This study has shown the existence of an optimal flow rate of the sample in flame spectroscopy, confirming theoretical predictions. In addition it has elucidated the relationships between line intensity, flame position, and flow rate, and shown them to be of critical importance in work with the cyanogenoxygen and hydrogen-oxygen flames. Appropriate values of the parameters to be used in analytical work have been determined and utilized.
ACKNOWLEDGMENT
The cyanogen used I\ as generously supplied by t h r S e w Products Division,
American Cyanamid Co., Stamford, Conn. LITERATURE CITED
(1) Baker, hl. R., FuNa, K., Thiers, R. E., Vallee, B. L , J . O p t . SOC.A m . 48, 576 (1958). (2) Baker, 11. R., Vallee, B. L., ANAL. CHEM.31, 2036 (1959). (3) Baker, .\I. R., Vallee, B. L., J . O p t . Soc. Ana. 45, 773 (1955). (4) Conway, J. B., Smith, W. F. R., Liddell, W. J., Grosse, -4. V.,J . Am. Chena. SOC. 77, 2026 (1955). (5) ConRay, J. B , JVilson, R. H., Grosse, A . V., Ibzd , 75, 499 (1953). (6) Fuwa, K , Thiers, R. E., Vallee, B. L., ANAL.CHEX31, 1419 (1959). (7) Gal d y , .4. C; , “The Spectroscopy of Flames, Wiley, N e w 7iork, 1957. (8) Mugoshe., hl., Vallee, B. L., AXAL.
CHEY.28, 180 (1956).
( 0 ) Ibid., p. 1066. (10) Pannetier, G., Gaydon, A. G., Compt. rend. 225, 1300 (1947). (11) Thiers, R. E., in Glick, I)., “Methods of Biochemical Analvsis.” Vol. 5. u. 273. I
_
1957. 12) Thomas, N., Gaydon, A . G., Brewer, L., J . Chem. Phys. 20,369 (1952). 13) Vallee, B. L., “Flame Spectrometry,” in “Trace L4nalysis,” J. H. Yoe, H. J. Koch, eds., Wiley, Yew York, 1957. 14) T‘allec, B. L.. Bartholomay, A. F., AYAL. CHEM.28, 1753 (1956). 15) Vallec, B. L,, hfsrgoshw, RT., Zbtd., 2 8 , 175 (1956). RECEIVEDfor review July 28, 1959. Accepted October 12, 195‘3. IYork supported by a grant from the Committee on Analytical Research, American Petroleum Institute, and by the Hoa.:ird Hughes hlediral Imtitute.
Determination of Water by Direct A m peromet ric Measureme nt F. A. KEIDEL Engineering Research laborafory, Engineering Department, E. I.du Pont de Nemours & Co., Inc., Wilmington, Del.
b A method for measuring water, based on quantitative electrolysis in a specially designed cell, has been developed. While especially applicable to measurement of water in gases a t concentrations less than 1 p.p.m. b y volume up to about 1000 p.p.m., higher concentrations can easily b e measured. Many liquids can be analyzed after vaporization. Other liquids and many solids can be analyzed b y stripping with an inert gas. Analysis of inert-gas supplies, gas and liquid process streams, and solid materials, and the measurement of film permeabilities are a few of its applications.
T
H L I ~ Ehas long been a need for a simple raontin7ious method for measuring small water concentrations in fluid streams. Methods applicable a t high concentrations, including those which employ alternating current conductivity measuremcmt, grnerally fail or t)erotne discouragingly conipleu when watc r concentrations unttrr a few thousand parts per million are to be dcterminetl. Yet the presence of water a t much lower concentrations often profoundly affects the entire course of a chemical reaction. Hence, it is often necessary to carry out accurate monitoring and control of water content a t low parts per million levels throughout the course of a process, whether a smallscale laboratory reaction or a full-scale plant operation.
Tlic scrioiisncss of the \ratcr-nicasurcmerit prohlem has lrd to the development of a completelj- new analytical instrument, n prtxliminary clcscription of which has hccn published (5’). Khilc designrd originally for thc continuous monit’orins of gas strrams containing low conccnt,rations of \vater (parts pvr niillion), sliglit motlification p t ~ i n i t sthe of liquid ?trc.anix and of fluids containing rrlxtivr~l~.higli concentratiow of n-atrr ill tlw Iit’r rent r a n g . Tlic method I n s also I ) w i succc3ssfulIy appliid to the batch analysis of sonic solid materials. When thus applicalilc it has an important advantage ovrr wright-loss mrthods lwcause accuracy is not tlepentirnt on nirasurcnicnt of small weight differcnces or on loss of othrr volatilr components from the sample. The method is uniquely suited to the study of polymer film permeability, where it can be used not only to determine steady-state rates of water transfer, but also, because of its rapid response. to observe transient behavior following changes in the environment of the film.
