摘要:

Proceedinas - - - - - ~ -of the Analytical Division ofThe Chemical Society19920320320821 121 8225228232232232233233233234234236CONTENTSSixth Theophilus Redwood LectureSummaries of Papers'Sampling''Determination of Prostaglandins''Pyrolysis Techniques for Analysis''Measurement and Toxicity ofMetallic and Organic Species'Safety in Analytical Laboratories:Basic Safety in Volumetric Ana-lysisEquipment NewsAnalytical Division DistinguishedService AwardSAC Silver MedalCS Research Fund 1978Procedures for the DeterminationCS Autumn MeetingConferences and MeetingsCoursesPublications ReceivedAnalytical Division Diaryof Lead and ChromiumVolume 14 No 8 Pages 199-236 August 197PADSDZ 14(8)199-236(1977)ISSN 0306-1 396August 1977PROCEEDINGSOF 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, Distribution Centre, Blackhorse Road,Letchworth, Herts., SG6 1 HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analysrand Analytical Abstracts.Q The Chemical Society 1977ANALYTICAL SCIENCES MONOGRAPH No.4Electrothermal Atomization forAtomic Absorption Spectrometryby C. W. FullerAt the present time the two most successful alternatives to the flame appear to bethe electrothermal atomizer and the inductively-coupled plasma. In this book anattempt has been made to provide the author's views on the historical develop-ment, commercial design features, theory, practical considerations, analyticalparameters of the elements, and areas of application of the first of these twotechniques, electrothermal atomization.The chapter headings are as follows: History; Theoretical Aspects of theAtomization Process; General Experimental Conditions; Analytical Conditionsfor the Determination of the Elements by Atomic Absorption Spectrometry;Applications (Oil and Oil Products; Metals; Rocks, Minerals and Soils; Waters;Plants; Food and Drugs; Biological Fluids; Biological Tissues; Air Particulates;Refractory Oxides and Related Materials; Other Analytical Applications;Theoretical).Clothbound 135pp 8ZI' x 5" 0 85186 777 4 f6.75 ($13.50)CS Members f5.50THE CHEMICAL SOCIETYDistribution Centre, Blackhorse Road, Letchworth,Herts., SG6 1 HN, Englan

ISSN:0306-1396    

DOI:10.1039/AD97714FX023

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

August, 1977 PUBLICATIONS RECEIVED 235Analytical Division Diary, continued“Modes of Thermal Decomposition ofAmmonium and Alkylammonium IonicForms of Crystalline Insoluble Acid Salts ofTetravalent Metals,” by J . P. Gupta andD. V. Nowell.“Heat of Formation of the Ordered Co - GaPhase,” by E.-Th. Henig and H. C. Lukas.“TG and DTA Studies on the Decompositionof Lead Sulphite,” by S. A. A. Jayaweeraand P. J . Sleeman.“Materials Testing by ThermomechanicalAnalysis and Dynamic MechanicalAnalysis,” by 111. G. Lofthouse.“Hot-stage Microscopy of Alkaline-earthMetal Sulphites,” by P. O’Neill.“Effect of Processing Variables on the GlassTemperature of Polymers,” by M. J .Richardson.“Studies of Dental-enamel Surfaces by FlowMicrocalorimetry,” by M.V. Stack.Plymouth Polytechnic, Plymouth, Devon.Tuesday to Thursday, 20th to 22nd:AberdeenCS Autumn Meeting : Analytical DivisionSymposium on “Soils, Geochemistry andthe Exploitation of Mineral Resources.”Tzresday, 20th-“Analytical Aspects of Soil Trace Element“Techniques in the Analysis of Soil forAgricultural Purposes,” by R. J . Hall.“Spectrochemical Techniques in Soil Analy-sis,” by R. 0. Scott and Dr. M. L. Berrow.“Chemical Characterisation of Mineral Com-ponents in Soil,” by B. D. Mitchell andB. F. L. Smith.“Lead Levels in Soils from Urban and RuralAreas of Birmingham,” by A. K. Khera andProfessor D. G. Wibberley.“Natural Isotopic Abundances in Soil OrganicMatter,” by D. D. Harkness.“The Application of the Inductively CoupledPlasma (ICP) as an Excitation Source inApplied Geochemical Analysis,” by M.Thompson.“Studies of Metal Complexes on Clay Min-erals,” by Parissa Monsef-Mirzai, J .W.Gaskarth and W. R. McWhinnie.Wednesday, 2 1st (a.m.) -“Analysis in Mineral Exploitation,” byP. J . Moore.“Carrock Fell : The Development and Oper-ation of a Small United Kingdom TungstenMine,” by P. Knowles.“Rare Earths : Their Determination andSignificance in Geochemical Studies,” byP. Bowden and J . E. Whitley.Studies,” by R. L. Mitchell. The University, AberdeenAnalytical Division DiarySEPTEMBERThursday, 8th, 12.15 p.m.: NorwichEast Anglia Region : Visit to the ResearchLaboratories of the British Sugar Corpor-ation, Colney, Xorwich.Monday to Thursday, 12th to 15th: SalfordParticle Size Analysis Gvoup : Particle SizePlenary Lectures“Particle Size Measurement in the Sub-micronRange with Particular Reference to Pig-ments,” by W.Carr.“Particle Characterisation,” by ProfessorClyde Orr, Jr.“Sieve Analysis,” by Professor K. Leschonski.The University, Salford.Analysis Conference 1977.Tuesday to Thursday, 13th to 15th: LondonElectroanalytical Group, jointly with the Elec-trochemistry Group of the Faraday Divi-sion: Anglo - Czech Symposium on Polaro-WPhY.Tuesday 13th and Wednesday 14th : Papers onelectrochemistry.Thursday 15th 9.30 a.m. : “Electroanalysis.”“Development of Electrochemical Instru-mentation Derived from Polarography,” byR. Kalvoda.“Recent Developments in Ion-selectiveElectrodes/Potentiometry,” by J.D. R.Thomas.“Measurement of Potassium Levels in BloodUsing Ion-selective Electrodes,” by D. M.Band and T. Treasure.“The Uses of Electrochemical Techniques inBiology and Clinical Analysis,” by Dr. A1Serak.“Continuous Blood Gas Analysis in the Clini-cal Environment,” by D. Parker.“Enzyme Electrodes-A Survey,” by B.Fleet.“New Directions in Instrumentation forPolarography,” by G. C. Barker.Imperial College, South Kensington, London,s.w.7.Tuesday to Friday, 13th to 16th: BathRadiochemical Methods Group : ScintillationThe Assembly Rooms, Bath.Counting Symposium.Monday to Wednesday, 19th to 21st: Ply-mouthThermal Methods Group, jointly with Associa-tion Franqaise de Calorimetrie et d’ AnalyseThermique : Symposium on Thermal Analy-sis and Calorimetry.“Caractkristiques Thermiques du VerreCd,GeAs, et Cinktique de Cristallisation,” byB.Auguin, A. Defresne, Nguyen Van Dongand Tran Huu Danh.“Some Aspects of Simultaneous ThermalAnalysis - Mass Spectroscopy,” by P. A.Barnes.“Thermogravimetric Studies on the Oxidationof Zinc Sulphide,” by B. Basak, D. R.Glasson and S. A. A. Jayaweera.“Review of Thermal Instrumentation Deve-loped at NHLBI and Applications toEnzyme Kinetics and Thermodynamics, ”by R. L. Berger.“Thermogravimetric Studies of the Formationand Oxidation of Silicon Nitride,” by B. J .Brockington, D. R. Glasson and J . A.Jones.“Study of Exothermic Reactions by Quantit-ative DTA,” by E. L. Charsley.“Thermogravimetric Studies of the Oxidationof Boron Carbide,” by A. A. Chaudhry,D. R. Glasson and J . A. Jones.“Thermosonimetry,” by G. M. Clark.“Thermal Analysis of Textile Fibres,” by J . S.Crighton.“Enthalpies of Formation of Co - Cr Alloysby Sn-solution Calorimetry,” by D. B.Downie.“Thermogravimetric Test Procedures forPolymer and Elastomer Formulations,” by0. Dugdale.“Rapid Characterisation of Coal by Thermo-gravimetric and Scanning Calorimetricanalysis,” by R. L. Fyons.“Thermogravimetric Studies of Milled Hydr-ated and Carbonated Limes,” by R. B.Gammage, D. R. Glasson and R. Srodzinski.“Weight Change Studies of the Formationof Polybenzoxazole,” by F. Ghaffari andK. A. Hodd.“Thermogravimetric Studies of Natural andSynthetic Calcium and Magnesium Phos-phates,’’ by D. R. Glasson and Diane E.B. Linstead-Smith.[continued inside back coverPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97714BX025

