ivITHE ANALYST [November, 1973THE ANALYSTE D ITORl AL ADV IS0 RY BOARDChairman: H. J. Cluley (Wembley).*L. S. Bark (Solford)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Woltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)E. A. M. F. Dahmen (The Netherlands)*J. B. Dawson (Leeds)A. C. Docherty (BillinghamjD. Dyrssen (Sweden)*W. T. Elwell (Birmingham)*D. C. Garratt (London)*R. Goulden (Sittingbourne)1. Hoste (Belgium)D. N. Hume (U.S.A.)H. M. N. H. Irving (Leeds)A. G. Jones (Welwyn Garden City)M. T. Kelley (U.S.A.)*J. A. Hunter (Edinburgh)W. Kemula (Poland)*G. F. Kirkbright (London)G. W. C. Milner (Harwell)G. H. Morrison (U.S.A.)*J. M. Ottaway (Glosgow)*G. E. Penketh (Billingham)S. A. Price (Tadworth)D. 1. Rees (LondonjE.B. Sandell (U.S.A.)*R. Sawyer (London)A. A. Smales, O.B.E. (Harwell)H. E. Stagg (Manchester)E. Stahl (Germany)A. Walsh (Australia)T. S. West (London)P. Zuman (U.S.A.)*A. Townshend (Birmingham)* Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Anolyst, Analytical Abstracts and Proceedings should beThe Chemical Society, Publications Sales Ofice,Blackhorse Road, Letchworth, Herts.Rates for 1973(other than Members of the Society)sent to:(a) The Analyst, Analytical Abstracts, and Proceedings, with indexes . . . . €37.00(b) The Analyst, Analytical Abstracts printed on one side of the paper (without(c) The Analyst, Analytical Abstracts printed on one side of the paper (withindex), and Proceedings .. . . . . . . . . . . . . €38.00index), and Proceedings . . . . . . . . . . . . . . f45.00The Analyst and Analytical Abstracts without Proceedings-(e) The Analyst, and Analytical Abstracts printed OR one side of the paper (without(f) The Analyst, and Analytical Abstracts printed on one side of the paper (with(d) The Analyst and Analytical Abstracts. with indexes . . . . . . . . €34.00index) . . . . . . . . . . . . . . . . . . €35.00. . . . . . . . . . . . . . . . . . index) f42.00(Subscriptions are NOT accepted for The Analyst and/or for Proceedings alonevi SUMMARIES O F PAPERS I N THIS ISSUE [November, 1973Summaries of Papers in this IssueDifferential Electrolytic Potentiometry with Periodic PolarisationPart XXIII.The Effect of Bias and Distortion on Periodic DifferentialElectrolytic Potentiometry, the D.C. Output Produced and Time-biassed Differential Electrolytic Potentiometry in Oxidation -Reduction TitrationsAny departure from the pure, symmetrical, bias-free input waveform ;external d.c. bias; internal d.c. offset, distortion, amplitude or mark-to-space(time) bias ; produces a deterioration in the periodic differential electrolyticpotentiometric titration curve. The peak potential is decreased, the peakbecomes less sharp, the discrimination becomes worse, errors are introducedand the electrodes more quickly become deactivated when any bias or dis-tortion is present in the input current waveform, and this effect is manifestwith 2 per cent.contamination of the waveform and destructive a t 5 percent. A d.c. bias causes the peak to split into two peaks. At the same time,the electrodes produce a d.c. output; the symmetrical polarisation showsno d.c. component in the output; and for d.c. offset and amplitude bias,this d.c. output is the same as for classical d.c. differential electrolyticpotentiometry. With a time-biassed periodic input of any waveform, ad.c. output of unique properties is produced. This output has the same formsas the classical d.c. differential electrolytic potentiometric curves, but theend-points are sharper, the discrimination is better, the end-points are error-free with dichromate and cerium(1V) titrants, the d.c. potential stabilises veryquickly and remains drift-free, even for type I1 (b) curves, the high-qualityend-point persists to very low concentrations, the electrodes retain theiractivity for a long time and the process is independent of frequency.Suchtitrations can be performed as fast as titrations with visual indicators. Thepositive errors in classical d.c. differential electrolytic potentiometric ti trationswith cerium(1V) , chromium(V1) and in zero-current potentiometric titrationswith vanadium(V) are explained.E. BISHOP and T. J. N. WEBBERChemistry Department, University of Exeter, Stocker Road, Exeter, EX4 4QD.Analyst, 1973, 98, 769-776.Monte CarPo Simulation of Matrix Correction EffectsMonte Carlo simulation is useful for the precise evaluation of the effectsof complex systems of matrix correction equations (such as occur in spectro-graphic analysis).If the error distributions for the interfering elements areexperimentally determined, that induced by interaction in the correctionequation system for the elements subject to interference can be predicted.R. J. HOWARTHApplied Geochemistry Research Group, Department of Geology, Imperial Collegeof Science and Technology, London, SW7 2BP.Analyst, 1973, 98, 777-781.Spectrophotometric Determination of Low Levels of Mono-, Di-and Triethylene Glycols in Surface WatersA method is proposed for the determination of