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THE ANALYSIS OF SYNTHETIC DETERGENTS 513
THE ANALYSIS OF SYNTHETIC DETERGENTS
W. B. SMITH*
A lecturedelivered efore he Societyon 15th May 1963.
The subject is introduced with a classification o• surface active agents
that are used in all types o• detergents. This is •ollowed by a review o• the
older qualitative tests and then an outline o• a new l•aper chromatographic
l•rocedure. Quantitative analysis, confined to the determination o• the active
constituents, is described under headings o• solvent extraction, colorimetric
determination, anionic-cationic titration, and miscellaneous methods.
THE WORDdetergentnowadayssuggestshe packet of spray-driedpowder
used for domesticwash'rag urposes, ut liquid productsused n the same
field may alsocome o mind. For the purposes f this paperother cleansing
materials,namely shampoos nd toothpastes,will be regardedas detergents;
soap s excludedas not failing within the definition of synthetic. However,
onlythe organicsurface ctive ngredientsof the detergentswill be considered.
Most surfaceactive agentswhich are used as detergentshave molecules
which are essentiallyinear and containat one end groupshaving an affinity
for water (hydrophilicgroups),and at the other end groupswhich are anti-
pathic to water (hydrophobicgroups). Surface active agents are classed
according o whether the active speciess an anton, a cation, a non-ionizing
groupor an ampholyticgroup. An ampholyticgroup s one which may act
as either anionicor cationicdepending n the circumstances,rincipallyoa
the pH value of the solution. Hydrophobicgroupsmay be classed nder
the headingsof carboxylicacids (mainly naturally occurringacids),alcohols,
hydrocarbons mainly synthetichydrocarbons erived from petroleum),and
others polyoxy propylene hains). Between he hydrophilicand the hydro-
phobicgroup, the moleculemay conta'ma linking group which may be an
ether, ester, or amide. The listing and classification f possiblestructural
groups s an essentialprerequisite o the construction f a schemeof quali-
tative analysis,and we still find the classificationdrawn up five years ago
to be a usefulstarting po'mt. The best systematicprocedure s to identify
first the hydrophilicgroup, hen the linking group, f any, and lastly the
hydrophobicgroup.
QUALITATIVEANALYSIS
Hydrophilicgroups
One of the best tests for anionic and cationic active compoundss tc•
*Marchon Products, Ltd., Whitehaven, Cumberland.
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514 JOURNAL OF THE SOCIETY OF COSMETICCHEMISTS
treat the substancewith a coloured eagent of the opposite onogenic ype
and shake he aqueousmixture with a non-polar iquid such as chloroform.
The reagentshouldbe such hat its saltswith inorganic onsare not extracted
by the solvent,but its salts with surfaceactive agents,containinga hydro-
phobicgroup n eachmolecule,will be readily extracted; the appearance f
the colouredmolecule n the organic ayer will show he presence f a surface
active agent.
The usualreagent for anionicsurfactants s methyleneblue, but this can
be used only in acid solution and cannot therefore detect the carboxylate
group. Dimidium bromide can be usedover a wide rangeof pH valuesand
can therefore be used for carboxylate groups as well as sulphate and sul-
phonate. For cationic surfactants,a wide range of dyes and indicators
containing he su phonategroup is available and bromophenolblue seems
to be most commonlyused.
An alternative procedure or detectinganionicor cationicsurfactants s
to test whether the substancewill discharge he colour producedwith a
known surfactant of opposite ype and an appropriate reagent. To test
for an anionic surfactant, an aqueousalkaline solution of bromophenolblue
plus a trace of a cationicsurfactant s shakenwith chloroform,and then the
sample is added and the mixture again shaken. To test for a cationic
surfactant, the material is added to acid methyleneblue plus a trace of
dodecylbenzeneulphonate lus chloroform. A compoundwhich discharges
the colour of the chloroform ayers in both anionic and cationic tests is an
ampho yticsurfactant.
