摘要:

Proceedingsof the Analytical Division 0.fThe Chemical SocietyCONTENTS1 Education, Training and Researchin Analytical Chemistry in Univer-sities and Polytechnics7 Summaries of Papers7 'The Determination of Anion-formingElements'16 Fourth SAC Conference17 Conferences and Meetings18 Analytical Division DiaryVolume 14 No 1 Pages 1-1 8 January 197PADSDZ 14(1)1-18(1977)ISSN 0306-1 396PROCEEDINGSJanuary 1977OF THEANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof the Chemical SocietyPresidentD. W. WilsonHon. SecretaryP. G. W. CobbSecretaryMiss P. E. HutchinsonHon. Treasurer Hon. Assistant SecretariesJ. K. Foreman D. I . Coomber, O.B.E.; D. C. M. Squirrel1Editor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864.Telex 268001.Subscriptions (non-members): The Chemical Society, Publications Sales Office, Blackhorse Road, Letch-worth, Hens., SG6 1HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.The Chemical Society 1977THE FIFTEENTH DIVISIONAL ANNUAL MEETINGonR AND D TOPICS IN ANALYTICAL CHEMISTRYwill be held atChelsea College, University of LondononMay 3rd and 4th, 1977Papers are invited describing work carried out by postgraduate research studentsin Universities and Colleges and by young research workers in industrial and otherestablishments. Contributions are to be presented by the student or his industrialcounterpart during a 20-minute lecture.Those who wish to offer a paper or who have any queries about the meetingDr. D. I. Coomber, Analytical Division, Chemical Society, Burlington House,should write to-Piccadilly, London W1 V OBN

ISSN:0306-1396    

DOI:10.1039/AD97714FX001

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

January, 1977 CONFERENCES AND MEETINGSAnalytical Division Diary, continuedFebruary, continuedTuesday, 22nd, 2.30 p.m.: ReadingSouth East Region, Microchemical Methodsand Electroanalytical Groups.“An Analyst Appraises Electroanalysis, ”by Professor E. Bishop.Discussion t o be led by B. Fleet and 1’. 0.Kane.Chemistry Department, Palmer Building,Room G-02, The University, Reading.Maps are available from Dr. B. Birch,Port Sunlight Laboratory, Unilever Ltd.,Port Sunlight, Merseyside L62 4XN (Tel.051-645-2000).Tuesday, 22nd, 7 p.m. : SwanseaWestern Region, jointly with the South WalesWest Section of the CS.“Two Hundred Years of Brewing,” by Pro-Chemistry Department, University Collegefessor R. Belcher.of Swansea, Swansea.Wednesday, 23rd, 10.30 a.m.; LondonRadiochemical Methods Group on “ResearchTopics .”Chemistry Department, Queen ElizabethCollege, Atkins Building, Campden Hill,Kensington, London, W.8.Thursday, 24th, 4.15 p.m.: Old AberdeenScottish Region, jointly with the Aberdeen andNorth of Scotland Section of the CS and theAberdeen University Chemical Society.“Dithizone-A New Look a t an Old Reagent,”by Professor H. M. N. H. Irving.Department of Chemistry, University ofAberdeen, Meston Walk, Old AberdeenAnalytical Division DiaryJANUARYFriday, 21st, 6.30 p.m. : SalfordNorth West Region : Annual General Meeting,followed by the Address of the retiringChairman.“Analysts or Analytical Scientists,” by L. S.Bark.Theatre 3, Chapman Building, The University,Salford.Friday, 21st, 6 p.m.: BristolWestern Region : Annual General Meeting.School of Chemistry, Thc University, Bristol.South East Region : Annual General Meeting,6 p.m.Microchemical Methods Group : Annual Gene-ral Meeting, 6.15 p.m., followed by a JointMeeting, 6.30 p.m.“Opium-Analysis and Anecdotes, ” by C.A.Johnson.Linnean Society, Rurlington House, Picca-dilly, London, W. 1.“MECA,” by A. Townshend.Tuesday, 25th : LondonWednesday, 26th, 7.15 p.m. : ThornabyNorth East Region : Annual General Meeting.Discussion on “Analytical Chemistry in theNorth East, Past, Present and Future,”to be introduced by R. C. Chirnside.Golden Eagle Hotel, Thornaby, Cleveland.FEBRUARYWednesday, 2nd, 10.30 a.m. : StevenageAnalytical Division, in conjunction with theAutomatic Methods Groztp, on “On-lineTechniques for Process Monitoring.”Tour of Warren Spring Laboratory.“Sampling of Heterogeneous Materials,” byC.Jepson.“Automatic Control of Waterside ChemicalConditions in Power Station Boilers UsingConductivity Instruments,” by T. P.Smith.“Fast Titration in Flow-through Systems,”by V. Griepink and H. Verbruggen.“Applications of Process Gas Chromato-graphy,” by D. J. Burgess.Warren Spring Laboratory, Gunnels WoodRoad, Stevenage, Herts.Tuesday, 8th, 4.30 p.m. : EdinburghScottish Region, jointly with the Edinburghand East of Scotland Section of the CS andthe Edinburgh University Chemical Society.“Gas Chromatography - Mass Spectrometry,Prostaglandins and Semen,” by R.W. Kelly.Lecture Theatre T-100, Department ofChemistry, The University, Kings Buildings,West Mains Road, Edinburgli.Wednesday, 9th, 2.15 p.m.: BathWestern Region and Special TechniquesGroup on “Acoustical Methods of Analysis.”“Analytical Optoacoustic Spectrometry” :“Fundamentals and Instrumentation,” byG. F. Kirkbright and M. J . Adams.“Applications and Future Developments,”by G. F. Kirkbright and M. J. Adams.“Optoacoustic Spectrometry with a CarbonDepartment of Chemistry, The University,Dioxide Laser,” by J . D. Wilson.Bath.Wednesday, 9th, 6.30 p.m. ; LondonMicrochemical Methods Group.Discussion on “Some Snags in the Determina-tion of Sulphur in Organic Compounds,”to be introduced by B. T. Saunderson.The Savoy Tavern, Savoy Street, London,w.c.2.Monday, 14th, 6.30 p.m.: ChesterNorth West Region, jointly with the StanlowBranch of the Institute of Petroleum.“Mass Spectrometry up to Date,” by A.Quayle.Shell Research Ltcl., Thornton ResearchCentre. Nr. Chester.Wednesday, 16th, 11.30 a.m. : ColchesterEast Anglia Region and Chromatography andElectrophoresis Group, jointly with theEssex Section of the CS, on “What We Eat ?”“Analytical Methods for the Identification ofFood Colours,” by N. T. Crosby.“Ion Exchange Chromatography of Carbo-hydrates,” by A. M. C. Davies.“Identification of Food Proteins,” by R. A.Lawrie.“Dietary Fats and Fatty Acid Analysis,” byM. Crawford.“Isoelectric Focusing of Proteins,” by J . W.Llewellyn .University of Essex, Wivenhoe Park, Col-Chester.Tuesday, 22nd, 4.15 p.m.: LoughboroughMidlands Region, jointly with the Lough-borough University Chemical Society.“Approaches to Automation,” by J. K.Foreman.Lecture Theatre JOOl, Edward HerbertBuilding, University of Technology, Lough-borough.[continued inside back coverPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97714BX003

