摘要:

Proceedings of the Society for Analytical Chemistry Analytical Division Chemical Society CONTENTS Proc. SOC. Analyt. Chem. VoI. 9 No. 8 Pages 159470 Special Techniques Group . . 159 Reports of Meetings “Selectivity in Trace Analysis,” “Kinetic Data from Thermal “Safety and Legal Aspects of Stirling . . .. .. 160 Analysis” . . .. .. 162 Food Additives” . . .. 168 Notices . . .. .. .. 169 Papers Accepted for The Analyst I69 Publications Received .. 170 Forthcoming Meetings Back Cover August 1972 PAYCAL Vol. 9 No. 8 August 1972 PROCEED I N GS THE SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISION CHEMICAL SOCIETY OF Hon. Secretary W. H. C. Shaw Officers of The Society for Analytical Chemistry and the Analytical Division of The Chemical Society President C. Whalley Hon. Treasurer Hon.Assistant Secretaries G. W. C. Milner D. I. Coomber O.B.E.; D. W. Wilson Secretary Miss P. E. Hutchinson 9/10 SAVILE ROW LONDON WIX IAF Tclephone 01-734 9864 Editor J . B. Attrill Assistant Editor P. C . Weston Proceedings is published by The Society for Analytical Chemistry and distributed t o all members of the Analytical Division and to subscribers with The Analyst; subscriptions cannot be accepted for Proceedings alone. Single copies can be obtained direct from The Chemical Society Publications Sales Office Blackhorse Road Letchworth Herts. SG6 I HN (NOT through Trade Agents) price 25p. post free. Remittances MUST accompany orders. 0 The Society for Analytical Chemistry ANNUAL REPORTS ON ANALYTICAL ATOMIC SPECTROSCOPY Volume 1-1971 The Society for Analytical Chemistry announces the publication of the first volume of an important new series.A comprehensive and critical report of developments in analytical atomic spectroscopy is to be produced as a single volume annually and this first volume has been compiled from more than 1000 reports received from world-wide correspondents who are internationally recognised authorities in the field and who constitute the Editorial Board. In addition to the rapid publication of a comprehensive survey of developments throughout the world published in national or international journals a particular aim of the series will be to include less widely accessible reports from local national and international symposia and conferences concerned with atomic spectroscopy. The first volume of this series concerned with the year 1971 has just been published. Obtainable from Society for Analytical Chemistry Book Department 9/10 Savile Row London WIX IAF. Price 25.00. Members may buy personal copies at the special price of 23.00

ISSN:0037-9697    

DOI:10.1039/SA97209FX027

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISIOX CHEMICAL SOCIETY Forthcoming Meetings-coniinzred September Thursday 14th and Friday 15th CANTERBURY Friday 15th HULL \\Tednesday 20th HEREFORD !Monday 25th CARDIFF Tli u r sda y 2 8 th SALFORD “Analytical Techniques for the Determination of Contaminants in Factory “,%nalysis for Residues of Pesticides and Their Degradation Products in “The Determination of Lead in the Environment-X Multi-technique The University of Kent Canterbury. SORTH EAST REGION jointly with the Hull and District Section of the “The Determination of Alcohol for IicVenue Purposes,” by R. J. Mesley. “The Determination of Alcohol in Pharmaceutical Preparations,” by “The Determinationation of Alcohol in Blood and Urinc,” by -1. S. Curry. The University Hull; 2 p.m. WESTERN and MIDLANDS REGIONS.“Recent Developments in X-ray Fluorescence Analysis,” by P. 11.. Hurley. Henry Wiggin & Co. Hereford; 6 p.m. “Enzymes in Analysis,” by Professor G. G. Guilbault. Chemistry Department University of \Tales Institute of Science and NORTH WEST REGION and THERMAL ~IETHODS GROUP on “Organic *1ppli- “The Thermal Degradation of Cellulose in Nitrogcn,” b>- D. Dollimore and “Thermometric Titrimetry,” by L. S. Hark. “Thermal Analysis of Fats and Oils,” by D. Tresser. The University Salford; 2 p.m. Atmospheres,” by R. Wood. the Environment,” by I<. I. Beynon. Approach,” by J . S. Hislop A. Parker and M. S. \L7. LVebb. CS on “Alcohol-Its Determination.” D. A. Elvidge. U‘ESTERN REGION. Technology Cathays Park Cardiff; 3.30 p.m. cations of Thermal Analysis.” B Holt.SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISION CHEhlICAL SOCIETY Forthcoming Meetings August Monday 28th to EUROANALYSIS I jointly with the Analytical Chemistry Division of the Gesellschaft Deutscher Chemiker and the Analytical Chemistry Section of the Koninklij ke Nederlandse Chemische Vereniging. Friday Septem- ber 1st HEIDELBERG Chemistry Department The University Heidelberg. September Tuesday 5th RiIIDLANDs REGION on “Liquid Chromatography.” NOTTINGHAM “High Performance Liquid - Solid Adsorption Chromatography,” by “High Efficiency Liquid Chromatography and its Applications in the The Boots Co. Ltd. Pennyfoot Street Nottingham; 6.0 p.m. JOINT PHARMACEUTICAL ANALYSIS GROUP (part of British Pharmaceutical Conference 1972) on “The Training of the Analyst What Do We Need and What Are We Getting?” R.Amos. Pharmaceutical Industry,” by F. Bailey. Tuesday 12th KEELE “Needs of Larger Industrial Units,” by C. Daglish. “Needs of Smaller Industrial Units,” by D. 0. Singleton. “Needs of Official Laboratories and Institutions,” by G. F. Phillips. “Undergraduate Training,” by C. G. Butler. “Postgraduate Training,” by W. D. Williams. The Foundation Year Theatre The University Keele; 2.15 p.m. Wednesday 13th PARTICLE SIZE ANALYSIS GROUP Colloquium on “Techniques for Particle and Thursday 14th Characterisation.” SALFORD Thursday 14th and Friday 15th CANTERBURY Plenary lectures to include “Projected Area Measurement,” by M. I. Barnett. “Hydrodynamic Techniques,” by R. G. Blezard. “Volume Measurement,” by T. Allen. “Surface Area Measurement,” by N. R.Thompson. “Presentation of Data and Statistical Analysis,” by C. R. G. Treasure. The University Salford. MICROCHEMICAL METHODS CHROMATOGRAPHY AND ELECTROPHORESIS AUTOMATIC METHODS RADIOCHEMICAL METHODS and ELECTRO- ANALYTICAL GROUPS on “Chemical Analysis and the Environment.” Septevnber 14tlz- Introduction by Professor R. F. Hudson. Plenary Lecture by H. Egan. “Analysis for Airborne Contaminants to Assess Effects on Health,” by “Methods of Analysis for Traffic Pollutants,” by H. N. M. Stewart. “Radiochemical Analysis a t the Laboratory of the Government Chemist Septevnbev 15tJa- “Sea Water Analysis with Special Reference to Pollution,” by Professor J . P. Riley. “Sampling and Analysis of River Water,” by D. C. Hinge. “Analysis of Toxic Species in IVater,” by M. J . Stiff. “Analytical Problems Associated with Marine Radioactive Iiaste Disposal,” “Measurement and Control of Toxic Hazards in the Industrial Environ- [continued i m i d e back c w e v B. T. Commins. for Pollution Control,” by D. I. Coomber. by J . W. R. Dutton. ment,” by S. J . Silk. Printed by W Heffer & Sons Ltd Cambridge England

