ANALYTICAL CHEMISTRY
198 Similar comparisons of the relative polarizabilities, solubilities, and polarizations of the various metal chelates will account for the observed adsorption sequence in every instance except one. The relative Rj value of the iron(II1) chelate is large, although this chelate has the greatest polarizability and one of the greatest polarizations of the group. The solubility of the iron(II1) chelate is, however, five- to sixfold greater than that of any other chelate. The relatively large sollJbility would probably be sufficient to overcome the differenccs in adsorbability of the various metal chelates due to the relatively small differences in polarizabilities and polarizationheentire oil residue in isopropyl alcohol and quantitativrly transfer to the platinum dish, using a medicine dropper. Remove t>hesolvent b>- evaporation on a steam bath. Heat with a Bunsen burner until the contents ignite and burn, theii maintain a t such a temperature that only ash and carbon remain after burning ceases. Ignite over a burner, or in a muffle furnace :It 500" to 550" C., until the osidation of carbon is complete. Cool and add 3 to 4 drops of sulfuric acid (36N). Fume off the sulfuric acid over a burner in a hood. Add another 3 to 4 drops of sulfuric acid ( 3 6 5 ) and again remove the acid by fuming. J\-hen fuming ceases, heat in n muffle furnace a t 800" to 1000" ('. t o constant weight. Cool the dish in a desiccator after removing from the muffle and prior to weighing. Determination of Deoiled Total Solids. Measure the volume of the oil-free alcohol solution of inorganic salts and sodium sulfonates and pipet a 25-ml. aliquot into a tared 150-ml. beaker, evaporate to dryness on a steam bath, and dry in an atmospheric oven a,t, 120" C. for 8 hours. If alkyl sulfates are present, add 0.2 ml. of 0.1N sodium carbonate solution to the aliquot and dry in an oven a t 75' C. Cool the dry residue in a desiccator after removing from the oven and prior t o weighing. Determine the water content of the residue, using the major amount of the residue.
199
Separation of Sodium Sulfonates and Carboxylates from Inorganic Salts. Add 65 ml. of isopropyl alcohol to the mixing cylinder and warm in a water bath a t 40' to 50' C. Add 18 grams of anhydrous sodium carbonate per 100 ml. of alcohol solution remaining in the mixing cylinder. Admit only a few grains to the mixing cylinder a t first and allow the dissolved petroleum ether to evaporate slowly. When danger of boiling is past, add the remainder of the carbonate and shake the misture vigorously. Allow to stand for a few minutes and repeat the shaking. Allow the phases to separate, swirling the solution to dislodge any solid particles clinging to the upper part of the mixing cylinder. Replace the mixing cylinder in the water bath a t 40' to 50' C. until separation into two layers is complete. Cool the mixing cylinder to room temperature ( 3 to 4 hours) and measure the volume of the alcohol phase. Determination of Sodium Sulfonates and Carboxylates. Pipet a 76-ml. aliquot of the alcohol phase into a tared 250-ml. beaker and evaporate it to dryness on a steam bath. Dry for 8 hours in an atmospheric oven a t 120" C. If sodium alkyl sulfates are present, add 10-ml. portions of water and evaporate to dryness several times to remove alcohol and dry in an oven a t 75' C. Cool the residue in a desiccator after removing from the oven and prior t o weighing. Determine the water content of the residue using approximately one third of the residue. Determination of Sodium Carboxylates. Weigh a portion of the sodium sulfonates and carboxylates residue into a beaker; dissolve in a 100-ml. portion of water and transfer the solution quantitatively to a 500-ml. separatory funnel. Wash out, the beaker with two 75-ml. portions of water and add the washings to the funnel. Add 50 ml. of 12N hydrochloric acid to the funnel and shake vigorously. Allow the solution to cool and then estract the liberated acids with two 100-ml. portions of ethyl ether. Combine the ether estracts in a 500-ml. separatory funnel. Wash the combined ether extracts unt,il free of strong acid by