V O L U M E 22, NO. 1 2 , D E C E M B E R 1 9 5 0
1533
ESTIMATION O F INTERFERENCE
In addition to the limiting interference ratios, measurements were nia,de to eecure information concerning the amount of interference mused by higher concentrations of cations. It was
ratios caused less deviation than the straight-line correlation would indicate, so blended knowns analyzed a t the same time as the unknoim must be selected within limited concentration ranges
found that straight-line relationships existed hetween concentrat.ion ratios of the cations and deviations in the determinations. Figure 6 shows several correlations in which high concentrations of interfering cations were used. The concentration ratios between interfering elements and the element to be determined wer(. plotted against deviations found in determining the element. A positive deviation \vas found which directly correlated with the concentr:ttion ratios. These correlations were used to determine correction factors for the roncvntration of the unknown element.
0
-
0 I 0.2 ERROR rp.m,ba
Figure 8.
I I
I
L
I
I
I
I
I
I
Specitic.ally A emissions w r e determined for both elements at their emitting wave lengths and were then corrected through calibration curves similar to those in Figure 1 to apparent concentrations, and their concentration ratios were calculated. The ratio was used, with a curve prepared a t the same time and similar to those in Figure 6 , to determine the deviation caused by the interference. These deviations were subtracted from the apparent concentration of the unknown element to obtain the actual concentrat ion. By this method, an accuracy of *loyo was obtained. In operation, however, the method was not simple, for several known solutions were required. These included two known solutions of the element to be determined, two of the interfering cation, and two of blends of the ahove. LIMITED R 4 N G E OF ESTIMATED INTERFERENCES
The straight-line ielationships in Interferences did not apply to a i d e ranges of varviiig (#oncentrationratios ( 4 ) . Extremelv high
03
0
0.04 008 ERRORpp,m,Ll -P
Deviation Due to Interference
The work reported on cationic interferences is not complete, because innumerable combinations and conditions might he measured. The measurements reported here cover only the problems which arose in analyzing common petroleum oils containing additives, They were useful as a guide to corrective bteps when interference was present. They were never used as permanent correction curves, but \yere rechecked m ith each unknonn sample analysiq. LITERATURE CITED
Barnes, R. B.. Richardson, D.. Berry, J. \V., and Hood, R. L., ISD. EXG.CHEM.,ANALED.,17,605 (1915). Reckman Bull. 193-B 11948). Berry, J. I%-.,Chappell, D. G., and Barnes, R. B., ISD. ESG. CHEM.,ASLL. ED.,18,19 (1946). Bills, C. E., SIacDonald, F. G., Niedeimeier, \ V , ~and Fchwartz, M. C.,SAL. THEM., 21,1076 (1949). Child, C. D., Phil. Mag., 16,1141 (19.73). Child, C:. D., P h y s . Rcc., 38,699 (1931). Cholak, J., and Hubbard, D. bf., IND. ENG.CHEY., SAL. ED., 16,i 2 8 (1944). Huldt, L., A r k . M a t . , A s t r o n . Fysik, A33,22 (1946). Jansen, If’. H., and Heyes, J., 2. p h y s i k . Chem., A168,257 (1934). XIitchell. R. L.. and Robertson, I. M., -1.SOC.Chem. Ind.,55, 269 (1936).
Parks. T. D.. .Johnson. H . 0..and Lvkken. L.. A s . ~ L C. H E Y . , 20, 822 (1948).
Roth, E., Mogunr Chem. Foluorrnt, 40, G5 (1934). RECEIVED March 3, 1950. Presented before the Pittsburgh Conference o n Analytical Chemistry and Applied Spectroxopy. February 17. 19.50.
lodometric Determination of Ozone of High Concentration E. 1). ROELTEK, G . L. PCTN-iII, AND E. I . LkSII, Cnicersity of F a s h i n g t o n , Seattle, P u s h .