ISSN:0037-9697    

DOI:10.1039/SA97209BX029

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

August 1972 PROCEEDINGS OF Vol. 9 No. 8 THE SOCIETY FOR ANALYTICAL CHEMISTRY ANALYTICAL DIVISION CHEMICAL SOCIETY The Special Techniques Group IN 1043 a meeting of the Society of Public Analysts approved a proposal by the Council for the formation of Groups for special branches of analytical chemistry. Successive issues of The Analyst in 1944 gave notice of the proposed formation of a Group dealing with physical methods of analysis listing spectrographic photometric polarographic and X-ray diffraction methods as examples. 115 members responded to this invitation and the inaugural meeting of the Physical Methods Group was held on February 7th 1945 the 70th anniversary of the foundation of the Society. Dr. R. C. Chirnside was elected the first Chairman and delivered the inaugural address and it is a matter of pride to the Group that both he and Dr.A. A. Smales Chairman in 1953-55 were subsequently elected to the office of President of the Society. The rapid growth in the use of physical methods in analysis was reflected in the growth of membership which topped the thousand mark by 1965. During this period a number of entirely new techniques such as gas - liquid chromatography and atomic-absorption spectro- scopy (to give only two examples) were introduced and the Group was always quick to arrange meetings at which leading exponents of these methods could introduce them to a wider audience. In the particular field of spectroscopy the Group has co-operated with other interested bodies through membership of the British Spectroscopists Co-ordinating Committee now re-constituted as the Association of British Spectroscopists.P. B. Smith R. M . Dagiinll S. Greenfield Early in its life the Group set up a Polarograpliic Panel which helped considerably in bringing together the workers involved in the establishment of this technique in the U.K. By the late 1950s however this panel had fulfilled its main objective and was disbanded but the Group continued to organise meetings on polarography. In 1962-63 the Group was asked by Council to set up panels dealing specifically with atomic-absorption spectroscopy and thin-layer chromatography two techniques that were making a big impact on analytical chemistry. An innovation was the opening of membership of these panels to non-members of the Society. These panels were immediately successful and later became Groups in their own right when the Society’s new Group Structure came into being in 1964.The new structure took into account that many physical methods had become accepted as normal practice in analytical chemistry and the Physical Methods Group became the Special Techniques Group with responsibility for very new developments and older but highly specialised physical methods not covered by other Groups. Recent topics have 159 1 GO SELECTIVITY I N TRACE ANALYSIS [ P m . SOC. Analyt. Chew. included mass Auger Mossbauer nuclear quadrupole resonance and electron spin resonance spectroscopy the application of solid-state detector systems fluorescence analysis and high accuracy gas analysis. This is strong evidence that the forward-looking tradition built up by the Physical Methods Group is being maintained in the Special Techniques Group.This Group is the only one whose title does not limit it to a particular field of analytical chemistry and successive Committees have endeavoured to define the Group’s objectives and functions. At the same time it has been necessary for them to arrange meetings on “Special Techniques” and following the experience of 8 years’ programmes the present Committee has formulated the following statement of its object and terms of reference- “The object of the Special Techniques Group is to encourage assist and extend the knowledge of the less common techniques of analytical chemistry. The techniques which do not fall within the terms of reference of other Groups of the Analytical Division of The Chemical Society or those which are of very recent orib‘ rin are considered the province of the Group. Neglected or little used techniques which in the opinion of the Committee merit further attention are also considered to be the province of the Group.” The foregoing account was written by Dr. T. L. Parkinson who for many years was an active member of the Committee serving as Honorary Secretary and Treasurer from 1958 to 1965 followed by 4 years as Vice-chairman and Chairman. The present Committee asked Dr. Parkinson to write this account in appreciation of his past services to the Group