Most non-ionicdetergentsare of the polyethanoxy ype and these will
combine with large anions, such as ferrocyanide, cobaltothiocyanate,
molybdophosphate,giving precipitates with the cations present, barium
being needed n the case of the last. Another test for ethanoxy groups s
due to Rosen and consistsof heating with phosphoricacid and testing for
acetaldehyde. The polyhydric alcohol type of non-ionic surfactant also
reacts with large anions; complex odidesare often used, but hexanitrato-
cerate is a simpler though lessspecific eagent.
Linking groups
The linking group is best investigatedby studying the stability of the
molecule owards acid and alkaline hydrolysis. In the caseof an anionic
surfactant, aliquot parts of a solution are assayed by a colorimetric or
titrimetric method (a) without hydrolysis, b) after refluxing n N alkali for
30 minutes, and (c) after refluxing n 2N sulphuricor hydrochloricacid for
2 hours. The sulphate group itself is essentially stable to alkali and is
hydrolyzed in acid solution, esters are completelyhydrolyzed in both acid
and alkaline solutions,while amidesare partly hydrolyzed n both media,
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THE ANALYSIS OF SYNTHETIC DETERGENTS 515
the extent being characteristic f the particular am/de. If the sample s a
sulphate,or is a non-ioniccompound, hen more specific ests for the ester
and amide inks are needed. The hydroxamic est for esters s very useful ,
while amides can be detected through the primary or secondaryamine
producedon hydrolysis.
Hydrophobic roups
The hydrophobicgroupsare examinedafter hydrolysisof the surfactant:
mild alkaline hydrolysis is sufficient for carboxylic esters, moderate acid
hydrolysis or sulphateswithout a linking group, prolongedacid hydrolysis
for amides, hydrolysiswith hydriodic or hydrobromic acid for ethers, and
hydrolysiswith concentratedphosphoricacid for sulphonateswithout a
linking group. The liberated acid or alcoholmay be analyzed or acid value
or hydroxylvalue,but a muchmoreuseful echniques gaschromatography,
which is applicable to hydrocarbonsalso. Aromatic rings and ethylene
bondsmay be detectedwithout hydrolysis;ultra-violet spectroscopys most
useful or the formerwhilst otherphysicalmethods uchas nfra-redspectro-
photometryand massspectraanalysismay also be used.
PAPER CHROMATOGRAPHY
This technique s one of qualitative analysis,but it is usefu ]ydiscussed
under a separateheading. Over the past few years we have developeda
comprehensivecheme f identificationof detergentcomponents singpaper
chromatography. Tolueneand xy enesulphonates, rea, and alkano arnines
or metals used for neutralization are tested for in addition to the main
surfactants hichareexamined n respect f their hydrophilicgroups,inking
groupsand hydrophobic roups. Full detailshave recentlybeen given by
Drewry5 and, therefore, he presentpaperwill be restricted o a brief outline
of the schemeand an account of the developments hat have been made
since he former paper was written.
Paper chromatographys essentiallya separationby partition between
the stationarywater and movingorganicsolvents, nd the first requirement
is an optimum rdtia water contentof the paper. In our laboratory it has
been found that washing he paper (Whatman No. 1) in 50% ethanol, and
allowing t to dry in the air is sufficient. In other laboratories t may be
necessary o experiment with different drying conditions.
Initially, a large number of solventswas tried, but a mixture based on
tertiary butanol was the only one that gave a uniform development n the
presence f surfaceactive components. Later it was found that an ethyl
acetate mixture as describedby Gaspari• et al6 gave equivalent results o
the butanol solvent, hough n a development ime of only 2-3 hours nstead
of 15-20 hours. The solvent also contains a little ammonia and methanol.
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THE ANALYSIS OF SYNTHETIC DETERGENTS 517
made from the publishedprocedure s the rather obvioussimplificationof
using one marker solutioncontainingall the referencecompounds.