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

January, 19 7 7 THE DETERMINATION O F ANION-FORMING ELEMENTS 7 The Determination of Anion-forming Elements The following are summaries of four of the papers presented at a Meeting of the Western Region and the Microchemical Methods Group held on September 16th and 17th, 1976, at University College, Swansea. Ion-selective Electrode Sensors for Determining Anion-forming Elements J. D. R. Thomas Chemistry Department, UWIST, Cardifl, CF1 3NU Ion-selective electrodes are commercially available for several anions, including fluoride, chloride, bromide, iodide, cyanide, thiocyanate, nitrate, tetrafluoroborate, perchlorate and sulphide, and electrodes have been described for sulphate, carbonate, surfactant anions and even saccharin.Some ion-selective electrodes can readily be adapted and used for ions other than those for which they were designed, for example, the nitrate-sensing system can readily be adapted for chloratel and the perchlorate system for periodate and chloramine T., The scope of determinations by ion-selective electrodes can be widened by various conver- sions, for example, organic sulphur-containing material can be converted by the oxygen-flask procedure into sulphate and the sulphate determined by potentiometric titration with lead( 11) perchlorate using a lead ion-selective electrode or with barium perchlorate using a barium ion- selective electrode.Sulphide can, with appropriate precaution^,^,^ be determined directly with a sulphide ion-selective electrode or converted into hydrogen sulphide for determination with a hydrogen sulphide gas5 or air-gap elect rode.Sulphite can be oxidised to sulphate with hydrogen peroxide. Principles and Interferences The basic principles of ion-selective electrodes have been adequately discussed e l s e ~ h e r e , ~ ~ ~ but it is important to realise that they detect what they “see” and that this can include activity considerations and the effect of interfering species. Also chemical reactions, such as oxidation, can quickly convert the sought species into species that are not detectable by ion-selective electrodes.Most ion-selective electrodes respond to the species concerned in the middle pH ranges, with pH interferences setting in at the extremes. Sulphide, however, is susceptible to appreciable hydrolysis in the middle pH range : S2- + H,O + HS- + OH- HS- + H,O + H,S + OH- Only the first step affects the sulphide ion concentration in moderately alkaline solutions.Thus, in the pH range 11.4-1 1.8 the sulphide ion activity, [S2-1, sensed by a sulphide electrode is lower than the total level, [S2-IT, according to the relationships [SZ-] = f s2- [SZ-] &+ F) where K , is the ionisation constant of HS- andfs2- is the activity coefficient of the sulphide ion.Rather than calculate [S2-IT from this relationship, it is simpler, when interest is in total sulphide, to take direct measurements in very alkaline solutions such as 1 M sodium hydroxide solution. Many simple and ingenious techniques have been devised for off setting general interferences. In addition to the technique of pH adjustment, they include precipitation, oxidation - reduc- tion, masking or resort to gas sensors.Sometimes other techniques can be employed, such as the low-pH buffer system containing silver sulphate and aluminium sulphate used by Milham et aL9 in nitrate determinations. This buffer maintains the equilibrium hydrogen carbonate An antioxidant reduces oxidation problem^.^8 THE DETERMINATION OF ANION-FORMING ELEMENTS Proc.Analyt. Div. Chem. Soc. level low, keeps the water-extractable organic acids undissociated, removes chloride as silver chloride and complexes anions of organic acids with aluminium. The buffer systems can also function as ionic strength adjusters, but it is important that their constituents do not complex with the primary ion, and the selectivity coefficient, kg! must be negligible; B in this instance is the ionic strength adjuster constituent.For fluoride determinations, TISAB (total ionic strength buffer) is well known.1° With a pH of about 5 it is composed of 1 mol dm-3 sodium chloride, 0.25 mol dm-3 acetic acid, 0.75 mol dm-3 sodium acetate and 1 x mol dm-3 sodium citrate. Defects of ionic strength adjusters have been reported and doubt over the carboxylate content has led to the citrate in TISAB being replacedll by 1,2-diaminocyclohexane-NNN’N’-tetraacetic acid (DCTA) .However, the lanthanum flouride electrode is only minimally affected by acetate and citrate.12 Illustrative Applications From the standpoint of anion-forming elements, ion-selective electrodes have been used in the study of complexes, reaction rates, biomedical, environmental and industrial applications, organic and pharmaceutical analysis, etc.Of the various applications, it is the fluoride, halide, sulphide and nitrate ion-selective electrodes that have been the most widely used. From a microchemical standpoint, determination of fluoride in tooth enamel is an interesting example in view of the associated sampling problems.Biopsy techniques are difficult because sampling modifies teeth surfaces and identical surfaces are considered unlikely. Manual abrasion with silicon carbide slurries for about 1 min provides thin-layer enamel samples,13 but greater abrasive control is achieved with motor-driven pressure-controlled devices.14J5 In this way as little as 33 pg of enamel, equivalent to a 0.3-pm layer, can be removed and analysed directly after dissolution in 0.5 mol dm-3 perchloric acid and the addition of TISAB. First biopsies for fluoride in the outer 1-2-pm enamels of intact anterior human teeth had similar fluoride values,16 but within a population the mean fluoride