high lead values found using isooctane alone, a wide variety of experimental and instrumental factors were investi- gated. No improvement was found, for instance, in changing the length or di- ameter of the nylon burner feed tubing or even dispensing with i t altogether. The use of oxygen in place of compressed air failed to cause any significant varia- tion in the results as did various instru- mental settings such as the photomulti- plier voltages, cathode currents, slit nidths, etc.

.kt this point it appeared a certainty that the trouble involved the complex phenomena associated with the vapori- zation and burning of the lead solutions at the burner tip and in the flame itself. In view of current thinking on the nature of these phenomena (4, 6, 7 ) , various mixed solvents were tried and a 1 : l mixture of acetone and isooctane was

selected on the basis of vastly improved results (Table I).

I t is difficult to pinpoint exact reasons for the success of the mixed solvent. Part of the story may lie in the fact that the measured vapor pressure of the iso- octane standards is only about one quarter that of raw gasolines. The ace- tone increases the vapor pressure of the solvent to the point where raw samples, diluted samples, and standards are all nearly identical. On the other hand, the acetone may improve the solubility of the T E L in the solvent, particularly as it emerges from the burner tip, but such an event would be most difficult to study.

ACKNOWLEDGMENT

The author expresses his appreciation to G. del3oer for his valuable assist- ance in this work.

LITERATURE CITED

(1) Am. Soc. Testing Materials, Standard Method 11526-61 (1961), 1965 Book of Standards, part, 17, pp. 272-6 Phila- delphia, Pa., 1965.

( 2 ) Am. Soc. Testing Afaterials, Standard Method D1269-61 (1961), 1965 Book of Standards, part 17, pp. 571-6, Phila- delphia, Pa., 1965.

( 3 ) I1agiial1, lt . &I., West, T. S., Talanla 11, 1553 (1964).

(4) AIenzies, A. c., ANAL. CHEX. 32, 905 (1'360).

(5) ltaiin, C. S., The Element #9, Aztec Instruments Inc., Westport, Conn., 1965.

(6) Robinson, J. W., Anal. Chim. Acta 24, 451 (1961).

(7) Robinson, J. K., The Element #5, Aztec Instruments Iiic.) Westport, Conn., 1065.

H. W. WILSOX British American Research and

Sheridan Park Ontario, Canada

1)evelopment Co.

Analysis of a-Olefin-Derived Sodium Sulfonates by Ion Exchange and Potentiometric Titrimetry

SIR: A simple, yet rapid, niethod of analysis was needed for a-olefin-derived sodium sulfonates. These products normally consist of the sodium sul- fonates and a few per cent of sodium sulfate. The alkyl sulfonate analysis is usually obtained by ASTM D-1681 (2) , a variation of two separate methods developed by Epton (6) and by Barr, Oliver, and Stubbing ( 3 ) . This niethod involves titration with a standardized cationic reagent and uses the distribu- tion of methylene blue between two liquid phases for detection of the end point. This method, however, is not applicable to lower molecular weight sulfonates. Sodium sulfate is fre- quently determined as the alcohol in- soluble content (1) or by precipitation as barium sulfate after ether extraction to remove the sulfonate. 130th of these procedures are quite lengthy for routine application.

Recently an instruniental method based on x-ray fluorescence and infrared s1)ectronietry has been reported ('7); however, it 15-ould require quit'e espen- sive equipment for routine plant analyses. The procedure reported here consists of passing an aqueous solution of the sulfonate-sulfate sample through a sulfonic acid ion exchange column, diluting the effluent with acetone, and titrating with tetrabutylammonium hydroxide.

EXPERIMENTAL

Apparatus. Titration curves were obtained with a Sargent Model D automatic recording t i t ra tor equipped with a 10-nil. buret and Leeds and

- 4 0 0 t- - 2 0 0 -

5 0 - 1 0 0 - = 0 -

F I O 0 - 2 0 0 -

I N F L f C l l O W C "

a o o - 4 0 0 -.

0 I O 2 . 0 3 0 V O L U Y f O f 1 1 1 1 1 N T IN Y l L L l L l l l R S

Figure 1 . Titration of acids from a typical a-olefin-derived sodium SUI- fonate with tetrabuylammonium hydroxide

S o r t h r u p general purpose glass and calomel electrodes without modifica- tion.

The ion exchange column was a 1-em. diameter glass tube, 15 cm. long, with a 3-mni.-bore Teflon stopcock at the bottom and 50-ml. reservoir at the top. It contained 15 ml. of 50- to 100-mesh Dovr-ex 50W-X8, ion ex- change resin in the acid form.