Another method of identifying amides, applicableboth to the nonionic
alkanolamidesusedas additives and to amide sulphonates nd carboxylates
used as the main anionic surfactants, s to apply paper chromatography
after acid hydrolysis. The aidehydenitroprussidespray is the most useful
as it distinguishes rimary amines such as monoethanolamine nd taurine
(khaki spots) rom secondary minessuchas diethanolamine,N-methyltaur-
ine and sarcosinebluespots), ll liberatedby hydrolysis f the corresponding
fatty acid amide.
•)UANTITATIVEANALYSISBY SOLVENT XTRACTIONS
The most reliable technique of analysing mixtures of surfactants s a
seriesof extractions,with solventsand ion-exchange esins,before and after
hydrolysis, o separate the individual fractions which are then weighed.
Each fractioncan, f desired, e characterized y further analysisncluding
physicalmethodssuchas gas chromatography. A seriesof separations an
be assembledn a variety of ways and therefore t seemsbest here to discuss
the subject under sub-headings f the solvents. The general method for
liquid-liquid extractions is to use stopperedseparating funnels, and for
liquid-solid extractions s simple stirring in a beaker or centrifuge tube,
followed by filtration or centrifuging.
Light petroleum
Typical procedures or petroleum extraction are described n the B.P.
and U.S.P. monographsor sodium auryl sulphate. The sample s dissolved
in 50% ethanol, for the unsulphated alcohol is less soluble n this than in
an aqueous olutionof the sample (owing o reducedmiceilar effects)and
emulsification ifficultiesare fewer. Three extractionswith petroleum are
made. The combined extracts are dried, the solvent is distilled off and the
residue s weighed. A certain proportion of free lauryl alcohol remains
solubilized n the surfactant solution, as is shown by tests on synthetic
mixtures, even after 5 or 10 extractions. The loss dependson the con-
centrationof surfactants nd, for reproducibleesults, he latter is arbitrarily
fixed at about 5% w/v. Besides he questionof completenessf extraction
there are severalother difficulties n arriving at a standard method of high
reproducibility. Washing the petroleumextracts is always liable to cause
losses, nd thesemust be balancedagainst he errorsdue to contaminants.
Drying the extracts with sodium sulphate or another desiccantmay lead
to a loss,but omission f the drying step may cause osses y volatilisation
in steam. Removal of the solvent without loss of volatile alcohol is also a
problemand, finally, errorsassociatedwith weighing he residue n a large
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518 JOURNALOF THE SOCIETY OF COSMETICCHEMISTS
glass lask,namely,adsorption f moistureon the glass, lectrostatic harges,
and buoyancy errors, can all be significant.
Other uses of light petroleum as an extractant are to separate unsul-
phonatedoil from alky ar¾1sulphonates,nd to extract fatty acids iberated
by acidificationof soapsolutions. The solvent s alsoused o extract acids
and alcohols iberated by the hydrolysis of amides and esters .
Ethyl ether
Ethyl ether extracts he samecompounds s ight petroleum,and several
others too, particularly alkanolamides. Being a singlecompoundof low
boilingpoint it can be distilled rom the extract with lessuncertainty han
attends the removal of light petroleum, a•d for this reason t is preferred
in such determinationsas the total fatty alcohol n alkyl sulphates. Dis-
advantagesof ethyl ether are its higher solubility for water and for hydro-
chloric acid. It can only be used with dilute aqueousethanolicsolutions
and is thereforenot very satisfactory or extractingalcohols nd acids from
solutionsof sulphonates s a moderate ethanol content s needed o reduce
miceliar effects. Ethyl ether will extract hydroxy-acids which light
petroleum will not.
Ethyl ether will also extract alkylarylsulphonic cids from 2N hydro-
chloric acid, and this is useful for separating hese acids rom toluene- and
xylene sulphonates.
Accurate quantitative determinationsare limited by the same actors as
describedor light petroleum,and thesealsoapply in varying degree o the
other solvents below.