concentration varied from 430 to 2540 mg kg-l.Second biopsies the next day or even 5 weeks later from the same teeth revealed considerably less fluoride.l6 Fluoride is an important trace element in animals, ranging from 0.5 to 1.0 pmol dm-3 in normal human serum.The frequent discrepancies can be related to variation in the fluoride level in potable waters. The wide interest in urinary and serum fluoride stems from this and from fluoridation programmes, environmental factors (proximity to aluminium manufacturing, etc.) and the use of inhalent anaesthetics.In this last respect, the need for a sensitive serum fluoride monitor is paramount as renal failure, attributed to serum inorganic fluoride,17 occasionally follows anaesthesis with methoxyflurane.18 Patients anaesthetised with this compound without supplementation with dinitrogen oxide have had serum valuesf7 peaking to 190.4 If: 20.9 pmol dm-3.Vegetation and animals may sustain severe damage when exposed to fluoride from industrial complexes. Vegetation samples can be leached with perchloric acid or combusted in a Schoniger flask followed by treatment with TISAB. A comparison of results from the lengthy Willard - Winter distillation - titration technique and the ion-selective electrode method for 148 vegetation samples ranging from 0.15 to 26.3 mmol kg-l showed a 0.993 c0rre1ation.l~ Cystic fibrosis is a disease that arises from a disfunction of the exocrine glands and among other systems is characterised by high sodium and chloride in the sweat and saliva.The combination chloride ion-selective electrode - reference electrode system has made possible large-scale monitoring in its The same combination electrode assembly can conveniently be used for determination of chloride in fruits and vegetables either directly or following extraction.21 The analytical potential of the nitrate ion-selective electrode is fulfilled mainly in soil analysis and the related control of fertilisation programmes and plant nutrient surveys.22 Most field crops range from about 9 to about 450 mmol kg-1 of nitrate.The sample extract may need pre-treatment with ion-exchange resin or with buffer* such as that mentioned above, but speed is important in order to avoid biological losses. Oxides of nitrogen in ambient air have been determined with a nitrate ion-selective electrode following conversion into nitrate with 2% hydrogen peroxide solution.23 The ion-selective electrode method gave “nitrate” levels in Tucson air that agreed to within 1.5-2% relative standard deviation of those obtained by the colorimetric xylenol method.Oxides of nitrogen in combustion gases have been similarly analysed following oxidative absorption on lead( IV)Jauitavy, 1977 THE DETERMINATION OF ANION-FORMING ELEMENTS 9 oxide,24 while alkali scrubbing of cigarette smoke yields nitrate and nitrite, each of which can be determined with the nitrate ion-selective electrode, nitrite being oxidised with permangan- ate.25 The sulphide ion-selective electrode offers the possibility of measuring extremely low levels of sulphide.Although calibration checks to low levels are diffic~lt,~ there are indications that sulphide can be detected to low levels, for example down to 10-l2 mol dm-3 for the sulphide produced by the sulphate-reducing Desulphovibrio desuZphuricans26 and down to 10-ls mol dm-3 for the sulphide that remains following oxygen purging of alkaline “black liquor” in the pulp and paper trades2’ A final illustration concerns the level of organic matter in water, an important pollution parameter.Classical methods for its measurement are based on the 5-d biological oxygen demand or shorter chemical oxygen demand tests. Afl ingenious scheme based on the air-gap electrode has been described28 for the determination of total inorganic carbon (TIC) comprising dissolved carbon dioxide, carbonate and hydrogen carbonate, total carbon (TC) and total organic carbon (TOC).1 . 3. 4. 5 . 6. 7 . 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 7 d. References Hiiro, K., Moody, G. J., and Thomas, J. D. R., Talanta, 1975, 22, 918. Hadjiioannou, T. P., personal communication. Hseu, T. M., and Rechnitz, G. A., Analyt. Chem., 1968, 40, 1054. Crombie, D. J., Moody, G.J., and Thomas, J. D. R., Analytica Chim. Acta, 1974, 80, 1. Ross, J. W., Riseman, J. H., and Krueger, J. A., Pure Appl. Chem., 1973, 36, 473. Hansen, E. H., and Rfiiieka, J., Analytica Chim. Acta, 1974, 72, 353. Moody, G. J., and Thomas, J. D. R., “Selective Ion Sensitive Electrodes,” Merrow Publishing CO., Moody, G. J., and Thomas, J. D. R., Sel. A . Rev. Analyt. Sci., 1973, 3, 59.Milham, P. J., Awad, A. S., P a d , R. E., and Bull, J. H., Analyst, 1970, 95, 751. Frant, M. S., and Ross, J. W., Analyt. Chem., 1968, 40, 1169. Orion Research Inc., “Applications Bulletin,” No. 5A, 1969. Evans, P. A., Moody, G. J.. and Thomas, J. D. R., Lab. Pract., 1971, 20, 644. Larsen, M. J., Kold, M., and van der Fehr, F. R., Caries Res., 1972, 6, 193. Ileene, H. J., Crossman, F.D., Pedersen, E. D., Mellberg, J . R., and Nicholson, C. R., Cavies Res., Wei, S. H. Y., and Wefel, J. S., J . Dent. Res., 1975, 54, 201. Brudevold, F., McGann, H. G., and Grern, P., Archs Oval Biol., 1968, 13, 877. Mazze, R. I., Trudell, J. R., and Cousins, M. J., Anesthesiology, 1971, 35, 247. Taves, D. R., Fry, B. W., Freeman, R. B., and Gillies, A. J., J . Am. Med.Ass., 1970, 214, 91. Gyoerskes, T., White, D. A., and Luthy, R. L., J . Metals, N.Y., 1970, 22, 294. Bray, P. T., Clark, G. C. F., Moody, G. J., and Thomas, J . D. R., “A Perspective of Sodium and Chloride Ion-sensitive Electrode Sweat Tests for Screening in Cystic Fibrosis,” UWIST, Cardiff, 1975. Moody, G. J., and Thomas, J. D. R., J . Fd Technol., in the press. Moody, G. J. and Thomas, J.D. R., J . Sci. Fd Agric., 1975, 27, 43. Kneebone, B. M., and Freiser, H., Analyt. Chem., 1973, 45, 449. Driscoll, J . N., Berger, A. W., Becker, J. H., Funkhouser, J. T., and Valentine, J. R., J . A i r Pollut. Morie, G. P., Ledford, C. J., and Clover, C. A., Analytica Clzim. Acta, 1972, 60, 397. Crombie, D. J.. Moody, G. J., and Thomas, J . D. R., to be published. Swartz, J .L., and Light, T. S., TAPPI, 1970, 53, 90. Fiedler, U., Hansen, E. H.. and RhiiEka, J., Analytica Chim. Acta, 1975, 74, 423. Watford, 1971. 