ISSN:0037-9697    

DOI:10.1039/SA9720900159

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

1 GO SELECTIVITY I N TRACE ANALYSIS [ P m . SOC. Analyt. Chew. Selectivity in Trace Analysis University of Stirling June 21st to 24th 1972 A JOINT Meeting of the Atomic Spectroscopy the Chromatography and Electrophoresis the Microchemical Methods and the Radiochemical Methods Groups and the North East North West and Scottish Regions of the Society was held at the University of Stirling from June 21st to 24th 1972. The subject of the meeting was “Selectivity in Trace Analysis” and papers on a wide range of techniques attracted over 100 delegates and guests including a number from overseas. The scientific programme opened on the evening of Wednesday June 21st with a Discussion Meeting on “Detection Limits” led by Dr. G. F. Kirkbright and Dr. D. A. Pantony. A lively and wide-ranging discussion on the statistical interpretation and relevance of detection limits ensued in which Messrs.D. J. Hobbs and L. R. Morris also played a prominent part. The morning and afternoon of June 22nd and 23rd were taken up with lecture sessions which were held in Lecture Theatre ALT3 of Building T70 opposite the McRobert Centre. At the Opening Session Mr. W. Dunnet Vice-chairman of the Scottish Region introduced Mr. C. Whalley President of the Society and Professor W. Parker Head of the Chemistry Department of the University of Stirling. Mr. Whalley welcomed delegates to the meeting and suggested that multi-group Joint Meetings might well become a more common feature in the Society’s programme in the future and would receive the support of the Society. Pro- fessor Parker welcomed delegates to the University of Stirling and mentioned that the Analytical Division was the first Division of the Chemical Society to hold a meeting at the University and hoped that they would enjoy the facilities offered and return on subsequent occasions.The scientific programme consisted of two Plenary Lectures and twenty original con- tributions. The Plenary Lecturers delivered the opening lecture on each morning of the meeting and the first “Selectivity in Trace Element Analysis” by Dr. A. A. Smales of A.E.R.E. Harwell got the meeting off to a lively start with a series of demonstrations that illustrated the selective properties of particular reactions and techniques. He also challenged some current views of the potentialities of atomic-fluorescence spectrometry. Dr. H. Egan the Government Chemist in the second Plenary Lecture “Selectivity in Trace Analysis The Detection and Estimation of Compounds,” discussed mainly the determination of organic compounds by chromatographic techniques and the coupling of these with instrumental methods used for August 19721 SELECTIVITY I N TRACE ANALYSIS 161 identification.The other papers covered a wide range of subjects from determination of trace elements in steel river water silica and biological materials to selective chromatographic techniques for the determination of phenols and the coupling of gas chromatography with mass spectrometry. One of the most interesting papers was that by R. 0. Scott and A. M. Ure on “Some Sources of Contamination in Trace Analysis,” in which Dr. Scott outlined the many possible sources of elemental contamination that may be derived from ordinary lab- oratory equipment and he surprised the delegates with the wide range and high concentrations of possible contaminants.Summaries of the papers will be published in Procscdings shortly. (L-R) Dr. S. J . Lyle (Chairman Radiochemical Methods Group) All/. W. Dunnet (Vice- Chairman Scottish Region) Dr. H . Egan (Plenary Lecturer) Dr. A . A . Smales (Plenary Lecturer) Dr. D . A . Pantony ( Vice-Chairman Microchcinical Methods Gvoup) MY. D. W . Wilsoa (Chairman Group Liaison and Policy Committee) Mr. W . R. N d l (Chairman Atomic Speclvoscopy G ~ o u p ) and Mr. C . WJialley (President) Delegates were accommodated in Murray Hall of the University of Stirling and meals were taken in the McRobert Centre. Transfer from Murray Hall to the McRobert Centre is by a footbridge across Airthrey Loch which is situated in the middle of the University site and must surely make it one of the most beautiful University sites in the country.The Conference Dinner was held in the McRobert Centre on the Thursday evening and diners were entertained by a speech from Dr. Magnus Pyke on the theme of “Science and Conviviality.” Mr. C. Whalley President of the Society thanked the organisers of the meeting and in par- ticular members from the Glenochil Technical Centre at hlenstrie for their help in setting up the meeting and for arranging the visit to the Carsebridge Distillery. This took place on the Friday evening and was enjoyed by all those who went. The Social Programme was concluded by a coach trip to the Trossachs on Saturday June 24th which also included a sail on Loch Katrine. While the delegates were taking part in the scientific sessions a number of lady guests had their own programme which included a full-day coach trip around Perthshire and a morning visit to Stirling Castle.

