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ANALYTICAL CHEMISTRY
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ahove solutions, provihd that large liquid volumes are used. It criticism of Donald H. .4ndrews of The Johns Hopkins University should then be possible to obtain accurate total pressure-compoand the fellowship award of the Standard Oi' "- -' I' sition data, and such information i8 especially significant because LITERATURE CITED i t is possible to predict vapor-li %I (1) Smeier. K. M., to be published. pressure data. (2) Scatchard, G., Wood, S. E., and Mochel, J. N.. J . An. Cham. Soe. 68, 1957 (1946). ACKNOU
Theauthor wishes to ackuowleuge m z VUUBUIB
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RECEIV for ~ review ~ February 29, 1952. Accepted July 7 , 1952. Based on thesis submitted to The Johns Hopkins University. October 1949. in partial fulallmentof the requirementsof P ~ . D degree. .
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Manometric Gas Analysis Apparatus - _ JAIlES N. PITTS, JR., DONALD D. DEFORD, ARID GERALD W. RECKTENWALD Department of Chemistry, Northwestern Unieersity, Eoanston, I l l .
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Although great strides have been made i n recent years i n the development of new and improved methods of gas analysis, most of these methods have the disadvantage of requiring expensive and elaborate equipment and sliilled operators or of being restricted to the determination of a particular gas i n a narrow oonocntration range. The work reported i n this paper was undertaken to develop an inexpensive, aocurate, and versatile gas analysis apparatus which could be operated with a minimum of training and effort. An apparatus which requires only 2 to 6 m l . of sample and employs "bead" reagents for selective removal of the various components i n the sample has heen developed. Expensive burets are eliminated by measurementof pressure changes rather than volume changes. The precision and aecuraoy are of the order of +0.2% absolute for oxygen and oarbon dioxide. Despite its simplicity, the apparatus promises to be very useful for accurate analyses of a wide variety of gaseous samples.
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N TWO comprehensive review articles (6, 7) Nash has sum-
manzed the extensive literature dealing hith recent analytical methods far the quantitative analysis of gases. Much of the ourrent work is concerned with specific instrumental methods based an physical properties suoh as density, thermal conduetivity, and magnetism, and less attention has been devoted to the development of new apparatus employing volumetric or manometric techniques. The instrumental methods have achieved considerable SuccesE in the analysis of two- or threecomponent systems, hut, in general, these methods do not permit a complete analysis of a multicomponent gas sample. Although great progress has heen made in the application of mass spectrometric and infrared techniques to the analysis of multicomponent systems, the high cost of commercial instruments precludes their use in many leborat,ories. A t the present time volumetric procedures based on the removal of the various components by selective ohemieal reactions seem best suited for the analysis of gaseous mixtures with inespensive apparatus. The fundamental design and operntion of macrovolumetric apparatus of the Orsat type (8) is well known, and this type of equipment has been widely used. Recently, Brooks et ai. (8) and many others have devoted considerable attention to refinements in the Orset method. These improvements increase the versatility, accuracy, and precision of the method, but in many cases the speed and simplicity of the hasir Omat unit. hsa been sacrificed. Several excellent microvolumetric analyzers 81%available (1. 5. 9). The constant orensure &vI)aratusof Blacet, and Leigh-
tremely useful under circumstanoes in which only small quantities of gas (0.1 to 0.5 ml.) are available. The B-L method utilizes solid "bead" reagents for the most part, thus eliminating error8 due to undesired absorption of gases in reagent solutions or confining liquids. In the hands of a trained analvst this method is capable of excellent accuracy and precision. However, to obtain results of high accuracy with this apparatus, the operator must he well trained, and i t is us1idly necessary to exercise considerable citie in making the analy:i s . In D rdei to overcome the difficulties inherent in the Orsat-type tus, snd to avoid working appara ~. in the micro range, the authors have developed B simple, versatile, acourate, and inexpensive gas analysis apparatus of the manometric type. Osygen and carbon dioxide may be determined with this instrument, s h a m in Figures 1, 2 and 3, with an average accuracy and precision of the order of 0.2% absolute. A minimum expenditure of time and'effort on the part of t,he analyst is necessary to carry oat the determinations. DESCRIPTION OF .4PPARATUS
