187
V O L U M E 2 5 , N O . 1, J A N U A R Y 1 9 5 3 ment is unn~cessary. The thermally and catalytically cracked gasoline cuts, on the other hand, show very large interference effects that must be removed by the treatment. One treatment does not completely remove the interfering compounds but does eliminate the background a t the wave lengths used in this analysis. I n vieTy of the spread that occurs among the absorptivities for a particular class a t a specific x a v e length, it is believed that the success of the method rests primarily upon the extensive averaging that is utilized. The method is only fairly accurate for the determination of concentrations of the individual classes; it is believed to be satisfactory for total aromatic concentrations. Since this method requires only data a t four wave lengths and no particular deviation from established procedures, it may be done as rapidly as a routine analysis of a sample for xylenes and ethylbenzene.
ACK3OWLEDGMENT
The authors are indebted to R, E. Snyder for performing the chromatographic analyses. They would also like to express appreciation t o the management of Gulf Research & Development Co. for permission to publish this material. LITERATURE CITED
(1) -4m. Petroleum Inst., “Selected Values of Properties of Hydrocarbons,” Research Project 44, Washington, D. C., U. S. G o i t .
Printing Office, NOT..1947. ( 2 ) Coggeshall, N. D., “Physical Chemistry of Hydrocarbons,” ed. by A. Farkas, New York, Academic Press, 1950. Chap. 5. (3) Criddle, D. W., and LeTourneau, R. L., ANAL.CHEY.,23, 1620
(1951). (4) Tunnicliff, D. D., Brattain, R. R.. and Zumwalt, L. R . . Ibid., 21, 890 (1949). RECEIVED June 26, 1952. Accepted September 2 3 , 1962
Semimicrodetermination of Dissolved Oxygen E. L. HARPER, Pacific Biological Station, Fisheries Research Board of Canada, Nanaimo, B. C . H E Winkler method (1, 3 ) has long been recognized as one the simplest and most accurate for the determination of dissolved oxygen. The following semimicro modification has been found satisfactory for oceanographers where the volume of sample available for analysis is small, as from the Spilhaus sea sampler (4),and for limnologists who find a light, portable kit convenient.
through a small bore (‘/s-inch) rubber tube which is slowly withdrawn as the vial is filled, so that the end remains below the surface of the sample. Three drops (0.1 ml.) of reagent 1, manganous sulfate solution, are dropped on the surface of the sample from the reagent bottle, and sink rapidly t o the bottom. The vial is closed with the one-hole stopper (Figure 1) 80 t h a t no air is entrapped. Air bubbles may be eliminated by pressing the stopper down, forcing some of the sample out the tube.
REAGENTS
The reagents and their concentrations are given by Scott ( 3 ) or in (1). If the sample contains much organic matter the iodide concentration may be increased as recommended by Pomproy (23). APPARATUS
Reagent Bottles. The reagents are carried in small dropping bottles, capacity about 30 ml., or in bottles fitted with fine-tipped eye droppers through rubber stoppers. The volume of the average drop delivered by each bottle or eye dropper should be predet,ermined and the number of drops constituting the necessary volume (0.1 ml.) of each reagent should be noted. Sample Bottles. Borosilicate glass Shell vials, 25 bv 75 mm. (capacity about 37 ml.), are used. They should be choskn so that their diameters are constant within 0.2 mm. Stoppers. Each vial is provided with a tightly fitting one-hole rubber stopper (No. 5 ) through which a glass tube, 6 mm. in outside diameter, is fitted flush Q-ith the bottom and projecting 2 or 3 mm. above the top. The upper end is flared as shown in Figure 1. Measuring Device. A tv-o-hole rubber stopper is fit’ted with two glass tubes (4mm. in diameter) vulcanized in position. One tube is long enough to reach the bott’om of the vial, and the other is 1 cm. shorter. When the vial is inverted, the solution drains to the level of the shorter tube leaving the aliquant in the vial. The volume of the aliquant is dependent on the length of the shorter tube, which is constant, and the diameter of the vial. The maximum variation in diameter, 0.2 mm., may result in a 0.9TGvolume error. Each measuring device is standardized by weighing the volume of distilled water remaining in the vial. Tn-o measuring devices were tpsted. I n both cases the results of eight weigh,ings varied hy +0.05 gram in 21 grams, indicating a 0 . 2 4 7 ~deviation from thtx m e m . Buret. 4 2-ml. pipet, graduated to 0.05 nil., is made into an automatic: buret by fitting to it a three-way stopcock, and connecting it t o a solution bottle. The titer is usually lcss than 2 1111. and can be estimated t o 0.005 ml. Tvhich provides sufficient accuraq- while the titer exceeds 0.500 ml. PROCEDURE
The clean sampling vial is rinsed three times with about 5 ml. of the sample. The sample is then let into the bottom of the vial
T
&SAMPLE
AND REAGENI
SAMPLE BOTTLE
ADD REAGENTS 2.3 I rnmGLAiSS TUBE ONE HOLE RUBBER STOPPER SAMPLE AND REAGENTS / , 2 . 5 SAMPLE WITH RUGENTS
SUPPLY SIPHON
AIR VEUT
3 WAY STOPCOCK
&l@JANT MEASURING TU8E STIRRER TUBES VULCANIZED I N STOPPER
ALlqUANT of SAMPLE (abed 10 m l )
MEASURING THE WqWNT %RATION
Figure 1.