shaking with two or more 50-ml. portions of aqueous sodium sulfate (20%) containing methyl orange indicator. Discard the salt washings. Drain off as much water as possible from the washed ether estract. Lay the separatory funnel on its side and introduce about 10 grams of anhydrous sodium sulfate. Shake the mist'ure vigorously for 3 to 4 minutes, venting frequently. Filter the ether solution, using a small plug of cotton in the vortex of a filter funnel, into a 250-ml. Erlenmeyer flask. Rinse the funnel and filter with 20 ml. of ethyl ether, add the rinsings to the main ether solution, and remove all the ether by evaporation on a steam bath. Determine the acid content of the residue as follows: .\dd 4 or 5 drops of phenolphthalein indicator and 50 ml. of 50y0 isopropyl alcohol, previously neutralized. Warm if necessary to dissolve the sample and titrate with ptandard 0.l.Y sodium hydroxide solution to a definite pink color. Determination of the Average Combining Weight of the Sodium Sulfonates. Weigh approximately one third of the drird sodium sulfonates and carbosylates rcsidue into a tared, ignited platinuni dish. Ignite and ash the contents of the dish using the procedure given earlier. Determination of Inorganic Salt Contaminants in the Deoiled, CARBOSATE:. Desalted Alcoholic Sulfonate Solution. SODIUM Pipet 25 ml. of the deoiled, desalted alcoholic sulfonate solution into a 150-ml. beaker containing 50 ml. of distilled water and a few drops of phenolphthalein indicat,or. Heat to a gentle boil and titrate x i t h standard 0 . 1 S sulfuric acid to the disappearance of the pink color. Repeat until the pink color fails to return on additional boiling. SODIVM CHLORIDE. If sodium chloride is present in the original sample, determine the sodium chloride content of a 25-ml. aliquot of the isopropyl alcohol solution by amperometric titration ( 1 9 ) or, with somewhat lowered accuracy, by the Volhard method. Determination of the Water Content of the Sample. Determine the water content of dried detergent samples by the Fischer method. Introduce 10 ml. of anhydrous methanol and 10 ml. of anhydrous pyridine into a clean 100-ml. volumetric flask, avoiding wetting the neck of the flask. Titrate with Fischer reagent until the straw-yellow color changes to an orange-red which remains after shaking the stoppered flask; view the color by transmitted light. Avoid wetting the neck of the flask when shaking. Weigh the stoppered flask to the nearest centigram and then insert a piece of paper, rolled into a tube, part-way down the neck of the flask and add 2 to 3 grams of sample. Remove the paper and reweigh the stoppered flask. Titrate with Fischer reagent to the orange-red color of a reference blank. I n Figure 1 is presented a diagram of the entire procedure for the analysis of sodium alkyl aryl sulfonate detergents.
ANALYTICAL CHEMISTRY
200
SODIUM SULFONATE. SODNY CARBOXYLATE. MOROANIC SALTS. FREE ALKALI. AND WATER
I I Suspend sample In
isopropyl alcohol-rater
I
IC
I
water
Neutralire
I'
Extract w i t h ptmlcum ether
I
I
PETROLEUM ETHER PHASE
ALCOHOL PHASE
NEUTRAL OIL. TRACE O F SODIUM SULFONATE
,Combme
I
-
SODIUM SULFONATE. SODIUM CARBOXYLATE. ISORGANIC SALTS
I
I
Wash with 50 per cent (by volume) isopropyl alcohol
I
Measure volume ( 0 )
1 ,
I
-ALCOHOL PHASE
Alrqvot
REMAINDER
I
PETROLEUM ETHER PHASE
Add isopropyl ilcohol
I
I
~~~~~
zzEciTE,
+
I
I I I Measure volume (H)
I
RESIDUE (D): MINERAL OIL. TRACE SODIUl JLFONATE
A L C O H ~ LPHASE
AQUEOUS PHASE
I
r'
Discard
.
Correctlo"
I
Ash
I
RESIDUE (SI): SODIUM SULFONATE. SODIUM CARBOXYLATE, INORGANIC SALTS, WATER
Saturate with (anhydrous) Na,CO,
Filler. evaporate lo
I
Evaporate to dryness
AND FREE ALKALI OR ACID CONTENT
Allquol
I
Evaporate to dryness SO1
H
SUI
TE
I
RESIDUE (Sz) SODIUM SULFONATE. SODlU M CARBOXYLATE , TRACE O F INORGANIC SALTS WATER I
Portlo"
I
D i s s o l v e portion in water. treat with HCI IIZNI. exlracl wtEh ethyl ether
I
ETHER PHASE
SULFONIC ACID
AQUEOUS PHASE
I
D1sc8rd
CARBOXYLIC ACID
i Portion
I
RESIDUE IS,) SODIUM SULFONATE. SODIUM CARBOXYLATE. TRACE OF INORGANIC SALTS, WATER
.Cor,
ion
RESIDUE:. SODIUM SULFONATE. CARBOXYLIC ACID
SUI
Ll*.