ISSN:0037-9697    

DOI:10.1039/SA9720900160

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

162 Kinetic Data from Thermal Analysis The following are summaries of six of tlie papers presented at a meeting of the Thermal Analysis Group held on February 22Rd and 23rd 1072 and reported in tlie Jlarch issue of Proceedings (p. 56). Some Observations on the Shapes of Thermogravimetric Curves and the Kinetic Parameters Derived from These Curves BY ni. A. HUGHES (Bradford Uiiivrr2ity. BYadfovd S’C iksltive) THE shape of the weight-loss curve obtained when isothermal decompositions take place is solely dependent upon the mechanism that accompanies the decomposition at that tempera- ture. In contrast the shape of the t hermogravimetric curve obtained from programmed- t emperature experiments is dictated by the values of the kinetic parameters A (pre-exponential factor) and E* (activa- tion energy) the heating rate ( a ) and the mechanism.A computer program was described that affords plots of cc (fraction decomposed) ijt’YSZLS time for simulated thermogravimetric curves the analogue simulation language B.A.S.E. being used. Vb7ith the aid of this program the experimental thermogravimetric curve can be compared with simulated curves. The equation used to set up the patch diagram was jdor = -IT exp(-E::::/RT)dl. Such mechanisms are described by a number of kinetic equations. 2 = 1.0 A T2 a .r o! = 0.0 This work shows that the shape of the thermogravimetric curves is very sensitive to small changes of value of A and E* but less sensitive to changes in mechanism and heating rate. Results to date indicate that E* values obtained from temperature-programmed experi- ments are higher than E* values obtained from isothermal experiments on the same substance.In some instances a complete fit of the simulated curve over the whole experimental curve is not obtained; this could be due to a changing mechanism during the course of reaction (with changing values of A and E*) or because self-cooling has occurred or because the basic equation above used in the program. does not give a complete description of tlie reaction. Reaction Kinetics in the Neighbourhood of Hot Wires BE’ R. A. W. HIIL CERTAIN compositions used as fuses in explosives technology react with the evolution of a large amount of heat and evolve relatively little gas. They would therefore appear to be ideal subjects for study by differential thermal analysis. However as these compositions are liable to sudden ignition with the onset of self-propagating reactions the usual niethods of differential thermal analysis are not altogether suitable.Nevertheless thermal methods related to differential thermal analysis can be applied and the reaction rate can be measured in terms of heat evolution. The compositions under discussion are usually intimate mixtures of finely powdered oxidising agents potassium permanganate (KAInO,) trilead tetroxide (Pb,O,) lead dioxide (PbO,) or barium peroxide (BaO,) plus reducing agents iron niolybdenuni silicon or antimony consolidated by pressure to give a compact unifoim material capable o f ignition and of sustained reaction. The higher the temperature the more likely are melting and vaporisation to occur during the process. However basically the compositions are “gasless,” in tliat no large volumes of permanent gas are evolved.For tlie lower range of final temperatures 600 to 1500 “C thermocouple temperature sensors have been used to follow heat evolution in these mixtures and in some instances it has been possible to deduce rates of reaction and kinetic parameters from temperature measure- ments. ( Ciiicfi/sity of Stua!hslydr Grovge Styect Glasgow C.l) The temperatures reached may be between 600 and 2500 “C. .iugust 19721 KINETIC DATA FROhl THERMAL AXALYSIS 163 Two situations both of which are of technical importance have been investigated in some detail (1) Reaction propagating at constant rate in a steady state. (2) Initiation of reaction by wires embedded in the mixture and electrically heated. THI<ORY- Ordinary heat conduction theory can be applied and if melting and vaporisation are slight changes in density heat capacity and thermal conductivity are not large and can be allowed for.At any point in the mixture where h is the thermal conductivity c is the specific heat p is the density q is the heat of reaction and E is the fraction reacted. For aisteady planar wave where d,y/dt is a constant equal to the velocity of propagation V equation (1) becomes d2T de A d2T V 2 dtz x - = c dT dX2 P'X + P 4 . Z = -- This equation represents an S-shaped temperature front as shown in Fig. 1. Time or distance Fig. 1. Temperature front in a steady planar wave Some fairly accurate measurements of temperature were made on the potassium perman- ganate P l z ~ iron or molybdenum mixtures and by application of equation (2) in the inte- grated form 1 r 1'7- - T") - -.-I h d T c=- Tf - T cpV2 dt (3) kinetic parameters were ~btained.l-~ I t was found that in potassium permanganate - iron mixtures2 the kinetics depended on the degree of consolidation.Heavily compressed mixtures were shown to react with a uniform activation energy of 25 k J mol-l whereas lightly compressed mixtures began with a high activation energy of about 200 kJ mol-l and finished with a low activation energy of less than 8 k J mol-l. Potassium permanganate - molybdenum mixtures3 reacted in t ~ 7 0 stages there being two distinct waves of reaction. The first stage was carefully analysed. Even in the narrow temperature range from 20 to 120 "C it was shown to be kinetically complex and a range of distinct but variable activation energies was recorded.In view of these interesting and rather unexpected results experiments were devised to investigate reactions initiated by heated wires. I t was thought that these would be even more interesting as reaction conditions could in principle be made more flexible than those obtaining in a steady wave where at any point in the wave E and T are strictly related i.e. E increases with T in a definite and unalterable way. 164 KINETIC DATA FROM THERMAL ANALYSIS [Proc. SOC. Analyt. Chew. REACTION INITIATED BY ELECTRICALLY HEATED WIRES- A constant electrical power was dissipated in a wire embedded in a reactive fuse mixture and the temperature of the wire was recorded. Relating the results to kinetic parameters of the reaction was of course much more difficult than for a steady-state propagating wave for several reasons (a) the non-steady state is more difficult to deal with theoretically; ( b ) the temperature was measured a t only one point whereas with a steady-state wave the temperature - time record is equivalent to a temperature distance record as dx/dt = V = constant; (c) as a result of equation (l) kinetics in the bulk of the mixture could be related to wire temperature only by an integration procedure ; and (d) cylindrical symmetry is more difficult mathematically than planar symmetry.In cylindrical coordinates we can write a2T 1 aT pq 8c cp aT -+-.