1v SUMMARIES OF PAPERS I N THIS ISSUE August, 1979Summaries of Papers in this IssueElectrochemical Studies of Strongly Chelating AnthraquinoneDerivativesAnalytically important, strongly chelating anthraquinones and their deriva-tives were studied by d.c. polarography, cyclic voltammetry and micro-coulometry to investigate their redox characteristics. All 18 substanceswere reduced in a two-electron reversible or quasi-reversible process in bothaqueous and 75% ethanolic solutions. Depending on pH and the medium,single or double polarographic reduction waves appeared, which were diffusioncontrolled, although in some instances adsorption pre-waves were alsoobserved. This behaviour is similar to the known behaviour of simplerquinone systems. The variation of the IlkoviC coefficient and half-wavepotential with pH was studied in detail to investigate the acid - base behaviourof the species involved in the reduction process.As a result, it was possibleto describe the reduction mechanism of the anthraquinones involved.A number of new pK values were determined and others confirmed.Attempts to find linear free energy relationships were generally unsuccessful.Keywords ; Anthraquinone derivatives ; polarography ; cyclic voltammetry ;half-wave potentials; PIC. valuesG. ALI QURESHI, G. SVEHLA and M. A. LEONARDDepartment of Analytical Chemistry, The Queen’s University, Belfast, NorthernIreland, BT9 5AG.Analyst, 1979, 104, 705-722.Direct Differential-pulse Polarographic Determination of Mixturesof the Food Colouring Matters Tartrazinq - Sunset Yellow FCF,Tartrazine - Green S and Amaranth - Green S in Soft DrinksTartrazine and Sunset Yellow FCF can be determined directly in orangeadeby differential-pulse (d.p.) polarography on the addition of pH 9 Britton -Robinson buffer and tetraphenylphosphonium chloride. The tetraphenyl-phosphonium chloride removes the large polarographic maximum obtainedwith tartrazine a t pH > 4 and causes the d.p.polarographic peaks of the twocolouring matters to be separated.Tartrazine in limeade can be determined in a similar supporting electrolytebut these conditions are not suitable for the determination of Green S, whichis usually present a t a low concentration relative to the tartrazine and forwhich the d.p.polarographic peak is depressed by the addition of tetra-phenylphosphonium chloride. Green S can be determined after adding pH 4Britton - Robinson buffer and tetramethylammonium chloride to the limeade :the addition of tetramethylammonium chloride gives a better base line inthe presence of tartrazine. The solution is then re-adjusted to pH 9 andtetraphenylphosphonium chloride is added in order to determine thetartrazine.At pH 4 the sugar present in blackcurrant syrup gives a small d.p. polaro-graphic peak at the same potential as Green S. At pH > 6 the peak of thesugar disappears but amaranth gives a broad polarographic maximum. Thismaximum is suppressed at pH 7.8 by the addition of tetramethylammoniumchloride. Under these conditions the Green S peak is separate but the smallconcentrations of Green S normally present in blackcurrant drinks can onlyjust be detected.The procedures have been tested on soft drinks prepared with knownconcentrations of colouring matter.Keywords : Difleerential-pulse Polavogeraphy ; food colouring matters ; tavtvazine ;Green S ; amaranthA.G. FOGG and K. S. YO0Chemistry Department, Loughborough University of Technology, Loughborough,Leicestershire, LE11 3TU.Analyst, 1979, 104, 723-729vi SUMMARIES OF PAPERS I N THIS ISSUEIon-selective Polymeric-membrane Electrodes with ImmobilisedIon- exchange SitesPart I. Development of a Calcium ElectrodeAugust, 19 79A new type of ion-selective electrode is described in which ion-exchange sitesare immobilised in a polymeric membrane by covalent bonding.Membraneswere prepared by cross-linking a styrene - butadiene - styrene triblockcopolymer with triallyl phosphate. After subsequent hydrolysis thesemembranes were evaluated as Ca2+ sensors. The electrodes formed exhibitedan extended Nernstian response to Ca2+ ( 10-1-10-6 M) and good selectivityover other alkaline earth and alkali metals. Such electrodes offer very fastresponse times, extended lifetimes and a wide pH working range. Thepossibilities of this new class of ion-selective electrode are also discussed.Keywords : Ion-selective electrode ; calcium analysis ; electroanalytical chemistry ;polymeric membrane ; immobilised ion-exchange groups.L. EBDON, A. T. ELLIS and G. C. CORFIELDDepartment of Chemistry, She ffield City Polytechnic, Pond Street, Sheffield, S 1 1 WB.Analyst, 1979, 104, 730-738.High-frequency Microtitrimetric Determination of Acidic andBasic Constituents in