Ash M
I
Dlsrolve In 50 p r cent alcohol. ncutrallr to phenolphthalein
I WATER
NEUTRAL OIL
SODIUM CARBOXYLATE
SODNY SULFONATE
COMBINING WEIGHT O F SODIUM SULFONATE
INORGANIC SALTS
Figure 1. Outline of method of analysis of sodium alkyl aryl sulfonate detergents
FREE ALKALI
OR ACID
V O L U M E 27, NO. 2, F E B R U A R Y 1 9 5 5
20 1
C A LCU LATIOVS
Free acidity as sulfuric acid:
-
(100 V) Dry weight of So residue = (SZ) _ _ (100)
~ (1)
(10)
Sodium carboxylate content:
Weight of sodium wlfonate in SI arid S3 residues: T V = (0.053) ( S )(0)
+ (0.0585) ( R ) + F.298) ( K ) ( L )( 8 2 ) (3) ( J )
S2 (corrected) = [So (dry)] S3 (corrected)
=
+
0.0011
- 3 (W)
(-3- 8 ) [S2 (corrected)] (82)
(4)
Omit the term of +0.02 in Equation 5 unless sodium carbonate solution was added to stabilize sodium alkyl sulfates. Average combining weight of sodium sulfonates:
[S3(corrected)] .y = (71) ill (corrected)
-
Sodium sulfonate content, per cent, = ( 1 0 0 ) [ S 2(corrected)]
[
(‘41
Basicity as sodium hydroxide: (9)
Table I.
SI (dry) =
(3)
Omit the term (+0.0011) in Equation 2 unless sodium carbona t e solution was added to stabilize sodium alkyl sulfates. The factors (0.053), (0.0585), and (0.298) in Equation 2 are the weights in grams per milliequivalent of sodium carbonate, sodium chloride, and sodium carboxylate, respectively. The last factor is an assumed value and when known the accurate value should he u-etl. The numbei 3 in the denominator is an aliquot factor. Corrwted sulfate aqh:
Seutral oil content, per cent, = [ ___ “ 0 ; 3
Inorganic salts:
(2)
(SI) (100
-
V)
(100)
Inorganic salt content, per cent, = [(loo) j?)(dry)l
];[I
-
Nomenclature = weight of original sample taken for analysis, grams = volume of sulfuric acid or sodium hydroxide required t o neutralize free alkali or acid, milliliters C = sodium hydroxide or sulfuric acid solution, -1D = weight of oil residue, grams E = weight of oil residue taken for ashing, grams F = weight of sodium sulfate ash from oil residue, grains G = volume of alcoholic deoiled salt and sulfonate solution, milliliters H = volume of salted-out alcohol layer, milliliters J = weight of portion of sodium sulfonate and carbo\vlate residue taken for carboxylate determination, grams K = volume of sodium hvdroxide required to neutralize the carboxylic acids, milliliters L = sodium hydroxide used to neutralize the carboxylic acids, N .If = weight of sulfate ash from deoiled, desalted sulfonate and carboxylate residue taken for combining weight determination, grams S = volume of sulfuric acid required to neutralize sodium carbonate contaminants, milliliters 0 = sulfuric acid used to neutralize sodium carbonate contaminants, S R = milliequivalents of chloride determined in 25 ml. of the salted-out alcohol phase S I = weight of residue from determination of deoiled total solids, grams 82 = weight of residue from determination of sodium sulfonates and sodium carboxylates, grams Ss = weight of deoiled, desalted sodium sulfonate and sodium carboxylate residue taken for determination of combining weight of the sodium sulfonates, grams U = water content of SIresidue, per cent
A B
Results Obtained in the Analysis of Unbuilt Sodium Alkyl . h y l Sulfonate Detergents Sodium Dodecyltoluene Sulfonate Detergent
Sodium Dodecylbenzene Sulfonate Detergents Sample 2 Analyst h Analyst B Saniple 3
Sample 1 Determination 0.7 0.7 1.9 2.3 1.5 1.j 1.4 3.2 3.2 S e u t r a l oil. wt. ?& 37.8 38.2 33.6 33.2 36.8 36.9 36.8 95.2 93.7 Sodium sulfonate, wt. % 59.9 59.5 63.9 63.3 59.8 59.9 59.1 0.1 0.1 Inorganic salts. wt. % 0.4 0.3 0.4 0.5 ... ... . . , 0.1 0.1 Sodium carboxylate, w t , % ... ... ... . 0.05 0.00 0.1 Acidity (as %Sod.w t . %m Basicity (as N a O H ) . wt. ,o 0 . 0 0 3 0.005 0.06 0.06 .. . .., ... F-arious .Added Inorganic Salt Builders (The inorganic salts were added to 9.0-gram portions of a n unbuilt sodium C r t o l u e n e sulfonate drtergent (357, sodium sulfonate) and t h e niiature m a p analyzed) _______ Inorganic Salt Builder Inorganic Salt Builder .4nioun t Found in Deoiled added, Cesalted Sulfonate 8. Soln., e . Formula Na6PIOLa 1 j8 0.0032 NazIIPO; 2 26 0.0081 Nad'zO, 2 23 0.0080 SasPaOla 2 2; 0.0041 SazBdO; 0 84 0.0009 KaBOa 0.57 0.0013