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

Vol. 14 No. 8 August 1977 of the Analytical Division of the Chemical Society Sixth Theophilus Redwood Lecture* Analysis with a Purpose D. R. Deans Imperial Chemical Industries Limited, Petrochemicals Division, P.O. Box 90, Wilton, Cleveland, TS6 SJE Some time ago I visited a Department of Analytical Chemistry at a well known American University, where I was asked to interview some PhD students to talk about their research work.I asked about the precision of their results and discovered that they did not know the difference between repeatability and reproducibility. My immediate reaction was to be appalled. In the room where we were sitting were the 48 volumes of The American Society For Testing and Materials, which contained literally thousands of analytical methods, each of which gives a value for precision in terms of repeatability and reproducibility. These methods and others like them that use the same definition of repeatability and reproducibility form the base-load of all quantitative chemical analysis done throughout the world.On more sober reflection, I realised perhaps I should not be so appalled. Many of the people in the Department were high- calibre scientists with international reputations and they were carrying out, as far as I could judge, some excellent research.Why, then, did their PhD students not use or know about this very elementary concept of precision of analysis? The reason was obvious. No-one actually had to use the results obtained by the students. I believe this pinpoints a very real problem in the difference between the teach- ing of analysis and the practice of analysis.I do not offer any solution to this problem, except perhaps that it is important to be aware that there is a problem. Analysis with a purpose is analysis when some action or decision has to be taken on the basis of the analytical results. I hope to show that it is the purpose for which the analytical results are used that is often all important in the choice and development of an analytical method and in the reporting of the results.. In the first part of this paper some of the problems of doing analysis with a purpose are described and illustrated. Although some of the themes discussed may be well known, the problems do not change, and I believe, as I have already shown, that they are not universally taken into account.Later in the paper I shall consider how far we have got in tackling them and then where we might go in the future. Dr. D. R. Deans Problems with the Purpose Some may be used for teaching purposes, but the majority of analytical results are used as the basis for taking some decision or action. Even results that are accumulated over a period for record purposes are accumulated with the intention, in the end, of taking some decision on the basis of them.A main and fairly obvious plank of my argument is that it is the decision, the theory and the action that are to be based on the analysis that should be correct. It should not be the * Presented on March 31st, 1977, at the CS Annual Congress, University College London.199 Nearly all analytical results are produced for a reason.200 SIXTH THEOPHILUS REDWOOD LECTURE Proc. Analyt. Div. Ckem. SOC. analyst’s aim to obtain an accurate analytical result, but to provide the basis for a correct decision or action. He might think that if the result is accurate then this is the best that he, the analyst, can do to help in taking the correct decision.But this, I fear, is both naive and uneconomic. I t is important to choose or develop a method in which the error characteristics are most suitable for the decisions to be taken. If we are to determine the level of copper in, say, the human liver in the UK and we want to compare the results with some obtained in Japan to see what the effect of levels of copper in the environment is, then in order to make the comparison valid we must have not the most accurate method we can obtain, but a method that has exactly the same bias as the method used by the workers in Japan.In the determination of alcohol in blood to provide evidence relating to motoring offences, the general requirement is to be able to analyse for alcohol in blood over the range from 0 to, say, 400 mg per 100 ml.The main decision that will be taken on the basis of the results is whether or not the driver is legally drunk or sober. It is a go - no-go test, and it needs to be really accurate only near the value at which a decision will be made. It is important that any-one who has less than the specified limit is always reported as having less, but it does not matter if the result is reported as, say, 40 mg per 100 ml when it is really 30 mg per 100 ml.Similarly, accuracy above the specified limit is not so important. Hence the analyst who is developing a method for this purpose would select a detector and analytical system that show good discrimination and repeatability near the specified limit, but would sacrifice linearity. He would therefore make sure that the limit value occurred in the most accurate part in the range and that the calibration was accurate at that point only.It is interesting to note that the limit value under present legislation in the UK is nominally 80 mg per 100 ml, but the actual go - no-go point is usually 86 mg per 100 ml, to allow for possible error in the analysis. It is the actual limit value that should be the most accurate, not the nominal value.In order to select or develop the appropriate analytical method it is important that the analyst should know exactly what the criterion is for the decision or action and not just the nominal criterion. Equation (1) is the Van Laar equation, which relates the activity coefficient, y , to the tem- perature, T , and composition for two components in a mixture in vapour - liquid equilibrium.All analytical methods have some sort of error associated with them. AX,^ Logy = T(x2 + B X J 2 It plays an important role in the design of distillation columns. required in order to determine constants A and B. trations of the two components. determined by gas chromatography. ally manipulated. Much experimental work is Variables x1 and x2 are the liquid concen- For many applications the concentrations x1 and x2 would be Equation (2) shows the same relationship mathematic- If we use equation (2) we need only to determine the ratio of x, to x 2 , but if we use equation (1) we need to determine the absolute values of x1 and x2. The precision of the analysis by gas chromatography is much better in the determination of ratios than in the determination of absolute values, so if we use equation (2) we obtain much better values for the activity coefficient.The choice of measured parameters in mathematical models of chemical processes can have a significant effect on the precision and validity of the model. Parameters that mathematically should give the best model do not necessarily give the best results in practice.A compromise often has to be made between parameters that give good mathematical models but have poor error characteristics and parameters that give poorer models but have good error characteris- tics. In order to obtain the best compromise, discussion with the mathematician at an early stage is imperative. The message is clear: for any analysis the analyst must ask the question, “How are the results going to be used?” But more than this, he must discuss in detail with the userA ugust, 197 7 SIXTH THEOPHILUS REDWOOD LECTURE 201 exactly what the implications of the various error characteristics that can be chosen for different analytical methods are on the correctness of the decision that will be taken on the basis of the results.Another problem with results for a purpose is that when one has produced the results they may not be used effectively. In a chemical plant process control room where everything is running smoothly and normally, if an analytical result is presented which shows that the product has gone off specification, immediate action will be taken only if the result is believed.If the result was wrong, then the action taken may result in a loss of money. On the other hand, if the result was not believed and no action is taken except to have the result checked, then by the time the check has been done and if the result happened to be correct, again a great deal of money may have been lost in making off-specification material.If the result is unexpected, do you believe it? A result is likely to have a high credibility only if in the past similar results have never been known to be wrong. “Wrong results” in this context means results that are in error because of a mistake or malfunction of some sort, e.g., wrong knob setting or transcrip- tion error. A wrong result does not mean one that falls within the normal precision of the method used.I assume that the method selected for any analysis in this context will have adequate precision for the decision-taking purpose. The analyst’s problem, then, is to produce correct (in the terms of the decision to be taken), credible results. A vital characteristic of a result, then, is its credibility. How Far Have We Got in Solving These Problems? Over the past few years, instrument manufacturers have accepted that there is a problem with credibility of results from their instruments.There are now a number of instruments on the market that have self-checking routines in them and warning lights to show when some pre-set condition is not being achieved. These self-checking routines have proved to be a great help in eliminating some of the sources of error due to instrument malfunction and hence have improved the credibility of the results produced.There is, however, an area in instrument design that has not made as much progress as we might have hoped, namely the design and layout of instrument controls. If we are to help an operator to eliminate sources of mistakes then the control knobs and switches must be very clearly different from each other for each different function, and they should also be positive switches rather than continuously variable functions. Instrument manufacturers, however, need to make their instruments look attractive and they obviously feel that symmetrically placed identical knobs give the most attractive layout.This approach results in an unfor- tunate conflict with the real needs of the customer and I hope that instrument manufac- turers will in the future find some way round this difficulty.Knobs that control continuous variables are to be avoided if possible, because any inadvertent change of the position of a knob cannot easily be rectified so as to move the knob back to exactly where it was. If they cannot be made as switched variables, they should at least have positive locks on them.Another area where we had hoped that considerable improvements would be made in the credibility of our analyses is that of the reports produced from computer systems. In these reports, it should be possible to apply a number of tests to see whether the analysis falls within the norm for analyses of that type.For example, in gas-chromatographic analysis it should be possible to check whether the base line is within a noise specification and whether the base-line drift is within a specification, and similarly whether the retention times of a number of peaks are within specification. It should also be possible to check that the ratios of the peaks present fall within a normal pattern for that type of analysis.In some modern computer systems dealing with gas chromatographs it is possible for the user to write his own program in order to do some of these checks, but for most systems these facilities are not available. Progress towards making sure that an analytical method and its results generate the right decision has, in my experience, been patchy. A great deal depends on the attitude of the analyst designing or selecting the method and that of the customer.Here, I believe that universities and colleges could help in the teaching of analysts, firstly by introducing the concept that it is possible to select or change the error characteristics of an analytical method, and secondly by teaching that it is not the accuracy of the analysis that is important but the rightness of the decision taken on the basis of the analysis.202 SIXTH THEOPHILUS REDWOOD LECTURE PYOC. Analyt.DiV. Ckem. SOC. The use of computers has helped in some instances because where the analytical results have been used immediately in programs for further calculations some over-all co-operation in discussing the nature of the results and the decisions has been forced on the analyst and the customer. Where Are We Going? Over the next few years, a number of breakthroughs in the technology of analysis can be expected, but I believe that by far the major impact on the way we do analyses will come from outside.The impact is expected to come from the availability of cheap data-handling and calculation facilities. The cost of these facilities has been decreasing rapidly over the last few years.For example, the pocket calculator, which 3 years ago might have cost 430, can now be bought for L5, despite inflation. This cost reduction is expected to continue to the stage where processing power and memory are likely to become almost negligible in cost. However, connectors, wiring, switches, boxes, etc., are not likely to fall in cost.The economic impetus will be to put as much data handling and automatic control, in the form of micro- computers, into all possible types of analytical equipment. It is likely to be much cheaper to build a high-powered computer into a small piece of analytical equipment than to pay for the wiring and connectors to connect it to a central computer. The power of the data-processing facilities and the automatic control will enable better analytical results to be produced than on previous equipment.For example, complex mathematics can be carried out and readings taken at high speed. Built-in data-handling facilities are likely to be cheaper than, for example, present-day amplifiers, which just produce a voltage output. This characteristic of being both better and cheaper in many instances than existing systems will bring about a very rapid transition to microprocessor-controlled automation and data-handling facilities.In introducing microcomputer systems and modern electronics generally to analysis, it will be relatively easy to add a microcomputer and automation on to what we do already, but if we do this we are unlikely to get the best out of the combination.It should be possible, in each instance, to go back to the fundamental principles of analysis and to design from scratch an appropriate system. An automatic titrator is a good example of such a system that has already been developed. Instead of titrating to a fixed pH end-point, the microcomputer canmakeuseof the whole curve of pH against volume and, by differentiation, pick out the inflec- tion point.This means that the difficulties of titrating to a fixed pH end-point, including the need to slow up the titration as the end-point is approached and the need for temperature compensation, are eliminated. Also, because the end-point is defined by the inflection in a curve, the need for an accurate voltmeter or even a linear electrode is removed.By careful design of the equipment, much of the electromechanical, expensive, less reliable parts of the conventional autotitrator are unnecessary. In a “Tomorrow’s World” programme on television not long ago, a farmer was shown squeezing juice out of the stem of a cabbage plant on to a test paper. He then compared the colour of the paper with a guide to tell him the concentration of nitrates in the plant juice.This seems typical of the result of the analyst and the customer not getting together. The concentration of nitrates in the plant juice means nothing to the farmer-what he wants to know is whether he needs to add nitrogenous fertiliser to the soil and, if so, how much in tons per acre. In order to obtain this result he may have to put in more information, such as time of year, type of plant and nature of the soil, and some sort of chart would probably be necessary.In the long run, the test paper will probably be replaced with some sort of ion-selective electrode. This probe could be attached to a device like a pocket calculator into which the farmer puts the relevant information.One can imagine such a relatively cheap, simple device being feasible in the future. The possible savings in uneconomic distribution of fertiliser would be very significant. Interchangeable probes for different ions is a possibility. The Role of the Analyst One of these roles, which the introduction of automation and data handling is tending to remove, is that of expert In the past, the analyst has had a number of different roles to play.A ugus t , 19 7 7 SAMPLING 203 manipulator of apparatus and expert interpreter of readings and indications.It is this particular role that has, in my belief, been responsible for many of the failures of the analyst t o do his job properly. The reason is that any query about the validity or the precision of a result is a slight on the expertise of the analyst. He therefore becomes defensive and finds it difficult to discuss analytical errors objectively because it necessarily includes his own errors. He may tend to adopt the attitude, “I will produce accurate analyses, what you do with the results is your responsibility.” The sooner we get away from the analyst’s manipulative skills being involved in the preci- sion and accuracy of the results, the better. If we remove the need for these manipulative skills then we have something of a managerial problem. The analyst may feel that his job is being downgraded and he can lose the job satisfaction of exercising the skills. It is important, therefore, that he should be encouraged to develop and exercise his other, more important skills. In particular, his knowledge of the capabilities and error characteristics of the various analytical methods available should be enhanced. He will then be better able to select and, where appropriate, develop methods that are suitable for the problem in hand. An analyst should never be just an expert number or identity producer, He should always use his expertise by being involved in helping to solve the problems of his customers.

