 liters of air wing standard sampling technique (4). The composite sample was retrapped at the exit of the detector cell and chromatographed on a tri-rn-cresyl phosphate column (Figure 1, inset). Figure 2 shows the results of a similar experiment with a mixture of sulfur dioxide, carbon tetrachloride, and trichloroethylene. A higher detector sensitivity was used during chromatography. The effect of variation of flow rate a t a constant temperature (80" C.) on the distribution of concentrations was studied (Figure 3). The effect of' temperature between 30" and 100" C. a t a helium flow rate of 10 ml. per minute was also observed.
~~~~
400
ANALYTICAL CHEMISTRY
DISCUSSION
Compounds varying widely in their physical and chemical properties exhibit almost identical distribution of concentration in nonturbulent helium flow (Table I). I n spite of differences in molecular weight, boiling points, and other physicalproperties, the-emergence time for different compounds is the same. The time Of of the sample constituents is entirely governed by the linear velocity of the
helium, because the component of the diffusive motion in the direction of flow is negligible compared to the linear velocity of the carrier gas. For this reason also, the expulsion of air prior to desorption and transference of the sample into the helium stream is essential. Polarity and, to a greater extent, latent heat of vaporization are responsible for tailing effects in regular gas chromatography (4). Because there is no mass transfer or change of state in the empty tube experiments, the absence of tails and the identical nature of the distribution curves are to be expected. It was first anticipated that in the absence of complicating influences of mass transfer and change of state, the areas under the curves would be simply related to the thermal conductivity and the number of moles of the solutes involved. Khen the quantities of mass (Table I) are expressed as number of moles, they are all of the same order of magnitude The recorder actually plots the voltage unbalance in the bridge circuit produced by the change in resistance of the measuring hot wire. The out-of-balance voltage is given by the expression E = s p ( l ) ,where p is the change in mole fraction of the vapor and 7 is the sensitivity parameter of the thermal conductivity cell. Table I shows that so long as the molecular weights and the thermal
conductivities of the different compounds are not very different, calibration curves can be constructed by plotting the mole fraction of any arbitrary compound against height or the area of its peak. For compounds with small molecular weights and large thermal conductivities-as in the case of ammoniaE, and consequently the area, will be appreciably different. For the majority of the compounds, it was satisfactory to express the quantity in terms of volume for quantitative Calibration in this kind of wo;!;. For example, the areas obtained varied between 4 and 5 sq. cm. for the same volume ( 2 pl.) of different liquids, although the molecular weights, densities, and thermal conductivities were different. The total error from such an approximation rarely exceeds 20%, which would be acceptable for an air pollution index, alarm system, or certain survey studies. Figure 3 shows that a shorter emergence time and a deviation from Gaussian distribution occur with increasing flow rate. For most practical applications, a slow flow rate is preferred. Changes in temperature have little effect on distribution. Figures 1 and 2 show that the complexity of the sample did not interfere with the general dispersion pattern. Solutes of different molecular weights
and densities, when introduced together into the helium stream, produced one resultant distribution curve which may be used as a general index for the total amount of pollutants. When the total amount of the pollutants is such that further analysis is desirable, it can be done with the same sample (Figures 2 and 3). The method described can be used for rapid determination of total pollutants in air without losing the sample. Separate calibration curves are required, however, for the quantitative interpretation of the results of the flow tube experiments and of the chromatogram. The technique might possibly be used for experimentally studying the changes of thermal conductivity with change of mole fraction and also for determining the diffusion coefficient of gases. LITERATURE CITED
(1) Keulemans, ,4.I. M., “Gas Chromatography,” Reinhold, New York, 1957. ( 2 ) Tavlor, Geoffrey, Proc. Roy. SOC. ( L o d o n )A219, 186 (1953). (3) Ibid., A225, 473 (1954). (4) West, P. W., Sen, B., Gibson, N. A., -4N.4L.
CHEM. 30, 1390 (1958).
RECEIVEDfor review June 19, 1958. Accepted October 16, 1958. Investigation supported by Research Grant S-43, Study Section of Sanitary Engineering and Occu ational Health, Division of Research &rants, Public Health Service.
Combustion Method for Determination of Sulfur in Ferrous Alloys Modifications for Minimizing Errors J. W. F U L T O N and R. E. FRYXELL Transformer Division, General Electric Co., Piffsfield, Mass.
b The origin of losses has been studied using radioactive sulfur-35 and found to b e primarily the result of adsorption of sulfur trioxide on the glassware which delivers combustion gases to the absorption vessel. Modifications in apparatus and procedure are described. These, together with substitution of alkali for iodate as titrant, result in significantly better recovery of sulfur.
T
combustion method termination of sulfur admittedly entails losses not well understood (3. 5 ) . HE
for the dein metals which are For many
years, the empirical 93% recovery factor has been generally accepted and used for correcting values obtained by potassium iodate titration (ASTM E 30-56). However, in the past few years, it has been increasingly evident that the actual per cent recovery is intolerably variable between laboratories and even between operators. In private communications from other laboratories, the authors have learned of recoveries ranging from about 70% to almost 100%. Although results obtained with induction heating are a t hand from only a few laboratories, it would appear that resistance heating
leads to more serious and variable errors. These errors are commonly considered toarise from one or more of the folloTing : Insufficient temperature of the burning sample to expel all of the sulfur. Loss of sulfur oxides in the delivery system between the burning sample and the absorption vessel. This may occur by either adsorption by fine metal oxide particles which are transferred to cooler regions of the system, or absorption by moisture in the oxygen which may condense on walls of the tubing. To minimize the former, various types of filters or plugs are used to retain oxides in the hot region of the VOL. 31, NO. 3, MARCH 1959
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