The apparatus consists principally of pipet, manometer, and syringe units, each of which is descrihed in detail. Pipet Unit. The essential features of this unit are a reaotion Figure 1. Assembled cup, R, a three-way T Stopcock, Apparatus S. with 1-mm. cavillaw arms. a'water-jacketed pa; pipet, P,of approlrimately 5-ml. volume, and spherical expansion chamber, E, about 3.5 em. in diameter. , ,,, .~~., .L.-.L ..... > / ! ~ ~ , r n e volumes 0 1 m e pipcb aiiu snpauawn c i i i t i i ~ v ~&IC: r noz ormca.~. A small beaker containing mercury is placed beneath the reaction cup; the height of the mercury level in the beaker is adjusted so that. the lower edge of the cup is immersed to a depth of 1to 2 em. The reaction cup is butt-joined to one arm of the stnpoock with Tygon tubing, so that the cup can be replaced reaflily. Components R, S,P, and E are joined with I-mm. borosihate glass capillary tubing. The confining volume of the pipet is indicated by two fiducial marks, Mx and M2, inscribed on the capillary tubing in the positions indicated. The expansion chamber is sealed directly to a 12/3 ball joint, so that the entire pipet Bystem can be removed for cleaning or replaced by another pipet unit. In order to avoid trapping small amounts of sample, it is imnortant that the hore of the plug of stopcock S be sdl aligned with the cspil-
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P and eliminate It through SA as b e f o r e . T h e a p p a r a t u s should now he eomnletelv ~" fipe from air and ready for mer&I
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arm SA. Fbr msximuk precision the sample size should be such that after compression between marks M , and M a the pressure will he ahout 950 n k A 6 m l . sample was suffioient for the particular pipet used in theseexperiments. With S in the auurouriate position, a-ithdraw thk sGrinse
eolumnreachesma&MI.~ Cl&"e S a n d compress or expand the gas to mark Ma. Read and re-' cord the initial D ~ P R R U P C . n.~ Open S and force the gas bdFk into R. Insert the reagent holder with the appropriate reagent to remove the desired
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lary side a r m . For the same rearun, L _ I A ~ :V U I ~ . UL LLIC awp~utix must not he countersunk. Manometer Unit. The pipet and manometer units are cannrcted with a 12/3 hall and socket joint held together rrith a spring clamp. One end of the 7-mm. borosilicate glass manometer tube terminates in the socket, while the other end terminates in a high grade vacuum stopcock, V . A meter stick is placed behind the manometer tube. This stick, which is mounted on the 5 X 40 inch vertical support, is slotted so that it can be moved vertically over a range of ahout 1 cm. for making the zero adjustment. A side arm (1' in Figure 2) of 7-mm. borosilicate glass tubing is joined to the manometer just below the socket joint. This tube, about 7 cm. in length, extends to the hack of the instrument and provides a means for connecting the syringe unit to the manometer and pipet units. Syringe Unit. The essential part of this unit (Figure 4) is a simple 50-ml. glass hypodermic syringe. The barrel of the syringe is held firmly in place by brackets. The plunger is guided by a guide bar and actuated by a ' / r Z O feed BCTBW. The syringe is connected to the manometer system with Tygon tubing. The metal parts of the unit are of cold-rolled steel mounted on a Transite base, n'nieh is in turn mounted on a 11 X 14 inch wooden platform fitted Yith a0.25-inch rim. Reagent Holders. The reagents are introduced into reaction hulb R by means of reagent holders which are similar to, but larger than, those employed by Blacet and Leighton ( 1 ) . These reagent holders, shown in Figure 5, are of 4mm. soft-glass rod and terminate in small loops of platinum wire, for use wit.h p o t a s sium hydroxide and phosphorus pentoxide heads, or in glass cups if white phosphorus is to he employed. EXPERIMENTAL PROCEDURE
Preparation of Apparatus.
Fill the syringe with memum.
Pipet tinit
Figure 4.
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Syringe Unit
. .^ .. . . . component. Alter wartlngthe required time to allow complete reaction, draw the sample hack into the pipet, and, when the trailing mercury line reaches fiducial mark MI, clwe stopcock S. E w a n d or compress the gas to mark Mz and read the new pressure, p,. Calculate the percentage of the desired component from the relztionship, % =. 100(po - P M h . If a second component is to he determined, force the sample hack into thereaction cup, inserta newreagentto remove that component, and proceed with the determination as described above. Follow this procedure until all the desired components are removed. Should the pipet unit become dirty, it can he removed readily for cleaning a b without disturbing the manometer or Figure Resyringe units. Open side arm SA to the : agent Holders atmosphere and withdraw the mercury into the syringe until theair reaches the spherical socket of the hall and socket joint. Inmen the clamps and remove the pipet unit. Clean the pipet unit by drawing dilute nitric acid, water, acetone, and air t,hrough it in that order. In lieu of this, a new pipet system of the same or differentsize may be inserted.
