...Vlll SUMMARIES OF PAPERS I N THIS ISSUEDetermination of Selenium in Soil Digests by Non-dispersiveAtomic-fluorescence Spectrometry Using an Argon - HydrogenFlame and the Hydride Generation TechniqueMavch, 197.9The determination of selenium a t submicrogram levels by atomic-fluorescencespectrometry, based on the evolution of hydrogen selenide into an argon -hydrogen air-entrained flame, is described. Using a simple purpose-builtnon-dispersive atomic-fluorescence spectrometer a detection limit of 10 ng cm-3of selenium is obtained. The technique has been applied to the determina-tion of selenium in soil digests and experiments have been carried out inorder to study the interference of other elements on the determination.Procedures for the elimination of interferences from copper are recommended.Keywords : Selenium determination ; atomic-fluorescence spectrometry ; hydridegeneration ; soil digestsJ. AZAD, G.F. KIRKBRIGHT and R. D. SNOOKDepartment of Chemistry, Imperial College, London, SW7 2BP.Analyst, 1979, 104, 232-240.Investigations on Reaction Mechanisms in the Determinationof Non-ionic Surfactants in Waters as Potassium PicrateActive SubstancesThe two-phase extraction and spectrophotometric determination of poly-oxyethylene non-ionic surfactants in water a t trace levels is examined indetail by considering both monodisperse and polydisperse surfactants of thetype RO(CH,CH,O),H, where R = $)-tert-nonylphenyl and .M. is the degree ofpolymerisation. Potassium picrate is used as a reagent for the polyoxyethylenechain and 1,2-dichloroethane as an extracting phase.Monodisperse surfactants with n from 4 to 15 were isolated by liquid - solidabsorption chromatography.Their purity was checked by temperature-programmed gas - liquid chromatography. Their reactivity to the reagent isexplained qualitatively by considering the equilibria involved in the extrac-tion.Polydisperse surfactants with YZ (number-average degree of polymerisation)ranging from 3.3 to 21.5 are also considered and compared with other poly-disperse surfactants in which R = dodecyl. The concentration of these non-ionics in waters is conveniently expressed as potassium picrate active sub-stances (PPAS). It can be referred to the standard synthetic monodispersesurfactant RO(CH,CH,O),H, where R = dodecyl, which gives a spectrophoto-metric response acceptably near to that of the examined series of commercialsurfactants.Keywords : Polyoxyethylene alkylplaenyl ether non-ionic surfactant tracedetermination ; watev analysis ; spectrophotovlzetry ; potassium picrate ;reaction mechanismL.FAVRETTO, B. STANCHER and F. TUNISIstituto di Merceologia, Universita di Trieste, 34100 Trieste, ItalyAnalyst, 1979, 104, 241-24SUMMARIES OF PAPERS IN THIS ISSUE March, 1979Limit of Detection in Analysis with Ion- selective ElectrodesThe limit of detection in analysis with ion-selective electrodes is discussedand definitions that are based only on the deviation of an electrode’s cali-bration from the theoretical, and take no account of the random errors ofmeasurement, are shown to be inadequate.Equations are derived thatexpress the limit of detection in terms of the random error of measurementand the factors determining the deviation of the electrode response fromthe Nernstian value, i.e., reagent blanks, solubility products and inter-ferences. The equations enable one to predict ( a ) the degree of precision withwhich the e.m.f. has to be measured if an electrode is to attain a desired limitof detection in specified conditions or (b) whether changing the conditionsmight bring the desired limit of detection within reach of a given precisionof measurement. Practical examples with ion-selective electrodes justifythe proposed statistical treatment of limit of detection and demonstrate thatthe errors for electrodes operating in the non-Nernstian region are normallydistributed.Keywovds : Ion-seleciive electvodes ; flotentiometvy ; limit of detectionDEREK MIDGLEYCentral Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey,KT22 7SE.Analyst, 1979, 104, 248-257.Spectrophotometric Method for the Determination of ParaquatShort PaperKeywords : Pavaquat detevmination ; spectvophotometvyM.GANESAN, S. NATESAN and V. RANGANATHANDepartment of Chemistry, United Planters’ Association of Southern India, TeaResearch Station, Cinchona 642 106, India.Analyst, 1979, 104, 258-261.Titrimetric Determination of Reducing Sugars with Copper(I1)SulphateShovt PaPevKeywords : Reducing sugar detevmination ; coppev(II) sulphate Yeduction ;titvimetvyT. H. KHANDepartment of Industries (Chemical Directorate), 58, Dilkusha Commercial Area,Dacca-2, Bangladesh.Analyst, 1979, 104, 261-265.Determination of Dimetridazole in Pig and Poultry Feeds byHigh-performance Liquid ChromatographyShort PapevKeywovds : Dimetvidazole detevmhation ; animal feeds ; high-perfovmanceliquid chvomatogvaphyA. D. JONES, I. W. BURNS and S. 6. SELLINGSUnilever Research Laboratory, Colworth House, Sharnbrook, Bedfordshire,MK44 1LQ.Analyst, 1979, 104, 265-268.