ASSEMBLY
Apparatus
Three drops (0.1 ml.) of reagent 2 , hydroxide-iodide solution, are dropped into the flared tube through the stopper. Within 30 seconds the reagent sinks t o the bottom, forming a brownish precipitate. With one finger over the flared tube the vial is inverted several times t o mix the contents. The solution is allowed to stand for about 10 minutes or until about a third of the solution is clear. Three drops (0.1 ml.) of reagent 3, concentrated sulfuric acid, are then added through the flared tube. This should be done sloa-ly to allow the drops to sink into the solution with no substantial amount of the reagent being lost in the overflow. When the reagent has drained completely into the vial it is reagitated
188
ANALYTICAL CHEMISTRY
and allowed to stand until the piecipitate has completely dissolved. The one-hole rubber stopper is then replaced by the measuring device with the shorter tube in the crnter of the vial to ensure accurate measurement. The vial is inverted, and thrs solution above the short tube allowed t o drain to waste. The sample bottle is then turnrci upright, the nitmuring device IS removed, and the remaining aliquant is titi atrd-in the sample bottle, using a glass stirring loop-with sodium thiowlfatr, from the 2-ml. buret to a starch end point.
Trial 1
\Iacro (116 1sL Titei A l p 0%liter 11 08 Y 06 11 OC 9 00 11 10 9 0: 11 05 9 04
\Iicro (21 111 ) Titer 1 i y Odlitei 2 00 9 00 2 00 5 00 2 01 5 05 2 01 9 05
I i e r a g e s , \Ig 0, liter
C A LCL LATION
3Iilligrams of oxygen per liter
Table 1. Comparison of Concentration of Dissolred Oxygen Obseried in Sea Water by Standard Winkler Procedure and 5eniimicroprocedure
Trial 1 Trial 2 Trial 3
=
9 04 8 56 8 87
0 04 1 0 05 + 0 05 +=
Difference 9.02 * 0 . 0 2 8.92 1 0 . 0 4 8.84 * 0.03
0 02 0 04 0.03
titer X normalitvof Sa25203 ___ 'Oo0 X volume of sample titrated a-here the volume of the sainl)lc~titrated is equal to volume of aliquant inscxittd. Both reagents 1 and 2 may br added Volume of aliquant x volume of reagents 1 and 2 volume of sample through the hole after stoppering, -. - if sufficient time is Only the volumes of reaernts 1 and 2 need be considered since allowed for complete drainagr of the first reagent bereagent 3 difiplaces only ox\ gm-flee sample. fore adding the second. For prrcise work the measuring stopper should be identified NOTES ON AMMETHOD only with the vial in which it is standardized, in u h i r h case the The precision of raoh step of the proposed semimicroprocedure volume error dors not exceed 0.23%. n as comparrd with the s t m d x d macroprocedure, and the optiThe usual precautions in using the Kinkler method must be mum conditions werr drtermintd. I n r:wh trial, 3 to 5 samplrs observed ( 1 ) . The sodium thiosulfnte should be standardized n r i e d r a m by siphon from :t pail of freshly obtained seawater under the s:tine conditions used in the andvses into biochemical oxygen demand bottlrs (approximately 300 ml.) and trratpd in the standard m:mnrr ( 1 ) . At the same time, a LITERATURE CITED siinilw number of seniiinic-ro samples werr taken and treated (1) dmerican Public Health -issociation, "Standard Methods for the according to t h r exprrirnental procedure. One measuring devicc. Examination of Kater and Sewage," pp. 127-9, New York, JYas used ith the series of sample vials. A comparison of rrwltq American Public Health =issociation. 