ISSN:0306-1396    

DOI:10.1039/AD9771400199

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

A ugus t , 19 7 7 SAMPLING 203 Sampling The following is the summary of a paper presented at a Joint Meeting of the Atomic Spectro- scopy and Particle Size Analysis Groups held on November 30th, 1976, at the Geological Society, Burlington House, London. Some Measurements of Atmospheric Pollution by Aerosols in an Urban Environment D. J. Ball Environmental Sciences Group, Scientific Branch, Greater London Council, County Hall, London, SE1 7PB Of the many pollutants to be found in urban atmospheres, that which has attracted the most attention, doubtless because of its high degree of visibility, is smoke, which is defined as dark particulate matter.In Britain, complaints about smoke have been recorded from at least as early as 1371,l and there have been many legislative attempts to ameliorate the situation.Unfortunately, these were generally piecemeal or ephemeral, and following the industrial revolution pollution by smoke became an increasing hazard in urban areas. Thus, in 1873 smoke was implicated as the primary constituent of the “fog” which led to several hundred premature deaths in London. As recently as 1952 over 400 premature deaths, due almost entirely to circulatory or respiratory disorders, were attributed to a single incident of “smog,” of which the primary constituents were smoke, sulphur dioxide and sulphuric acid aerosol.On this occasion public outcry was so great that central Government established the Clean Air Act of 1956. This Act empowers local authorities to designate smoke-control areas, within which the emission of dark smoke from stationary sources is curtailed by restrictions on the type of fuel and burning appliances that can be used.In urban Britain most premises are now within smoke-control areas. Smoke Measurement by the Smoke Shade Technique In order to monitor the progress of the Clean Air Act, the National Survey of Air Pollution was established in 1962 with a network of several hundred sites around Britain to measure 24-h mean concentrations of smoke and sulphur dioxide.Primarily for reasons of economics and for ease of operation, it was decided that the National Survey should use the “smoke shade technique”2 for measurement of smoke concentrations. In this method, a known volume of air is drawn through a Whatman No. 1 filter-paper over a 24-h period, and the darkness of the stain produced is measured with a reflectometer.By means of a standardised ~alibration,~ last carried out in about 1962, the results are expressed as micrograms per cubic metre of “standard smoke,” where the latter term refers to typical urban smoke of that period.204 SAMPLING PYOC. Analyt. Div. Chem. SOC. I ’ l l 1 1955 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 Year Fig.1. Annual averages of smoke and sulphur dioxide at ground level for seven inner-London National Survey sites. There is little doubt that there has been a considerable reduction in smoke concentrations since the formulation of the Clean Air Act, and data of the type shown in Fig. 1 are often cited as evidence of the success of the Act.It would also appear from a simple interpretation of these data that the Greater London Council guideline for smoke4s5 of 40 pg m-3 has been achieved in central London. However, some attribute the reduction in smoke concentrations to socio-economic changes,6 e.g., preference for gas rather than solid-fuel heating systems, which changes in turn raise questions, not only about the interpretation of smoke shade data, but about the relevance of National Survey measurements to today’s urban pollution problems. For example, in Greater London, sales of domestic house coal, formerly considered the main source of smoke,’ have decreased by an order of magnitude since the inception of the Clean Air Act while, a t the same time, motor spirit and diesel fuel sales have increased by a factor of three, with consequent increases in vehicular smoke emissions.Emission estimates show that, particularly in central London, but also to a large extent in the whole of Greater London, vehicles are now the main source of smoke.8 Because particulate pollution from different sources, be it smoke from motor vehicles, fly-ash from oil-burning appliances, etc., has different absorptivities from that of “standard ~ m o k e , ” ~ ~ l ~ it is not to be expected that the smoke shade readings will give a reliable indication of mass concentration.It is possibly more appropriate to consider them as a soiling index, although chemical nature, method of collection and particle-size distribution considerations detract from this interpretation. In addition, National Survey sites are selected on the basis of a number of criteria, one of which is that they should not be close to busy roads.This selectivity means that one important aspect of smoke pollu- tion by vehicles (i.e., level of soiling) is not represented by the data in Fig. 1 and represents a serious omission in a country where urban centres are focal points for both motor vehicles and human activity.Comparison of Gravimetrically Determined Particulate Matter with Smoke Shade Measurements A number of countries have adopted a gravimetric method of assessing ambient pollution by particulate matter which uses a “high-volume sampler.”11 This device draws air at a rate of 1.5-2.0 m3 min-1 through an 8 x 10 in glass-fibre filter. The mass concentration of suspended particulate matter is calculated from the mass of particles collected and volume of air sampled, usually over a 24-h period.During the period from May 1975 to April 1976, high-volume and smoke shade samplers were run side-by-side at a non-street side location on the roof of County Hall in central London on most weekdays. Fig. 2 shows representative data for summer and winter periods, from which it is apparent that the smoke shade sampler underestimates the total mass of particulate matter at this location by an appreciable factor, which was found to vary from 1 to 6 during the year.Bernard and Duggan12 have reported the reverse situation from street-side sites,A ugust, 197 7 SAMPLING 205 with the smoke shade overestimating the gravimetric concentration by as much as 3-fold, from which it appears that the smoke shade technique is greatly influenced by traffic-generated smoke.Confirmatory evidence of the importance of vehicular smoke was gained by linear regression of the 24-h smoke shade measurements against the lead content of the high-volume particulate matter samples from the County Hall site, as measured by atomic-absorption spectrophotometry. A correlation coefficient of 0.98 was obtained for the 168 data sets.Because the only significant widespread source of lead in Greater London is the petrol engine, which is representative of smoke emissions by both petrol and diesel engines in this situation where the mix of traffic is constant,13 the high correlation is in accord with the hypothesis that vehicles are now the predominant source of smoke, even at non-kerbside locations, in central London.A more complete analysis of these data* indicated that vehicular sources account for as much as about 77% of the smoke shade readings at the County Hall site, but that this repre- sents only about 15% by mass of the total suspended particulate matter, the remainder of which goes largely undetected because of its low absorptivity.This analysis emphasises the need for caution in interpreting data of the type shown in Fig. 1 when dealing with a technique such as the smoke shade method with which readings are dependent not only on the total particulate matter concentration but also on other factors, such as particle-size distributions and scattering and absorption coefficients, unless these are known to have remained constant throughout the monitoring period.50 - 0 . 1 I I ~ I I I I 1 I I l I I I I 1 I I I I 1 1 I I I I I I I I ' 150 I I 100 I- n I 4 6 l! 13 18 20 25 27 2 4 9 11 16 18 23 25 June 1975 July 1975 r) I December 1975 January 1976 Fig. 2. Comparison of smoke shade (lower line) and gravimetric (upper line) measurements of particulate matter at the non-kerbside, roof-top site of County Hall in central London.Short-term and Continuous Measurements of Particulate Matter Situations often arise in which short-term or continuous measurement of particulate matter concentrations are desired. These include monitoring of trial traffic-management schemes where information is required on rush-hour concentrations, or high-pollution incidents where continuous recordings can help to elucidate underlying mechanisms of pollution formation and build-up.A number of techniques are now available for this purpose, including a simple modification to the smoke shade technique whereby a continuous roll of filter-paper is automatic-206 SAMPLING Proc. Analyt. Div. Chem.SOC. ally wound on after whatever time interval is desired. A difficulty with this technique is that the retention efficiency of Whatman paper approaches 100% only with increasing particulate matter loading,14 implying that the calibration becomes dependent upon sampling period and particle-size distribution, as well as individual scattering and absorption coeffici- ents.l5 Other more sophisticated methods include the use of the integrating nephelometer, the quartz-crystal microbalance and the /3-absorption dust monitor, all of which provide continuous readings related to atmospheric aerosol concentrations in a form suitable for data logging on magnetic tape.16 At the County Hall site, a broad-band integrating nephelometer has been used for monitoring atmospheric light scattering for a number of periods since 1975, and has provided valuable information on high-pollution incidents of both the traditional “smog” type during winter and the summertime photochemical type, as well as some preliminary data for correlation against other methods.The instrument measures the amount of light scatter from a pulsed source operating in the visible spectrum inside a sampling chamber through which ambient air is pumped.In the situation where light scattering is dominated by airborne particulate matter, the scattering coefficient (&cat.), the parameter measured by the instrument, can be related to the visible range, L,, by Koschmieder visibility theory1’ : Lv = 3-9/bscat. As an example, Fig. 3 shows the variation of bscat.during the photochemical incident of June 26-30th, 1976. It may be that the formation of these visibility-reducing aerosols is implicitly associated with the unprecedented ozone concentrations over central London. Current information suggests that a likely aerosol candidate may be sulphuric acid dropletd8 formed by oxidation of sulphur dioxide as part of the general photochemical reactions that evidently take place.lS 0 I 26 June 27 June 28 June 29 June 30June 1976 Fig.3. Scattering coefficient in the visible range and concentrations of ozone (A), nitrogen dioxide (B) and sulphur dioxide (C), from the County Hall site duringthe photochemical incident of June 26-30th, 1976. Apart from their undoubted use in measuring visibility, nephelometers have also been pro- posed as suitable for determining particulate mass concentrations.A number of simplified semi-empirical expressions have been suggested, for example that by Charlson et aZ.,20 and the suppliers of the nephelometer used in this study recommend Particulate mass (pg m-3) = 38b,,,t.(10-4 m-l) based on experiments carried out primarily in the USA. Using 24-h averaged nephelometer readings, a limited number of which overlapped the earlier programme of high-volumeAugust, 1977 SAMPLING 207 gravimetric measurements, the scatter diagram shown in Fig.4 has been plotted. The data fall on two curves, for days with and without precipitation, which may be in part attributable cq 400 I cn =L C E -g 300 L + C 0 0 V L E 200 + i al + m S u (0 Q V - .- 100 .- L * .- E Fig.4. Scatter diagram of the 24-h mean scattering coefficients and gravimetric particulate matter con- centrations for the County Hall site. Numerals on graphs indicate relative humidity. x , No precipitation; 0, precipitation. to aerosol swelling at high relative humidity. Linear regression of bscat. against particulate macc fnr rIax7c withniit nrprinitatinn xrieldc bscat.m-l) = -0.1 + 0.022 x mass (pg m-3) which is comparable with analyses for other European21 and US cities.20 However, because nephelonieter readings are affected by the nature, complex refractive index, and size distribu- tion of the aerosol, caution must be applied in drawing too many inferences, as with the smoke shade technique. The device is of more use in following temporal changes in dispersion at a fixed site, rather than for measuring spatial variations in concentration when different particles and particle-size distributions are more likely to be encountered.The author thanks the Scientific Adviser to the GLC, Mr. R. T. Kelly, for permission to The opinions expressed are those of the author and are not necessarily publish this paper. those of the Council.References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Masters, B. R., Clean Air, Spring 1974, 22. Ministry of Technology, “National Survey of Smoke and Sulphur Dioxide-Instruction Manual.” HM Stationery Office, London, 1966. BS 1747: Part 2: 1964, British Standards Institution, London. “London’s Air-Guideline Concentrations,” Joint Report of the Planning and Public Services Com- mittee, Greater London Council, London, July 22nd, 1975.Reed, S. B., R. SOC. Hlth J.. 1976. 6, 256. Auliciems, A., and Burton, I., Atmosph. Envir., 1973, 7 , 1063. Scorer, R. S., J . Inst. Fuel, 1957, 110. Ball, D. J., and Hume, R., Atmosph. Envir., in the press. Wallin, S. C., Int. J . Air Wat. Pollut., 1965, 9, 351. Pedace, E. A., and Sansone, R., J . Air Pollut. Control Ass., 1972, 22, 348.Fed. Regist., 1971, 36, No. 84, 8190.208 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. DETERMINATION OF PROSTAGLANDINS Proc. Analyt. Div. Chem. SOC. Bernard, R. E., and Duggan, 1%. J., “Measurements of Five Traffic Produced Pollutants in York Road, Munt, P. W., personal communication. Biles, B., and Ellison, J. Mc,K., Atmosph. Envir., 1975, 9, 1030. Ball, D. J., and Hume, R., London,” Greater London Council, Scientific Branch Report, DG/SB/ESG/R34, 1976. Some Notes on the Limitations of 2-hour Smoke Shade Samplers and an Integrating Nephelometer for Short Term Particulate Measurements,” Greater London Council, Scientific Branch Report, DG/SB/ESG/R46, 1977. Freedman, R., Hyde, J., and Reed, S. B., J . Envir. Hlth, 1974, 3. Middleton, W. E. K., “Vision through the Atmosphere,” University of Toronto Press, Toronto, 1963. Stephens, E. R., and Price, M. A., “Aerosols and Atmospheric Chemistry,” Academic Press, New York, 1972. Ball, D. J., and Bernard, R. E., “Photochemical Oxidants in Greater London: 1976 Summary and Situation Report,” Greater London Council, Scientific Branch Report, DG/SB/ESG/R49, 1977. Charlson, R. J., Ahlquist, N. C., and Horvath, H., Atmosph. Envir., 1968, 2, 455. Kretzchmar, J. G., Atmosph. Envir., 1975, 9, 931.