M
BST conflicting statements regarding the iodomctric
method for ozone determination may be found in the literature. The generally accepted ( 1 , 4 , 8, 19) reaction foi, thrl ahsorption of ozonr in noutral potassium iodide solutions is:
2KI
+ H?O + O:j
2KOH
+ Ip + Oy
Lechner (6) claimed that the solution should be highly alkaline during absorption to avoid the loss of iodine vapor and reported that the method givcs about one half the error of the “neut,ral” iodide method. Riesenfeld ( 1 2 ) concluded that highly alkaline solutions give serious errors, due to the reaction :
KI
+
(1.3
+ KIOi
As inany as 2 . i niolcs of iodine were said to he liberated per mole of ozone. T o eliminate this error he proposed the use of boric acid-buffered absorbants (11, 13), and w e d this method in his determination of the niolecular weight for ozonc; the procedure was standardized with known volumes of pure ozone ( I S ) . Riesenfeld claimed that the use of boric acid prevented the formation of iodate and also of hydrogen peroxide (11). Many workers ( 2 , 14, 18) have shown errors up to 50% when the absorbants are strongly acid, reportedly owing to the react.ion:
403
+ IOHI ---+
H202
+ 512 + 4H20 + 302
Ruyssen (14, 1 6 ) , more recently, stated t h a t t,he use of boric acid or solutions buffered a t pH 5 to 7 gives results that are too
ANALYTICAL CHEMISTRY
1534
I he iodonietric niethocl for the detrrniination o f 4 to 20 weight R ozonc. w a s standardized by the gas density niethocl. The ozoiie used was a nitrogen oxidefree electrolj tic product. It w a s found that potassium iodide ahsorbants in thc pH range 2.3 to 12.3 give correct results for concentrations of ozone tip to 20 weight Y,, if the s o l u ~ i o ni s acidified w - i t h sulfuric acid before titration with sodium thiosulfate. -1ddition o f aliiniiniitn chloridc to the ahsorption solutions, in concentratioiis itp to 0.055 I-, causes no crror. r .
high l)y iiiuclr :is 10yc; Iiut tli:it solutions t)uffcwtl t o ; I p I I of 7 to 9.2 givv results no diffmxnt fi,oni thc w u n l iodomctric nwthotl. d that huffc’rcd solutions inrrcase thc scnsitiv, hut \ r i t h ozone co1ic(mtrations of I t w th:i~i 0.1% do not introduccn i’rrors :IS will f r w :lci(is, and piuposrc‘l :i mcthod using an aluminum chloridc-:rminoriium chloridr hufft,r (pII approximately 3 . 5 ) . lfost prorcdures .specify :icidifimtioii witli strong :rcitl twforc titration, hut Thorp fount1 thxt i f thc ozorw conccntration i y l i w t,h:in 0.1Yc,o n c n c ~ t not l iiciclify I)(,forcB titration. The “nc~utral” iodomctric mrthod hiis tiwii st;intl:irtlizc~rl l)y c:ireful nicxasui.cments of gas dcnpities ( 2 , 6 , 18). E w n with t h r w ahsolutc mcasurements thc w e of th(, nirthods fnr higher mncc~ntmtionsof ozone was unccrtain, t w c a u s t ~of thc. powihility of chain carricr re:tctiona of ozoiic (3, pinduring high results in
T h r uncwtaintiee ($1) conccrriiug the ni:inv iohnictrir mrtliods for ozone tletrrmination and thoir quitstionatilc 11s~’for high concentratioiis of ozonc madr this investigation impcretivc. I’ROC EI)U R E