Chloroform
This solventwill extract most ethylene oxide derivatives, ncluding hose
with chains of six or more units which are not extracted with ethyl ether.
It will also extract alkylarylsulphonates, nd many other surfactants, rom
neutral solutions. One disadvantageof chloroform s that any ethanol in
the aqueoussolution must first be expelled, and even in the absenceof
ethanol, emulsification is often troublesome.
Alcohol
Extraction with ethanol is used to determine the total organic content
of built detergents, nd by separatelydeterminingunsulphonatedmatter,
additive, chloride, etc. the surfactant content can be found. To ensure ex-
traction of small quantitiesof active material containedwithin the beadsof
spray-driedpowders, t is necessaryo take the residueafter a few extrac-
tions, dissolvet in a smallquantity of water, and reprecipitatewith alcohol.
As ethanol is miscible with water it is clear that extraction from a solid
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THE ANALYSIS OF SYNTHETIC DETERGENTS 519
is the only suitable technique. However, butanol and higher molecular
weight alcoholsare immisciblewith water, while isopropanols immiscible
with a concentrated aqueoussolution of sodium carbonate, and these can
be used in liquid-liquid extractions.
Ion-exchange esins
The use of ion-exchangeresins differs from the solvent extraction
techniques, ut it is usefullyconsideredwith them as, alongwith extractions,
it can be built into a compositeanalytical schemeof separations. Ion-
exchangeesinsprovide he only simplemeansof separating nionic,cationic,
and non-ionicsurfactants. Though simple n principle, he practical use of
ion-exchange esinswith surface-active olutions nvolvesseveralcomplicat-
ing factors such as the polarity of the solvent, usually an aqueousalcoholic
medium, the swellingand shrinkingof the resin, and hydrolysisof the sur-
factant on the resin or during elution. A great deal of work on the subject
has been done by P. Voogt, amongothers,but only a little of this has yet
been published '•ø.
Comprehensivecheme f analysis
The number of combinations f different surfactants hat may be present
in a commercial detergent is infinite, and no efficient general scheme of
separationcan be drawn up; the method of analysismust be chosen o deal
with the particular types of ingredientknown or expected o be present.
One decision o be made in dealing with several componentss whether to
extract them one at a time by the successivepplicationof specificechniques
or whether o proceed y divisionand sub-division, .g.with six components,
first separate wo or three from the others, hen proceedseparatelywith each
group. The latter technique is more complicated, but errors are smaller.
Another decision s whether to separate each component n a reasonably
pure form, or whether to extract two more more ingredients together and
deduce he contents y difference. The caseof a simpledetergentcontaining
free oil, ethanolamide,and alkylarylsulphonate,ogetherwith inorganicsalts
and water may be taken as au example. Scheme is to extract the free
oil with light petroleum from a 50% aqueousethanolic solution of the
sample,then the alkanolamidewith ethyl ether after dilution to 20-30%
ethanol, and finally the alkylarylsulphonatewith chloroform from the
residual aqueous solution, or with ethanol from a dried residue. Scheme
2 is to extract the first two components ogether, using ethyl ether, then
separate hese ater and to extract the alkylarylsulphonate rom the aqueous
layer. Scheme$ involves extraction of free oil with light petroleum,
free oil plus a kanolamidewith ethyl ether, and the total of the organic
compounds with ethanol, all on separate samples and the individual
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522 JOURNALOF THE SOCIETYOF COSMETIC HEMISTS
is importantand showshe reasons hy end-pointsb) and (d), at which
most of the indicator s in the aqueous haseand nearly all the surfactant
in the organicphase,are unsatisfactory ith commercialmatehals. End-
point (a) is rarely usedbecauset givesno warningof its approach. It also
has the disadvantagehat trace mpurities n the indicator,particularlyof
the oxidationproducts n methyleneblue, may impart a bluishcolour o
the aqueous ayer well before the end-point. The same impurities also
interfere n end-point e) and from our experiencewe recommendhe use
of this end-pointonly with the artionic ndicatorswhich are purer and more
stable han the cationic nes. This eaves nd-pointsc) and (f) as the best
for cationic indicatorssuch as methylene blue.