-+ -.-=-.- ay2 Y a!. x at x at with a boundary condition at the wire surface r = a (4) where clpl refers to the wire and Q is the power dissipated (in J s-1 cm-I). UThen q = 0 a solution of equation (4) is possible in terms of Ressel functions and a record of the wire tem- perature can be used to deduce A and cp of the medium surrounding the wire.A useful procedure was devised.4 When the medium is reactive chemically only numerical solutions are possible. These solutions were obtained by using the National Physical Laboratory DEUCE computer as early as 1957-1958 but it is not likely that they could be usefully improved upon by modern methods. The precision of computation of wire temperature was better than 5 per cent. and often as good as 1 per cent. Following hints from the kinetics of self-sustained reaction the reaction rate was given the form dt = B(l - E ) exp dc with A and B chosen to give reasonable over-all reaction rates. h'alues of A from 20 to 200 kJ mol-l were tried and satisfactory results were obtained except for the highest value of A a t the highest temperatures.The form of these theoretical results was reasonable and reaction showed itself as a change in the curvature of the temperature - time record (Fig. 2). * Time Fig. 2 . Computed effect of chemical reaction on temperature of a heated wire (a) no reaction; (b) reaction with a low activation energy; and (c) reaction with a higher activa- tion energy. Power Q is switched on a t x and off a t y In view of the experimental and theoretical difficulties no attempt was made to find exact fits between experimental and theoretical results. Rather the method was regarded as a means of obtaining some idea of the operative value of A. In all instances this turned out to be low about 20 kJ mol-l in general agreement with the results of measurements on steady-state propagating reactions but perhaps surprising in view of the different experimental conditions (unpublished work).L4ugust 19721 KINETIC DATA FROM THERMAL ANALYSIS 166 REFERENCES 1. 2. 3. 4. Hill R. A. W. and Cottrell T. L. “The Fourth Symposium on Combustion,” \Villiams B Wilkins Baltimore 1953 p. 349. Hill R. A. W. Proc. R. Soc. A 1954 226 455. Hill R. A. W. and Welsh J. N. Trans. Faraday Soc. 1959 55 390. Hill R. A. W. PYOC. R. SOC. A 1957 239 476. Some Problems Encountered in Obtaining Kinetic Data from Thermoanalytical Measurements BY M. D. JUDD (Depavtruzent of Chemistry Povtsmouth Polytechnic Portsinoutla Hanifishive) IN studies of the kinetics of solid-state decomposition reactions whether isothermal or dynamic techniques are used many problems can be encountered.These problems are frequently of an experimental nature; for example sample size shape and packing will have a marked effect on the observed kinetics of a reaction. This will also be true for changes in specific surface and density of the sample which occur during the majority of solid-state processes. It is frequently found necessary to vary the experimental conditions to obtain a true representation of the decomposition mechanism. The kinetics of the isothermal (room temperature) decomposition under low vacuum (about 10-1 torr) have been shown to be an example of a reaction that is very dependent on the amount of the sample used in the experimental measurements. Initial experiments were carried out with a 500-mg sample when the process was found1 to be deceleratory throughout yielding the stable crystalline monohydrate.If the results were plotted in the form of a veYsz6s t/t,. (where is the time at which a = 0.5) as suggested by Sharp Brindley and Achar,2 the mechanism was found to approximate to a phase boundary controlled process above a = 0.30 with a value of n = 0.70. Below a = 0.30 there was evidence to suggest that diffusional effects were pronounced. However if the dehydration was carried out with a 20-mg sample the results gave an excellent fit to the contracting sphere equation (n = 0.67) over the a range from 0.1 to 0-95. Compacting a sample of the octahydrate into a thin disc (1 mm x 13 mm diameter) led to a value of n = 0-50 (contracting disc equation) suggesting that the particle shape strongly affects the decomposition mechanism.Hence the initial experiments with a large sample of the octahydrate were not truly representative of the reaction process. An example of the effects of sample impurities was found in a study3 of the decomposition under high vacuum of the alkaline-earth carbonates. Activation energies were calculated from thermogravimetric results by using the Coats and Redfern equation assuming a value of n = W (this was previously found to give the best fit for calcium carbonate). It was shown that for a sample of strontium carbonate the presence of about 5 per cent. of strontium oxide formed by decomposition of the hydroxide impurity increased AE from 222 k J mol-l for the pure carbonate to 352 k J mol-l. 1. 2. 3.REFERENCES Judd M. D. and Pope M. I. J . Thermal Analysis 1971 3 397. Sharp J . H. Brindley G. W. and Achar B. N. N. J . Amev. Ceifam. Soc. 1966 49 379. J ~ i d d M. D. and Pope RI. I. J . Thermal Analysis 1972 4 31. Kinetic Studies by Thermal Volatilisation Analysis BY I. C. MCNEILL (Chemistry Department Univevsily of Glasgow Glasgow W.2) THERMAL volatilisation analysis is a kinetic technique in which the rate of transfer of volatile products measured with a Pirani gauge is recorded as a function of time (isothermal con- ditions) or temperature (programmed heating). The Pirani response can be quantitatively related to the rate by means of calibration experiments when single products are involved. The area under a thermal volatilisation analysis curve can be used as a means of determining extent of reaction.Polychloroprene has been studied by thermal volatilisation analysis 1 G6 [Proc. SOC. Analyt. Chew,. under isothermal and non-isothermal conditions and the energy of activation for dehydro- chlorination has been calculated ; for comparison this has also been calculated from non-iso- thermal thermogravimetric and evolved gas analysis (titration with hydrochloric acid) results. A411 four approaches give E values in the region of 33 to 40 kcal mol-l (138 to 167 kJ mol-l). This result was compared with the reported values for PVC breakdown and discussed in rela- tion to the respective degradation mechanisms. The value of a combination of the thermal vol- atilisation and thermogravimetric analytical approaches as a means of extracting the maximum information about decomposition mechanisms was emphasised.The extreme sensitivity of the thermal volatilisation analysis method was illustrated by reference to work on polystyrene in which samples from 0.01 to 100 mg were degraded in the same apparatus; the smallest samples were in the form of films of average thickness 10 nm. Unusual degradation beliaviour was found for verj7 thin films. KINETIC DATA FROM THERMAL