1975, 9, 244. Control Ass., 1972, 22, 119. ESCA with Special Reference to the Determination of Anions D. Briggs Impevial Chemical Industries Limited, Corporate Laboratory, Runco~n, Cheshire The basic process in X-ray photoelectron spectroscopy (XPS, often referred to as ESCA, Electron Spectroscopy for Chemical Analysis) is the emission of photoelectrons from a sample by irradiation with soft X-rays.The emitted electrons fall into three categories: core and valence electrons by direct photoemission and Auger electrons. The Auger electrons result from one of the decay processes of the photo-ionised (hole) state.Experimentally, the kinetic10 THE DETERMINATION OF ANION-FORMING ELEMENTS Proc. A rtai’yt. Div. Cherrz. SOC. energy of the emitted electrons is measured as a function of intensity, giving the photoelectron spectrum. The parameter of most interest is the binding energy (BE) of a particular photo- electron peak, which is given simply by BE = hv - KE where hv is the exciting energy and KE the measured kinetic energy of the electrons (strictly this equation holds only for an instrument that is calibrated so that instrumental parameters, e.g., work function, are cancelled).Note that the kinetic energy values of the Auger peaks are independent of the exciting energy, hv, which allows them to be distinguished from photo- electron peaks. With the commonly used Mg K a (1 253.6 eV) and A1 K a (1 486.6 eV) X-ray sources core electrons can be excited for all elements with 2 > 2.Apart from the first-row elements (1s level excited) at least two core levels are seen and this is useful in the rare instance of peak overlap. The binding energies of these core levels are highly characteristic. For example, for first-row elements the binding energies of the 1s electrons are: lithium, 55; beryllium, 111 ; boron, 188; carbon, 284; nitrogen, 399; oxygen, 532; and fluorine, 686 eV.With typical peak widths of 1-2 eV and positional accuracy of 5 0 . 2 eV there is no difficulty with element identification. Relative sensitivities vary only about 50-fold for the most intense peaks of all elements except lithium, for which low sensitivity is obtained.Thus, ESCA is at least a qualitative analysis tool and does not suffer from inherent sensitivity defects, cf. X-ray fluorescence, which is inherently insensitive to elements of low atomic number. However, the exact binding energy of a core-level electron is a reflection of the charge density on the atom and change in binding energy, chemical shift, is a monitor of chemical environment, oxidation state, etc.Chemical shifts do not usually span more than 10 eV for a given element (see Table I). TABLE I BINDING ENERGIES OF THE NITROGEN 1s AND CHLORINE 2p ELECTRONS I N DIFFERENT ENVIRONMENTS Electronic energy Compound level Nitrogen 1s CrN NaN, NaNO, NaNO, NaC10, NaC10, NaC10, Chlorine 2p NaCl Binding energyleV 396.6 403.7 (1) 404.1 407.4 199.1 203.1 205.7 208.7 399.3 (2) Values for chemical shifts are difficult to reproduce from one laboratory to another because However, Wagner has proposed the of calibration problems related to sample charging.analytical use of the “Auger parameter” : a = EAuger - E photoelectron This parameter is the separation between the most prominent Auger and photoelectron signals when both are present in the spectrum, and is independent of charging effects.For many elements of interest in this respect, e.g., sulphur, phosphorus and nitrogen, Auger peaks are not seen when using A1 Ka or Mg K a radiation and therefore a future trend will be the use of higher energies, e g . , Cr Ka and Ti Ka. Bulk sensitivities obtained with ESCA are not particularly good (about 0.1%) but ESCA has gained prominence as a surface probe.The photoelectrons, which are energy analysed, must emerge elastically. The ESCA sampling depth is about 3A, whereh is the inelastic mean free path length of the electron concerned ( A is kinetic-energy dependent, varying between 0.5 and 3.0 nm for electrons of 100-1 200 eV). Chemisorption experiments indicate that 2 x Assuming a sample area of 1 cm2 and 1015 atoms cm-2 monolayer-l, this amount corresponds to 1012 atoms or about 10-log.monolayers of mercury can be detected on gold.January, 1977 THE DETERMINATION OF ANION-FORMING ELEMENTS 11 In principle, therefore, ESCA is capable of trace analysis at the sub-nanogram level, provided the sample is presented in a "monolayer" form. By using a solution evaporation method we have already shown that less than 1OPsg of lead can be detected from a 1O-pl sample of a solution of lead(I1) nitrate in a single scan.The nitrate ion is also detectable but at somewhat lower sensitivity owing to the lower photo- emission cross-section of nitrogen 1s relative to lead 4f. With this procedure charging effects are minimised so that identification of the chemical state of anions from the binding energy of the relevant core level should be straightforward.Linearity of response over the approximate range 10-s-10-6 g for lead has been demonstrated. Hence, with suitable calibration the method should be quantitative. Perhaps the greatest advantage of all is the absence of interference effects, which plague most conventional