It might be mentionedat this point that methyleneblue seems o be
practically the only cationic indicator that is used for the titration and
despite he limitations t seems o be preferred o anionic ndicators n most
commercialanalytical laboratories n the U.K. and abroad. A wide choice
of artionicndicators f the sulphonphthalein,ulphonic cid,and fluorescein
classess available,but the vast majority of workersappear o follow closely
the techniqueof the early workers,Barr, Oliver, and Stubbins,and to use
bromophenolblue.
Standardisation
At the end of the titration in cases a) and (e) the wholeof the indicator
is in combination with surfactant, and a blank correction,which is constant,
calcu ab e, eproducible nd readily determined,must be applied. In cases
(c) and (f) only part of the indicator remains combinedwith surfactant and
the necessary orrectiondependsupon the proportion nvolved, and this
dependsn turn upon he relative volumesof aqueous nd chloroformayers.
Experimental determinations of the blank or of a correction factor have
been describedby severalwriters, but for routine analysis t is sufficient
to standardise he titrant under similar conditions o thoseof a determination,
thus eliminating the correction. The standard substancen this approach
must be of a similar composition o that being determined,which means n
many cases hat it must contain a mixture of isomersor of homologues s
do the commercialmaterials, and its composition an therefore only be
established y other analyticalmethods,principallyby extractionor ion-
exchangemethods. For na kyl sulphates,t is possibleo prepare he pure
matehals, and these can be used as standards in this field.
Miscellaneous Factors
After the choiceof indicator, of end-point and of standard,that of the
titrant is the most mportant. Cetyltrimethylammonium hloride nd cety -
pyridiniumbromideseem o be most frequentlyused or anionicdetergents.
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THE ANALYSIS OF SYNTHETIC DETERGENTS
The stearylcompoundsave the disadvantage f lowersolubility,while the
myristylandshorter hainhomologuesay react ncompletely. owever,we
have found hat N-alkyl-N-benzyldimethylammoniumhlorides ive much
sharper nd-pointshan the other wo groups f titrant. The stearylcom-
poundagain s of low solubility,but the lauryl, myristyl and cetyl com-
pounds ll havesimilarperformancesnd there s little to choose mong
themexcept hat the cetylcompound,f owest olubility,s the most eadily
purified by crystallisation.
Regardinghe concentrationf the titrant, many workers ollowEpton
in using itrationsof about 10 ml with .004 or .0053{ itrant, but larger
titrations with more dilute solutions,e.g. around 20 ml or .0013{ as used
by Barr et al normally give more precise esults,and are at least as accurate
if due regard is paid to the blank.
All titration proceduresre equallysuitable or determining nionicor
cationic urfactants,he concentrationf the otherbeingknown,and it is
also mmaterialwhether he solution f unknown oncentrations placed n
the titration vesselor in the burette, although he former is usually he
most convenient.
The singlephase itration
The earliestworkby Hartley and Runnicles seda single-phaseitration
of aniordc nd cationic urfactants,ut the end-pointwith bromophenol
bluewasnot soclearas when he two-phaseechnique asapplied. How-
ever, with fluorescent indicators such as eosin 5 and dichlorotetraiodo-
fluorescein6 the end-pointmay be as sharpas with the two-phasemethod,
and such ndicatorsmay repay urtherstudy. Their main disadvantage
is that large amounts of inorganic salts, and moderate amounts of inactive
organiccompounds,end to obscure he end-point.
OTHER •/[ETHODS OF ASSAY
Methods asedon the formationof an aminesalt with artionic urfactants,
usingan ordinaryprimary amine,have beenused or a long time. One
procedure* uses oluidine as the amine, extracts the salt with carbon tetra-
chloride,and determineshe amine n the extract by additionof ethanol
and itrationwithalkali. A similar rocedureauses enzidinendseparates
the salt by filtration. The salt may be weighed efore itration o givean
indication f the equivalent eight,whichcannotbe determinedy any
volumetric method.