ANALYSIS Polymerisation Kinetics by Thermal Analysis BY K. E. J. BARRETT (Imperial Chernicnl Industries Ltd. Paints Division Slougli Rucks.) ALTHOUGH specialised calorimetric and temperature-rise techniques have previously been used for following certain polymerisation reactions the availability of commercial apparatus for carrying out differential thermal analysis and differential scanning calorimetry on organic materials now makes it possible to use thermal techniques more widely.Differential thermal analysis has been used to determine the activation energy of free- radical polymerisations from a single run,l but with certain reactive monomers the larger temperature rises obtained led to erroneous results.2 Decomposition rates and activation energies of free-radical polymerisation initiators both in solution3 and in the solid ~ t a t e ~ have also been determined by differential scanning calorimetry with a temperature-scanning mode. However for complex polymerisation reactions the use of differential scanning calori- metry under isothermal conditions is preferred. This method provides a measure of the rate of polymerisation directly and continuously and it can also be applied to gelled or hetero- geneous systems.This technique has been used to follow the diffusion-controlled bulk polymerisation of methyl methacrylate and styrene5 and also the copolymerisation of diethyl fumarate with styrene.6 Dispersion polymerisation i.e. the free-radical polymerisation of monomers soluble in aliphatic hydrocarbons to yield stable polymer dispersions has also been studied by this method. In this way the kinetics of the dispersion polymerisation of methyl metha~rylate,~ vinyl acetates and acrylonitrile and related monomers9 were determined. With the addition of a magnetic stirrer kinetic data for the emulsion polymerisation of methyl methacrylate in water have also been obtained.l0 The rates of cure of various reactive resins have also been measured by the differential scanning calorimetry techniques by using either a direct isothermal or scanning mode or by the measurement of the residual heat of reaction of partly cured samples.In this way the curing rates of polyester fumarate - styrenell and epoxy resin - diamine12-14 compositions have been determined. 1. 2. 3. 4. 5 . 6. 8. 9. 10. 11. 12. 13. 14. P REFERENCES Hoyer IT. \Ir. Sartaro A. V. and Rarrett I<. J. J . Polwa. Sci. A - I 1908 6 1033. Haas €I. C. Manning 11.1. J. and Hollander S . L ~ Ihid. 1070 8 3637. Rarrett Ii. E. J. J . Afipl. Pol~w~. Sci. 1067 11 1617. *\mbrovic P. and Lazar RI. Euv. Pol-ynz. J . SzippZ. 1969 361. Elorie I<. PIita I. and Kambc H. J . Polynz. Sci. .4-1 1968 6 2663. __ __ __ I b i d . 1969 7 2561. Harrbtt I< E. J. and Thomas H. R.I b i d . 1969 7 2(;2l. Rarrett I<. E. J. Thomas 13. R. and Tolman R. J. IUP1>,4 C Int. S?wp. ,Ilncronzol. Chenz. Pvepv. 1969 3 369. Barrett I<. E. J . and Thomas H. R. I b X 1969 3 37.7. __ __ BY. Polyra. J . 1970 2 45. Horie K. Mita I. and Kambe H. J . Polyiiz. Sci. A-1 1970 8 2530. Fava R. A. Polymev 19G8 9 137. Horie K. Hiura II. Sawada M. Mita I. and Kambc H. 7. Polyi~~. Sci. A-1 1970 8 1367. Taylor I,. J. and Watson S. M'. AitaZyt. Chena. 1970 42 297. 1 August 19721 KINETIC DATA FROhl THERMAL AKALYSIS The Thermal Decomposition of Lead (11) Carbonate BY 11. C. BALL (Loughbovougk Univevsiiy of Technology Loughbovottgh Lcics. LE11 3TU) 167 THE decomposition of lead(I1) carbonate has been extensively studied and a wide range of oxy- carbonate intermediates has been postu1ated.l Only two such intermediates have been found in the present work which mainly involved a study of the effects of varying partial pressures of carbon dioxide on the kinetics of decomposition.Tlie decomposition is as follows 6PbC0 -3(PbO.PbCO,) + 3C0 . . . . Stage (1) 3(Pb0.PbC03) -+ 2(2Pb0.PbC03) + CO . . Stage (2) Z(2PbO.PbCOS) -+ 6Pb0 + 2C0 . . . . . . Stage (3) and it seems that the kinetic rather than the thermodynamic behaviour is the explanation of the reported complexities of the decomposition. In a nitrogen atmosphere the 1 1 compound does not exist but at low pressures of carbon dioxide the decomposition proceeds as given above. At higher carbon dioxide pressures reaction (2) becomes more rapid and begins to overlap with reaction ( l ) giving rise to inflec- tions in the thermogravimetric curve apparently corresponding to other intermediates.This may account for the large number of intermediates previously postulated through variations in carbon dioxide pressure caused by particular experimental techniques. . . KIKETICS- Isothermal runs were carried out at controlled pressures of carbon dioxide and niechan- isms decided by reduced time plots2; activation energies were also calculated. The rate- controlling step was a diffusion process for all reactions and the thermogravimetric results were processed by a modified Coats and Redfern treatment.3 Some of the Arrhenius para- meters are shown in Table I and it can be seen that the values of both activation energy and frequency factor are much higher than might be expected for a diffusion process or accounted for in terms of theory.TABLE I ARRHEXIUS PARAMETERS FOR THE DECOMPOSITION OF LEAD(I1) CARBONATE Stage (1) Stage (2) Stage (3) L- r--Ap- ~ r~ _-__ h 7 7 PcoI E/kJ mol-1 A is-' E/kJ mol-l A is-' E /l J mol-1 A is-' 1-0 472.8 1.4 x 1010 665.3 2.7 x 1052 849.4 1.4 x 10'' 0.5 443.5 1.1 x 1038 556.5 2.3 x loJ4 895.4 1.6 x 10" 0.1 401-7 6 x 338.9 1 x 1 0 2 9 451.7 4.5 x 106' 443.5 4.0 x lo3')* 698.7 1.8 x 1051)* * Values in parentheses arc from isothermal runs. There are at least three possible explanations for these high Arrhenius terms particularly at high carbon dioxide pressures (1) Adsorption of carbon dioxide occurs on high energy sites that would normally de- compose fairly readily thus "deactivating" the material. (2) The range of decomposition temperatures is small at high carbon dioxide pressures for thermodynamic reasons and therefore the Arrhenius plots contain large errors leading to the observed high values.(3) The decomposition and recombination reaction rates are similar and the net measured rate is small The temperature coefficient of the reaction (the activation energy) varies as the difference between these two. The last of these explanations seems the most likely but here one comes up against one of the major flaws in the technique. It is obviously not possible to derive any real rate constants that might be treated to decide which of the possible explanations is most nearly correct. This information can obviously come only from a lengthy isothermal study. I thank R4r. 11. J. Casson who carried out the work described. 168 SAFETY AND LEGAL ASPECTS OF FOOD ADDITIVES [Proc. SOC. Analyt. Chem. REFERENCES 1. 2. 3. Grisafe D. A. and 1% hite W. B. Awer. Mixer. 1964 49 1154. Sharp J. H. Brindley G . IV. and Achar B. N. N. J . Awzer. Ceratn. SOC. 1966 49 379. Coats A. W. and Redfern J. P. Nature 1964 201 68.