Lubricating OilsPart 11.Determination of Total Base NumberA high-frequency microtitration method is described for the determinationof total base number in new and used lubricating oils. The sample, dissolvedin toluene - propan-2-01 - water (5 + 4.95 + 0.05), is titrated with standardalcoholic hydrochloric acid solution. A study of solvents, titrants, samplesize and other experimental parameters is reported. This method providessharp breaks at the end-points of the titration graphs and more repeatableand faster results than those obtained with the standard potentiometricmethod. The method can also be used for macrotitrations, with a com-mercially available oscillator, and can be suggested as an alternative toASTM and IP methods for the determination of total base number.Keywords : Total base number determination ; lubricating oils ; high-frequencytitrationT.FERNANDEZ, J. M. ROCHA, N. RUFINO and A. GARCfA LUISCompaiiia Espaiiola de Petrbleos, S.A., Research Laboratory, Santa Cruz de Tenerife,Canary Islands.and F. GARCfA MONTELONGODepartment of Analytical Chemistry, University of La Laguna, Tenerife, CanaryIslands.Analyst, 1979, 104, 739-749August, 1979 SUMMARIES OF PAPERS I N THIS ISSUEContinuous Solvent-extraction Method for the SpectrophotometricDetermination of Cationic SurfactantsviiA rapid and automated spectrophotometric method for the determination ofcationic surfactants, using the AutoAnalyzer, has been developed.Thismethod is based on the continuous solvent extraction of the ion-pair complexformed in the reaction of Orange I1 with a cationic surfactant. Good tracesand identical molar responses were obtained with seven different types ofsurfactant using methanol in the Orange I1 reagent. Fatty amines inmixtures of the amines and quaternary ammonium surfactants were deter-mined by changing the pH of the aqueous phase. The proposed method wasapplied to the determination of cationic surfactants in several commercialproducts. The results agreed with those obtained by the two-phase titrationprocedure.The detection limit is 5 p~ and the capacity is 10-20 samplesper hour, with a relative precision of better than 1.5%.Keywords : A utomatic analysis ; cationic surfactant determination ; fattyamine determination ; spectrophotometry ; Orange I IJIRO KAWASE and MAKOTO YAMANAKATochigi Research Laboratories, Kao Soap Co. Ltd., 2606 Akabane, Ichikai-machi,Tochigi, Japan.Analyst, 1979, 104, 750-755.Automatic Emission Spectrometer for the Determinationof Nitrogen- 15An automatic nitrogen-15 analyser, employing a novel use of a rhodium -platinum catalyst for the generation of nitrogen and capable of analysing 60samples per hour, is described. Nitrogen compounds of biological origin arefirst converted into ammonium chloride by conventional Kj eldahl digestionand distillation methods.The ammonium chloride sample (about 5 p1containing about 10 pg of nitrogen) is injected into a soda-lime reactor at590 "C through which flows a stream of purified helium. Ammonia that isreleased passes directly into the catalyst tube and the generated nitrogenand hydrogen are separated by passage through a gas-chromatographiccolumn, which also retains the water.After passing through a pressure restrictor the nitrogen flows in thehelium stream through a Spectrosil discharge tube located in a microwavecavity. The emitted radiation is analysed by means of a specially con-structed dual-wavelength monochromator and the intensities of the 14N14N(297.7 nm) and 14N15N (298.3 nm) bands are measured simultaneously bytwo photomultipliers.Amplified signals, proportional to the peak intensities,are fed through phase-sensitive detectors into a ratiometer, the output fromwhich is fed to a digital voltmeter and printed out in terms of nitrogen-15abundance. A peak detector indicates the total nitrogen content of eachsample and actuates the nitrogen-15 print-out.The response of the instrument is slightly curvilinear but may be regardedas linear over limited ranges. Calibration can therefore be achieved byrunning suitably chosen standards to fix upper and lower set points. Carry-over between samples is very small and is eliminated by running duplicates.Standard deviations of replicate measurements of natural abundance andenriched standards are less than 0.01 atom-%, while determinations ofnitrogen-15 in biological samples were shown to be accurate to 50.01atom- yo by comparison with a Statron NOI-4 nitrogen- 15 analyser.Keywords : Nitrogen- 15 determination ; catalytic nitrogen generation ; auto-mated emission spectrometerJ. D. S. GOULDEN and D. N. SALTERNational Institute for Research in Dairying, Shinfield, Reading, RG2 9AT.Analyst, 1979, 104, 756-765