For determiningationic urfactants,everalprecipitantsontaining
large artionsmay be used, and in a review by Chinnickand Lincoln 9,
phosphotungsticcid s recommended. on-ionic urface ctiveagentswith
an ethanoxy hainof suitableength or detergencyanalsobe precipitated
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524 JOURNALOF THE SOCIETY OF COSMETICCHEMISTS
with the heteropoly-acids; hosphomolybdiccid is preferred,as the pre-
cipitate can readily be analysed o determine he surfactant contentwhich
varies with different compounds. Ampholyticsurfactantsof the amino-
carboxylategroup are usually analyzed by the methods employed or
catiordcs,with specialattention to reactions n acid solution. Thoseof the
aminosulphonate roup are analyzed by the methodsused for anionics.
Ampholytics ontaining sulphategroupare subjected o acid hydrolysis
to yield an aminewhich is analyzedas a true cationiccompound.
CONCLUSION
A great deal of work on new methodsof detergentanalysis s being
undertaken n this country and abroad, but most of this falls into two
classes.The first is a thoroughexaminationof the traditional methods n
endearours o draw up national and international standards,and the second
is concernedwith new types of detergents,mainly biodegradable nionic
surfactants, nd a wide range of ampholytics.
Mostof thispaperhasbeenconfinedo a discussionf analyticalmethods
that have stoodup to the recent scrutinyand that are likely to be issued
as standards in the near future.
Among these procedures are two that have hitherto survived severe
criticism,but which have such nherent defects hat they are liable to be
supersededn the secondgenerationof standards. The first is the large
group of analysesby solvent extraction. Each operation s limited by an
equilibrium artition coefficient nd, thoughseries ontaining p to a dozen
extractionand washingstepshave beenrecommended,he overall accuracy
and precision f many is barely acceptable. With chromatographicro-
cedures n the other hand, usingcolumnsof ion-exchange esins,of alumina,
cellulose, nd silica, separationsmay involve hundredsof theoreticalequi-
librium stageswith no more than a few minutes'attention of the analyst.
Such methodswill becomewidely used n the future, but a great deal of
tedious study is needed before results can be accepted as reliable and
reproducible, speciallyamong different aboratories.
The secondprocedure s the two-phasecationic-anionicitration using
methylene blue and this suffers rom the same limitations of equilibrium
partition as the first method. The best hope for improvement ies in the
synthesis f a cationic ndicator designed pecially or this application. The
ideal indicator will probably contain only one basic group, this being a
quaternary nitrogen, and will have an intense colour, preferably blue.
Nevertheless, n ideal indicator may not overcome he inherent defectsof
the competing quilibria, or many investigators eem o ignore he extracta-
bility of both anionic and cationic surfactants, n the absenceof indicator,
in solventssuch as chloroform. The factors appear to be more serious n
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THE ANALYSIS OF SYNTHETIC DETERGENTS 525
alkaline solutions, which underlines the need for a better indicator that is
usableat low pH values.
The other ieldof muchcurrentendearours the developmentf analytical
methodso dealwith newer ypesof surfactants. The searchor a detergent
that is readily decomposedn sewage reatment plants s to a large extent
concernedwith derivativesof natural fats, particularly of tallow which is
available n larger quantities han coconutand palm kernel oils; derivatives
are being made and tested at a faster rate than the necessarymethodsof
analysiscan be devised. The field of ampholyticsurfactantss another n
which new compounds re frequently appearing. When commercialcon-
siderations ave led to a more stablepattern of supplyand demandof both
typesof surfactant, hen the analystcan developprocedureshat are worthy
of publication. This situation is not likely to be reachedwithin the next
year or two.
(Received:7thMay 1963)
REFERENCES
Many references given in the first paper below have not been listed again. The
books referred to under 4 and 7 below are useful general works, and the former contains
a good guide to the literature, excluding the anionic-cationic titration.