203 builders listed in Table IV or by sodium silicates, which distributed into the sulfonate phase. INORGANIC SALT. The applicability of the method to the determination of the inorganic salt content of a built detergent depends upon total solids content, which involves heating a t 120" C. for 8 hours. The builder need not necessarily be soluble in the water-isopropyl alcohol mivture used for dissolving the sample, since such samples can be analyzed by deoiling a separate portion and obtaining a total solids value on the entire raffinate, containing undissolved builder. Sodium bicarbonate decomposes on being heated; consequently, this salt should be converted to sodium sulfate, prior to a determination of total solids, by titration to a permanent phenolphthalein end point in boiling aqueous-alcoholic solution. Sodium perborate also decomposes on being heated (to give sodium borate); consequently, a separate determination of perborate in the original sample and in the total solids residue should be made and a correction applied for the decomposition of the perborate. The phosphates and the silicates are stable. BASICITYOR ACIDITY. The inorganic salt builders under consideration are all basic to phenolphthalein, in aqueous or alcohol solution. Titration of these materials to the phenolphthalein end point would give an erroneous apparent sodium hydroxide content and the use of such a value would cause an error in the subsequent calculation of the inorganic salt content. Consequentlj-, if a basic inorganic salt is present, it is preferable to omit the initial neutralization of the sample. WATER. Bryant and his co-workers ( 7 ) found that water combined with several inorganic phosphates could be determined accurately by the Fischer method and it does not appear likely that any of the inorganic phosphate builders used in commercial detergents \\-auld interfere. However, sodium tetraborate and sodium perborate interfere in the direct determination of water by the Fischer method (21, 22). The correction factors for these salts are 7 and 3 moles of water per mole of salt, respectively. APPLICATI~X TO COMIIERCIAL DETERGESTS. Results obtained with several typical commercial sodium alkyl aryl sulfonate detergents which contain inorganic salt builders are given in Table V. The inorganic constituents were determined by conventional analytical methods. The values obtained for combining weight of the sodium sulfonate were those expected from products prepared from commercial Cl*-C1, benzene alkylates. These materials were found free of alkyl sulfates by the application of the acid hydrolysis method (IO).
Table V. Results Obtained in Analysis of Commercial Sodium Alkyl .4ry1 Sulfonate Detergents Containing Inorganic Salt Builders Determination S e u t r a l oil, wt. 70 Sodium sulfonate, wt. pc Inoreanic salts. wt 5% Sodium carboxylate, ivt. 5 Aciditv (as HrSOd). -,. wt. % " Water; +t. %Combining wt. of sodium sulfonate, grams per equiv. Inorganic constituents, wt. R Phosphorus, calcd. as NanPaOln Silica, calcd. a s IlazSiaOi Sulfate, calcd. a s S-azS01
.4
B
1.0 18.0 75.7 0.6
0.5, 0.9 29.4.29.8 66.4. 66.5
..
C
D 1.2 32.8 29.8 55.5 65.4 0.2 _. i.0 11.4 2 . 3 1 5
5.8
Q : 2 . by2 2.5,' 2 . 6
355
355, 3513
352
5.4
34.8 5.4 4.5 14.7,14.9 Sir5
4t:. 5
5.0 14.5
58:9
351
Analysis of Detergents Containing Organic Additives. SoIn the analysis of commerCARBOXYMETHYLCELLT-LOSE. cial sulfonate detergents, any sodium carboxymethylcellulose present remains as a suspension during the neutralization and extraction procedures. During separation of the sodium sulfonate from inorganic salt, the sodium carboxymethylcellulose appears as an interfacial cuff. Since the amount present is DIUM
ANALYTICAL CHEMISTRY
204
usually small (1 to 2%), i t does not interfere in the measurement of the volume of the alcohol phase or in the determination of sulfonate content or combining weight. T o test the analytical behavior of this material, samples were prepared having an exaggeratedly high content (10%) of technical sodium carboxymethylcellulose and the mixture was analyzed by the method. Because of the large amount of suspended material present, the deoiled solution was centrifuged t o remove the bulk of the sodium carboxymethylcellulose. As is shown in Table VI, close agreement was found b e t m e n the deterniined and known values for neutral oil, sodium sulfonate content, and combining weight. Table VI. Results Obtained in the Analysis of a 3Iixture of Sodium Carboxymethylcellulose and a Sulfonate Detergent Determination Sodium carboxyrrletlrylrcll~ilose *
S e u t r a l oil Sodium sulfonate Combining wt. of sodium sulfonnta. grams per equiv. As teclinical material.
