摘要:

Proceedingsof the Analytical Division OFThe Chemical SocietyCONTENTS253 Summaries of Papers253 'Developments in PharmaceuticalAnalysis'268 Equipment News271 Correspondence271 New British Standard271 Analytical Division DistinguishedService Award272 Conference272 Course272 Publications Received274 Analytical Division DiaryVolume 15 No 9 Pages 253-274 September 197PADSDZ 15(9)253-274(1978)ISSN 0306-1 396September 1978PROCEEDINGSOF THEANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof The Chemical SocietyFresidentR. BelcherHon. SecretaryP. G . W. CobbSecretaryMiss P. E. HutchinsonHon. Treasurer Hon. Assistant SecretariesJ. K. Foreman D. I. Coomber, O.B.E.; D. C. M. Squirrel1Editor, ProceedtngsP.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 Analystand Analytical Abstracts.@ The Chemical Society 1978Meeting onAffinity ChromatographyFebruary 7th, 1979The AD is organising a meeting on “Affinity Chromatography” at the ScientificSocieties Lecture Theatre, 23 Savile Row, London, W.1, on Wednesday,February 7th, 1979.The meeting will consist of two lectures, by Dr. P. G. D. Dean of the Uni-versity of Liverpool and Dr. C. R. Lowe of the University of Southampton, and anumber of poster presentations, which will be exhibited in two sessions in themorning and afternoon. Authors wishing to exhibit posters are invited tocommunicate, before November 7th, 1978, with the Programmes Secretary ofthe Analytical Division, The Chemical Society, Burlington House, London,WIV OBN