methods for the determination of anions.Decomposition Problems in Fluorine Analysis G. J. Kakabadse Department of Chemistry, University of Manchester Institute of Science and Technology, Manchester, M60 1Q D The decomposition of fluorine-containing compounds, involving the conversion of bonded fluorine to water-soluble fluoride ion, plays a key role in fluorine analysis. A wide range of standard decomposition technique+ 2 includes acid digestion, ashing, fusion, combustions by Parr bomb, the oxygen-flask procedure and pyrohydrolysis.The type of decomposition method depends, in part, on the nature of the fluorine compound, e.g., acid digestion is used for inorganic fluorides (M-F bonds) and the oxygen-flask procedure for organofluorine com- pounds (R-F bonds).As biological materials can contain both types of bond, we investigated the effect of various decomposition techniques on organically bound fluorine. We found that R-F bonds are largely unaffected by acid digestion a l o ~ e l ~ ~ (15 h in 60% perchloric acid at 60 "C). Ashing, particularly popular with biological materials,1~*~5 was tested on model organic compounds (Table I).Prior to drying and ashing, the compound and an excess of additive were made into a paste with a small volume of distilled water in a small platinum crucible to achieve better mixing, while magnesium succinate and lithium hydroxide, both in excess, were added to the compound as aqueous so1utions.l The covered crucible was placed inside a large platinum crucible, which was then itself covered, for drying and subsequent ashing for 24 h at TABLE I DECOMPOSITION OF ORGANOFLUORINE COMPOUNDS BY ASHING Ashing of a pre-dried paste of compound with magnesium oxide or magnesium succinate + lithium hydroxide at 500 "C for 24 h.Melting- Fluorine, yo Loss of point/ r-A-------, fluorine, No. Compound "C Observed Calculated yo relative 1 Perfluoro(tricyc1o- [5,2, 1,02vG]deca-3,8- diene), C,,F,, 45 9.7 65.5 85 C,HFl,O, 52 21.7 66.5 67 C,H,F,NO* 88 (a) 17.5 30.1 42 (b) 21.6 28 2 Perfluorooctanoic acid, 3 Trifluoroacetanilide, (c) 2.0 93 4 p-Fluorobenzoic acid, C,H,FO2 184 11.2 13.6 17 5 Teflon,t (CF,), 327 71.3 76.0 6 * (a) Ashed with magnesium succinate; ( b ) ashed with magnesium succinate and lithium hydroxide ; (c) trifluoroacetanilide - magnesium oxide paste introduced suddenly into an atmosphere of 400 "C.t Ashed at 700 "C.12 THE DETERMINATION OF ANION-FORMING ELEMENTS R o c . Analyt. Div. Chem. SOC. 500 "C. In all instances, except for compound 3(c), the temperature of the electric muffle furnace was increased slowly. The results given in Table I indicate that the loss of fluorine through ashing may be qualitatively related to the volatility* of the organic compound in question.The loss of 6% of fluorine from Teflon (compound 5 ) is probably due, in view of its high decomposition point (400 "C), to the inability of the magnesium oxide - oxygen system to achieve, even at 700 "C, quantitative conversion of fluorine into fluoride In search of a decomposition technique that would be satisfactory with both M-F and R-F bond situations, we chose the pyrohydrolytic meth0d.6-~ The proposed method, suitably modified in the light of our experience, proved successful for all types of fluorine compounds known to us, including the following: (i) thermally stable polymers (breaking strong C-F bonds) ; (ii) low-boiling liquids and air- and moisture-sensitive compounds (cracking a sealed sample inside the leak-proof apparatus) ; (iii) biological materials (equally applicable to organically and inorganically bound fluorine) ; and (iv) compounds containing trace amounts of fluorine (combustion on a gram scale resulting in a 1 000-fold increase in concentration).This technique, devised in 1969 by Manohin and Kakabadse, has proved successful in tests on about 5 000 fluorine compounds, covering a wide range of chemical situations, especially as regards organofluorine species and problems of trace fluorine determination.Fig. 1. Combustion train: S, syringe for injecting distilled water through T-piece into silica-wool plug, QM; B, gas micro-burner; MF, movable furnace for heating sample (plus additive) ; QP, plain silica-wool; F, furnace permanently maintained at 1 100 "C; R, plastic receiver containing distilled water for the absorption of hydrofluoric acid ; and SF, safety flask containing distilled water.The combustion train is shown diagrammatically in Fig. 1. The silica combustion tube has an inside diameter ranging from 11 mm (milligram-scale combustion) to 35 mm (gram-scale combustion), narrowing to 5 mm, and bent at right-angles just beyond the constriction.9 The sample in a platinum boat is set inside the movable furnace, MF, about 7 cm away from the high-temperature furnace, F, and a loosely packed silica-wool plug, QM, (wrapped in platinum gauze) is inserted near the inlet end of the combustion tube.QM is kept moist by injecting distilled water intermittently from the plastic syringe, S, through the T-piece; S has a capacity of 10 cm3 for an 11 mm bore tube and 30 cm3 for a 25 mm bore tube.Moisture carried by oxygen or air (preferably the latter to reduce the risk of explosions) at a flow-rate varying from 0.1 to 0.5 1 min-l is vaporised by the gas microburner, B. In order to prevent loss of hydrofluoric acid from the plastic receiver, R, the latter is connected to a small silica flask, SF.The portion of the combustion tube inside F is loosely packed with platinised silica-wool, while the layer QP consists of plain silica-wool. The latter hinders the penetration of trace amounts of vanadium(V) oxide (additive) into F and it also aids and indicates the progress in the degradation of carbonaceous materiallo in the vicinity of