Content, W t . yo --_________ Known Found 11.3a S o t determined 1o.oa 1.4 1 J 1.4 1 7 32.7 32.2 33.2 32.7 340 340
342 344
Table VII.
Results Obtained in the .4nalysis of Sodium Alkanesulfates Sodium 1-Decylsulfonate
Sodium 1-Dodecylsulfonate
Determination Pu'eutral oil, wt. 70 1.0 0.5 Sodium sulfonate, wt. yo 98.3 99.0 Inorganic salts, wt. Yo 0.5 0.4 0.01 0.01 Acidity (as H%SOa),wt. % Water, wt. 7G 0.9 0.8 Total, w t . % 100.7 100.7 Combining wt. of spdiuin sulfonate, grams per equiv. Theor. 244 272 Det. 246 274 Organic material in separated a(i. phase, calcd. as sodium sulfonate, as wt. % of orig. samplea 0.18 0.27 NazCOa content of desalted ale. phase, expressed as wt. "lo of total solid in alc. phase 0.62 0.49 a Calculated from carbon content of aqueous phase, determined by wet oxidation after removal of alcohol and carbonate.
applicable to the analysis of sodium alkyl sulfate detergents, provided certain precautions are taken to ensure the stability of the alkyl sulfate during the drying periods. It is not possible to dry the sodium alkyl sulfate residues a t 120' C., as they decompoee a t this temperature, turning brown and becoming acidic. The decomposition has been prevented by drying a t a lower temperature and by maintaining basic conditions during the heating period, since the decomposition of alkyl sulfates is acid-catalyzed. Several alkyl sulfate detergents, ranging from CIOt o C1,, were analyzed employing these modifications. The analytical data obtained are given in Table VIII. Apparently satisfactory values were obtained in all determinations. Total values were generally close to 100%. The combining weight values were in (,lose agreement with the theoretical values, indicating the stabilitv of the sodium alkyl sulfates during the drying period. Combining weight was determined on the alkyl sulfate fractions both by the conventional ashing procedure and by acid hydrolysis (IO). In this latter procedure the sulfuric acid liberated by hydrolysis I S measured by titration with base and is a measure of the sulfate ester originally present. In the neutral oil determination, only some 0.1% of sodium alkyl sulfates was removed by the petroleum ether extraction. This is qomewhat less than that found with the sodium alkyl
ON ON IONIC DETERGENTS. I n an attempt to apply the method to a sodium alkyl aryl sulfonate detergent containing an added nonionic detergent, Renex (a commercial nonionic detergent reported to consist of a mixture of polyethylene glycol esters of fatty and rosin acids), it was found that the nonionic detergent accompanied the sodium alkyl aryl sulfonate in the procedures; the two were found together in the deoiled desalted alcohol solution which normally contains only the sulfonate. The mixture of the two materials was separated by passing it, in aqueousalcohol solution, through a cation exchange resin (Dowex 50 in the acid form) and an anion exchange resin (-4mberlite IR-4B) in turn. The nonionic detergent isolated by this procedure contained less than 1% of sulfonate as determined by the methylene blue-cetyl pyridinium bromide method (8). The recovery of nonionic detergent was nearly complete. It was found possible to desorb the sulfonate adsorbed on the anion exchange resin by use of a 2% solution of sodium hpdrouide in R 1 to 1 isopropyl alcohol-water mixture; a 96y0 recovery of sulfonate wa3 01)tained. Analysis of Sodium AlkaneTable VIII. Results Obtained in the .4nalysis of Sodium iilkyl Sulfate Detergents sulfonate Detergents. Several Commercial Sodium-TiSodium-n- Sodium Alkyl Sodium-nSodium-n- Sodium Sodium members of this class of surDecyl-1Cetyl Stearyl Dodecyl-2- Tetradecyl- OctadecylSulfate face active material have been 2-sulfate Detergent Sulfate 2-sulfate Sulfate Sulfate sulfate examined, t,he analytical data Determination 2.7 2.6, 2.6 1.1 1.0 1.7 Neutral oil, wt. % 0.1 1.0 obtained being given in Table Sodium alkyl sulfate, 9 8 , 4 3 7.3, 38.0 9 9 . 2 98.2 9 9 . 3 9 8 . 9 9 8 . 6 wt % VII. These compounds had 0.7