ISSN:0306-1396    

DOI:10.1039/AD9771400203

出版商:RSC    

年代:1977

数据来源: RSC

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208 DETERMINATION OF PROSTAGLANDINS Proc. Analyt. Div. Chem. SOC. Determination of Prostaglandins The following is a summary of the paper presented at a Joint Meeting of the Scottish Region with the Edinburgh and East of Scotland Section of the CS and the Edinburgh University Chemical Society held on February 8th, 1977, at Edinburgh. Gas Chromatography - Mass Spectrometry in the Determination of Prostaglandins in Semen R.W. Kelly Medical Research Council, Unit of Reproductive Biology, 2 Forrest Road, Edinburgh, EH1 2Q W Substances in human semen that stimulate smooth muscle were first noticed in about 1931 by an American gynaecologist, Kurzrok, who noticed an active substance that contracted uteri during his attempts at artificial inseminati0n.l A Swedish physiologist, Von Euler, followed these observations by a careful study of the spectrum of pharmacological activity of the active substance, which he named prostaglandin as he believed (incorrectly) that the origin of this material was the prostate gland.At the same time Von Euler found another substance in the semen of monkeys, which he named vesiglandin.2 These original findings were followed by a period during which little progress was apparent in the prostaglandin field. However, in 1960 Bergstrom and Sjoval13 isolated crystalline PG El from sheep seminal vesicles and in 1963 the Swedish group reported the structures of PGs El, Fla and FJI.4 This development was followed by the identification of PGs El, E,, E,, Fla and F2a in human semen.5 In 1966 a further eight seminal prostaglandins were identified: PG A,, B,, A,, B,, 19-OH A,, 19-OH A,, 19-OH B, and 19-OH B2,6 where the A and the B series are dehydrated forms of the E prostaglandins that have lost the hydroxyl group from the cyclopentane ring.The concentrations of the 19-OH PG As and 19-OH PG Bs together were reported to be up to 100 pg ml-l compared with PG E concentrations of about 50 pg ml-1.Apart from the uniquely high concentrations of the seminal prostaglandins (peripheral blood has a concentration of PG E about lo7 times less than that in semen) they are of interest becaused of several claims that low seminal PG E levels are correlated with otherwise un- explained infer ti lit^.'-^ Recent research has shown that the main prostaglandins in human semen are 9-keto-11,15, 19-trihydroxyprost-13-enoic acid (19-OH PG El) and 9-keto-l1,15,19-trihydroxyprosta-5,13- dienoic acid (19-OH PG E,)l0J1; the presence of these compounds in large amounts (up to 1 mg ml-1) indicates that the previously identified 19-OH As and 19-OH Bs are probably artif acts produced during storage or extraction.Further investigation of the more polar fractions of human semen revealed 19-OH PG Fs at a total concentration of 20 pg ml-l.12 Subsequent research on human semen has provided evidence for the existence of di-nor forms of most of the seminal prostaglandins.13 The PG Es and 19-OH PG Es in human semen are present in sufficient amounts to allow measurement by gas chromatography with flame-ionisation detection.These measurements are carried out after the PG Es and 19-OH PG Es have been converted into methyl oximesAugust, 1977 DETERMINATION OF PROSTAGLANDINS 209 by using an aqueous oximation technique14 and then extracted and further converted to methyl ester and trimethylsilyl ether derivatives.A tracing from a typical semen sample is shown in Fig. 1. The concentration of the PG Fs and 19-OH PG Fs in semen is an order of magnitude lower than that of the corresponding PG Es, and consequently more sensitive methods of analysis must be used.The 19-OH PG Fs are very polar and therefore it is difficult to extract them from semen. However, when a highly specific method of analysis is used, such as gas chroma- tography - mass spectrometry (GC - MS) with selected-ion monitoring, measurements can be made by adding ethanol to the semen sample in order to precipitate protein, and then drying and derivatising the solution and subjecting it directly to GC - MS.The derivative chosen for the 19-OH Fs is the methyl ester, butyl boronate, t-butyl dimethylsilyl (tBDMS) ether. tBDMS ethers are the best derivatives in most quantitative GC - MS assays of prostaglandins because of the abundance of the M - 57 peak.l5 However, with the tetra-tBDMS derivative of 19-OH PG F2(x the base peak at m/e 783 (M-57) is too high to monitor conveniently and there- fore the 9- and ll-hydroxyl groups are formed into the butyl boronate before tBDMS form- ation, thus allowing the measurement of 19-OH PG Fzcc at m/e 621 (M-57).I6 The internal standard used in these measurements is the ethyl ester of 19-OH PG F2cc, introduced into the natural material after the methylation stage.This ester acts as standard to compensate for loss during subsequent derivatisation and allows quantitation from the final measured ratio of the peaks of the methyl and ethyl esters. PG Fs are measured similarly by GC-MS, using deuterated prostaglandins as the internal standa.rd.12 8 4 0 Retention ti m e/m i n Fig. 1. Gas chromatogram of human semen analysed on an SCOT capillary column (SGE Ltd.). Cholesterol acetate is added as internal standard for the purpose of quantitation. The derivative used is the methyl oxime, methyl ester, TMSi ether. The small peaks preceding the PG Es are due to the other oxime isomers. A, PG E2; B, 19-OH PG El; and E, cholesterol acetate.Initial temperature 190 "C, programmed to rise a t 4 "C min-l. PG El; C, 19-OH PG E2; D, =Goon OH OH OH 0 ;OoH I OH O H OOH OH OH OH )OH I OH OH Mean concentration in fertile men/ pg mi-' 19-OH E2 E;} 85 19-OH F CY 19-OH Fia} -*' Fig. 2. Prostaglandins in human semen.210 DETERMINATION OF PROSTAGLANDINS Proc. Analyt. Div. Chem. SOC. Methods such as those described above lead to the establishment of the normal levels of prostaglandins in human semen (Fig.2); these show that there are two major groups of seminal prostaglandins, the PG Es and the 19-OH PG Es. Apart from these groups there are many minor prostaglandin components and it is this complexity of the mixture that requires the use of the highly specific gas-phase method of measurement. The PG Es have only been found in large concentrations (greater than 5 pg ml-l) in human, sheep and goat semen, and the 19-OH PG Es are restricted to the primates.17 Sub-human primates show a preponderance of 19-OH PG E, (Fig.3), which strongly suggests that 19-OH PG El is the vesiglandin that Von Euler first reported 40 years ago. t 40 30 20 10 Retention time/min Fig.3. Analysis of semen sample from a chimpanzee. This sample was analysed on a 6 f t x 3/16 in i.d. column packed with 1% Dexsil300 on Chromosorb G, programmed at 2 “C min-l from 200 “C. A, Isomer of oxime pair; B, 19-OH PG El; and C, cholesterol acetate internal standard. The derivative is as in Fig. 1. Despite the abundance of prostaglandins in semen, their function remains obscure.PG Es have a profound relaxing effect on the non-pregnant human uterus in vitro and so do the 19-OH PG Esls; therefore they may act on the female reproductive tract after coitus. However, it is not certain that the seminal prostaglandins could reach the uterus in sufficient amounts to exert their action because of rapid metabolism of prostaglandins by the lung. It is equally possible that the seminal prostaglandins may have an effect on spermatozoa1 metabolism, playing a role in the induction of maximum motility and forward progression which characterises ejaculated spermatozo;l..lS 1.2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. References Kurzrok, R.,rand Lieb, C., Proc. SOC. Ex$. Biol. Med., 1931, 28, 268. Von Euler, U.S., J . Physiol., Lond., 1936, 88, 213. Bergstrom, S., and Sjovall, J., Ada Chern. Scand., 1960, 14, 1701. Bergstrom, S., Ryhage, R., Samuelsson, B., and Sjovall, J., J . Biol. Chem., 1963,238, 3555.1 Samuelsson, B., J . Biol. Chem., 1963, 238, 3229. Hamberg, M., and Samuelsson, B., J . Biol. Chem., 1966, 241, 257. Bygdeman, M., Fredricsson, B., Svanborg, K., and Samuelsson, B., Fertil.Steril., 1970,21,622. Brummer, H. C., and Gillespie, A., Clin. Endow., 1972, 1, 363. Collier, J. G., Flower, R. J., and Stanton, S. L., Fertil. Steril., 1975, 26, 868. Taylor, P. L., and Kelly, R. W., Nature, Lond., 1974, 250, 665. Jonsson, H. T., Middleditch, B. S., and Desiderio, D. M., Science, N.Y., 1975, 187, 1093. Taylor, P. L., and Kelly, R. W., FEBS Lett., 1975, 57, 22. Taylor, P. L., Cooper, I., and Kelly, R. W., unpublished results. Chalmers, R. A., and Watts, R. W. E., Analyst, 1972, 97, 958. Kelly, R. W., and Taylor, P. L., Analyt. Chem., 1976, 48. 465. Kelly, R. W., i n de Leenheer, A. P., and Ronucci, R. R., Editors, “Quantitative Mass Spectrometryin Kelly, R. W., Taylor, P. L., Hearn, J. P., Short, R. V., Martin, D. E., and Marston, J. H., Nature, Russel, J. A., Taylor, P. L., and Kelly, R. W., unpublished results. Kelly, R. W., J . Reprod. Fert., 1977, 50, 217. Life Sciences,” Elsevier, Amsterdam, 1977. Lond., 1976, 260, 544.