Reagents. All chemicals were rea- gent grade or equivalent. Standard 0.1.V tetrabutylammonium hydroxide was prepared by diluting 1lZT tetra- butylammonium hydroxide (Eastman Organic Chemicals) 9: 1 with a solution of 70% benzene-30yo methanol. The titrant was protected from the atmos- phere by use of a drying tube containing

hscarite and Drierite and was stand- ardized each day with benzoic acid in a 9 : l acetone-water solvent. Commercial sulfonic acids and the sulfonic acid salt were purchased from Eastman Organic Chemicals and the l ldr ich Chemical Co. and used without further purifica- tion.

Procedure. The samples were pre- pared for titration by dissolving 0.45 gram in 50 nil. of water. Because of solubility problems, some of the higher molecular weight' sulfonate solutions ivere maintained a t a tein- perat'ure of 55' C. .I 5-nil. aliquot was pipetted into the column reser- voir and the stopcock was opened. When the solution level reached the top of the resin bed, washes were added in the following order : two 3-ml. volumes of water and four 6-ml. volumes of acetone. The effluent was collected in a 150-ml. beaker, diluted to 100 ml. with acetone, and titrated automatically wit'h the standard 0 . 1 s tetrabutyl- ammonium hydroxide solution. The resin should be immediately regenerated by washing with 50 ml. of 10% hgdro- chloric acid and then with distilled water until the effluent is neutral. Acetone, when kept, in contact with the resin for more than 20 minutes, caused erratically high results.

X typical curve for the titration of the acids obtained by passing a sample of C I ~ a-olefin-derived sulfonate through the ion exchange column is shown in Figure 1. Inflection A represents the neutralization of the sulfonic acid and one hydrogen from the sulfuric acid. Inflection B represents the neutraliza- tion of the second hydrogen from sulfuric acid. Inflection C represents impurities and does not enter into the calculations. These impurities are probably in the acetone since the volume of titrant to

VOL. 38, NO. 7, JUNE 1966 921

Table 1. Determination of Sodium Sulfate in a Blended Sulfonate-Sulfate Sample

-400

-300

-200 m

5 -100

g - 2

I O 0 d - & 2 0 0 Y : 300

400

5 0 0

1 0 0

7 0 0

Sodium sulfate, 7c Sodium sulfonate, yo Calcd. Found Error Calcd. Found Error

- - - -

0 -

- - - - - - -

. . . 1 . 6 . . . 85.3 3 .6 3 . 7 +o: 1 83.5 82.9 B O 6 . 4 +0 .4 81.5 79.8

-0 .6 -1 7

8 . 8 9 . 1 + 0 . 3 79.1 78.6 -0 .5

Table II. Comparison of Total Sulfur Values for Different Structure Sulfonic

Acids Containing Sulfuric Acid yo Sulfur

High Proposed tem-

titra- pera- tion ture tech- com-

Sample type nique bustion Methanesulfonic acid

( Aldrich) 30.5 30.4 Methanesulfonic acid

(Eastman) 32.8 33.7 d-10-Camphorsulfonic

acid 12.9 12.8 Benzenesiilfonic acid 17.0 17.4 Benzenesiilfonic acid

(sodium salt) 15.7 16.1

obtain inflection C increases propor- tionally with the amount of acetone.

The calculations for the percentages of the sulfate and sulfonate salts are given by the following equations:

% Sodium sulfate =

(nil. of titrant) (normality) (142) 100 (sample weight in grams) 1000

where milliliters of titrant = (ml. a t Inflection B) - (ml. at Inflection A )

% Sodium sulfonate =

iml. of titrant) (normalitv) ‘-(molecular &iiht) 100 ’

(sample weight in grams) 1000

where ml. of titrant = ( 2 ) (ml. at Inflection A ) - (ml. a t Inflection B )

RESULTS AND DISCUSSION

h‘,N-dimethyl fa t ty amide (9), pyri- dine (4, and acetone (4 , 6, 8) can be used for the differential titration of sul- fonic and sulfuric acids but none of these solvents will dissolve a-olefin-derived sodium sulfonates. R a t e r will dissolve the sulfate and sulfonate salts; however, i t will not readily dissolve the resulting sulfonic acid nor will it act as a differenti- ating, solvent. Therefore, a differentiat- ing solvent must be used in conjunction with water to obtain a final titration solvent.