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Preparation and Utilization of Reagent Beads. In general, the reagent beads for removal of water vapor and carbon dioxide were prepared as indicated by Blacet and Leighton ( I ) . A somewhat different technique %-as used with the white phosphorus for oxygen removal.
the &nosphere, raise the mercury level La the fiducial m&k, M i Adjust the meter stick so that the manometer reads aero. Close the three-way stopcock, S, and with stopcock V open, force mercury up the manometer tube and t,hrough V. Close V, and withdraw the plunger of the syringe until the mercury level in the manometer falls 10 to 20 mm. This creates, in essence, a closedPHOSPHORUS PENTOXIDE FOR REMOVAL OF WATER VAPOR. end manometer. Open S to side arm SA and, by insertion of the Dip the platinum loop, on a holder of the type shown in Figure syringe plunger, drive the air from the pipet unit. Draw the ~ i r 5, n, into dry, pordered phosphorus pentoxide and allow the
ANALYTICAL CHEMISTRY
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material in the loop to become sticky. Repeat this procedure three or four times until a sticky ball 3 or 4 mm. in diameter is Table I. Typical Carbon Dioxide Analyses obtained. Place a fresh surface of the anhydrous phosphorus Original pentoxide on the ball and then immediately insert the bead into Pressureof Carbon Dioxide, 70 Deviation from the reaction cup containing the sample. The water vapor is Run Sample, Mm. Taken Found Error Mean, % completely removed after 3 to 4 minutes. If moisture is to be 1 790 11.310.2 11.5 +0.2 0.0 removed from several samples, the bead can be retained and a 2 430 11.3+0.2 11.4 +0.1 0.1 3 937 11.3-1;0.2 11.4 +0.1 0.1 fresh surface of phosphorus pentoxide added for each subsequent 4 276 1 1 . 3 1 0 . 2 1 1 . 6 + 0 . 3 0 .1 determination. Av. 11.5 +0.2 0.1 POTASSIUM HYDROXIDE FOR REMOVAL O F WATER VAPOR. Scrape the surface coating of carbonate from a pellet of reagent grade potassium hydroxide and place it on the loop of a reagent Table 11. Determination of Oxygen i n Lower holder (Figure 5, a). Hold the loop and pellet close to a glowing Concentration Range electric heating coil until the pellet fuses to the platinum loop. Total Pressure, Mm. Oxy en Difference, Allow the bead to cool slightly, insert it into the reaction cup, and Run (5-Ml. Volume) Taken, o/c F o u n t , % 70 leave it for 4 or 5 minutes. I n order to ensure complete removal, 1 847.3 3.64 3.70 +O. 06 a “follow up” bead may be used, but one bead is usually sufficient. 2 938.0 2.24 2.14 -0.10 As potassium hydroxide reacts with carbon dioxide as well as 3 909.0 1.67 1.38 -0.29 4 951.0 2.67 2.75 4-0.07 with water vapor, phosphorus pentoxide must be employed for 1 . 3 0 5 8 9 4 . 2 1 . 3 1 +0.01 the removal of water vapor in samples containing carbon dioxide. REMOVAL OF CARBON DIOXIDE BY POTASSIUM HYDROXIDE. Clean one potassium hydroxide pellet and fuse it to a platinum loop as indicated above. Allow the bead to cool and absorb moisair contains 20.9401, oxygen. A series of five analyses (Table 11) ture from the air until it attains a shiny surface. Insert the bead into the sample and allow it to remain for 4 or 5 minutes. in the concentration range from 1.3 to 3.6% oxygen gave an average accuracy of 0.1% absolute. One bead of potassium hydroxide gave quantitative removal As it was the prime purpose of this paper to describe the conof carbon dioxide in samples containing up to about 11% of this struction, operation, and performance of this new instrument, component. When the sample contained 52% carbon dioxide a a discufision of the utilization of this apparatus for the deterfollow-up bead was necessary for good results. Thus for accumination of hydrogen, carbon monoxide, olefins, and other gases rate work it seems advisable to use a follow-up bead for high conwill be deferred until comprehensive studies can be made to detercentrations of carbon dioxide. mine reagent8 and procedures which are most suitable for reWater vapor, if present in the sample, must be removed before moval of these components. Such studies are now in progress in determining carbon dioxide and oxygen. this laboratory. REMOVAL OF OXYGEN BY WHITEPHOSPHORUS. Cut a small The total over-all cost of this instrument, excluding the shop piece of white hosphorus, about 2 X 2 X 5 mm., rinse