ISSN:0306-1396    

DOI:10.1039/AD9771400208

出版商:RSC    

年代:1977

数据来源: RSC

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August, 1977 PYROLYSIS TECHNIQUES FOR ANALYSIS 21 1 Pyrolysis Techniques for Analysis The following are summaries of three of the papers presented at the Annual General Meeting of the Analytical Division held on March 17th and 18th, 1977, at York. Use of Thermal Degradation for the Characterisation of Textile Materials: A Comparison of Pyrolysis - Gas Chromatography and Thermogravimetry J.S. Crighton Schools of Textiles, University of Bradford, Bradford, West Yorkshire, BD7 1DP Observations of the thermal degradation of macromolecules have been widely used for both qualitative and quantitative analysis. Because of the general availability of gas chromato- graphs, pyrolysis - gas-chromatographic methods have proved popular for characterisati0ns.l Therrnogravimetry has also been demonstrated as a useful tool for the characterisation of polymeric substrates2 Textiles are composed of fibrous elements that are themselves composed of essentially linear molecules greater than 10 000 in relative molecular mass.Within the textile industry basic characterisation requirements include fibre identification (either of single-fibre or blended systems), quantitative blend analysis, and the identification and determination of extent of any applied physical or chemical treatments.The samples for analysis can take a wide variety of forms, ranging from parts of individual fibres, through yarns, to pieces of textile fabric. The analytical procedures that can be employed are restricted by the nature of the substrate. Frequently either the fibrous material is insoluble or the characteristic physical structure is lost by dissolution of the sample.Examination of the intact fibre form is usually necessary and the presented sample size must also be adequate to ensure that it is truly representative. The smallest practical element for presentation in analysis is short lengths (200 pm) of fibre whose diameters are normally of the order of 20 pm.The practical utility of pyrolysis - gas chromatography and thermogravimetry for the characterisation of textile substrates can be considered in terms of the need to achieve repro- ducible thermal degradations consistent with the nature of the sample and the optimum experi- mental conditions required for the specific technique. The principal difficulties associated with the application of pyrolysis - gas chromatography to the analysis of textile materials are the following.(a) Problems arise associated with control of the precise “pyrolysis temperature” of the substrate and the rate of temperature rise (uniformity, reproducibility). (b) It is difficult to achieve reproducible presentation of a representative sample. (c) Difficulties frequently arise consequent upon (a) and ( b ) and the size and form of the sample.( d ) Problems can arise in achieving immediate removal and detection of volatile products. (e) A single set of chromatographic conditions for effective general use with a wide range of substrates cannot be attained. (f) Quantitative results are difficult to achieve. (g) Owing to the nature of the sample, control and elimination of component interactions are difficult to achieve.(h) A wide range of types and sizes of pyrolysis product is obtained, which makes detailed separation difficult, but which renders the pyrogram more characteristic of the chemical nature of the substrate. (i) Identification of physical differences is hardly ever possible. ( j ) Pyrolysis conditions are restricted by the requirements of the chromatography. In contrast with pyrolysis - gas chromatography the use of thermogravimetry shows the (a) An accurate and stable slow heating rate is readily attainable.(6) Reproducible sample heating conditions are achieved. (c) With slow heating a more uniform temperature distribution is established throughout the sample. following advantages :PYROLYSIS TECHNIQUES FOR ANALYSIS Proc. AnaZyt.Div. Chem. SOC. A more positive control of the sample presentation is practical with potential for reduc- ing component interactions. A relatively wide range of sample forms and sizes can be handled reproducibly. Degradation conditions (including atmosphere) are under positive control with greater flexibility in the choice of such conditions.Observation of the immediate release of volatile degradation products is possible. Reproducible identification of both physical and chemical differences in substrates is possible. Although the observations are basically empirical, they can be used to provide quantita- tive information. Losses in mass are a consequence of the elimination of (basically) small molecules; the temperatures at which they are lost and the amounts involved are characteristic of the substrate.A single set of degradation conditions can be applied with equal effect to a wide range of samples. With care, *experimental conditions for pyrolysis - gas chromatography can be achieved that will enable reproducible pyrograms to be ~btained.~ These chromatographic conditions will be specific to a particular substrate.Differences in physical structure frequently cannot be identified. A standard set of operating conditions for thermogravimetry can be defined that are applicable for all fibre systems and a wider range of sample sizes can be accom- modated. Provided that no thermally induced modification occurs prior to degradation, structural differences are usually dete~table.~ Both qualitative and quantitative analysis can be accomplished using thermogravimetry.The slow rates of heating (1-1.0 “C min-1) employed in thennogravimetry can be reproduced accurately and there are only small temperature gradients across the presented sample. Various forms of evolved-gas detection and analysis that employ comparable rates of heating to thermogravimetry when used in conjunction with non-sensitive sample presentation arrangements suggest themselves as useful tools for the examination of all types of macro- molecular substrate.References 1. Stevens, M. P., “Characterisation and Analysis of Polymers by Gas Chromatography,” Marcel Dekker, 2. Keattch, C. J., and Dollimore, D., “An Introduction to Thermogravimetry,” Second Edition, Heyden, 3.Crighton, J. S., in Jones, C.E.R., and Cramers, C. A., Editors, “Analytical Pyrolysis,” Elsevier, New York, 1969. London, 1975 Amsterdam, 1977, p. 337. Automatic Analysis of Tyre Rubber Blends By Computer-linked Pyrolysis - Gas Chromatography* G. L. Coulter and W. C . Thompson Dunlop Limited, Tyre Chemical Laboratory, Fort Dunlop, Birmingham, B24 9QT Before discussing automatic analysis of tyre polymers, we shall describe the problems con- fronting the analytical chemist and the development of the manual pyrolysis - gas chromato- graphic method for identifying tyre polymers.The polymer to be analysed is not in the pure state as a single substance, but is part of a rubber mix. There are numerous different mixes, and each rubber mix contains rubber polymers, sometimes one, often a blend of two or more.The more commonly used polymers are natural rubber (NR), synthetic polykoprene or isoprene rubber (IR), polybutadiene or butadiene rubber (BR) and styrene - butadiene rubber (SBR). In addition to the polymers, each rubber mix contains between 10 and 20 other ingredients, such as sulphur, zinc oxide, carbon black, stearic acid, mineral oil, pine tar, resins, antioxidants and accelerators.* First presented a t the Third International Symposium on Analytical Pyrolysis, Amsterdam, September 1976, and published in full in the Proceedings (C. E. R. Jones and C. A. Cramers, Editors, Elsevier, Amster- dam, 1977).August, 1977 PYROLYSIS TECHNIQUES FOR ANALYSIS 213 The tyre chemist is expected to be able to analyse very small samples taken from tyres or unvulcanised mixes and a fundamental question is, "What polymers are present and in what proportions?" We use pyrolysis as the preliminary separative stage to break down polymers mainly into monomers and dimers.A t first the liquid pyralysate was manually injected into a gas chromatograph for identification.It was realised by Davison, Slaney and Wragg and later by Blenkin that the more volatile products were lost by this procedure. Working at the Dunlop Research Centre in the UK, they developed a technique of connecting a furnace at 550 "C directly to the inlet port of the gas chr0matograph.l When Curie-point pyrolysis became available, we realised the advantages and we chose pure iron metal, which gives a pyrolysis temperature of 770 "C.For manual handling, the sample of rubber was cut into a thin sliver (weighing 0.2-0.4 mg), which was fitted inside an iron-wire coil and suspended in the Curie-point pyrolyser.2 A new form of sample handling (described later) has since been introduced for automatic operation. For manual operation we used 3-m stainless-steel columns packed with 10% Apiezon L on Celite, and the column oven was programmed from 50 to 150 "C at 6 "C min-1 after an initial 3-min hold.The integrator used was of the electronic variety, mechanical ones being vulner- able to breakdown. The pyrograms contained all of the information required to identify the polymer system, the peaks of interest being isoprene and dipentene from NR and IR, butadiene, vinylcyclohexene and styrene from SBR, and butadiene and vinylcyclohexene from BR.Calculation of NR : SBR : BR ratios from peak areas was by simple though tedious arith- metic involving calibration factors and blank values3 Although the manual system gave satisfactory results, the number of samples that could be analysed in a working day was relatively low, even using three gas chromatographs.It was inconvenient to have to introduce a new sample by hand into the apparatus every 30 min and it was impossible to deal with enough samples for adequate quality control of factory- made mixes. I t was decided, therefore, to investigate the possibility of making the technique automatic so that the gas chromatographs could operate during the night as well as in normal working hours.This would increase the number of possible analyses from about 50 per week to 200 per week for each instrument. For samples received in any one day, the analytical results would be available the following morning, thereby making practicable a quality audit scheme. The automation of a gas chromatograph introduces two main tasks: getting the sample in and out of the pyrolysis unit, and linking the gas chromatograph to a computer. Peak recognition is a major problem, as pyrolysates contain many ingredients. At this time it was found that Pye Unicam were marketing an auto-solids unit, which was a closed system for injecting low-boiling-point solids into a heated inlet port.We thought that such a system could be applied to pyrolysis - gas chromatography and one auto-solids unit was acquired for modification. The auto-solids injector consists of an electronic control system, a set of glass sample holders held in a magazine and an inject - eject system using solenoids. The key breakthrough was the realisation that the glass sample holders supplied with the auto-solids unit could be made to carry our coil of Curie-point metal containing the rubber sample.After placing the rubber sample in the coil, the end of the wire was cut off and crimped so that when placed in the glass holder it was held firmly. This system worked well, but the most tedious stage was now the insertion of samples into coils, the hole inside the coil being very small (less than 1 mm across).Further examination showed that we could simplify the sample preparation by using a thin metal sheet instead of a coil. Some sheets of pure iron foil (0.1 mm thick) were obtained from Goodfellow Metals and divided into oblong pieces 14 x 4 mm, then folded to form a shallow V. The samplewasplaced in the V and the foil then squeezed flat around the sample. The foil was crimped into a Z shape and pushed into the glass holder. Each sample took about 1 min to prepare compared with about 3 min using a coil. Metal-to-sample contact was much better than when using a coil, and the pyrolysis products generated were much more consistent.Also, the proportion of monomer was greater. This sample-handling procedure was therefore adopted as standard. Up to 35 glass sample holders can be loaded into a brass magazine.The magazine, full of samples, is placed in a glass cylinder and a gas-tight top screwed on. The solenoid is activated We used this so-called flash pyrolysis successfully for several years.214 PYROLYSIS TECHNIQUES FOR ANALYSIS Proc. Analyt. Div. Chem. SOC. by the control box and injects the first sample into the pyrolysis unit.The sample falls on to the solenoid pin, which we have extended right through the inlet port into the pyrolyser. The glass chromatography column has also been extended through the pyrolyser to a new connector and nitrogen inlet. The control box activates the pyrolysis, re-sets the amplifier base line and integrator and puts a chart mark on the recorder. After pyrolysis, the used sample holder is ejected upwards by the lower solenoid into a receiver. Finally, the inject solenoid retracts, allowing all of the samples to move down the magazine under gravity and then switches off for a pre-set time interval depending on the expected time for complete elution (see Fig.1). The automatic equipment described above is a “stand-alone” system and will operate without assistance from a computer.The number of samples to be analysed can be set on a dial on the control box, and when all of the samples have been analysed the control box ceases to insert any more sample holders. The time between injections of successive samples is controlled by a clock on the control box, which can be set for any period up to 90 min. We usually allow 30 min between successive samples.After an overnight run, a chemist would be faced with the time-consuming job of interpret- ing up to 35 pyrograms and integrams and using the peak areas to calculate NR : SBR : BR ratios. To save time and labour, an IBM System/7 process control computer has been install- ed and linked to each gas chromatograph (see Fig. 2). The computer has taken over the cycle time control and issues a digital output command to start the inject cycle when theprevious sample has finished.If anything goes wrong with the automatic inject - eject, or the gas chromatograph, so that no peaks arise, the computer will not issue a “start” command and no more samples will be injected. Unused samples remain stacked up ready for analysis later when the fault has been corrected. Sa ho -Mounting block Oven head 4-Column packing Fig.1. Apparatus for automatic injection of samples into Curie-point pyrolyser fitted on top of the gas chromatograph oven and directly connected to the column. Six sample holders are shown waiting in the magazine: one is in the pyrolyser and three have already been pyrolysed and ejected and now lie in the glass receiver.Detector Auto-solids injector Reca Laboratory terminal Amplifier Automatic control unit 1’ II ~ irder Run Multi- plexor L& ‘I ,,w0 1rAL A/I D l d ‘ D/I P/I D/O 501 2 1/0 module d b Master ...... terminal OOOOO ...... ...... D/I = Digital D/O = Digital System/7 input U u P/I = OUiPUt Process interrupt Fig. 2. Diagram showing how a gas chromato- graph is connected t o the computer.Several gas chromatographs can be connected in similar fashion to one computer. Each gas chromatograph is identified to the system by means of a job tape. This tape contains information that instructs the computer where to look for the required peaks, howAugust, 1977 PYROLYSIS TECHNIQUES FOR ANALYSIS 215 long the analysis is to run, which gas chromatograph is being used, etc.When calibration factors are being determined special job tapes are used. Programming to ensure that the computer picks the correct peaks is one of the most difficult aspects. It was found that temperature programming of the column oven resulted in vari- ability in peak retention times that could not be tolerated. A change to isothermal operation at 110 "C resulted in much more consistent retention times and all analyses are now carried out at this temperature.Any time saved by temperature programming is lost by the con- siderable dead-time which has to be allowed for the column to cool to a steady starting temper- ature. Provided that all goes well, the computer measures the peak areas, finds the peaks it wants by their retention times and carries out all of the calculations to convert the peak areas into an NR : SBR : BR ratio.The computer prints out the result on a terminal as soon as each sample has been analysed. Hence, after a night's run 35 results from each gas chromatograph are immediately available. We insert a standard (known) sample after every four unknowns, and before drawing any conclusions from the print-out of results, we check that the standards have been analysed correctly.If not, we look at the recorder traces and can then tell whether the wrong peaks have been selected. The regular analysis of factory mixes by staff working normal office hours has been carried out successfully over the last 3 years by dealing with samples overnight using computer- controlled, automatic pyrolysis - gas chromatography.This has led to an improvement in consistency of the rubber mixes and a subsequent improvement in the final product-the tyre. Thanks are due to the Directors of Dunlop Limited for permission to present this paper, to J. Islip for all computer programming, and to our colleagues in the Tyre Chemical Laboratory. References 1. Blenkin, J., "Proceedings of the Fourth Rubber Technology Conference, London," Institution of the Rubber Industry, London, 1962, p.575. 2. Thompson, W. C., Lab. Pract., 1969, 18, 1074. 3. Coulter, G. L., and Thompson, W. C., Column, 1970, 3, No. 3, p. 6. Role of Pyrolysis - Gas Chromatography - Mass Spectrometry in the Analysis of Drugs J. A. Slack and W. J. Irwin Department of Pharmacy, University of Aston in Birmingham, Gosta Green, Birmingham, B4 7ET The analysis of materials of biological interest by pyrolysis - gas chromatography was first described by Janakl in 1960 when he pyrolysed various natural oils and fats and also a series of barbiturates.The pyrograms generated by these drugs yielded structural information concerning the substituents on the parent molecule. Kingston and Kirk2 reported the use of pyrolysis - gas chromatography in the analysis of 21 alkaloids that were differentiated by using multivariate statistical methods on the ratios of the lower hydrocarbon pyrolysis products, trimethylamine and acetic acid.Antibiotic structural characterisation by both high- (600- 1 300 "C) and low- (200400 "C) temperature pyrolysis - gas chromatography has been described by Brodasky.3 The three major positions of alkyl substitution in lincomycins were characterised by low-temperature pyrolysis and some of these fragments have been identified, enabling prediction of the substituents to be made. Both low- and high-temperature pyro- lysis - gas chromatography were used by Burrows and Calam4 to establish the identity of the polyene antifungal antibiotics candicidin, levorin and trichomycin.The Curie point pyrolysis - gas chromatography of five sterols and their derivatives was reported by Gassiot-Matas and Julia-Dane~.~ In this study the pyrograms were divided into volatile and non-volatile zones. Roy and Szinai6 used pyrolysis - gas chromatography - mass spectrometry in the study of fourteen penicillins and cephalosporins ; structural information concerning the substituent on the nucleus was obtained by identifying the fragments produced from fission about the amide216 PYROLYSIS TECHNIQUES FOR ANALYSIS Proc.Analyt. Diu. Chem. SOC. linkage. In a quantitative study of this pyrolysis, standard graphs were obtained based on the height of the most intense peak in the pyrogram and linearity was reported in the range 10 ng- We have previously reported the study of medicinal sulphonamides by Curie point pyrolysis - gas chromatography - mass spe~trometry,~ and have shown that significant structural information can be obtained from the pyrogranis. The majority of the sulphonamides studied underwent simple fission about the sulphonamido group to yield a characteristic heterocyclic amine and aniline, which was present in all of the pyrograms and could be used as an internal standard.The sulphonamide under test could be identified by retention time data alone but by using pyrolysis - gas chromatography - mass spectrometry a rapid and accurate classifica- tion was possible. This technique was found to be applicable to formulated products and was utilised in the analysis of formulated mixtures as the presence of other drugs did not have any discernible effect on the fragmentation process.A study of the Curie point pyrolysis - gas chromatography - mass spectrometry of a series of propionic acid derivatives has recently been undertaken. These drugs are currently marketed in the UK as analgesics and antipyretics.The propionic acid molecule is substituted in position 2 and the structures are shown in Table I. One major advantage of using pyrolysis - gas chromatography - mass spectrometry is that very little sample preparation is required and for the analysis of a formulated drug of this type, a small portion of the tablet is ground, sus- pended in a suitable solvent and a known amount is applied to a rotating wire8 that is held in a stream of warm air.After evaporation of the solvent the material is pyrolysed in a Curie point pyrolyser at 770 "C for 5 s and the pyrolysate is flushed directly on to a Carbowax 20M - potassium hydroxide column that is then temperature programmed from 100 to 245 "C. On pyrolysis the propionic acid derivatives underwent re-arrangements to give two major fragments.The component with the shorter retention time was the ethyl derivative (R-CH,CH,), which was generated by decarboxylation and proton rearrangement. The second component was formed by decarboxylation to yield the vinyl derivative (R-CH=CH,), 10 %* TABLE I RETENTION DATA FROM PYROLYSIS - GAS CHROMATOGRAPHY - MASS SPECTROMETRY OF PROPIONIC ACID DERIVATIVES R I CHj-CH-COOH Retention indices (aniline = 1.00) Drug Ibuprofen Fenoprofen 1 Fraction Fraction Radical R R-CHZCH, R-CH = CH, C H ~ - C H ( C H S ) ~ 0.36 0.58 1.51 1.73 Naproxen Ketoprofen 0 1.91 2.16 2.27 2.52Aagicst, 1977 PYROLYSIS TECHNIQUES FOR ANALYSIS 217 which had a longer retention time on the polar column.The identification of these two major peaks yields significant structural information concerning the parent molecule.These peaks are much more intense than those produced by pyrolysis of the excipients in the tablets, e.g., magnesium stearate or starch. With the exception of ibuprofen the ethyl derivative was the predominant peak but in ibuprofen the vinyl derivative predominated. A third fragment was produced by fenoprofen where, in addition to the ethyl and vinyl derivatives, a small peak (retention index = 1.37) was seen and identified as the methvl derivative.The use of pyrolysis - gas chromatography as a screening method for abnormal cell types has been discussed by Reiner.g We were interested in the possibility of using pyrolysis - gas chromatography - mass spectrometry as a screening technique for the metabolites of the analgesic drugs and fenoprogen and ibuprofen were chosen as examples.The drugs were taken by volunteers from whom control urine samples had been obtained prior to administration. The sample preparation is simple : an aliquot of the urine, normally 25 ml, is lyophilised and a small amount of the total solids remaining is re-dissolved in distilled water and coated on to the revolving wire.After coating, the wires are stored under vacuum until required. As previously reported’ the pyrograms of the control urine samples are re- producible and relatively simple. There are fifteen peaks in the area of interest but all are substantially smaller than the peaks due to the metabolites. An earlier report on the metabo- lism of fenoprofenlO indicated that the drug was excreted in the urine as its glucuronide (45%) and as the 4‘-hydroxyfenoprofen glucuronide (45%), with the unconjugated forms excreted only in small amounts (4-10%). Pyrograms of urine from a volunteer taking fenoprofen displayed the characteristic peaks of fenoprofen (retention index = 1.51 and 1.73) superimposed on those present in the control urine, tog2ther with a significant increase in the intensity of a short retention time peak (retention index = 0.16).The largest peak characteristic of fenoprofen (R-CH2-CH,) was the most intense in the whole pyrogram. The metabolism of ibuprofenll is more complex with four metabolites being formed and a number of conjugates. The metabolised part of the molecule is the isobutyl fraction and therefore as well as decarboxylation and rearrangement of the propionic acid moiety on pyrolysis there is also the possibility of a similar reaction occurring at the metabolised isobutyl end of the molecule. This effect is seen on examination of the pyrogram from the test urine with six new characteristic peaks appearing and an increase in the intensity of the same low retention time peak as in the fenoprofen.The increase in intensity of this low reten- tion time peak appears to be a pointer to the formation of glucuronide conjugates. From this brief discussion it can be seen that the advantage of pyrolysis - gas chromato- graphy - mass spectrometry is that significant structural information can be obtained concern- ing the material pyrolysed with a minimal amount of sample preparation. Another advantage is the speed at which the results are obtained. Good results may be obtained by using pyrolysis - gas chromatography as a comparative technique but with the disadvantage that adequate standards must be available. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Janak, J., Nature, Lond., 1960, 185, 684. Kingston, C. R., and Kirk, P. L., Bull. Narcot., 1965, 17, 19. Brodasky, T. F., J . Gas Chromat., 1967, 5, 311. Burrows, H. J.. and Calam, D. H., J . Chromat., 1970, 53, 566. Gasiot-Matas, M., and Julia-Danes, E., Chromatographia, 1976, 9, 151. Roy, T. A., and Szinai, S. S., J . Chromat. Sci., 1976, 14, 580. Irwin, W. J., and Slack, J. A., in Jones, C. E. R., and Cramers, C. A., Editovs, “Analytical Pyrolysis,” Meuzelaar, H. L. C.. and in’t Veld, R. A., J . Chromat. Sci., 1972, 10, 213. Reiner, E., and Hicks, J. J., Chromatographia, 1972, 5, 525. Rubin, A., Warrick, P., Wolen, R. L., Chernish, S. M., Ridolfo, A. S., and Gruber, C . M., J. Pharmac. Brooks, C. J. W., and Gilbert, 33. T., J . Chromat., 1974, 99, 541. Elsevier, Amsterdam, 1977, p. 107. Exp. Ther., 1972, 183, 449.

