Tetraethylenepentamine as a Colorimetric Reagent for Copper 'TIIO\I i S B. CHL \IYLEH, Richardson Chemical Laboratory, Tulane L'nicersity, Set* Orleans, La. The possibility of using tetraethylenepentamine as a colorimetric reagent for copper has been investigated. The blue color is independent of the amount of excess amine, is stable, and obejs the Beer-Lambert law. This amine is nonFolatile, practically odorless and colorless, and provides a color reaction w ith cupric ion which is about 3.5 times as sensitite as ammonia.
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given above compares favorably 17 ith this. A% similar calculation from Figure 1 of the paper of Toe and Barton ( 4 ) for triethanolamine gives a specific extinction of 0.00011. It is seen that tetraethylenepentamine is approximately 3.5 times as sensitive as ammonia and twice as sensitive as triethanolamine.
rapid routine colorimet'ric determination of copper in small amounts several highly sensitive reagents are available. These very sensitive reagents are applicable only where quantities of the order of 1 to 2 p.p.m. of cupric ion are to be measured. For larger quantities ranging up to 200 p.p.m. the sensitive reagents cannot be used without measuring small aliquot portions of the sample. For these higher ranges ammonia has been investigat,ed by Mehlig (3) and by Yoe and Crumpler ( 5 ) and also used satisfactorily by Hoffpauir and O'Connor (1) in analysis of mildewproofed textiles. The principal disadvantages are the odor and volatility of ammonia and the dependence of color on ammonia concentration (3, 4 ) . Toe and Barton (4) have suggested triet'hanolaminebecause it is odorless and the color is independent of the amount of amine in excess. This paper reports the investigation of several amines in a search for one which provides in color reaction with cupric ion a sensitivity intermediate betlveen ammonia and the recently developed reagents of high sensitivity.
EFFECT OF EXCESS REAGEYT
The effect of increasing the concentration of tetraetliylenepentamine with the cupric ion concentration fixed at 50 p.p.m. is shown in Figure 1. The ordinates are photoelectric colorimeter scale readings which are proportional to photometric demit!.
APPARATUS AND REAGENTS
The visual spectrophotomet,er used in this study was constructed in the Tulane University shop. It is of conventional design and accomplishes photometric balance by means of a neutral glass wedie. The cell thickness was 100 mm. h clinical model Klett,-Summerson photoelectric colorimeter !{-as employed for colorimetric observations, using the color filter with maximum transmission a t 640 to 700 mp. Electrolytic deposition shoved the concentrat'ioii of t,he stock copper sulfate solution t o be 9.94,grams per liter of cupric ion. Suitable dilutions provided the var~oust w t solutions. The purification of t,hc amines studied has becn prcviously reported ( 2 ) . solutions of amines \vere preparc'd by dissolving weighed portions of purified amine. The ammonia was of C.P. grad?.
0
0.1
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 hfillimoles of Tetraeth, lenrpentamine
Figure 1.
1.0
1.1
1.2
Effect of Excess Reagent
CO3IPARISON OF AMINES
To compare their sensitivities, spectrophotometric extinction curves of the blue complexes formed by the various amines witJh cupric ion were obtained over the range 500 to 710 mp. The specific extinction values (expressed as extinction per centimeter per p.p.m. of cupric ion) at the wave length of maximum extinction are given in Table I.
Table I. Amine Atnmonia
It i.; seen that the color deielopment i5 independelit 01 excess amine. The break in the curve ju-t preceding coniplete coloi development is as yet unexplained. S o speculation is n o ~ vbeing advanced. The phenomenon is being investigated further by spectrophotometric techniques.
Comparison of Amines Wave Length
CONFOR3IITY TO BEER-L43lBERT LAM Yperitir Extinction
Photoelectric colorimeter scale readings were tak'en with concentiatioiis of copper ranging fiom 0 to 160 p.p.m. In each instance a 25% excess of tetraethylenepentamine over that required for maximum color development vias present. X plot of the results gives a straight line which shows that the color reaction obeys the Beer-Lambert la\\ over the entire concent ration range investigated.
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It ha. been pointcd out (9, 4)that the evtinctiori of the ropper'ammonia compkx depends upon ammonia concentration, ivhich in thiq instance naq 0.12 molar. Calculation of a value of -pecific extinction from Figure 2 given by Toe and Barton (4)a t 0.12 molar and :it 625 mp yields 0.00066. The v ~ l i i e0.00065
L S E I \ COLORIMETRY
To prepare 100-ml. portions of colored solution of the coppertetraethylenepentamine complex with, cupric ion mnwntrations
325
ANALYTICAL CHEMISTRY
326 of 0 to 200 p.p.m., 10 ml. of 2% aqueous solution of amine should be used. This provides a plentiful excess of amine if the p H of the copper solution is not less than 3.5 to 4.0. Regulation of the p H t o this range can be satisfactorily accomplished by dropwise addition of dilute sodium hydroxide solution and testing with an indicator paper. If too much sodium hydroxide is added and cupric hydroxide precipitate;, it is all right to add the amine but the mixture must be allowed to stand several’minutes to permit complete solution of the cupric hydroxide. Observations over a period of 48 hours reveal that the color is perfectly stable for a t least this time. The ions R hich interfere with this amine are the ones which interfere with ammonia ( 3 ) .