mono-, di- and triethyleneglycols in surface waters, based on the oxidation of the glycols to aldehydes.These are made to react with 3-methylbenzotliiazol-2-one hydrazone hydro-chloride to give green cationic chromogens, which are then measured spectro-photometrically a t 630 nm.Sample blank values, to compensate for naturalinterferences, are obtained by omitting the oxidation stage. The methodenables glycol levels of upwards of 0.5 mg 1-1 to be determined, satisfactoryrecoveries of each glycol being obtained for concentrations of 1 to 5 mg 1-1,with a precision of 7 per cent., for a range of water samples. A sensitivevariation of the method, for the determination of monoethylene glycol alone,is described separately.W. H. EVANS and A. DENNISDepartment of Trade and Industry, Laboratory of the Government Chemist, Cornwall,House, Stamford Street, London, SE1 9NQ.Analyst, 1973, 98, 782-791.X THE ANALYST [November, 1973Analytical Standards forTrace Elements AnalysisModern trace analysis techniques more and more frequently call for the use of referencestandards of metals.Spectrography, Atomic Absorption Spectrophotometry, Emission Spectrophotometry, X rayFluorescence are techniques which particularly require the use of these standards.It is however necessary to make a distinction between application of such techniques towater, or to other solutions whatever the basic solvent, oil or hydrocarbon.In fact if one uses the same technique on an aqueous solvent, one must use an aqueoussolution.If one uses a non-aqueous solvent the standards used must be soluble in thissolvent.Standards for atomic absorptionshould actually be called standard solutions for metaltrace anlysis, where the metal is in an aqueoussolution acidified by nitric acid, and may therefore beused as a standard for any analytical techniquerequiring it.Atomic absorption spectrophotometry is now beingused more and more in analysis in both research andindustrial laboratories, as this is the fastest andeasiest independent method for metal determinations.It may be applied to any soluble matrix.As for any instrumental technique, it is important tohave available standards of the metals involved,to set both the method and apparatus, and to revealany interference or positive or negative effects(caused by the matrix, solvent, etc.).In any case a control against a standard is advisablewhen plotting calibration curves.In fact in atomicabsorption spectrophotometry, the theoretical linearrelationship between absorbance and concentration,known as Beer’s law, is effective only within verynarrow limits.It will now be clear how important it is to haveavailable solutions with a known content, at least forthe most frequently determined metals.Carlo Erba STANDARDS for Atomic Absorption are thefollowing concentrated solutions of metal nitratewhich, when diluted to 1000 ml with distilled water,give a slightly acidic solution (about 0.1% HNO,) at aconcentration of metal ion of 1000 ppm:Metallorganic standardsThese compounds are in fact improperly calledmetallorganic, as they are generally metal salts ofcarboxylic organic acids or organic metal complexes;but this expression has been chosen because it givesa more immediate idea of the metal atom being linkedto an organic radical which eases solution in oils,even when the substance involved is not an alkyl oran aryl.They are used as oil-soluble standards in thespectrographic analysis of traces of metals in oils andfats, in petroleum derivatives and in lubricatingagents.The analysis of metals in non-aqueous media iscarried out with spectographs and atomic absorptionspectrophotometers using samples of known contentas controls.Therefore it has been necessary to studyand develop organometallic compounds and organicsalts of metals, having a known metal content.The stability is obtained by the use of solubilisingagents such as 2-1 -Ethylhexanoic acid,6-Methly-2,4-heptandione, 2-Ethyl-hexylarnine, andb is-(2-Et h y I hexy I) d i t h i ocarbam i cacid-bis-(2-ethylhexyl)ammonium salt, with Xylene.Thus, clear and stable solutions in an oil base areobtained, with concentrations up to 500 ppm of metal.It is also possible to prepare solutions containingmore than one metal, bearing in mind that mixtures ofmetals are more soluble than the individualconstituents.Aluminium STANDARD Lithium STANDARDBarium STANDARDCadmium STANDARD M~~~~~~~~ STANDARD vials concern the following elements:~~~~~~i~~ STANDARD Carlo Erba metallorganic standards available in 5 g.Calcium STANDARD NickGI STANDARDChromium STANDARD Potassium STANDARD Aluminium, Barium, Bismuth, Boron, Cadmium,Cobalt STANDARD Silver STANDARD Calcium, Chromium, Cobalt, Copper, Iron,Copper STANDARD Sodium STANDARD Lanthanum, Lead, Lithium, Magnesium, Manganese,iron STANDARD Strontium STANDARD Nickel, Phosphorus, Potassium, Silicium, Silver,Lead STANDARD Zinc STANDARD Sodium, Strontium, Tin, Vanadium, Zinc.Special bookkt available on request( CARLO EBBA I D~V~SIONE CHIMICA I VIA CARLO IMBONATI 24 I 201x1 MILAN