the platinum boat.January, I9 77 THE DETERMINATION O F ANION-FORMING ELEMENTS 13 While F is permanently maintained at 1 100 “C, M F is switched on after the introduction of the sample and its temperature is raised to between 750 and 1000 “C, depending on the compound and the additive.On a semi-micro scale, the combustion is complete within 25 min . Organic compounds do not require additives but the presence of moisture is imperative.Clark,ll using a similar combustion train, but employing a stream of dry oxygen, found that consistently low results were obtained. The reported interference by s i l i ~ a , ~ 1 ~ ~ , ~ ~ when present in biological materials, does not present a problem in pyrohydrolysis. Pyrohydrolysis combined with low-temperature ashing offers a simple and elegant means of distinguishing between organically and inorganically bound fluorine.Oxygen excited by a radio-frequency electromagnetic field ensures a controlled removal of organic materials while the original morphology of the inorganic constituents of the ash is maintained. Samples of Darjeeling tea subjected to decomposition by pyrohydrolysis (total fluorine) and also to low-temperature ashing followed by pyrohydrolysis (inorganic fluorine) gave the values of 104 and 106 p.p.m.of fluorine, respectively, clearly indicating the absence of organic fluorine in tea.3 This finding is in agreement with Peters and Shorthouse,l4 who used alkaline hydrolysis to liberate organic fluorine in tea. Schematically, decomposition by pyrohydrolysis can be represented as follows : Inorganic fluorides: MF,, + nH,O = MO, + 2nHF Organofluorines: RF4 + x0, + 2H20 = xC0, -t xH20 + 4HF The assistance of J.M. Bather, R. Perry, S. Sasiadek, A. E. Tipping, E. C. Weller and P. Woodbridge is gratefully acknowledged. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Re€erences Hall, R. J., Analyst, 1968, 93, 461; 1963, 88, 76.Dixon, J. P., “Modern Methods of Organic Microanalysis,” Van Nostrand, New York, London, 1968. Kakabadse, G. J.,,Manohin, B., Bather, J. M., Weller, E. C., and Woodbridge, P., Nature, Lond., Samachson, J., Slovik, N., and Sobel, A. E., Analyt. Chem., 1957, 29, 1889. Taves. D. R., Nature, Lond., 1968, 217, 1050. Furman, N. IT, Editor, “Standard Methods of Chemical Analysis,” Volume 1, Van Nostrand, New Nardozzi, M.J., and Lewis, L. L., Analyt. Chem., 1961, 33, 1261. Shiraishi, N., Nakagawa, G., and Kodama, K., 8th International Fluorine Symposium, Kyoto, 1976, Newman, A. C. D., Analyst, 1968, 93, 827. Kakabadse. G. J., and Manohin, B., Mikrochim. Acta, 1965, 855 and 1136. Clark, H. S., Analyt. Chem., 1951, 23, 659. Remmert, L. F., and Parks, T.D., Analyt. Chem., 1953, 25, 450. Evans, W. H., and Sergeant, G. A., Analyst, 1967, 92, 690. Peters, R., and Shorthouse, M., Nature, Lond., 1964, 202, 21. 1971, 229, 626. York, London, 1966, p. 437. Paper 1-13. Problems and Solutions in the X-ray Fluorescence Analysis of Anion-forming Elements P. L. Warren Research Department. Analytical Divison, Imperial Chemical Industries Limited, Plastics Divisiom, Welwyn Garden City Problems arising from the determination of anion-forming elements by X-ray fluorescence techniques can be classified under three headings, vix., sample preparation, sensitivity and elemental losses.Techniques are described to solve these problems or, a t least, to mitigate their effects. Sample Preparation For quantitative work the specimen thickness must exceed the “critical depth” of the This depth occurs at the point where increasing the thickness of the fluorescent radiation.14 R o c .AnaZyt. Div. Chem. SOC. specimen produces no significant increase in the measured fluorescent radiation. Critical depth is a function of the wavelength of that radiation and the matrix of the specimen. Ele- ments of low atomic number, including many of the anion-forming elements, produce “soft” fluorescent radiation, i.e.characteristic radiation of long wavelength and low penetrating power. The relationship between atomic number, matrix and critical depth can be shown by comparing the halogens (see Table I). - THE DETERMINATION OF ANION-FORMING ELEMENTS TABLE I VARIATION OF CRITICAL DEPTH WITH WAVELENGTH AND MATRIX Critical depth/mm Atomic Analyte Wavelength/ Polyethylene Steei Element number line A* matrix matrix F 9 F Ka 18.3 0.006 0.001 c1 17 C1 Ka 4.7 0.26 0.004 Br 35 Br Kcc 1.04 19.3 0.029 I 53 I Ka 0.43 98.9 0.351 I La 3.14 0.87 0.013 * lii = 10-10 m.These considerations influence the choice of both the method of sample preparation and the analyte line to be used.When the critical depth for a particular analysis is small, then the effective volume of the sample being examined can represent only a small proportion of the total specimen volume. If the specimen surface is to be representative of the sample as a whole, the sample must be completely homogeneous. However, during the moulding of polymer discs prior to X-ray examination, organic additives, which are monitored by X-ray fluorescence, can migrate to or from the surface.This migration can seriously affect the X-ray intensities of the characteristic elements such as phosphorus, sulphur and chlorine. The consequences of migration can be minimised by careful skimming of the plastic disc on a lathe. The effects of this treatment on flame-retardant nylon are shown in Table 11.This treatment also gives a flat reproducible surface and removes any surface contamination picked up during moulding. TABLE I1 EFFECT OF SURFACE TREATMENT ON X-RAY INTENSITIES OF Sn Ka, C1 Ka AND Si Ka Thickness removed from surfacelmm Nil (original moulding) 0.01 0.02 0.06 0.11 0.19 0.25 0.31 0.50 (normal amount removed) * Sn Ka: critical depth 13 mm. 7 C1 Ka: critical depth 0.08 mm.2 Si Kcc: critical depth 0.03 mm. X-ray intensity ratios Chlorinated Tin oxide* hydrocarbon? 