Source of Ozone. Pivvious n.oi.k :it this 1:tboratoi.y pwvctl that ozone of very high purity a n d conctwtration r a n he productd by t+ct’rolysli of pcrchloi,ir acid solutions a t low. tt~mprr:iturrs ( 1 0 ) . i\ cell of improved design containing a glass-rloth diaphragm which srparatcd t h r cathodr produrt, hydrogen, from the oxygtw-ozonc mixture formed at the anode was t,hc sourcv of ozone. .ibsorption of the osygen-ozonc mixture in pyrogallol showed thc hydrogen content to lx considcrablj- I i w than 0.1 volume %. Analytical Method for Standardization. In order t o provc cwnclusively the validity of the analytical procedure it was necessary to measure the ozone by some direct, method. The absolute weight of ozone was thercforc determined by riirc>ful measurements of gas densities, using Regnault bulbs of approximately 500-ml. capacitv. Don-Corning silicone lubricants were d for the stopcocks and Tygon t,uhing for flcxible connection?;, hese materials have been found resistant to attack hv ozone at, this laboratory (see last paragraph on analytical method for effect of pH). The Regnault bulbs were evacuated, ueighed, filled with the oxygen-ozone misture which had been previously dried over magnesium perrhlorntc ( Anhydrone), and again weighed. From the density of the niisture and the known density of oxygen the weight of ozone was calculat,ed. Aft,er thc gas density was measured t,he contents \rei-his time, The correction was determined from successive measurements in the standard referenrc buffer and the elapsed time, and amounted to ahout 0.2 mg. during t,he %minute time lapse bet \reen the weighing and the gas iihsorption. RESULTS
Standardization of Potassium Iodide Method. The weight of ozone measured by titration, assuming the equivalent weight to he 24, checked within the experimental crror with the amount determined from the gas dciisities, as shown in Table I. One trial \vas made a t each ozone conccntration. Errors up to 15,8y0 n-erc obtained by Ladenberg and Quasig (a), while Treadwell and Anneler (18)had errors up to 8.7% using the same general method of analysis. The maximum concentration of ozone they studicd \vas only 9.86 weight %. The data in
V O L U M E 2 2 , N O . 12, D E C E M B E R 1 9 5 0
1535
T:ililv I d i o that ~ thc procedure cari be used for the detc~r~iiiiii:itioii of ozoric’ at concentrations at Icast its high as 20.2 w i g h t %. Effect of pH. T h r data i n Tahlr I1 show that p€I has iio c~fioc-tupon the accuracy of thc dctrrniination in thc p H imig(> 2.3 t o 12.3. The “neutral” iocloniotric iiicthoti also givrs rori.rct i ~ w i l t . . Thus, the mnclusion of Rirsc~rif(~ld ( 1 1-13) rqyrdiiig sei~ious(’rror in :ilkalinc solutions appears t o I)(- iiirorrect, as i? also the, c.I:riin f o r error iii boric acid sol~itioiisor acid huffercd solutions. 