~~~
~
~
DETERMINATION OF COMBINING WEIGHT
Thoroughly mix the dried and purified sulfonate by means of a spatula. Csing a 75- to 80-mg. sample. determine sulfur in accordance with the proposed ASTM procedure, using the induction-type furnace ( 2 ) . Titrate with 0.03119K potassium iodate solution (1 nil. = 0.5 mg. of sulfur). Calculate the combining weight of the sulfonate by means of the following equation: Combining- weight = 32( 100 - Z i C 1 from Sa2C03) 6 in purified sulfonate Table I s h o n i typical results on sulfonatci of n id(>lyvarying combining neight. Esperience in running several hundred samples has qhown that combining neightb on two samples of separately purified material nil1 usually differ by not mort’ than 1% of the average value. DISCUSSION
One purification step is the separation of sulfonate into an alcoholic phase by addition of solid sodium carbonate to the alcohol-water solution. K h e n the sodium carbonate content of the solution reaches a certain point, two liquid phases are formed. If the system is allowed to d a n d a t least 2 hours for complete separation, thr. sodium carbonate content of the alcoholic phase will be sinall and u-ill rarely exceed 1% of the purified sulfonate recovered on evaporation to dryness. The conibining weight based on sulfur determination i i subject to less error due to sodium carhonatr in the sulfonate than is the sulfated ash method. Table I1 s h o w the errors that would be made in a product having a combining reight of 350, if 1% of sodium carbonate in the sulfonate were ignored. Salts of carboxylic acids are sometimes present in petroleum sulfonates, but the amount rarely exceeds 1%. If carboxylates art’ known to be present.
Table I.
Combining Weight of Sulfonates
Sample Toluenesulfonic acid
Theory
Sodium 2,4-dimethylbenzenesulfonic acid
Combining M7eight Sulfated Induction ash p-Toluidine furnace method method method 176 174
172
...
208
Sodium alkylbenzene sulfonates h
C
D
F Sodium petroleum sulfonate Sodium dodecylbenzene sulfonate Oleum sulfonated Sulfan sulfonated
352 359 356 355 572
Barium dinonylnaphthalene sulfonate
Sodium carbonate impurity in recovered RS03Xa = 1% Sulfated Induction Ash Furnace Method Method Kithout lja2C03 332 6 353 9 correction With Na2C03 350 0 350 0 correction Correction 17 4 3.9
a portion of the sulfonic acid-oil residue may be titrated potentiometrically for
I
.
509 509 517 522 496 511 503 499 303 309
B
Table 11. Combining Weight Calculations with Respect to Sodium Carbonate Corrections Combining weight of RS03Na = 350
.
393 39 1 440 441 351 358 349 348
211 210
510 503 522 523 513 515 503 505 304 306 379 383 445 446 355 355 349 354 574
strong and Lveak acids ( 3 ) . This is simpler and probably more accurate than the ASTM method ( I ) , LITERATURE CITED
( 1 ) Am. Sac. Testing Materials, “Stand-
ards on Petroleum Products and Lubricants,” Designation D 855-56 ( S o vember 1956). (2) Ibid., p. 944. (3) Brooks, F., Peters, E. D., Lykken, L., ISD. ESG. CHEIM.,AKAL.ED., 18, 544 I1 9-46). \ - - - - I -
( 4 ) Marron, T. U., Schifferli, J., Ibid., 18, 49 (1946).
THIRDOklahoma Tetrasectional hZeeting ACS, Bartlesville, Okla., RIarch 1957.
Circulation-Type Apparatus for Spectrophotometric Titrations Thomas R. Sweet and James Zehner, McPherson Chemical Laboratory, The Ohio State University, Columbus 10, Ohio
photometric titrations, Fricker (2) suggested a n apparatus used with the Hilger Spekker absorptiometer. Lee, Edgerton, and Kelley (3) used a centrifugal pump in the spectrophotometric titration of radioactive samples. H o ~ ~ e v ethere r, was a need for a simple circulation-type apparatus that could easily be used lvith the Beckniaii DU spectrophotometer. FOR
APPARATUS
The cell is constructed from a con-
ventional I-cm. quartz cell by joining 6-mm. glass tubing a t the top and bottom, as shou-n in Figure 1. The cell is held in place by an ordinary cell holder, modified by the removal of a 9-mm. section from the center of one of the partitions. This makes room for the side tube and does not interfere with the ordinary use of the holder. A reference cell may be inserted in one of the other compartments to correct for any drift in the adjustments of the instrument or to observe the absorbance a t more than one wave length during a titration.