2.14 2.83 2.16 2.76 2.16 2.68 2.13 2.44 2.13 2.39 2.13 2.41 2.13 2.43 2.12 2.49 2.11 2.47 f A I Glass $ 1.60 2.02 2.42 3.23 3.40 3.32 3.22 3.13 3.15 Sensitivity and Lower Limit of Detection The sensitivity of any specific determination depends mainly on the count rate that can be achieved, i.e., the slope factor of the calibration.“Light” elements are adversely affected because of low fluorescent yield, the fact that useful radiation is attenuated by the windows of the X-ray tube and detector, and the poor diffraction efficiency of the special crystals. ForJanuary, 197‘7 THE DETERMINATION OF ANION-FORMING ELEMENTS 15 elements lighter than vanadium (2.5 A) the longer wavelength radiation is absorbed by the air path of the spectrometer.This effect can be remedied by applying vacuum conditions, or in the instance of volatile liquids by using a helium atmosphere. Attenuation of the fluorescent radiation by the window supporting the liquid (or powder, granules, etc.) also reduces sensitivity. The lower limit of detection is a function not only of count rate but also of background intensity and is defined as the amount that gives a net line intensity equal to three times the standard deviation (a) of the background count.The determination of phosphorus in nylon granules is complicated by the phosphorus impurity in the polyester window of the sample cell. A blank value of 2 700 counts (net counts when concentration of phosphorus = 0 p.p.m.) was reduced to 140 counts by using an alternative film (polypropylene).Consequently the l o ~ e r limit of detection fell from 20 to 5 p.p.m. Elemental Losses This volatility is made apparent in losses, which cause problems in the lack of permanence of standards and reference discs, as well as in stability of samples. Unstabilised poly(viny1 chloride) samples, on repeated irradiation, first discolour and then degrade with loss of hydrogen chloride.Standards for the determination of coat thicknesses of poly(viny1idene chloride) on polyester film have a limited life. Count rates (ClKor) have decreased by up to 20% over 3 years as the coating is gradually “burnt off” by repeated exposure to X-rays. During the fusion of glass reference beads sulphur, chlorine, bromine and iodine can be lost by reduction and volatilisation.Losses can be minimised by adding an oxidising agent (sodium nitrate) to the fusion mixture, which should have a low softening point. One characteristic of the anion-forming elements is their volatility. Pre-concentration Pre-concentration is a valuable technique in the determination of trace amounts of elements, especially of anion-forming elements, for which alternative wet-chemical methods can be very time consuming.Small amounts of anion-forming elements, present in polymeric and other organic materials, can be converted by the oxygen combustion technique into inorganic ions in solution. Anions in solution can be retained on ion-exchange resin loaded papers or precipitated and concentrated on Millipore filters.Determination of trace amounts of anion radicals such as halide and sulphate has been achieved by precipitation with silver( I) nitrate or barium chloride. Filtration on a membrane filter disc (Millipore) concentrates the anion uniformly over the surface. The disc is then mounted in a sample cell between two layers of polyester film.The net intensities are compared with those obtained from standard solutions, following the same procedure. The calibration graph is normally linear over the range 0-100 pg, giving a lower limit of detection of about Trace amounts of both anions and cations can be absorbed on special papers incorporating ion-exchange resins. Our investigations have concentrated on the iodide ion, using a strong base resin paper (Type SB-2).This particular paper has the resin in the chloride-ion form. However, as the hydroxide ion is more readily replaced by other ions, the papers are normally pre-treated with 1.0 M sodium hydroxide solution to convert to the hydroxide-ion form. A disc is cut from the paper and held flat in the filtering apparatus, exposing a surface area 1.5 cm in diameter. The test solution, which should be just acidic, is passed several times through the wet activated ion-exchange paper. To achieve the maximum exchange of ions the filtration process must be repeated until equilibrium is reached. Experiments with a standard solution (30 pg of iodide ion) proved that three filtration passes were enough to retain greater than 99% of the available ions. The dried paper is mounted in a sample cell with a backing of stretched polyester film to keep the disc flat. Sample and standards are examined, recording the net count rate of the I La line. Allowing for the X-ray intensity of the reagent blank, a lower limit of detection of 0.1 pg of iodide ion can be achieved. 2 pg. References 1. Berth, E. P., “Principles and Practice of X-ray Spectrometric Analysis,” Plenum, London, 1975.16 FOURTH SAC CONFERENCE PrOc. Analyt. DiV. Chenz. SOC. Jenkins, R., and De Vries, J. L., “Practical X-ray Spectrometry,” Macmillan, London, 1970. Squirrell, D. C. M., and Warren, P. L., “The Conversion of Philips PW1212 X-ray Spectrometer to Full Helium Path,” Proceedings of the 6th X-ray Analytical Conference, Southampton, 1968, N. V. Philips’ Gloeilampenfabrieken, Eindhoven, The Netherlands. Warren, P. L., “The Analysis of Plastic Materials in the Granular Form by X-ray Fluorescence,” Proceedings of the 9th X-ray Analytical Conference, Exeter, 1974, N. V. Philips’ Gloeilampenfabrieken, Eindhoven, The Netherlands. Campbell, W. J., Spano, E. F., andGreen, T. E., Analyt. Chem., 1966, 38, 987. 2. 3. 4. 5 .