1946. obtained in this nxinnrr is shown in T&lr I. ( 2 ) Pomeroy, R.. and Kimchman, H. D . , ' I x D .ENG.C H m f . , ;Isa~. It was found that if reagents 1 and 2 were added diiectl! to ED., 17, 715 (1945). (3) the surface of the sample brfore stoppt,ring the vial, the results . . Scott, J., "Standard Methods of Chemical Analysis," pp. 14367 , Sew York, D. Van Sostrand Co., 1925. v a l i d more than 1%. The, apparent concentration of dis(4) Spilhaus, A , F., "Bathythermograph and Sea Sampler," Woods solved oxygen may be too high ox\-ing to the reaction of reagrnts Hole Oceanographic Institution, 1941. a t the surface with the atmosphcarc; or too low owing to loss RECEIVED for revien. S u r e i n h e r 13. 1951. Accepted September 8, 1952 of manganic precipitates b>- displacement whrn t h t stopprr is
(
~
-
~~~~~
~
~
Determination of Osmium .-lpplication of Polarographic Kinetic Hydrogen Peroxide Current I. h l . KOLTEIOFF
AND
E. P. P..IRRl-1, School of Chemistry, Crniversity of Minnesota, M i n n .
r r H l < rcilurtioii of ferric iron to ferrous iron at t,he dropping mercury electrode in the presence of hydrogen peroxide causrs a cat'alytic ( k i n d ? ) reduction current of the peroxide ( 2 ) . The effect is too small to be of analytical use. On the other hand, traces of molybdate, tuiigsta,te, arid vanadate give rise to relatively large kinetic currents in the presence of hydrogen perosidr (3),and this effect could be used for determination of traces of these ions. I n a study of the specificity of the kinetic effect, it was found that lead(I1) in 0.1 -11 potassium nitrate and rut'hrnium(I'111) in 0.05 -11 to 0.5 31 sulfuric acid in the presence of hydrogen peroxide but absence of air give rise to nonreproducitile oxygen \vaves, indicating that a cata1,ytic decomposition of hydrogen peroxide is occurring in the solutions. [Rutheniuni(VIII) decomposes hydrogen peroxide with visible evo1ut)ion of oxygen in acetate buffers of pH 4 to 6.1 Titanium(1V) in saturated tartaric acid gives a kinetic current, but the effect is too small to be of analytical use. Similarly, copper(I1) in an ammonium chlorideammonium hydroxide buffer of p H 9 gives a kinetic. hydrogen peroxide wave which likewise is too small to be of analytical use. Azobenzene, uranyl, ferricyanide, boratc, quinone, cobaltic hexamminochloride, and pgrophosphatomanganate do not give any kinetic waves in the presence of hydrogen peroxide. On the other hand, osmium(VII1) gives 1 Present addresp, Department of Chemistry, Cniversity of Connccticut. Storrs, Conn.
rise t o rather large kinetic. currrnts which may hr of limited analjrtical usr. APPAR4TUS A R D &IATERIALS
T h r apparatus and most of the chemicals have been described ( 2 , 3 ) . A stock solution approximately 5 x 10-3 Jf in osmium tetroxide was prepared from Merck prrosmic acid ( 0 ~ 0 ~ ) . PROCEDURE
Solutions containing hydrogen peroxide and osmium tetroxide in contact with mercurv are very unstable. I n acid solutions osmium tetroxide is rapidly reduced by mercury, and in basic and neutral solution osmium tetroxide catalytically decomposes hydrogen peroxide. S o suitable organic liquid could be found to protect the layer of mercury on the bottom of the polarographic cell because of the ease of extraction of osmium tetroxide from the aqueous layer by the organic solvents used. I n acetate buffers of p H between 4 and 6, it v a s found that under experimental conditions the rate of reduction of osmium tetroxide by mercury was about 2% a minute, while no catalytic decomposition of hydrogen peroxide occurred. Therefore the following procedure was used: Place 5 to 10 ml. of 1J I acrtic acid and the same volume of 1 Jf sodium acetate in a 50-ml. volunwtric flask. .kid the appropriate