ISSN:0037-9697    

DOI:10.1039/SA9720900162

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

168 SAFETY AND LEGAL ASPECTS OF FOOD ADDITIVES [Proc. S O C . Analyt. Chem. Safety and Legal Aspects of Food Additives The following is a summary of one of the papers presented at a meeting of the East Anglia Region held on May 26th 1972 and reported in the June issue of Proceedings (p. 123). Determination of Trace Amounts of Metals in Foodstuffs by Atomic- absorption Spectroscopy BY G. NELSON AND D. L. SMITH (Rowntree Mackintoslz Limited Halifax Yorkshive) AN automated dry-ashing technique was described for the destruction of confectionery raw materials and finished products prior to the determination of their lead copper tin and zinc contents. The ashing was carried out in a temperature-programmable electric muffle furnace (Carbolite Co. Ltd. Bamford Sheffield) capable of housing forty 3-inch diameter crucibles.Each 10-g sample in a silica dish was treated with 10 ml of 20 per cent. sulphuric acid and subjected to a heating cycle increasing in temperature to 350 "C in 6 hours. The charred and sulphated samples were then treated with 10 ml of an 8 per cent. aqueous magnesium carbonate suspension. The ashing was completed by subjecting the samples to a second heating cycle which increased the temperature to a maximum of 550 "C in 2 hours and main- tained this temperature for 8 hours. The technique requires the minimum supervision by an analyst and is capable of ashing 200 samples in a normal 5-day working week. The ashes were extracted twice with 10 ml of boiling 50 per cent. hydrochloric acid and the resulting solutions analysed by atomic-absorption spectrophotometry by using an E.E.1,.240 instrument in conjunction with an automatic sampler (Evans Electroselenium Ltd. Halstead Essex.) A wet-ashing technique involving the use of a mixture of sulphuric and nitric acids1 was used for the destruction of confectionery materials prior to the measurement of their cadmium and mercury contents by atomic absorption. Cadmium was determined by using the con- ventional flame technique whereas mercury was determined by using the cold vapour tech- nique. Typical results were given on the levels of the trace metals present. I t was reported that vegetable carbon could be distinguished from Channel Black by virtue of their silicon contents. Thus the silicon contents of vegetable carbons were found t o be in the range 0.2 to 0.4 per cent. whereas Channel Black contained no silicon. A stainless- steel decomposition vessel (Uni-seal Decomposition Vessels Haifa Israel) lined with PTFE was used to dissolve the silicon after preliminary ashing of the carbon. The dissolution was accomplished by heating the siliceous material with a 1 + 1 mixture of hydrochloric and hydrofluoric acids in the sealed vessel for 2 hours in an air oven at 105 "C. It was reported that the presence of metallic iron in chocolate a t levels greater than 30 p.p.m. would lead to erroneous fat contents as measured by nuclear magnetic resonance spectroscopy. REFERENCE 1. Analytical Methods Committee Analyst 1965 90 515.