ISSN:0306-1396    

DOI:10.1039/AD9771400211

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

218 METALLIC AND ORGANIC SPECIES Proc. Analyt. Div. Ckem. SOC. Measurement and Toxicity of Metallic and Organic Species The following are summaries of three of the papers presented at a Meeting of the Scottish and North East Regions held on March 25th and 26th, 1977, at Pitlochry. Transport and Storage of Trace Metals in Animals 1. Bremner Rowett Research Institute, Bucksburn, A berdeen, AB2 9SB In the course of their absorption, transport and storage, important changes occur in the forms in which trace metals occur in biological fluids and tissues.Non-complexed forms of the metal can be present in the acid region of the alimentary tract, but the metals are more usually bound to proteins or other ligands. The nature of the complexes occurring in the intestinal lumen can influence both the absorption and tissue-distribution of metals.The retention of zinc, iron, copper and manganese is reduced, for example, in rats receiving diets containing high concentrations of phytic acid, probably because of the presence in the alimentary tract of insoluble metal phytate comp1exes.l This effect can readily lead to the development of trace-metal deficiency states. The susceptibility of animals to heavy-metal toxicosis is also influenced by dietary composi- tion, especially with regard to the concentration of other essential elements.For example, animals of low copper status are more at risk from cadmium and zinc poisoning than those on adequate copper intakes, because both cadmium and zinc exert a direct antagonistic effect on copper metabolism. This effect may arise from isomorphous replacement of the copper in specific proteins involved in its transport or storage.However, it is possible for the binding of an essential element to be modified in several ways when trace-metal imbalance occurs. In recent years it has become apparent that metallothionein is a major storage form of copper and zinc in both liver and kidney2J and there is some evidence that it functions in the intestinal mucosa in the control of metal absorption.4 The protein occurs in the tissue cytosol, has an apparent relative molecular mass of 12 000 and a cysteine content of about 30%.It has a high metal-binding capacity, one metal atom being bound per 2-3 cysteine residues, which gives a metal content of the protein of 7-10%.Its synthesis in several tissues can be induced by the administration of either copper2 or zinc,3 and also of cadmium, mercury or ~ i l v e r . ~ Although the concentrations of zinc and copper thioneins in the livers of monogastric animals are usually directly related to the hepatic zinc and copper content, neither zinc nor copper thioneins are found in the livers of zinc-deficient animals, regardless of their copper content.This implies that zinc must play an important role in the accumulation of the copper protein. It has been established from studies on zinc-deficient rats that zinc is not required for synthesis of copper thionein. However, the disappearance of copper from the induced protein is more rapid in zinc-deficient animals, as a consequence of the increased degradation of the protein moiety when it contains no zinc.6 This suggests that zinc can stabilise copper thionein and so influence the rate of utilisation of copper from the protein.The increased susceptibility of zinc-deficient animals to copper toxicosis may arise in part from these effects. Increased dietary intakes of molybdenum can induce a copper-deficiency state in ruminant animals, which can be associated with increased concentrations of copper in plasma and kid- neys. Fractionation of these has revealed abnormalities in the distribution of copper. Normally at least 90% of plasma copper is present as caeruloplasmin and the remainder is bound to albumin, which functions as a transport protein for copper.In molybdenum- supplemented sheep, however, about half of the plasma copper is bound to another protein with a relative molecular mass of 80-90 000, with which molybdenum may also be associated.Similarly, the copper which accumulates in the kidneys of these animals is not bound to thionein, as is normally the case in kidneys of high copper content, but is associated with It is thought that this is part of the normal detoxification process for these metals.August, 197 7 METALLIC AND ORGANIC SPECIES 219 proteins of higher relative molecular mass, with which molybdenum is again associated.It appears therefore that the presence of molybdenum can modify the copper-binding affinity of certain proteins and so convert some of the plasma and tissue copper into non-utilisable forms.These effects are only observed in sheep when the diet is supplemented with sulphate, indicat- ing possible involvement of sulphur in the binding of the other metals. This binding could arise from formation of thiomolybdates in the rumen, as they have been found to modify plasma copper distribution in a similar manner. These examples illustrate how the toxicity of metals is often manifested as a disturbance in the metabolism of other essential elements and how an explanation of these effects can be obtained by examination of the transport and storage forms of the metals.References 1 . Davies, N. T., and Nightingale, R., BY. J . Nutr., 1975, 34, 243. 2. Bremner, I., and Young, B. W., Biochem. J., 1976, 155, 631. 3. Bremner, I., and Davies, N.T., Biochem. J., 1975, 149, 733. 4 . Richards, M. P., and Cousins, R. J., Biochem. Biophys. Res. Commun., 1975, 64, 1215. 5 . Winge, D. R., Premakumar, R., and Rajagopalan, K. V., Archs. Biochem. Biophys., 1975, 170, 242. 6 . Bremner, I., and Davies, N. T., B r . J . Nutr., 1976, 36, 101. Uptake and Storage Mechanisms of Heavy Metals in Marine Organisms Thomas L. Coombs Institute of Marine Biochemistry, St.Fittick's Road, Aberdeen, AB1 3RA Concern for heavy metal pollution hazards in the aquatic environment has focused attention on the uptake and storage of heavy metals by marine organisms. Shellfish, which concentrate metals to a high degree and are often found in estuaries, are potentially at greater risk from industrial, agricultural and natural sources and have, therefore, received much attention.The application of atomic-absorption spectroscopy, anodic stripping voltammetry and X-ray microprobe analysis to the storage of lead in the common mussel, Mytilus eduZis L., is described here. Experimental Batches of 20 mature mussels, of 6-7 cm shell length, collected from the Ythan estuary, were kept unfed in aerated, filtered sea water at 15 "C and exposed to lead added either as nitrate or complexed with citrate, humic and alginic acids or pectin.Animals kept in sea water alone served as controls. The methods of preparation of the complexes, dissection of the tissues, wet- or dry-ashing for chemical analysis and fixation of the tissues for electron microscopy and X-ray analyses were similar to those used in cadmium-uptake studies1 Analyses for zinc, copper, iron , manganese and calcium were performed by atomic-absorption spectroscopy (Varian-Techtron AA5) and for lead by anodic stripping voltammetry (ESA- 2014).X-ray microprobe analyses were performed by courtesy of AEI Ltd. , Manchester, using an EMMA-4 instrument. Results and Discussion Effect of Complexing Agents The chemical form of a metal, i.e., its biological availability, can profoundly affect its absorption.2 The uptake of lead, therefore, at 0.1 p.p.m.in sea water, as nitrate or in different complexed forms, using the naturally occurring complexing agents citrate, humic and alginic acids and pectin, was followed over a period of 13 d. The changes in the concentrations of lead in the tissues are shown in Fig.1. For lead as nitrate, all of the tissues have absorbed the metal, with the highest concentration in the kidney (300 pg 8-l dry mass). When the lead is complexed with citrate a 3-4-fold increase is observed in both the rate and total220 METALLIC AND ORGANIC SPECIES Proc. AnaZyt. Div. Chem. SOC. accumulation in all of the tissues, with the greatest concentration in the kidney (1 000 pg g-1 dry mass).The high relative molecular mass complexes, humic and alginic acids and pectin, are not so effective, however, producing at best 1.5-2-fold increases. Thus complexation of lead does not change the tissue distribution, but can significantly increase the absorption. This pattern is specific for lead, however, for similar experiments with cadmium produced an equal increase for both low and high relative molecular mass complexes,1 but with iron, either an increase or decrease has been observed depending on the type of complex used, and changes in the tissue distribution have been r e ~ o r d e d .~ , ~ Effect of Lead on Other Metals Non-functional metals such as lead can produce toxic effects by competing with essential trace metals normally present in the tissues and can induce either deficiencies or transloca- t i o n ~ .~ Analyses for these biofunctional metals in the presence of lead in Afytilus showed significant increases of manganese and copper in mantle and visceral mass and a decrease of calcium in kidney, with iron and zinc remaining essentially constant. Histological Examination The electron micrographs revealed the presence of conglomerates of small electron-dense particles, suggestive of lead, within membrane-bound vesicles in gills, gut and kidney for all of the metal species tested (Fig.2), and particularly in the gut these are associated with less dense amorphous material (Fig. 2B). The X-ray microprobe analysis confirmed the presence of lead within the vesicles but in addition other elements such as phosphorus, calcium, iron, potassium and chlorine and in one instance titanium were detected.The X-ray spectra for one of the ringed selected areas in the kidney (Fig. 2C) and from another kidney preparation are reproduced in Fig. 3. This pattern of concentration and storage in membrane- limited vesicles is similar to that seen for copper uptake in a freshwater isopod, AseZZus,6 and for iron in MytiZus.7 ~~~ ~ Viscera I Muscle P / A P Gills / i E- Mantle 801 ;f 8 [ 3 40' Foot r$ y* A I 1 I I 3 6 10 13 Time of exposure to sea water containing lead/d Fig.1. Uptake of lead by Mytzlus edulis. Animals were exposed to 0.1 p.p.m. of lead in sea water and batches of four animals removed at the times indicated.The tissues were dissected and combined before determination of wet and dry masses and metal analysis as described. Lead added : as nitrate, 0 ; as citrate, ; as humate, A; as alginate, ; and as pectate, 4. Sea water alone (control), 0.August, 1.977 METALLIC AND ORGANIC SPECIES 92 1 The absorption route for lead and iron deduced from electron microscopy and iron-59 pulse- labelling is an endocytosis by gills and gut, followed by transfer via circulating amoebocytes Fig.2. Electron micrographs of Mytilus edulis tissues exposed to lead in sea water: (A), gills; (F), gut; and (C) kidney, showing particles (arrows) associated with less dense amorphous material within membrane-bound endocytotic vesicles. The circles in C indicate areas selected for X-ray analysis and the elements detected therein.V, Vesicles; X, nucleus; Mi, mitochondria; Lu, lumen; and Mv, microvilli. in the haemolymph to the kidney and other tissues for storage and eventual excretion. By this means Mytilus and other shellfish can tolerate high metal concentrations within their tissues, isolating the metal inside membranes to prevent access to vital centres within the cell 1 5 10 13 X-ray energylkev Fig.3. Two typical X-ray spectra, one obtained for the large selected arca shown in Fig. 2(C) and one from another kidney preparation. The high copper present in these spectra is from copper grids that support the tissue specimens. and thereby immobilising and detoxifying them. The generality of this mechanism for lead and other metals is a subject for continuing research at the Institute. The application of X-ray microprobe analysis has become a key factor in advancing our knowledge in this field.This work was supported in part under Contract No. 086/087-74-7-ENX U.K. of the EC The advice and assistance of Dr. S. G. George, Environmental Research Programme. Mr. B. J. S. Pirie and Mrs. A. R. Cheyne are gratefully acknowledged.References 1. George, S. G., and Coombs, T. L., Mar. Biol., 1977, 39, 261. 2. De Kock, P. C., and Mitchell, R. L., Soil Sci., 1957, 84, 55.222 METALLIC AND ORGANIC SPECIES Proc. Analyt. Div. Chew. SOC. 3. George, S. G., Pirie, B. J. S., and Coombs, T. L., in Hutchinson, T . C., Editor, “International Confer- ence on Heavy Metals in the Environment.” Symposium Proceedings Volume 2, University of Toronto, Toronto, 1977, p. 887.4. George, S. G., and Coombs, T. L., J . Ex?. Mar. Biol. Ecol., in press. 5. Coombs, T. L., in McIntyre, A. D., and Mills, C. F.,,72dZtors, “Ecological Toxicology Research. Effects 6. Brown, B., personal communication. 7. George, S. G., Pirie, B. J. S., and Coombs, T. L., J . Exp. Mar. Biol. Ecol., 1976,23, 71. of Heavy Metal and Organohalogen Compounds, Plenum Press, New York, 1975, p.187. Measurement and Effects of Sub-lethal Levels of Some Heavy Metals onMarine Life in Simulated Marine Ecosystems G. Topping Department of Agriculture and Fisheries for Scotland, Marine Laboratory, P.O. Box 101, Torry, Aberdeen Information on the toxicity of metals to marine organisms is largely confined to LC,, values- the concentration known to kill 50% of the test organisms over a period of time, usually 24,48 or 96 h.Some studies have been made on the effects of sub-lethal concentrations of metals on the physiology and biochemistry of marine organisms but these have been mainly confined to short-term studies of single species. Few workers have attempted to examine sub-lethal effects at realistic levels of metal contamination, i.e., those levels that are likely to be encountered in coastal and estuarine waters that receive discharges of industrial waste.Until recently no attempt had been made to examine these problems using a multi-species approach in which individual species formed part of a food chain. Over the last 7 years scientists at the Marine Laboratory have examined the effects of sub- lethal levels of metals on simple food chains in large enclosures at our field station at Loch Ewe, West Scotland.This paper describes briefly the equipment used in these studies and some of the results for copper and mercury. Experimental Enclosures and Food Chains Our studies are carried out in large glass-fibre tanks (6 m3) based on the shore at Firemore Bay and in large plastic bags (100 m3) moored out in deep water at Thurnaig Bay.Tank Studies Young plaice settle in the bay and feed on a wide range of benthic organisms that are found there. Tellina tenius is a common bivalve mollusc in the area and their inhalant siphons are a major component of the young plaice’s diet. Tellina in this area is predominantly a particle filter feeder and the major component of their diet is the phytoplankton in the water.The bottom of the tank is covered with sand to a depth of 10 cm and an adequate water supply provided to maintain a phytoplankton food supply for the Tellina. The growth of plaice, Tellina and phytoplankton can be studied under controlled conditions and in the presence of introduced metal salts.Experiments with copper were carried out using sub-lethal levels of 10,30 and 100 yg 1-l; the lowest level represented 3 times the background level of copper in sea water and the highest approximately l/lOth of the 96-h LC,, value for TelZina. Similar experiments were conducted using mercury levels of 0.1,l .O and 10.0 pg 1-l. Throughout each experiment samples of sea water, sand, TeZlina and plaice were collected at intervals to observe metal accumulation and to assess metabolic effect on Tellina and plaice.Firemore Bay is a nursery area for plaice. The young plaice/TeZlina food chain can be established in a tank ecosystem. Bag Studies Zooplankton form an important link between phytoplankton and fish and shellfish. The relationship between phytoplankton, zooplankton and bottom feeding organisms cannot be studied properly in tanks; larger and deeper enclosures are required to simulate this part of the food web,August, 19 7 7 METALLIC AND ORGANIC SPECIES 223 The enclosures used at Thurnaig Bay attempt to overcome the inadequacies of tank systems.They are made of nylon-reinforced polythene to provide strength and flexibility and are fabricated into a cylindrical shape (approximately 3 m diameter x 17 m deep) that is open to the atmosphere but closed at the bottom to allow the collection of any material that settles out of the water column.The integrity of the full bag is maintained by means of a rigid external framework. A number of bags are employed in each experiment; one is filled with uncon- taminated sea water to act as a control and the remainder are dosed with metal at a pre- determined level: the levels chosen for study were copper 10 pg 1-1 and mercury 1 and 10 Samples of sea water and settlement material are collected at intervals during the experiment to estimate losses of metals from the water column.The effects of the metals on the biological community are monitored by making frequent measurements of the quality and amount of plant and animal life in the control and test bags.pg 1-l. Chemical Analysis The first involved a pre-concentration of the copper on to Chelex-100 resin, elution with acid and determination by flame atomic-absorption spectrophotometry.l The second employed anodic stripping voltammetry directly on the sample.The procedure for the determination of mercury in sea water as follows. The sample was treated with sulphuric acid and potassium permanganate to oxidise the organic matter. It was then treated with tin(I1) chloride and aerated to remove the mercury. The volatilised mercury was trapped in a solution of sul- phuric acid and potassium permanganate. The mercury in this solution was determined by using a cold-vapour technique.2 This procedure gave a measure of the total amount of mercury in sea water.By omitting the oxidation step in this procedure it was possible to determine the amount of mercury that was not associated with organic matter in the water: this amount is termed “reactive” mercury. The determination of copper in sediments and organic tissue was carried out by flame atomic- absorption spectrophotometry following wet-digestion with concentrated acids.The mercury content of sediments and organic tissue was measured in the following way. The sample was dry-ashed at 1000 “C in a silica-lined furnace using a stream of oxygen to assist combustion. The volatilised mercury was trapped in a solution of sulphuric acid and potassium per- manganate and determined by using a cold-vapour technique.2 The determination of copper in sea water was carried out by using two methods.Summary of Results Tank Studies Copper had a distinct algicidal effect, which increased with level of exposure; this $educed the amount of food available for the Tellina. There was a reduction in the growth of Tellina and an indication that siphon regeneration was impaired.In consequence there was less food available for plaice. Mercury had no significant effect on phytoplankton and Tellirta but plaice growth was reduced at all levels of exposure. Both metals were found to accumulate in sand, Tellina shell and soft tissue and plaice tissue. Sand was the most important site of accumulation for both metals. The concentration of copper in whole-body Tellina tissue and in plaice viscera increased with exposure time and dose level whereas levels in plaice edible tissue were the same for control and dosed tanks.Mercury levels in Tellina soft tissue increased with dose level. Unlike copper the accumulation stopped after approximately 40 d and levels remained reasonably constant for the remainder bf the exposure period.About l-lO% of the total mercury in both plaice and Tellina was in the methylated form, which suggested that methylation of the inorganic mercury had occurred in the tank ecosystem. No detectable amount of methyl mercury was found in the sand. -4 detailed discussion of the copper experiment can be found el~ewhere.~ Bag Studies Although there was some evidence to show that copper had affected the quality and amount of phytoplankton and zooplankton the over-all conclusion was that the effect of the copper on the community was insignificant compared with other natural stresses in these enclosure^.^ Mercury at the 1 pg 1-1 level had a transitory effect on phytoplankton and zooplankton but the2.2 4 METALLIC AND ORGANIC SPECIES Proc.Analyt. Div. Chem. SOC. system recovered after a few days. The effects of mercury at the 10 pg 1-1 level were serious for zooplankton and no recovery was observed even after 2 months. The level of copper in the sea water fell rapidly over the period of the experiment, primarily owing to leakage in the bag system. I t was possible to demonstrate, however, that copper had been lost from the water column by settlement of detritus and that there was a linear relationship between the loss of copper and the carbon content of the settlement materiaL5 The mean value of copper in micrograms per gram of carbon for settlement material was found to be 835.0.30 c 4 0.20 t ‘b O.1° t 0 5 10 15 20 Time/d Fig. 1. Variation of mercury content of spiked sea water with time : A, total mercury ; and R, reactive mercury. At the 1 pg 1-1 level of mercury the total mercury in sea water remained steady for the first few days following addition and then fell gradually over the next 20 d to a level belowO.l pg 1-l. “Reactive” mercury levels were always significantly lower than total mercury and fell more rapidly with time; within a few days the “reactive” mercury had dropped to 10-20% of the total mercury in the water column (Fig. 1). Most of the mercury lost from the water column was found associated with the settlement material and there was a linear relationship between mercury loss and carbon content of the settlement material. The mean value of micrograms of mercury per gram of carbon was approximately 3000. References 1. Riley, J. P., and Taylor, D., Analytica Chirn. Acta, 1968, 40, 479. 2. Topping, G., and Pirie, J. M., Analytica Chim. Acta, 1972, 62, 200. 3. Saward, D., Stirling, A., and Topping, G., Mar. Biol., 1975, 29, 351. 4. Gamble, J. C., Davies. J. M., and Steele, J. H., Bztll. Mar. Sci., 1977, 27(1), 146. 5. Topping, G., and Windom, H. L., Bull. Mar. Sci., 1977, 27(1), 135.