ISSN:0306-1396    

DOI:10.1039/AD9771400007

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

16 FOURTH SAC CONFERENCE Proc. Analyt. Div. Chenz. Soc. Fourth SAC Conference J u l y 17-22, 1977, Birmingham Social Programme A full and varied social programme has been organised for the benefit of delegates and their guests at the 1977 SAC Conference, which is to be held at Birmingham. Information is given below about the tours and industrial visits, the Ladies’ Programme and various Conference functions.Tours Tuesday, July 19th A number of evening tours has been arranged, the first option being a steam-hauled dining excursion on the Severn Valley Railway. The Severn Valley Railway Company operates steam-hauled trains along 14 miles of line between Bridgnorth and Bewdley, both on the River Severn. Dinner will be taken in a Great Western Railway dining/kitchen set, built in 1932.The second tour is to the Fox Inn at Stourton for a wine tasting and the third is a 3-h cruise on the River Severn, beginning at Stourport-on-Severn, and during which there will be a buffet meal with wine. Tour No. 4 is to Malvern for a historical banquet at the Orangery, Mount Pleasant Hotel, and for Tour No. 5 transport has been arranged for delegates and their guests to visit theatres in Birmingham, Wolverhampton and Coventry.Wednesday, July 20th There will be six whole-day tours, one of these being to Harvey’s of Bristol. After visiting Harvey’s Wine Museum there will be a buffet lunch in the cellars and a tour of their modern production centre at Whitchurch. There will then be a visit to Brunel’s iron ship, the S.S. Great Britain, built in 1845, followed by dinner in Cheltenham.A tour of the Skol Lager Brewery at Wrexham has also been arranged and visitors will be able to enjoy a short visit to Chester before dining at a former stately home on the site of the Battle of Rowton Moor. The third tour begins with a visit to Berkeley Castle and after lunch at a hotel on the edge of the Cotswold Hills there will be a visit to the Falconry Centre.Tour No. 4, a visit to Warwick Castle and Charlecote Park, concludes with an evening spent at Stratford- upon-Avon and the opportunity to attend a performance at the Shakespeare Memorial Theatre. The fifth tour will consist of a visit to the Ironbridge Gorge Museum, The Coalbrookdale Museum housing Abraham Darby ’s Furnace, The Bedlam Furnaces, Blists Hill Open Air Museum, The Coalport China Works Museum, Tar Tunnel and the Hay Inclined Plane.In the evening delegates and their guests will partake of a grill at a nearby country inn and will then be taken to local hostelries where real ale is served. Industrial Visits Wednesday, July 20th delegates, in addition to the whole-day tours: The following visits have been arranged for Fisons Pharmaceutical Division, Lough- GKN Group Technological Centre Inco Europe Limited, Birmingham British Ceramic Research Association, Penk- Gladstone Pottery Museum, Longton, Stoke- borough hull, Stoke-on-Trent on-Trent Ladies’ Programme Monday, J u l y 18th A coffee party will be held in the morning.Committee members will then be available to act as guides for those wishing to have lunch in Birmingham and spend the afternoon shopping.There will also be an afternoon visit to Worces- ter, where arrangements have been made for a party to visit the Worcester Royal Porcelain Co. Ltd. Tuesday, J u l y 19th Two whole-day visits have been arranged, one to Blenheim Palace, at Woodstock, near Oxford,January, 1977 CONFERENCES AND MEETINGS and the other to ‘rutbury, a typical old English town near Burton-on-Trent. -\t Blenheim there will be a conducted tour followed by lunch in the Palace Restaurant.At Tutbury arrange- ments have been made for the party t o visit the Sheepskin Shop and factory a t the Old Mill. Lunch will be served a t a 14th century coaching inn and afterwards ladies may visit the ruins of the Anglo-Saxon Castle and also the Norman Priory Church of St.Mary. Thursday, J u l y 2 1st A whole-day trip has been arranged to Sudeley Castle, and there will be an afternoon visit to Aston Hall. Friday, July 22nd Visits to the Birmingham Art Gallery and the Botanical Gardens in the morning will be followed at noon by a sherry reception and lunch. A visit to Harvington Hall will take place in the afternoon. Conference Functions Various functions have been arranged for delegates and their guests, beginning on Sunday, July 17th, when sherry will be served with a cold collation. The following evening there will be a Grand Buffet. A Banquet has been arranged for Thursday, July Zlst, a t the Hotel Metropole in Birming- ham’s National Exhibition Centre, and will be preceded a t the Hotel by a Civic Reception given by kind invitation of the Lord Mayor of Birmingham. As a conclusion to the Conference an ox and pig roast will be held in the grounds of the University on Friday, July 22nd.

ISSN:0306-1396    

DOI:10.1039/AD9771400016

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

January, 1977 CONFERENCES AND MEETINGS 17 Conferences and Meet i ngs Chromatography Discussion Group Symposia February 16, 1977, London A one-day symposium entitled “Ion-exchange and Ion-pair Chromatography.” April 29, 1977, London The Annual General Meeting and Spring Symposium entitled “Applications of Chromato- graphy to Environmental Analysis.” For further information contact the Executive Secretary, Chromatography Discussion Group, Trent Polytechnic, Burton Street, Nottingham, NGl 4BU.Ninth Meeting of the British Mass Spectro- scopy Group September 27-29, 1977, Swansea This Meeting is an open one and will cover all aspects of mass spectrometry, including its chemical and physical applications. In addi- tion to specialist contributions, i t is hoped that a number of papers presented at this meeting will be able to provide an introduction to some of the applications of mass spectrometry for those with less experience in this field.There will also be an opportunity to present a number of papers in poster sessions. Intending contri- butors are invited to submit abstracts for short papers before April 30th, 1977. Further details can be obtained from Dr. J. R. Chapman, Secretary, British Mass Spectroscopy Group, AEI Scientific Apparatus Ltd., Barton Dock Road, Urmston, Manchester, M31 2LD.

ISSN:0306-1396    

DOI:10.1039/AD9771400017

出版商:RSC    

年代:1977

数据来源: RSC