1 q o r t c d by Ru>-ssen (14, 1.7). Thcs Ion- I - I ’ I Y ) ~with ~ dilute ~ ~ ~ i r t ~ t i t r : i t iofo ialuniinuni is rliloridr : i i i d 1iighi.r vrroi’s ;is the, c o n c ~ ~ ri i~t i t i o nin SCP can he cspl;iinc~d t)y tliv far1 t l m t at t h r ahsoi4)iiig surfnet) thcxrc, is :in alk:iliiie filni pl’cJdUCCd- , 1 tilt' f ~ ~ l l 1 i l t i l ) lOf l pot iuni hydroxitic. Although tht. 1)ulk of the solution nxiy tw :it p I I 3.5, tlir filin at thc surfacr of shvotytion is a t :i hig1ir.r pI1, 1)ecaur;cof the forniatioii of potassium hydi,oside iri tho film. I n ordcai, for t,hc newly foi,iiwtl pot:issiriin hytlro\.itir to diffusct into thc hiilk of t h e solution, a c o n r c ~ i 1r:rtioii gratlitvit must v s i r t , The iwction of potassium iotlidtx ~vitliozon(’ is c:strc~nit3ly ixpid, a s i n c l i c ~ i t c ~by i t,he ohwrvahle giuwth of iodiiir crj-stals a t t h c b interf;ic:cL of 10 w i g h t 70ozn11egas and 0.; .ll potassium ioclidc., :iiid also h y the precipit:ition of aluniiiiuni h y t i i w i d ( ~at f i l i i i ~ v h c ~:ii luniinum i chloridc is prcseiit. Thv thtv)ry of :it)sorptioii follo\\-c’d hy rapid irrevc~rsihlecheniic:il iwc.tioii i i i thv liquid p1i:iw h:is b w i i thoroughly developed and provcd b>- nuniet’ous espcriInentaI invcvtigations (16). BcC L I U P ( thv ~ film has a high pH, tlics formation of hydrogen pei,osidc is limitrcl ( 2 , 5 , 18). Whcn thc roncentrat~ion of aluminum chloridc is highor tho pH of tlirl film is lo\vrr: the ozone is actually :ihwrhctl u n d ( ~acid t ~ renditions causing greater error. The coiicc,iitiation of aluminum chloriclc givon by Thorp ( 1 7 ) is low enough to produce no error. Thorp, howvc>r, made no attempt t o evaluatc~the usti of such a I~uffcr a t ozone concentrat,ione greator than O.lyo. I t \vas found n-ith xluminum chloride buffcrs that it is not nercssary t o acidify \vith strong acid hrfore titi~:ition: however, no error \vas found if additional acid were atldctl. In :dl othor i n s t m c w it \\-:is nrcessary t o acidify with strong arid. I.:nlew acid is addtd hrfore titration, up t,o 50% or m o i ~vrror is caused hy failure of iodate, formed dui,ing ahsorption, to react with sodium thio,wlfatr. Possibly t h r rwction is
6KOH
Table 11. L I Hof Ti1 .\haorbant Pollition , . .
2.3 3.4 4.0 4.0 :i, .?I
3.5 3.5 3 5 1 2 4
4
%2
.1
3r& of Ozone per
__ 100 111. of Gas Addeda 18.8 27.0 25.7
Satd. HJ303 Satd HaBOa Satd. HaBOa
Measured27.5 35.5
Relati\ e E ~ 9; 46 +31 +27
+
12.4 9 1 22.1 10.2 20.2 1s . 9 20.0 17.2
38.4 13.0 9.1 21.3 10.7 21 . o 19 4 24.8 21.5
12 f, 17 15 6
12 5 17 7
-1
15 4
+1 -I
+50
-4 +;, 4-3
+22
++21 2.5
KHnPOa-XaOH ’I
12 4
12 3
-1
21 . O 11 . O 18.2 19,O I7 , 6
19.1 11.0 17.4 18.8 17.2
-4
10.2
HaB03-KCI-;2‘aOIIh H3BOa-KC1-SaOHb HaBOn-KCI-KaOH HsBOa-KCl-VaOHh H1BO3-KCI-kaOH
-2
12 3 12 3
0 2 .ti NaOH 0 . 2 M NaOH
22.8 23.9
22.5 23.9
-1 0
Sone Xane
24 8 24.2
24.6 24 2
-1
6+
10 10
*
0 -4
-1
0
tVeight determined from absorption in standard reference britrer ( p H = 6.98). See procedure. analytical method for standardization, and analytical method for effect of pH. Buffers prepared a s given by Clark ( 5 ) .