*V,N-dimethyl fatty amide (8) has been suggested as the best solvent for the titration of sulfonic and sulfuric acids. However, water, in concentra- tions of more than 4y0, leveled the in- flection points enough to make them un- suitable for analytical purposes. Pyri-

dine was investigated; however, it did not prove to be as satisfactory as ace- tone. Acetone (6) has been used as a differentiating solvent but Cundiff and hlarkunas (4 ) reported that it reacts with strong acids and yields nonstoi- chiometric titrations. To determine if the strong acids react with acetone in the presence of water, a sample of an a- olefin-derived sodium sulfonate con- taining sodium sulfate was converted to the corresponding acids and allowed to remain in contact with acetone con- taining about 10% water for various periods of time. The results indicate that there was no significant change in either sulfuric or sulfonic acid con- centration over a 6-hour period.

To determine the stiochiometry of acetone-water mixtures, samples of sulfuric acid were titrated in acetone containing increasing concentrations of water. Figure 2 shows these titrations. The titration in acetone results in only two inflections. The first represents the neutralization of one hydrogen of sul- furic acid. The second represents the neutralization of the second hydrogen of sulfuric acid plus impurities in acetone. The addition of water to the acetone causes a differentiation between the neutralization of the second hydro- gen of sulfuric acid and the impurities in acetone. As the concentration of water increases, the differentiation be- tween the inflections for the neutraliza- tion of sulfuric acid, Figure 2, becomes more poorly defined. However, a sol- vent containing as much as 20y0 water yields titration curves which are suitable for analytical purposes. It was found

that more acid is titrated between the first and second inflection points than between the second and third inflections, confirming Cundiff and Markunas’ (4) findings. Since the method is de- signed for samples containing less than 10% sodium sulfate, the error in the determinations is relatively small.

To determine the accuracy of the titration procedure a specially prepared and purified C16 a-olefin-derived sodium sulfonate was analyzed with the follow- ing results: carbon, found 58.74Y0, theory 58.85%, purity 99.8%; hydro- gen, found 9.54%, theory 9.57%, purity 99.7%; oxygen, found 14.68y0, theory 14.70%, purity 99.9%; sulfur, found 10.02’%, theory 9.84%, purity 101.8y’. The results obtained by the titration procedure, 0.16y0 sulfate and 99.2% sulfonate, agree very well with those calculated by elemental analysis.

The effect on the analysis of up to 10% sodium sulfate was determined by adding sodium sulfate to a typical a- olefin-derived sodium sulfonate (Table I). The average error was approxi- mately 1% for the sodium sulfonate and approximately 0.3y0 for the sodium sulfate.

Five samples of sulfonic acids of widely varying structure, containing small amounts of sulfuric acid, were analyzed. The results, expressed as total sulfur, were compared with sulfur values obtained by high temperature combustion (Table 11). These results further indicate that the titration is applicable to the analysis of sulfates and sulfonates in the presence of each other.

Typical samples of a-olefin-derived sodium sulfonates, varying in carbon number from Cs through C2,,, were analyzed using the titration procedure, Comparison sulfate values were ob- tained by ASTM-D-1568 (alcohol in- soluble method). The comparison sodium sulfonate results were obtained by ASTM-D-1681 (cationic titration) and, also, by a difference value obtained by subtracting percentages of the

-500

VOLUME OF T l l U A N l

Figure 2. Titration of sulfuric acid in acetone-water mixtures

922 ANALYTICAL CHEMISTRY

KO interferences have been found in the normal production a-olefin-derived sulfonates. Hoivever, any salts which would be converted by the ion exchange resin to acids that would be titrated with either of the hydrogens of sulfuric acid would interfere.

Table 111. Analysis of Typical a-Olefin-Derived Sodium Sulfonates Sulfate, “4

A G 3 X Carbon No. Titration insoluble

C8 3 . 8 4 . 3 C*O 2.6 1 .8

2 . 0 1.8 c14 9 . 5 12.0

7 . 8 8 . 7 7 . 0 7 . 4 5 . 8 6 . 4 4 . 4 4 . 3 2 . 2 1 . 9

ClS 8 . 9 8 . 4 2 . 2 1 . 6 1.1 1 .0

c20 3 . 1 3 . 1 2 . 2 1 . 9 2 . 5 3 . 2

Titration 99.4 94.3

100.2 81.5 !3.8 16.9 87.7 81.6 94.5

Sulfonate, yc ASTAI

19.7

60.7 80.7 79.8 65.4 79.5 87.4 97 0

__.___

D-1681

. . .

Difference method

91.2 94.5 95.3 80.4 85.0 75.6 84.5 80.1 95 ,7

77 .0 86.9 79.6 96.3 96.3 96.7 98.5 . . . 98.1 90.0 81.2 93.3 88.7 72.3 89 .7 88 .8 87.6 9 0 . 5 92.1 96.2 93.7 89.8 95.5 89.7 92.6 94.0 92.0

alcohol insolubles, neutral oils, and water from 100%. Representative re- sults are given in Table 111. For the sodium sulfonate values, the agreement is generally good between the titration and the difference results, while the cationic titration results are scattered. S o sample size dependence was observed with sample sizes varying from 0.3 to 1 gram.