ISSN:0306-1396    

DOI:10.1039/AD9771400218

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

August, 1977 BASIC SAFETY I N VOLUMETRIC ANALYSIS SAFETY IN ANALYTICAL LABORATORIES 225 This article continues the series of reports on aspects of safety of particular interest to analy- tical chemists. The first article, on the use of gas cylinders, appeared in the March 1977 issue of Proceedings (p. 57) and the second, on emergency procedures, in the May 1977 issue (p. 115). It is hoped that these articles will provide a forum for further discussion, and correspondence on the individual articles and on all safety matters is invited.Basic Safety in Volumetric Analysis In general, laboratory technicians or students are taught the basic technique of volumetric analysis very early in their practical training, when their general awareness of potential hazards is probably minimal.The aim of this article is to indicate some of the more basic hazards that might be encountered and to suggest some safety measures that could be applied. 1. Preparation of Solutions Many standard solutions are marketed by chemical suppliers but the occasion still arises when they need to be prepared in the laboratory. I t is advisable that all laboratory workers are fully trained in the correct, safe procedure for the preparation of these solutions.It should, for example, be emphasised to the laboratory technician that preparation of many solutions involves heat generation and that for this reason heat-resistant beakers or flasks should be used and not thick-walled glassware such as bottles or measuring cylinders. 1.1 Acids It is essential that the laboratory technician or student is fully conversant with the hazards involved in the dilution of concentrated acids and is fully trained in the precautions that are necessary when carrying out this operation.It needs to be stressed that full eye protection should always be worn when pouring concentrat- ed acids ' from Winchester bottles or large containers into other vessels.1.1.1. Hydrochloric acid solutions. Chemical goggles affording full eye protection and rubber gloves should be worn during the dilution of concentrated hydrochloric acid. The required volume of concentrated hydrochloric acid should be poured, with constant stirring, into twice its volume of water contained in a beaker. After cooling, the solution can be diluted to the volume required.1.1.2. Sulphuric acid solutions. Close-fitting eye protection such as that afforded by chemical goggles should be worn when pouring concen- trated sulphuric acid from one vessel to another. The wearing of a face shield over the goggles provides increased protection to the face and neck. Rubber gloves should also be worn and if large amounts of the acid are being handled it is advisable that a rubber apron be worn.It must be impressed on the technician or student that, when diluting sulphuric acid, the strong acid should be poured carefully into the water and that water must never be poured into the strong acid. The amount of heat generated when concentrated sulphuric acid is poured into water makes i t essential that the dilution is carried out in a controlled manner.The following method is recommended. A beaker containing a volume of water equivalent to about 20 times that of the con- centrated acid to be diluted should be placed in a trough or sink capable of containing, in the event of a spillage, the volume of solution being prepared. The acid should be poured slowly into the water with constant stirring and cooling throughout the addition.The solution should be allowed to cool before dilution to the final volume. 1.1.3. Nitric acid solutions. When using nitric acid the main hazards that the technician must guard against are that, as well as being corrosive, nitric acid is a powerful oxidant, giving rise to the risk of fire or explosion when mixed with combustible materials, and that its vapour is a serious respiratory poison.Rubber gloves should never be worn when using nitric acid but an alternative type such as disposable PVC or PVC gauntlets should be used. The acid should only be handled in a well ventilated area and as with other concentrated mineral acids full eye protection is required. In the preparation of solutions the acid should be initially diluted in about five times its volume of water and then cooled and diluted to the required volume.1.1.4. Hydrofluoric acid solutions. Hydro- gen fluoride is particularly hazardous as both the gas and the solutions are toxic and it is rapidly absorbed through the skin and deep into the226 BASIC SAFETY IN VOLUMETRIC ANALYSIS Proc. Analyt. Div. Chem. SOC. body tissues, causing severe pain and burns that are slow to heal.With diluted acid the irrita- tion of the skin and of the tissues becomes noticeable only after some time. It is impera- tive that medical attention is sought immediate- ly in all instances of skin contact. AnalaR hydrofluoric acid (nominally 40 yo hydrogen fluoride) is supplied in polythene bottles because of its etching action on glass. It is recommended that only technicians with con- siderable practical expertise should be allowed to use this reagent.Full eye protection, such as that afforded by chemical goggles, and also a face shield to give added protection to the face and neck, should be worn when handling all solutions of this compound. Rubber gloves should be tested very carefully for leaks before wearing.All operations involving the use of this acid should be carried out in a well venti- lated fume cupboard. Polythene equipment should be used for the preparation of all solu- tions and their storage. 1.1.5. Perchloric acid solutions. Perchloric acid is a powerful oxidising agent that may react explosively with reducing agents and organic compounds. Chemical goggles and a face shield should always be worn when pouring this reagent from one vessel to another and full eye protection should also be worn when hand- ling any solutions.As with any oxidising reagent rubber gloves are unsuitable and an alternative type such as PVC gloves should be worn. When preparing perchloric acid in acetic acid solutions there is the added hazard of the heat generated on the addition of the acetic anhydride required to react with the water in the perchloric acid.During prepara- tion the perchloric acid - acetic acid mixture, contained in a beaker set in a pneumatic trough of crushed ice and water, must be stirred efficiently by a mechanically operated glass stirrer throughout the addition of the acetic anhydride. The mixture should be cooled to 15 "C before starting the addition (in small increments from a burette), discontinued when the temperature reaches 20°C and not recom- menced until the mixture has again cooled to 15 "C.1.2. AIkalis It is of prime importance that the laboratory technician or student is aware that when making solutions from pellets of sodium or potassium hydroxide and water considerable heat is evolved.Because of this the operation should be carried out in a thin-walled heat-resistant beaker and the pellets should be added to water-never the other way round. 1.2.1. Sodium hydroxide solutions. Many accidents involving the preparation of sodium hydroxide solutions have been reported and i t is essential that the technician understands the correct procedure. Chemical goggles and rubber gloves should always be worn when making up solutions of sodium hydroxide pellets in water and when pouring solutions from Winchester bottles or other large containers into other vessels.When preparing solutions using pellets, flakes or sticks, the solid sodium hydroxide should be added to water contained in a beaker set in a cooling bath. It is essential that the solution is constantly and efficiently stirred during its preparation in order to prevent the build-up of a highly concentrated layer of caustic solution.On further dilution the heat generated can be sufficient to "boil" the water, which could result in the solution erupting. A mechanical glass stirrer is a suit- able means of achieving efficient stirring. The preparation of carbonate-free standard solutions may involve precipitation of the carbonate and its removal by filtration using suction.Con- sideration must be given to the size of Buchner flask to be used as those of more than 1-1 capacity should be protected by a suitable safety cage. 1.2.2. Aununonium hydroxide solutions. Al- though ammonium hydroxide solutions are seldom used as a standard alkali, because of their tendency to lose ammonia, they are used with other reagents. This makes it necessary for the laboratory technician to understand the hazards, and the precautions that need to be taken, when using these solutions. For ex- ample, he should be informed that the vapours cause severe irritation to the throat and lungs, that in contact with the eyes serious damage is produced, and that the solutions exert a local irritant action.Hence solutions should be used only in a well ventilated fume cupboard with the operator wearing full eye protection and rubber gloves. A warning needs to be given on the build-up of pressure in bottles of ammonia solutions, particularly strong solutions, and that stoppers must be slowly unscrewed to allow the vapours to escape in a controlled manner.The importance of storing solutions in a cool place needs to be stressed. 1,3. A mpoules A number of reagents are supplied in glass ampoules of various sizes. The associated hazards are that they usually contain material that is toxic, flammable, corrosive or volatile. The thickness of the glass in the body can vary greatly from base to neck and may be so thin a tAugust, 1977 BASIC SAFETY I N VOLUMETRIC ANALYSIS 227 the latter as to crush under finger pressure.The glass of the ampoule may also be under strain so that it shatters when opening is attempted. All opening operations ought to be done in a fume cupboard over a tray large enough to hold the contents of the ampoule if it breaks. If the contents are volatile they should be cooled before any operation is carried out.The hands should be fully protected and a face shield worn. To open ampoules with a neck diameter of less than 6 mm make a score mark on the neck with a sharp glass knife and snap off the top. If the diameter is 6 mm or greater, score completely round the neck, place the score mark on a sharp edge and tap the top of the ampoule with the glass knife.The top should break cleanly away from the base. An alternative method, which must not be used for flammable materials and must be carried out behind a safety screen, is to touch the score with the red-hot tip of a glass rod and then drip cold water on to the heated part. 1.4. Miscellaneous Specific instructions need to be given for the preparation and use of solutions that are particularly hazardous because of either the toxicity of the chemical, its instability or the means of preparation.Examples of a few of the more hazardous solutions are as follows. 1.4.1. Cyanide solutions. Cyanides are among the most toxic and rapidly acting sub- stances to be encountered in the chemical laboratory. Toxic symptoms occur if these materials are swallowed, inhaled or absorbed through the skin.A few inhalations of hydrogen cyanide can be fatal. It is recom- mended that only experienced laboratory personnel who are fully aware of the hazards involved and the safety precautions required, and are trained in the first aid and medical treatment necessary in the event of accident, are authorised to handle or prepare these solutions.In any operation requiring the use of cyanides at least two experienced persons should be present at all times. I t is not intended to cover the handling of hydrogen cyanide in this article but the follow- ing are guidelines applicable to potassium and sodium cyanide, the most commonly used cyanides in volumetric analysis. All experiments should be located in a well ventilated fume cupboard, which together with its ducting should be tested for leaks.The preparation of solutions should be carried out over a tray capable of containing the volume of solution being prepared. The minimum basic protective clothing required is rubber or PVC gloves or gauntlets, full eye protection and a rubber apron. Two independent compressed- air masks should be provided in case of a spillage or accident.A suitable antidote to be used in the event of ingestion should be kept close a t hand and amyl nitrite capsules should also be easily available. If skin contamination occurs the cyanide should be washed off with copious amounts of water but in every instance, whether it be inhalation, ingestion or contamin- ation, medical attention should be obtained immediately.When cyanide solutions are being used a warning notice to that effect should be prominently displayed. All cyanide waste must be made harmless by reaction with alkaline sodium hypochlorite solution before disposal. Solutions of silver salts and ammonia. ,411 solutions containing both silver salts and ammonia are potentially dangerous from the time of mixing the ingredients and therefore chemical goggles and a face mask must be worn during the preparation and use of these solu- tions.The solutions must in no circumstances be stored as they tend to deposit an explosive solid on standing. Only an amount sufficient for the job in hand should be prepared and any excess must be immediately discarded. Un- necessary heating must be avoided. 1.4.3. Bromine solutions.Contact with liquid bromine will lead to extremely painful burns and the dilute solutions can cause severe irritation. Slight concentrations of the gas have a strong irritant effect on the eyes and respiratory organs. The very hazardous nature of the chemical makes i t essential that it is used only in a. well ventilated fume cupboard. Closely fitting chemical goggles and gloves should always be worn when handling solutions, with the added protection of a face mask and apron for liquid bromine.The hazards associ- ated with the diluent used in the preparation of solutions, for example, acetic acid and carbon tetrachloride, must also be considered and the appropriate precautions taken. While in storage or transit bromine must be isolated from ammonia, unsaturated hydro- carbons, petroleum vapours, benzene, hydrogen and finely divided metal powders, and all solutions should be stored in a cool, well ventilated area.1.4.2. 2. Glassware 2.1. Cleaning and de-greasing Various methods are available for the de- greasing and cleaning of laboratory glassware. Chromic acid - sulphuric acid or chromic acid -228 EQUIPMENT NEWS Proc.Analyt. Div. Chem. SOC. nitric acid mixtures are not recommended for general use as incidents have been reported of the oxidising mixtures reacting vigorously with traces of chemicals left in the glassware, result- ing in injury to the operator. Preferably one of the proprietary brands of glass-cleaning fluids should be used; when the manufacturer’s instructions are followed these fluids are efficient and safe.2.2 Use of pipettes It cannot be too strongly urged that the practice of pipetting (or siphoning) any sub- stance by mouth be forbidden. The risk of admitting a corrosive liquid into the mouth is obvious. There is also a more insidious risk from toxic liquids, some of which, even with brief or low-level exposure, cause irreversible damage to bodily functions.A mechanical means of suction should always be used. 2.3. Burettes 2.3.1. Greasing of stopcock. The fracture of a burette at its weakest point, just above the stopcock, is commonly caused by the operator exerting too much pressure on an inadequately greased, glass-keyed stopcock that is sticking or has become siezed. This practice could result in injury to the hands and/or skin contamination by the contents of the burette.Correct greasing of the glass key is essential. Suitable greases are available commercially but probably the simplest lubricant is pure Vaseline. Sili- cone-type greases should be avoided as they creep along the length of the burette, with consequent contamination of the walls, and are difficult to remove. A correctly greased stop- cock should appear transparent with no visible lines.The bore should be free of grease and the key turn smoothly. A minimum amount of grease must be used to achieve this effect as excess will block the stopcock and may enter the jet and block this also. The following method is suitable: remove all old grease from the barrel and key, apply a thin film of grease to the key on each side of the bore and then replace the key in the barrel and distribute the grease by rotating the key slightly. 2.3.2.Fizzing. Instruction should be given on the correct method for filling a burette, pointing out that the top of the burette should be below eye level to guard against the danger of splashes to the eyes. The burette should be filled, via a funnel, from a small container that can be easily and safely handled. An alter- native is to store solutions in large containers fitted with a delivery tap.Microburettes vary in design and those with- out a filler cup at the top can be difficult to fill as the narrow diameter precludes the use of a funnel. The safest method for filling these is by suction. With self-filling and levelling burettes a quick- release device should be fitted to prevent the reservoir being over-pressurised .2.3.3. Clamping. There are many types of burette clamps available and it is important that the correct size clamp for the burette is used so that it is clamped securely but without any undue stress. 2.3.4. Manipulation of stopcock. When manipulating a stopcock during a titration it is recommended that the tap should be turned from the side opposite to the hand, with the hand round the tap to prevent the stopcock being pulled out with the ensuing danger of skin contamination. 3. Titrations It is not always obvious to the inexperienced operator that it is a dangerous practice to carry out a titration while seated and this point needs to be stressed. When titrations are carried out at elevated temperatures consideration should be given to the toxicity or flammability of any vapours that may be evolved and appropriate safety instructions given. 4. Conclusion It must be emphasised that the above are only guidelines and all contingencies are not covered. The first essential is to ensure that laboratory staff or students are made aware of, and clearly understand, any hazards involved in the work being carried out, and are trained to take any necessary safety precautions. The proper safety equipment must be provided and be ready to hand, otherwise it will be ignored. Similarly, appropriate first-aid equipment, antidotes, etc., need to be immediately available. Accident procedures must be known to individuals and must be marked out on the assumption that the worst will inevitably happen.