*
ACKNOWLEI)(:\lEVT
Tht, authors arc iiidehtcd to Res J . Itoliin,wn and R. W. SIoulton for valuablt: suggestions in prcp:iration of manuscri1)t. LITER.ZTURE CITED
Effect of pII on lodometric Method
Concentration of pH-Controlling iipent. 1 v HCl 0 1 .V HCI 0 1 A’ HCI 0 01 s HCI 0 028 .v AlCli 0 028 ’V AlCll 0 028 .v AlCla 0 05*5S AlCla 0 100 .\‘ .41Cli 0 166 S AlCli 0 166 JV .1ICI$
(5 . 1
6-+
(:O3(; LII S I O Y s
I’otassiuin iodide a l w r h a n t P in the pH r:iiipt. 2.3 t o 12.3 gi\o correct results for concentrations of ozoiie up t o 20 w i g h t 70, if the solution is acidified with i t i ~ i i i gacid hrforc titration ivith sodium thiosulftite. .Iddition of aluminurn chloritlr to ttie absorption solutioii iri concentrations u p to 0.055 .Y c a u s ( ~no rrror. Strongly acidified potassium iodide absortxitits give high riisults. The conceiitriitiori of the acid affwts t,hc degrre of rrror.
+ 37, .&KIO:: + 5Ie rc:i products condeiised in water mi.-t. T1ii.q a p p r ~ r sto hr iricoi iiiasmuch as the sinoke was alsu prodiicc,tl undvi imhytlrou$ c ~ ) i i t l i tions when an oxygen-ozoiic inistui,c, \\.us paswcl ovvr iwuI)linird iodine at room tenipctraturr. Tlii,. .c.trd n x s .wIut)k in watrr :tnd l i b r r i r t d i w l i w fro111 acidified pot:i+ sium iodide ~oiutioiis. To prc~-eiit( ~ i ~ i ~t)y or1 ~ 0 ~ sof these ositlt,s, nioiPtened glass-xool plugs n - c . 1 ~ uscd i r i t t i r g:rs lines to r o l l ( ~ ~ t t h c smoke formed during ;ihmrptiori. T h c h plugs iv(’r(> w i s h i d with distilled water and this \\-nshings f i , o i i i t ties(>plugs \vorv t h r i i :iddvd to the solution t)vEoi.e :icidific,:itiori a n d titration i v i t l i sodium thiosulfate.
~
~
Allen, 5 . .I s u . I < s ( ; , (‘HEM., .ix.ar.. En., 2, 55 (1930). Brndie. B. C . , Phil.Tram.. 162,435-85 (187’4). (‘lark. TV. 11.. “Determination of Hydrogen Ions,” 3l.d rd.. Baltimore. n’illiams & Wilkins Co.. 1928. Furniaii, ?;. H.. ”Scott’s Standard Xethoris of Analysis.“ 5th ed., Tol. 11.p. 2370, SeivYork, D. Van Snstrand Po., 1980. Ladenherg. A . . and Quasig. R., Rer.. 34,1184 (1901). Lechner. G.. Z. Elelitrochc7n.. 17, 412-14 (1411). Maslan, F. D., ‘‘IYet Oxidation of Sulfur Dioxide Promotrd b y Ozone.” 116th Meeting, A M , ( I H E x . Sor,.,Ahstrarts, p. 11 K, September 1949. llellnr, J . IV.,“Conipiehensivc Treatise o n Iiinrgaiiir and Theoretical (‘hemistry.” Tol. I, p. 905, Y e w York. Longmans, Green and Co.. 1922. Putnam, G. L., and Hahn, V, A , , 7 ’ w , ~Electrorhrvr. . ,%w., 93, (1948). discussion. ~ 355-7‘ , Putnam, G.L.,Moulton. K. IV., E’il1nioi.c.\V.\V.,and (‘lark, I,. H., J . Electrochem. SOC.. 93,211-21 (1948). Riesenfeld, E. H., A u g e w . Chem., 45,309 (1932). Riesenfeld, E. H . , and Benker, F.,%. 1r71orq. Chem., 98, 167 PO1 (1916). Riesenfeld, E. H., and Sehwib. G. 11.. Ber., 55, 2088 (1922). Ruyssen, R., ;Ynfzrurzc. Tijdaehr., 14, 245-53 (1932). Ihl’d., 15, 125-30 (1933). Sherwood, T. K., “.%bsorptioti and I