it with work on the syringe unit, was about $25. This low cost is due acetone, and alkw it to dry in air. Next place the hosphorus in in part to the fact that a common meter stick is the only piece the small glass cup of a reagent holder (Figure 5, by, heat gently of calibrated equipment; expensive calihrated burets are elimi(30” to 36” C.) to incipient ignition, and then quickly introduce it into the reaction cup. After a minute or two all the oxygen is nated. The use of a single reaction chamber and small quantities converted to oxides of phosphorus and the flame goes out. When of selective reagents permits the use of a very simple apparatus the reagent holder is withdrawn from the sample, the phosphorus and affords a considerable saving in expensive reagents. should reignite on exposure to the air. This indicates that suffiThe operation of the apparatus requires no special techniques. cient phosphorus was used for complete reaction with the oxygen in the sample. Undergraduate students TI ith no previous training in gas analysis can, after an hour or two of instruction and practice, achieve It is necessary to replace or to clean the reaction cup prior results comparable with those reported here. to subsequent determinations of oxygen in other samples. The For determination of certain components such as carbon disurface of the cup used for an analysis becomes coated with a oxide, the over-all precision attainable appears to be limited in mixture of phosphorus and its oxides, leading to low results for the present apparatus largely by the precision that can be realized oxygen if the same bulb is used in subsequent determinations. in reading the pressure. An improved manometer scale with a However, the pipet is apparently unaffected by the analysis vernier permitting measurement of pressure to the nearest 0.1 procedure, as more than 20 accurate determinations of oxygen mm. would undoubtedly result in more precise analyses, particuhave been made without cleaning this unit. larly in the lower range of concentrations. Although only pipets having a capacity of about 6 ml. have RESULTS AND DISCUSSION been employed with this apparatus, the use of smaller pipets It is evident from the results shown in Table I that determinashould permit equally precise analyses with comparably smaller tions of carbon dioxide in samples having a volume between 2 samples. ACKNOWLEDGMENT and 6 ml. can be performed with a precision and accuracy of the order of &0.2oJ, absolute. The fact that these results were The authors are indebted to Stanley Cassid and James Morris in agreement to within 0.1% over an initial pressure range for their expert assistance in constructing the final version of from 276 to 937 mm. is indicative of the accuracy and precision this apparatus] and to Jane Beasley, Donald Dieball, and Daniel attainable with this instrument. Teller for performing some of the analyses. In order to test the sensitivity of the apparatus, a series of LlTERATURE CITED determinations was made on an unknown sample that contained a (1) Blacet, F. E., and Leighton, P. A,, IND.EM+.CHEM.,ANAL.ED., low percentage of carbon dioxide. The values found in a tripli3 , 2 6 6 (1931). cate determination were 1.02, 1.03, and 1.03%. Two independ(2) Blacet, F. E., and MacDonald, G. D., Ibid., 6, 334 (1934). ent series of analyses on the same sample were carried out by (3) Brooks, F. R., Lykken, L., hlilligan, W. B., Nebeker, H. R., and other analysts, one using a gravimetric procedure and the other Zahn,V.,ANAL.CHEM.,21, 1105 (1949). (4) Dennis, L. M., “Gas Analysis,” p. 371, New York, Maomillan a titration method. The averages of their results were 1.00 co.,1920. and 1.02%, respectively. Although the excellent precision and (5) Lewis, V. M., ANAL.CHEM., 21, 636 (1949). accuracy realized in this particular determination were undoubt(6) Nash, L. K., Ibid., 22,108 (1950). edly fortuitous, the reliability of the instrument for determining (7) Zbid., 2 3 , 7 4 (1951). (8) Orsat, 0. O., Chem. News, 29, 177 (1874). low percentages of carbon dioxide is well established. (9) Spence, R., J . Chem. SOC.,1940,1300. A series of five determinations of the oxygen content of air gave an average value of 20.9 f 0.1%. Dennis ( 4 ) states that RECEIVED for review June 2, 1952. Accepted July 23, 1952. ~
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