ACKNOWLEDGME3TS
Two students, David A. Warriner and Isidore Cohn, provided valuable assistance in making some of the preliminary observations. The Carbon and Carbide Chemicals Corporation generously provided research samples of three amines. LITERATURE CITED
(1) Hoffpsuir and O’Connor, Am. DgestzcflRReptr., 31, 395 (1942). (2) Jonassen, Crumpler, and O’Brien. J : Am Chem. SOC.,67, 1709 (1945).
(3) Mehlig, I N D . ENG.CHEDI., A N 4 L . ED.,13, %3 (1941). (4) Y o e and Barton, Ibid., 12, 456 (1940). (5) Poe and Crurnpler, Ihzd.. 7, 281 (1936).
Determination of Water in Caustic Soda and Other Alkaline Materials A Distillation- Tit rirnet ric Met hod H . R. SCTER, Wyandotte Chemicals Corporution, Wyandotte, *With. A method has been developed by which 20 to 200 mg. of water may he determined in caustic soda or other alkaline inorganic material with an accuracy of * 5 % . It consists of a preliminary separation of the water by distillation with xylene and titration with Fischer reagent. It is generally applicable to inorganic materials, where numerous interferences with the dirert use of Fischer reagent exist.
R
ELI.1ULE niethods for the determination of water in caustic.
soda are lacking in the literature. The primary interest of producers and consumers is in the content of sodium hydroxide, salts, and metallic contaniinants, all of which are readily determinable by well-established chemical and spectrographic methods. Water is usually estimated by difference, if at all. Investigations carried out in this laboratory of reactions in molten caustic soda have necessitated direct determinations of water as a means of studying reaction mechanisms. The method here described permits direct determination of viater in solid caiistic soda or other alkaline inorganic materials. Conventional oven-drying methods are, of course, inapplicable because of carbonation of the caustic by the atmosphere. Attempts a t gravimetric determinations by fusing the samples, cont,ained in silver crucibles, in currents of dry, carbon dioxidefree air have yielded erratic results. Weighing difficulties due t o the extreme hygroscopic character of caustic soda, and the tendency of the fused caustic t o climb over the walls of the crucible, in addition t o the very slow rate of expulsion of water, are the principal objections to this method. These considerations indicate the use of distillation methods, which have the obvious advantage of providing a continuously renewed anhydrous atmosphere in int’imate contact with the particles of the solid being dried, so that there is practically no partial pressure of water vapor over the sample. This condition is probably never realized in a n air stream, since the bulk of the air passes around the container, not actually through the sample. Thus the vapor pressure equilibrium is displaced very slowly, being dependent on diffusion of the vapor out of the container. I n distillation methods, ordinarily the solvent used is one which is immiscible with water, so that the condensat,e separates into two phases, the water being retained in a graduated trap where its volume is measured. Separation in the trap is dependent on the difference in density between water and the entraining liquid, and
the excess of the latter passes through the trap and is recycled t o the still pot. Liquids commonly used are toluene, xylene, perchloroethylene, tetrachloroethane, and o-dichlorobenzene. Xone of the common types of stills and traps are well adapted to the collection and measurement of small amounts of water. I n the Bidwell-Sterling (4)type and modifications thereof, there is a tendency for the water vapor to condense a t a higher zone in the condenser than the entraining liquid, because of the lower boiling point of the former. Some of the water inevitably hangs on the walls of the condenser, and must be scrubbed doim a t the end of the distillation. Sharp separation of the phases is not readily obtained in the measuring tube, since the liquid there is static in most of these stills. I n the Thielepape and Lundin stills ( 1 2 , 17) the vapor is introduced a t the top of the condenser, so that the separated droplets of water are presumably continuously flushed downxnrd to the trap. Actually, experiments made in this laboratory show that as much as 0.3 ml. of xater may be held up in the condenser. Replacement of the spiral tube condenser with a bulb type resulted in no great improvement. I n these stills, the entire stream of condensed entraining liquid passes through the column of water in the measuring tube, which results in clean separation of the phases but necessitates a rather large bore to prevent the water from being pushed back into the distilling flask. There is no apparent way t o eliminate these errors in collection and measurement of the separated water. Lindsay (11) has designed a trap for small amounts, but he reports only a single recovery experiment, in which the error was 470. Usually the collection and measurement errors are minimized by collecting a fairly large volume-i.e., several milliliters. For materials containing low percentages, this requires inordinately large samples. In the method here presented, the entire distillate is collected in a flask which also serves as the condenser, and the water is determined by means of Fischer reagent. This permits the deter-