ISSN:0037-9697    

DOI:10.1039/SA9720900168

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

August 19721 PAPERS ACCEPTED FOR THE ANALYST 169 Papers Accepted for Publication in The Analyst THE following papers have been accepted for publication jn The Analyst and are expected to appear in the near future. “Potentiometric Determination of Monuron in Herbicide Formulations,” by S. H. Yuen and J. M. C. Palmer. “Quantitative Determination of Diosgenin in Dioscorea conzpositn by Gas - Liquid and Thin-layer Chromatography,” by Gulliver L6pez Sanchez Jorge C. Medina Acevedo and Roberto Ramirez Soto. “Analysis of Aluminosilicate Materials by X-ray Fluorescence Spectrometry,” by D. G. Ashley and K. W. Andrews. “Determination of Hydroxymethylfurfural in Honey,’’ by A. K. Dhar and B. R. Roy. “Determination of Boron in Plants by Emission Spectroscopy with the Nitrous Oxide - “A Simplified Gas - Liquid Chromatographic Method for Determining Diosgenin in “Inorganic Phosphate Sorption by Laboratory Ware Implications to Environmental “Enthalpimetric Determination of Nitrogen-containing Bases ” by L.S. Bark and “Automated Method for the Micro-determination of Sulphur,” by J. Keay P. M. A. “Thin-layer Chromatographic Separation and Colorimetric Determination of Rhamnose Hydrogen Flame.” by J. C.-M. Pau E. E. Pickett and S. R. Koirtyohann. Dioscovea Tubers,” by A. Rozanski. Phosphorus Methodology,” by J. C. Ryden J. K. Syers and R. F. Harris. J. K. Grime. Menag6 and G. A. Dean. Quinovose Fucose and Glucose,” by S. Singh and B. E. Stacey. 170 P U BLI CAT1 ON S RECEIVED [Proc. SOC. Analyt. Chcin. “The Complexation of Tin(1V) with Catechol Violet,” by B. \\‘. Budesinsky. “The Determination of Steam-volatile X-Nitrosamines by Formation of Electron- capturing Derivatives from Electrochemically Derived Amines,” by T. G. Alliston G. B. Cox and R. S. Kirk. “The Determination of Sulphur Dioxide in Neats,” by D. Barnett.

ISSN:0037-9697    

DOI:10.1039/SA972090169b

出版商:RSC    

年代:1972

数据来源: RSC

摘要:

170 P U BLI CAT1 ON S RECEIVED [Proc. SOC. Analyt. Chcin. Publications Keceived The publications listed below have been received by the Editor of The Analyst in which journal Book Reviews will continue to appear. QUALITY CONTROL IN THE FOOD INDUSTRY. Edited by S. h1. Herschdoerfer. Volume 3. Pp. xvi + 486. London and New York Academic Press. 1972. Price L8; $25. BIBLIOGRAPHY. Compiled by INA CALLOWXY BROWNRIDGE. Pp. xiv + 210. New York Washington and London IFI/Plenurn. 1972. Price $23. GREENWOOD E. J . I;. Ross AND B. P. STRAUGHAR. Pp. \Tiii + 754. London Butterworths. 1972. Price Ll5. MODERN ASPECTS OF ELECTROCHEMISTRY. Edited by B. E. COSWAY and J . 0’31. I~OCI<RIS. Pp. xii + 412. London Butterworths. 1972. Price Ll0. CHROMATOGRAPHY OF ENVIRONMENTAL HAZARDS. Volume 1. CARCINOGEKS MUTAGENS AKD TERATOGENS.By LAWRENCE FISHBEIN. Pp. viii + 499. Amsterdam London and New York Elsevier Publishing Company. 1972. Price Df1135; $42.25 approx. (BASED ON LECTURES GIVEN AT THE NATO ADVAXCED STUDY INSTITUTE HELD AT SPATIND NORWAY AUGUST 1971). Edited by L. T. Muus AND P. W. ATKINS. Pp. xiv + 537. New York and London Plenum Press. 1972. Price $29.50 ADVANCES IN X-RAY ANALYSIS. Volume 15. L’ROCEEDINGS OF THE TWEXTIETH ANNUAL Cos- FEKENCE ON L 4 ~ ~ ~ ~ ~ OF X-RAY IiNALYSIS HELD AUGUST 11-13 1971. Edited by KURT F. J. HEINRICH CHARLES S. BARRETT JOHN B. SEWKIRK and CLAYTON 0. RUL~D. Pp. xii + 573. New York Plenum Press. 1972. Price $25. TREATISE ox ANALYTICAL CHEMISTRY. Part I. THTIORY AND PRACTICE. Volume 10. Edited by I. M. KOLTIIOFF and PHILIP J. ELVING. New York London Sydney and Toronto Wiley-Interscience. 1972. Price L9.85. By E. W. COOK and I<. JOSES. Pp. xvi + 192. 1972. Price L1-50 $3.90; DM13 50 LITHIUM-DRIFTED GERhlANIUM DETECTORS THEIR FABRICATION AND USE. AN AKNOTATED IXDEX OF VIBRATIONAL SPECTRA O F IXORGAKIC -4XD OKGANOMETALLIC COMPOUNDS. B>I s. s. Volume 1 (1935 - 1960). No. 7. ELECTRON SPIN RELAXATION IN LIQUIDS. 1’13. xviii + 5939-6533. A PROGRAMMED INTRODUCTION TO INFRARED SPECTROSCOPY. London New York and Kheine Heyden & Sons Ltd.

ISSN:0037-9697    

DOI:10.1039/SA9720900170

出版商:RSC    

年代:1972

数据来源: RSC