ISSN:0306-1396    

DOI:10.1039/AD9771400225

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

228 EQUIPMENT NEWS Proc. Analyt. Div. Chem. SOC. Equipment News T4 RIA Kit A new kit, T4 RIA (PEG), is available that combines the technical and clinical performance of the present T4 RIA kit with the simplicity and convenience of a separation step based on polyethylene glycol (PEG) precipitation of the antiserum bound fraction. The Radiochemical Centre, Amersham, Bucks., HP7 9LL.August, 19 7’7’ EQUIPMENT NEWS 229 Metallurgical Microscope A metallurgical microscope known as the MetavaR is announced, which enables all known metallurgical examination techniques to be undertaken.Only one set of objectives is used, providing plane high contrast up to the edge of a large field. A combination of Semplan objectives with wide-field plan-compensating eyepieces, covers the steps of the ASTM stand- ard over the magnification range between 25 and 1600x. The incident-light equipment is available in three options, readily fitted or interchanged be- tween the stand and viewing tube, thus pro- ducing three instruments: MetavaR s, for polarised-light and bright-field examination, which allows rapid recognition and examination of heterogeneous material; MetavaR U, for examinations in bright-field, dark-field and polarised light, particularly useful for high- contrast presentation of contours on semi- conductor surfaces, grain boundaries of metals and scratches on polished surfaces; MetavaR IK, for interference contrast, polarised-light and bright-ground examinations, important for reproducing a clear, bright - dark three- dimensional contrast where structural details exhibit uniform reflection of colour.Supplementary equipment for the series includes a dual viewing projection screen, camera systems and drawing apparatus. Reichert- Jung UK, 820 Yeovil Road, Slough, Berks. Rare-gas Purifier A new version of the rare-gas purifier reduces impurities in commercial-grade rare gases (Ar, He, Kr, Xe) to less than 1 p.p.m.with flow-rates of up to 20 1 min-l. The reagents can be used continuously for at least 2 years without changing them. BOC Ltd., Special Gases, Deer Park Road, London, SW19 3UF. Ultraviolet Photometers A new range of direct-reading, calibrated exposure measurement and control instrumenta- tion is introduced. The range includes battery portable and multi-channel sets as well as integrator and digital monitoringlintegration control systems.Sensors are available in the spectral range 320-650 nm. The photometers give direct readings in either mW cm-2 from continuous light sources or p J cm-2 from pulsat- ing light sources. Micro-Image Technology (Engineering) Ltd., Greenhill Industrial Estate, Riddings, Derby, DE5 4UB. Ultrasonic Cleaners The Dawe range of Sonicleaners has been extended by the introduction of new units: Type 6445A, with a working capacity of 17.5 1 (32 gal) ; Type 6446A, 24 1 (54 gal) capacity; and Type 6447A, with a long narrow tank of 8 I (1: gal) capacity, especially designed for pipette cleaning, etc.Sonicleaners are operated at 50 kHz and are self-contained and self-tuning. Dawe Instruments Ltd., Concord Road, Western Avenue, London, W3 OSD.Refrigerated Baths New, seamless, stainless-steel refrigerated baths are available. No. 1062 is a table model and No. 1067 a standing model fitted with rollers. Both operate from -40 to +20 “C, with a variation of k0.5 “C. The range can be extended to +70 “C with the thermostat “Thermed 5004,” and both types can be used as deep-freeze cabinets at temperatures up to -30 “C without using any liquid.Anderman & Co. Ltd., Central Avenue, East Molesey, Surrey, KT8 OQZ. Gel-rod Electrophoresis Cell An all-purpose gel-rod electrophoresis cell, Model 155, is announced. It accommodates any of five assemblies, and is thus capable of handling electrophoresis tubes of 5, 7, 8, 13 and 17 mm o.d., the first three sizes in an 18-tube configuration and the larger ones in a 12-tube configuration. Bio-Rad Laboratories Ltd., 27 Homesdale Road, Bromley, Kent, BR2 9LY.Multi-point Ambient Air Monitors The MIRAN-IA multi-point monitor incorpor- ates and converts the MIRAN-IA portable gas analyser into a fixed station monitor with 11 sample points up to 400 f t distant, enabling a large number of toxic gases to be measured singly in the parts per million range.Continu- ous unattended operation is possible because the instrument is re-zeroed by automatically switch- ing to a “zero air” once every 12-min cycle. The MIRAN 201 is designed for continuous analysis of any one of over 300 toxic vapours a t the OSHA (USA) compliance levels from up to 15 locations. With the concentration in parts230 EQUIPMENT NEWS Proc.Analyt. Div. Chem. SOC. per million and time of day recorded on a digital printer for each location sequentially, time- weighted averages of exposure can be deter- mined. A concentration higher than the safe 1 imit actuates an adjustable high-level alarm. Wilks Scientific Ltd., 64 Burners Lane, Kiln Farm, Milton Keynes, Bucks. Electronic Gas Detector -4 range of instruments for detecting accumula- tions of flammable gases in the atmosphere is offered.The Taguchi semiconductor gas sensor can reliably detect concentrations down to less than 20% LEL. Type 720 is battery operated and hand-held, having only an on - off switch and a push-button for testing the electronic alarm circuit. Type 730, again hand-held, is larger and has a two-position switch enabling it to be partially selective for either hydrocarbon gases (e.g., CH,) or lighter gases (e.g., CO).Type 750 is mains-operated for permanent mounting, and can run off its own internal supply for more than 1 h in the event of a mains failure. Slave alarms in other locations can also be attached. Anacon Instruments Ltd., St. Peters Road, Maidenhead, Berks., SL6 7QA. Centrifugal Casting and Melting Unit Equipment to produce "button" samples for optical-emission and X-ray fluorescence analysis of metals is available, the Garricast ES825 centrifugal casting and melting unit.Garrick Equipment Co. Ltd., 13 Garrick Street, London, WCZE 9AR. Bactobridge The Bactobridge impediometer is an automated high-sensitivity instrument that monitors the growth of micro-organisms by changes in specific impedance caused by their metabolism. By using a comparative technique, it is capable of detecting the wanted signal in the presence of impedance changes caused by other processes.The instrument contains a matched pair of conductivity cells in adjacent arms of a bridge energised by a sinusoidal current of pure wave- form.It can detect a level of lo4 micro- organisms per millilitre in many commonly used media within 1 h. TEM Sales Ltd., Gatwick Road, Crawley, Sussex, RHlO 2RG. Polarising Microscope A transmitted-light polarising microscope, the Neovar-Pol R, has been developed. It is suit- able for all transmitted-light examinations and has strain-free Semplan objectives. The 40/0.90 objective has been specially computed to examine conoscopic images.A research and laboratory model, the Neovar- Pol 2, replaces the intermediate Pol tube with incident-light equipment for bright-field and polarised-light examinations, thus permitting quick and easy exchange of both components. Reichert- Jung UK, 820 Yeovil Road, Slough, Berks. Scanning Electron Microscopes Theo Super IIIA has a guaranteed resolution of 70 A and magnification is 10-200 OOOx .Split- screen dual magnification in steps of 3, 5 and lox with 3x zoom allows close examination of the specimen at two different magnifications a t the same time. Split-screen imaging also allows display of two signals a t the same time. One micrograph records both images and a micron bar gives a permanent record of magnification.Accelerating potentials are from 2 to 25 kV, stepped and compensated. The scanning system is a double-deflection type with five selections and dynamic focusing ensures edge- to-edge micrograph sharpness. Four-level gamma control enhances detail in dark areas of the specimen. Auto-emission eliminates manual adjustment of the filament current. Vacuum control is automatic with manual over-ride.The Super IIIA is fitted with the IS1 Uni- versal Stage for full specimen coverage of 4in diameter by 1 in thick specimens. X - Y movement is +20 mm, tilt is -10 to +70°, rotation from 0 to 360" is continuous and 2 (vertical) movement is externally adjustable from 8 to 38mm. Options include auto-brightness/contrast, an aperture system with three externally selectable apertures and 90" tilt stage.Internatianal Scientific Instruments, Inc. (UK), Waterwitch House, Exeter Road, New- market, Suffolk. The SEM 501 can guarantee 70-A resolution. Three-lens optics are designed to give high- resolution images, while a newly designed goniometer provides fully eucentric specimen tilting. Also incorporated are TV rate imaging, 30-kV electron optics, a micron marker, inde- pendent numbers of lines and line time selectioq a high-resolution photomonitor, digital displayAugust, 1977 EQUIPMENT NEWS 23 1 of magnification, Y modulation and a modular specimen rotation unit.Philips SV, P.O. Box 523, Eindhoven, The Xetherlands. Radiochromatogram Reader A radiochromatogram reader, Chromelec 101 NU 101, provides rapid high-resolution quantita- tion using a static detector.The radioactive region is coded by the delays between two signals inside the detector. The delays are coded through a time-to-amplitude fast converter followed by an amplitude converter storing information in a programmed memory connected to a display. The electronics permit the quantitation of double-labelled chromatograms.A windowless-mode facility permits the detec- tion of tritium with very high efficiency. h-umelec, 2 Petite Place, F78005 Versailles Cedex. France. Glass - to -tubing Union A zero dead volume union and T-piece for connecting 1 mm o.d. glass to 1/16 in 0.d. tubing is available. Scientific Glass Engineering (UK) Ltd., 657 North Circular Road, London, NW2 7AY. Digital Meters Three newly designed digital instruments are available.The Model 005 digital pH meter provides 3i-digit display with polarity indica- tion and an accuracy of f O . 0 1 pH or & 1 mV. Temperature within the range from 0 to 100 "C is manually selected. The Model 006 universal digital instrument has all the features of the Model 005, plus temperature-measuring capa- bility. Using a temperature probe and turning the mode selector to ""C" provides digital read- out of sample temperature in degrees centi- grade.The Model 008 digital conductivity meter has three-digit read-out, accuracy to approximately 104, and reproducibility to & 1 digit. Activion Glass Ltd., Colchester Road, Halstead, Essex, CO9 2DX. Linear Flow Meter A conventional orifice pIate is combined with a turbine flow meter to give a linear digital and analogue output.The combination of the Litre Meter flow meter and an orifice plate has been named Metre Meter (or LDOP) and to- gether they can be used for metering flow-rates from 1 drop s-1 to 5 t min-1, a ratio of 500 000 : 1. It is available in PVC, nylon, acrylic, or stainless steel and PTFE. Litre Meter Ltd., liyefield Crescent, North- wood, Middx., HA6 1NX.Multi-point Thermal Printing Recorder The Speed Servo 11 is a new multi-point recorder with thermal matrix printing. A linear servo motor combines with a solid-state semiconductor printing device to ensure positive multi-point channel identification. The print head thermally brands three basic types of read-out. International Instruments Ltd., Cross Lances Road, Hounslow, Middx. X-ray Fluorescence Spectrometer The VIiA 2 analyser has been re-designed to pro- vide a computer-controlled, crystal-dispersive, single-channel series spectrometer, the VRA 20-R.A version without the computer, the VRA 20-L, is also available. Average detect- ability ranges from 1 part in lo3 to lo5 for light elements and from 1 part in lo5 to lo7 for heavy elements, for all elements of atomic number 2 > 9 (fluorine).VEB Carl Zeiss Jena, 69 Jena, Carl-Zeiss- Strasse 1, East Germany. Atomic-absorption Spectrophotometer The AAS I N atomic-absorption spectrophoto- meter has a built-in dinitrogen oxide unit with automatic gas control that enables acetylene - dinitrogen oxide or acetylene - air flames to be used. Over 60 elements can now be determined by the use of suitable hollow-cathode lamps. VEB Carl Zeiss Jena, 69 Jena, Carl-Zeiss- Strasse 1, East Germany. Literature Application Report KO. 6, describing the use of infrared spectrometers to monitor ethylene oxide in work-place atmospheres, is available. Wilks Scientific Ltd., 64 Burners Lane, Kiln Farm, Milton Keynes, Bucks. A Kent Technical Review, No. 18, March 1977, contains articles on automatic control of a sewage works, metering flows of cryogenic liquids from road tankers, the use of conductivity cells to monitor the strength of concentrated acids and industrial and water meter instru- mentation. George Kent Ltd., Luton, Beds., LU3 IAL.

ISSN:0306-1396    

DOI:10.1039/AD9771400228

出版商:RSC    

年代:1977

数据来源: RSC

摘要:

232 ANALYTICAL DIVISION DISTINGUISHED SERVICE AWARD Proc. Analyt. Div. Chem. SOC. CS Research Fund 1978 A limited number of Research Fund grants, each of approximately &loo, will be awarded for the year 1978. Applications from Fellows of the Society will be considered on a merit basis, but account will also be taken of any other source of financial aid available to applicants. As funds are limited, preference will be given to those working in less well endowed institu- tions. Thus, applications from those working inAugust, 1977 CS AUTUMN MEETING UK universities will not normally be considered. The closing date for applications is November lst, 1977. Application forms, together with the regulations governing the awards, can be obtained from the Education Officer, The Chemical Society, Burlington House, London, W1V OBN. 233

ISSN:0306-1396    

DOI:10.1039/AD977140232c

出版商:RSC    

年代:1977

数据来源: RSC