• Smith. W. B. Analyst 84 77 (1959)
2 Holness, H., and Stone, W.R. Analyst 82 166 (1957)
a Rosen, M.J. Anal. Chem. 27 787 (1955)
4 Rosen, M. J., and Goldsmith, H.A. SystematicAnalysis of Surface-ActiveAgents
(1960) (Interscience, London)
5 Drewry, J. Analyst 88 225 (1963)
6 Gaspari6, J., Borecky, J., Obruba, K., and Hanzlik, J. CollectionCzechoslovak hem.
Commun. 20 2950 (1961)
* Longman, G. F., and Hilton, J. Methods or the Analysis of Non-soapy Detergent
(NSD) Products (1961) (The Society for Analytical Chemistry, London)
8 House, R., and Darragh, J.L. Anal. Chem. 20 1492 (1954)
9 Voogt, P. Rec. tray. chim. 78 899 (1959)
•0 Voogt, P. Proceedings, rd World Congress n Surface Active Agents II 78 (1960)
(University Press, Mainz)
• Jones, J. H. J. Assoc. O.l•c. Agr. Chemists28 398 (1945)
•a Abbott, D.C. Analyst 87 286 (1962)
•a Silverstein, R.M. Anal. Chem. 35 154 (1963)
•4 Cullum, D.C. Proceeding,$rd World Congress n Surface Active Agents II 42 (1960)
(University Press, Mainz)
•5 Dolezil, M., and Bulandr, J. ChemickeListy 51 255 (1957)
•6 Schwerdtner, H., Teztil u. Faserstofftechnik 569 (1955)
•? Marron, T. V., and Schifferli, J. Ind. Eng. Chem. Anal. Ed. 18 49 (1946)
•8 Blank, E. W. Soap Chem. Specialties $4 41 (January 1958)
•9 Chinnick, C. C. T., and Lincoln, P. A. Proceedings,1st World Conferenceon Surface
Active Agents I 209 (1954) (Chambre Syndical Tramagas, Paris)
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52•3 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
I)ISCUSSION
)/IR. G. A. C. PITT: What indicatorshave you tried other than methylene
blue and bromophenol lue ?
THE LECTURE•: Among anionic ndicators,methyl orange s the only
alternative to bromophenol blue that we have used. A wide range of
indicator types s available,but bromophenol lue has so few disadvantages
that there is little incentive to look elsewhere. With cationic indicators
the situation is quite different, and we have considered every coloured
organic ationiccompoundhat hasbeenbrought o our attention. Dimidium
bromidewas mentionedabove, and methyl yellow has also been usedby us.
Indicators such as methyl violet and methyl green gave less satisfactory
results than methylene blue; pinacyanol chloride and methylviologen
showedno promise. We think that the problem justifies attempts at the
special synthesisof an indicator, and some coloured organic compound
contairfingone quaternary ammoniumgroup and no other ionogenicgroup
in the moleculewould probably be suitable.
MR. J. S. LEAH¾: Has the use of thin layer chromatography een in-
vestigated n place of paper chromatographyn the qualitative analysisof
detergents It would appear o have advantages oth in time and possibly
conditions of detection.
THE L•C•URER: We havenot investigatedhe subjectand do not know
of any work on thin layer chromatography f detergents. In view of the
apparent advantageswe hope to look into the technique when time is
available.
A M•M•ER OF •H• AUDIENCE: How is phosphomolybdic cid used?
THE L•c•u•n•: Phosphomolybdicacid is slowly added to a dilute
acid solutionof the non-ionicsurfaceactive agent and of barium chloride,
and the non-ioniccompoundM is thereby precipitated as the complex
B%(PM%204o)2.xM.The precipitate s filtered off, dried, and weighed.