The over-all error of the method appears to be *lye for the sodium sul- fonate a t the 90-100% level and =t0.3Yc for sodium sulfate below the lOy0 level. The standard deviation for the analysis of approximately 70 a-olefin-derived sul- fonate samples was 0.5% for the sodium sulfonate a t the 90 to 1 0 0 ~ o level and 0.1% for the sodium sulfate below the 1OYc level.

LITERATURE CITED

( 1 ) ASTAI Std. D1568, American Society for Te>ting and Materiala, Philadelphia, Pa., 1960.

(2) AST31 Std. 111681, American Society for Testing and Xaterials, Philadelphia, Pa., 1960.

(3) Barr, T., Oliver, J., Stnbbing5, J., J. SOC. Chem. Zncl. 76 , 45 (1948).

(4) Ciindiff, R. H., RIarkunas, D. C., A x ~ L . CHEM. 30. 1447 (1938’1.

(5) Epton, s. R.,’ Trans. Faraday SOC. T’ol. XLIV, Part V, p. 226, April 1948.

(6) Gribova, E. A,, Zavoclsk. Lab. 25 (a), 154 (1961), Anal. Abslr. No. 3812 (1961).

(7) Kiillbom, S. D., Pollard, W. K., Smith, H. F., A x . 1 ~ . CHEM, 37, 1031 (196,i). \ _ _ _ _ ,

(8) Malm.tadt, H. T-., T-asiallo, 1). A.,

(9) ,Reynolds, C. A, , Little, J., Patten- Zbid., 31, 206 (1959).

gill, AI., Zbid., 35, 973 (1963).

CDUIU H. GRIFFIN, JR.’ EDGAR W. ALB \UGH

Giilf Research & Development Co. Pittsburgh, Pa.

Pre3ent address, Philip A. Hunt Chemica! Corp., Wayland Chemical Di- vision, Lincoln, R. I.

A Simple and Accurate Calibration Model for Hyd rogen-Content, Beta-Pa rticle Transmission Gauges

SIR: I n our recent work on the simultaneous use of beta-particle trans- mission and backscatter gauges for the analysis of three-component liquids (2) , we had occasion to examine the calibra- tion models previously used. The original calibration methods used by Smith and Otvos (6) and Jacobs, Lewis, and Piehl (3) and later refined by Rowan (5) are trial-and-error methods based on somewhat arbitrary mathe- matical models. An alternate model is proposed here that does not require a trial-and-error analysis and still gives an adequate fit of the data.

PREVIOUS MODELS

where p is liquid density, wE is the weight fraction of element i in the liquid, S, is the relative absorption cross section of element i, and A, is the atomic weight of element i. To use this calibra- tion model, one assumes that the value of S for hydrogen is unity and then makes experimental measurements on liquids containing only hydrogen and carbon in known amounts. One then assumes various values of S for carbon and does a least-squares analysis of data on Equation 1 for each assumed value of S for carbon. The minimum variance obtained for A dictates the correct value of S for carbon.

Jacobs, Lewis, and Piehl (3) used the

trial-and-error and least-squares method for determining the constants of Equa- tion 3.

PROPOSED MODEL

The calibration model proposed here is

(4) where Z, is the atomic number of ele- ment i.

The reasoning behind this model is that the cross sections for the four major interactions of beta particles with matter are given appro.;imately by p w ,Z , /A, and p w,Z,?/Az \$hen

R = 10Ki -t Kzp Z u , Z , / A l + K3p Z uIZi2 /A

model : beta-particle energy and sample thick- ness are held constant (cf. Ref. 1). It is

calibration model: R = K l p X w , S , / A , + R? (3 ) well known that the transmission of beta Smith and Otvos (6) proposed the

2 particles empirically follows the Beer- Lambert law over a wide range of

where R is the beta-particle tran~-&sion These authors chose to standardize on absorber thicknesses. Our model simply gauge response; Ki, Kz, and K3 are the S value for carbon and choose combines this empirical law for beta constants to be determined by a least- various values of the S value for particle transmission with the ap- squares analysis of data; and A is the hydrogen to best fit Equation 3 in the propriate cross sections for the four total cross section. A is defined by same manner used by Smith and Otvos. major interactions of beta particles.

(2) Rowan (5) described a graphical trial- To obtain a least-squares analysis for

R = K1 + K2A + K3AZ (1)

z and-error method and a combination this model one simply takes the A = ~ X W , S , / A ,

VOL. 38, NO. 7, JUNE 1966 923