t r o l j i s of 0.5 gram mole of \vatu (5.01 grams) requires 96.500 couloml)s. Tlir elcctrolj.tic analyzer crII is rlrsigncstl so that all current. ivhieli flow c~lwtrolyzri; n-atcxr. Tlii~rcforc~, tlie olisrr\,c~lcwrcxnt antl tlicl rat,(. of cntrancc~of 1vatc.r into tlic coil arc rolatt~tl to c~ac~lio t l w \\.it11 I)riniary-standarti accuracy. For niaiiy aiialj.tica1 al)l)lic~ations.u)!Icrntration of \vatu ratlwr than 111 ratr of cntrj- of wattxr iiito tl ’ must I)(’ kno\\-n. Hrrr it is !I(’( . to regulate thc saniplc flcnv a t soni(’ arhitrarj- prcdctcrminrtl valw. For convenience. a flow of 100 ml. per minutc (measured a t 25’ C. antl 1- atm. pressurr) is generally used for ideal gastous samples. Under these conditions, the clectrolysis current is 13.2 pa. pcr p.p.m. by volume. This easily measured current corresponds to t,hr not easily weighed water flow of 7.4 X grain per minute. Liquids are analyzed either after first vaporizing t,he sample or by first stripping the water from the sample with an inert gas which is then analyzed. ANALYZER DESIGN
OPERATING PRINCIPLE
Analysis is accomplished with a specially designed electrolysis cell in which all entering water is continuously and quantitatively absorbed and electrolyzed to hydrogen and oxygen. The electrolysis current is used as indication of water content. In accordance 11ith Faraday’s lam the elec-
Electrolytic Cell. The heart of the instrument is the electrolytic cell, in which absorption and electrolysis take place simultaneously. I n one practical design, the absorbing rnaterinl is in the form of a thin viscous film in contact with two spirally wound &mi! platinum electrode wires on the inside of an inert Teflon fluoroVOL. 31, NO. ’12, DECEMBER 1959
2043
] 05' . . .
Figure 1.
Longitudinal section of cell element
Figure 2. Typical completed cell housed in 4-incl--long pipe nipple (upper) and piece of element tubing (lower) shown for size comparison
scquireiiients. I t iiiust he capable of removing very low concentrations of \\-:iter froin the sample streain. 4ppliration of direct current potential hrtn-eiuelcct.ro,lrs in cont.net with the n i n t r r i a l must rcault in current flow only via the ~ ~ r o c e swhich s rrsults in elrctrolysis of wat,er. Fiiiiilly. the iii:itrrinl must he inert n-itli r w p e r t t o nll other comnoncnts iii tlic s:iiiiiile
stream. I'artiallv livdratcd nhosiihorits ariit-
I
Figure 4. Specific resistivity vs. composition for P~OS-H~O system
'
IO
5 E c 0
>-
2
IO'
m m w UI
O2
r--------
-
.LF:F
+iE';jDE
.
----I
~ - . l
Figure 5 . Specific resistivity of water solutions of P . 0 5 v s . vapor pressure of water above the solution a t various temperatures
Figure 6.
Schematic water unalyzer circuit5
Showing t h e basic circuit ( l e f t ) o n d o p r o c t i c c l circuit I . i z h t ! - s e d w ~ t h a n a l y z e r s hovlng several f u l l scale V o n g v s b e t w e z n 10 ~ 1 . 1 1 1093 p.p ? I .
VOL. 31, NO
1'2. DECE'nGER 1 9 5 9
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tion predicted by Faraday's law has been found necessary at low parts per million levels when a standard electrolysis tube is used, because the efficiency is somewhat less than 100%. This type of behavior is experienced with some of the Freon fluorinated hydrocarbons at low water concentrations. Application of the instrument to these materials has been more fully discussed ( 5 ) . Quantitative response can be approached hy employing longer and wider than standard element tubing and by applying a higher t,han standard voltage. Speed of Response. Response time depends in part on electrode spacing, absorbent film thickness, and applied crll voltage. Response t o increasing concentrations tends to he somewhat more rapid than t o decreasing concentrations, probably hecause of relatively d o ~ vrates of diffusion within the electrolyte elm. Under normal operating Conditions, earl?;model cells having electrodes spaced 0.005 inch apart required ahout 1 minute to reach 63% of final response to an upward change and about 2 minutes in response t,o a downivard change. hfuch faster response :,as been obtained with cells having morc closely spaced electrodes and more uniformly distributed absorbent films. Temperature Effects.. Temperatux changes affect the instrument only in two minor ways. First, there is an effect of temperature on the density of the gas. While the instrunirnt continues to indicate the mass flow rate of water, the changing gas density affects the conversion t o concentration by a small amount which can easilv be calculated by application of the gas laws. For a fixed vo!umet.ric sample flow of 100 ml. per minute, a t atmospheric. pressure, 1 1i.p.m. of Triter produces a response of rxactly 13.2 pa. only a t room temperatrrrc. or 298" I