A special cover for the cell compartment was designed to allow the cell to move freely in the compartment and yet shield it from all stray light. 4 diagram of the cover is shown in Figure 2. The sections in the diagram are fastened rigidly together except for the 19 x 1170 mm. strip in the section second from the top. This strip is allowed to slide freely with the cell. The cover is painted black and the tubes of the cell are covered with black tape. A wire is extended through the cover and hooked t o the handle of the cell holder, so that the whole assembly may be VOL. 30, NO. 10, OCTOBER 1958
1713
6 rnm
Figure 2. Sectional diagram of cell compartment cover
r
25mm
Figure 1. Absorption cell
easily removed. No drift in absorbance readings is observed when the beam of a flashlight is directed upon the apparatus from various angles. The pump is the titration beakcrstirrer combination. A 150-ml. beaker is most convenient, although larger titration beakers work satisfactorily. A 6-mm. glass tube is connected to the center of the bottom of the beaker and another glass tube is connected tangent to the outer edge near the bottom (Figure 3). A paddle stirrer, rotating in this beaker a t approximately 750 r.p.m., acts as a centrifugal pump. There were virtually no complications due to bubbles except at very high speeds of rotation. However, these high speeds are not necessary for efficient circulation. The beaker and cell may be connected by short (9-cm.) pieces of rubber tubing.
The solution circulates through a 150ml. titration vessel and a 10-mm., approximately 4d., quartz cell. Only a small percentage of the total volume of thc solution is outside the titration vessel at any one time. When aqueous solutions were used, the entire solution became homogeneous within 5 seconds aftcr the addition of the titrant to about 50 ml. of solution. EXPERIMENTAL
The apparatus was tested by the spectrophotometric titration of calcium and the recently developed method for the titration of copper and iron. The first test was made by a titration of calcium with (ethylene dinitri1o)tetraacetic acid (EDTA), using murexide as indicator (1). A, 10.Q1-ml.
volume of 0.001236M calcium chloride was introduced into a heaker with 10 ml. of 1M arnrnoniiirn hydroxide and the murexide indicator. The solution was diluted with water to a volume of 50 nil. The titration was made with 0.002109M EDTA and the absorbance was measured a t 480 mp. On the basis of 10 determinations, thc observed absolute standard dcviation of a single determination was 0.03 mg. for a sample known to contain 4.96 rng. of calcium. The absolute error of the mean T:LS 0.03 mg. Copper and iron were determinrd simultaneously according to the procedure of Underwood (4). Copper and ferric iron are titrated in a solution buffered with chloroacetic acid and the absorbance is measured at 745 m p . The first increase in absorbance gives the iron equivalence point; and the copper equivalence point is t.he point at which the absorbance again becomes constant. Equilibrium is established very slowly during the titration of iron. This agrees with the observations of Underwood. On the basis of eight determinations, the absolute standard deviation of a single determination was 0.8 mg. of copper and 0.5 mg. of iron for a sample known to contain 30.9 nig. of copper and 26.5 mg. of iron. The absolute error of the mean was 0.1 mg. for copper and 0.3 mg. for iron. LITERATURE CITED
(1) Chalmcrs, R. A., Analyst 79, 519
Figure 3.
1714
Titration beaker
ANALYTICAL CHEMISTRY
Figure 4.
Assembled apparatus
(1954). (2) Fricker, D. J., Chem. & Ind. (London) 1955,426. (3) Lee, J. E., Jr., Edgerton, J. H., Kelley, M. T., ANAL. CIIEM. 28, 1441 (1956). (4) Underwood, A. L., Zbid., 25, 1910 (1953).