The compositionof the precipitate is then determined by dissolvinga
weighed portion in excessof alkali and back-titrating the excess. The
overall reaction is :--
B%(PMo•20•0)• 46 NaOH +3 Na•SO4 3BaSO•-.4-24Na•MoO•+
2 Na•HPO•+22 H20
For a preciseend-point we back-titrate to excesswith hydrochloric cid,
then add a little neutral sodiumsulphate,and titrate again with sodium
hydroxide. This reduces he interferencedue to carbon dioxide, which may
be appreciablewhen solublebarium salts are present. Since460 ml 0.1N
sodiumhydroxideare equivalent o 4057 mg of barium phosphomolybdate,
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8/20/2019 pTHE ANALYSIS OF SYNTHETIC DETERGENTS - W. B. SMITH
15/15
THE ANALYSIS OF SYNTHETIC DETERGENTS •59.7
the inorganic ontentof the precipitate an be calculated. The rest of the
precipitate ompriseshe non-ionic urface ctiveagent he contentof which
in the originalsolution s thus determined. An analysisof the precipitate
is essential or every new type of non-ioniccompound,because he value
of x varies from one substance o another, and may even vary among com-
poundsof nominally the same composition.
Ml•. D. B^ss: Your method of analysis or ampho ytics s to estimate
as cationics under acid conditions. This method works well for the sub-
stituted aminoacid type, but do you obtain good esultsusing he betaine
type of ampholytic I am thinking n particularof difficulties hen here
is a degreeof internal compensation ithin the molecule s with the cyclo-
imidinium type.
T}m LECTURER: Yes, we find our normal method for cationics to be
satisfactory or the betaine type of surfaceactive agent. The two-phase
titration is performedn acid solutionwith chloroform s the organicphase,
sodiumdodecylbenzenesulphonates titrant, methyleneblue as indicator,
and we take complete ransferenceof colour to the organic phase as the
end-point.
BOOK REVIEW
Standard Methods of Chemical Analysis. Volume II (A and B). INDUSTRIAL &
NATURAL PRODUCTS & NONINSTRUMENTAL METHODS. Sixth Edition.
Editor: F. J. Welcher. Part IIA--Pp. xiv q- (1-1282) q- Ill. Part IIB--Pp. xi q-
(1283-2613) q- Ill. (1963). D. Van Nostrand Company, Inc., New York.
$25 each (not sold separately).
It is almost wenty-five years sincea revisededition of Standard Methodsof Chemical
Analysis has appeared. In 1939, the Fifth Edition was published as two volumes but
so great have been the modifications, efinementsand developmentsof the methods of
chemical analysissince hat time that the Sixth Edition appears n three volumes, with
Volume II expanded nto two parts, bound separately as Volume IIA and Volume IIB.
Despite its considerableexpansion the purpose of Volume II remains that it shall be a
collection of carefully selectedwell proved methodsof technical analysis, of practical
value to the professional chemist.
The lay-out of this edition is similar to the previous one, but the expansiondue to
the inclusionof new material adequately reflectssome of the important changes hat
have taken place in recent years in analytical techniques. The expansion includes
chapterson standard aboratory apparatus; detectionof cations and anions; mechanical
separation; separationsby filtration; separationsby electrolysis; solvent extraction;
separationsby distillation and evaporation; chromatography; ion exchange methods
in analysis; acid-base titrations in non-aqueoussolvents; statistical interpretations;
quantitative organic analysis; air pollutants; amino acid analysis of protein hydroly-
zates; chemicalanalysis n clinical medicine; fertilizers; gas analysiswith emphasison
vacuum techniques; pesticides; plastics; silicates,glasses, ocks, soils and vitamins.
There are numerous eferences o original papers and there is a good ndex at the
end of Part B only. It is somewhat annoying that Part B has to be consulted for work
that is known to be found in Part A, for these books are not lightweight ones. It is
difficult to understandwhy the index was not included n Part A as well; the book would
only be 22 pages larger than Part B had this been done.
Cosmetic chemists may be disappointed that the analysis of cosmetics does not