ISSN:0306-1396    

DOI:10.1039/AD97815FX033

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

272 CONFERENCE Proc. Analyt. Div. Chem. SOC.Analytical Division Diary, continuedOctobev, continuedWednesday, 25th, 2.38 p.m, : LondonAnalytical Divisioiz.“Strategy for Chromatography,” by ProfessorJ. H. Purnell.Followed by Demonstration and Discussionby Professor Purnell and S. Williams.Lecture Theatre B, Chemistry Department,Imperial College, South Kensington, Lon-don, S.W.7.Wednesday, 25th, 10 a.m. : GatesheadNovth East Region and Atomic SpectvoscopyGYO@ on “Problem Areas in AtomicAbsorption.”“Sample Preparation for Determination of theVolatile Elements by the Hydride Genera-tion Technique,” by C. A. Watson.“Some Experiences with Background Correc-tion in Electrothermal Atomisation,” byB. Fish.“Determination of Phosphorus and the Use ofElectrodeless Discharge Lamps,” by P.Whiteside.“Difficulties in the Analysis of EdibleMaterials,” by W.H. Hill.“The Use of the Graphite Furnace in EmissionAnalysis,” by R. C. Hutton.“Some Observations on the HSE 21-PointGuide on the Use of Acetylene,” by C. P.Cole.Discussion led by J . B. Dawson.Ravensworth Suite, Five Bridges Hotel,Gateshead, Tyne & WearSeptember, 1978 ANALYTICAL DIVISION DIARY 273Analytical Divisional Diary, continued “Future Analytical Instrumentation,” byOctober, continued“Chiral Shift Reagents in PharmaceuticalAnalysis,” by G. Dewar.“Multinuclear Applications to MedicinesProblems,” by C. P. Richards.“Specific Quantitative Applications inPharmaceutical Analysis,” by J. H. Hunt.Pharmaceutical Society of Great Britain, 1Lambeth High Street, London, W1M 5FT.Friday, 6th, 7 p.m.: DurhamNorth E a s t Region : Annual Social Evening.Dinner, followed by a talk on “Going for aRoyal County Hotel, Durham City.Song,” by R. E.Price.Monday to Wednesday, 9th to 11th: LondonRadiochemical Methods Group, jointly with theCentral Electricity Generating Board, on“The Determination of Radionuclides inEnvironmental and Biological Materials.”Monday, 9th-Opening Lecture by B. A. J. Lister.Session 1 on “Effluent Analysis.”Session 2 on “Bioassay.”Tuesday, 10th-Session 3 on “General EnvironmentalMonitoring.”Session 4 on “Neutron Activation andParticle Track Analysis.”Sessions 5 and 6 on “Radiochemical Deter-mination of Transuranic and NaturallyOccurring Nuclides.”Wednesday, 11th-Visits to CEGB, Central RadiochemicalLaboratory, Gravesend ; The Laboratory ofthe Government Chemist, London ; AERE,Harwell ; MAFF, Fisheries RadiobiologicalLaboratory, Lowestoft.Central Electricity Generating Board, Sud-bury House, 15 Newgate Street, London,EClA 7AU.Thursday, 12th, 2.15 p.m.: LondonBiological Methods Group on “Interface Be-tween Chemical and Biological Assays.”“The Changing Interface,” by W.H. C. Shaw.“Interface or Barrier? The Assay of Poly-“Problems of Interface,” by G. A. Sabey.National Institute for Biological Standardsand Control, Holly Hill, Hampstead,London, N.W.3.peptide Hormones,” by D. Calam.Friday, 13th, 5 p.m.: ExeterWestern Region, jointly with the PeninsulaSection of the CS.D.R. Deans.Exeter.Department of Chemistry, The University,Tuesday, 17th, 4.30 p.m. : EdinburghScottish Region, jointly with the Edinburghand East of Scotland Section of the CS andthe Edinburgh University ChemicalSociety.“Strategy for Chromatography,” by ProfessorJ. H. Purnell.Chemistry Department, The University,Kings Buildings, West Mains Road, Edin-burgh.Wednesday, 18th, 4 p.m. : LoughboroughMidlands Region.“An Infrared Interferometer for GC - IRTechniques,” by Miss A. Saunders.“Differential Pulse Polarographic Determina-tion of Disodium Cromoglycate in Urine,”by N. Fayad.“Electroanalytical Determination of Drugs inBiological Fluids,” by W. F. Smyth.Main Lecture Theatre, Fisons Pharma-ceuticals Division, Research and Develop-ment Laboratories, Bakewell Road,Loughborough.Wednesday, 18th, 2 p.m.: LoughboroughEducation and Training Group on “SomeAspects of the Teaching of NMR Spectro-“Lanthanide Shift Reagents-Basic Prin-ciples, Implications and Applications,” byB. D. Flockhart.“Quantitative NMR in the PharmaceuticalIndustry,” by G. Harron and B. Peutrell.“A Definition of the Minimal Amount ofTheory for Practical Comprehension andUse,” by G. Briggs.Fisons Pharmaceuticals Ltd., Bishop MeadowRoad, Loughborough.scopy. ’’Thursday, 19th, 4 p.m.: BelfastNorthern Ireland Sub-Committee, jointly withthe Andrews Club.“Thermometric and Enthalpimetric Methodsfor Rapid Assays of Fertilisers and Pharma-ceuticals,” by Professor L.S. Bark.5.30 p.m.: Annual General Meeting of theNorthern Ireland Sub-committee of theScottish Region.Chemistry Department, Queen’s University,Belfast.[continued on p. 27Analytical Division DiarySEPTEMBERTuesday to Thursday, 19th to 21st:CoventryC S Autumn Meeting : Analytical DivisionSymposium on “Lasers and their AnalyticalApplications. ”Wednesday, 20th-Introductory Lecture by Professor C. GreyMorgan.“Uses of Narrow-band Tunable Dye Lasersto Excite Molecular Fluorescence,” byM. A. A. Clyne.“Laser Spectroscopy of Molecular Systems,]by P. B. Davies.“The Use of a Laser for Cutting BoneSamples Prior to Chemical Analysis,” byJ. S. Hislop.“Laser Remote Sensing of AtmosphericPollutants,” by B.L. Sharp.“Automated Aerosol Sizing by Holography, ”Friday, 22nd-“Microchemistry and Meat,” by R. L. S.Patterson.“GC -MS Studies of Trace Quantities ofVolatile Compounds in Fruit Juices andCiders,” by 0. G. Tucknott.“The Determination of Residual Solvents inFlexible Packaging Materials,” by W. J.Carpenter.“Microchemistry at Imperial Tobacco Ltd.,”by D. Spincer.“Microchemistry and the Local Authority,”by A. J . Harrison.“Microchemical Methods in a Home OfficeForensic Science Laboratory]’’ by M. W.Duckworth.“Trace Organics in Water-Present Practiceand Future Aspirations,” by J. G. Jones.School of Chemistry, The University, Bristol.OCTOBERby R. Bexon.“Particle Characterisation by Intensity Fluc-tuation Spectroscopy,” by P.N. Pusey . Wednesday,Thursday, 21st- South East“The Applications of Laser Raman Spec- Centralmaston,“Particle Characterisation with Crossed Laser tion byfollowedtroscopy,” by P. J. Hendra.Beams,” by A. R. Jones.Qth, 2 p.m. : AldermastonRegion: Visit to the Home OfficeResearch Establishment, Alder-Reading, Berkshire. Introduc-the Deputy Director, K. Jones,by a conducted tour of the“Measurement of Particle/Droplet Size Dis-tribution by Laser Diffraction,’] by P. G.laboratory (numbers are limited)Felton.“Development of a Laser-based InstrumentSystem for Monitoring Concentration andCharacteristics of Solids in Suspension,”by N. Stanley-Wood and A. Taylor.“Laser Doppler Technology,” by A. J. Yule.University of Warwick, Coventry.Thursday and Friday, 21st and 22nd : BristolWestern Region and Microchemical MethodsGroup: Meeting on “The Use of Micro-chemistry in the Bristol Area.”Thursday, 21st-“Microchemistry, Yesterday and Today,”“Environmental Analysis and Carbon Skele-by Professor L.S. Bark.Thursday, 5th, 10 a.m.: ChesterNorth West Region and Automatic MethodsGroup on “Safety and Automation.”Visit to Bass Productions Ltd., Runcorn,followed in the afternoon by :“The Design and Evaluation of an AutomaticMonitor for Toxic Emissions from Stacks,”by C. J . Jackson.“Biological Containment of a ResearchLaboratory,” by G. J. Allen, A. T. Goodersand B. M. Richards.“Electrical Safety of Analysis and TestingEquipment in Flammable Atmospheres,”by R. C. Moore.Queen Hotel, Chester.ton Gas Chromatography,” by G. Nickless.“The Determination of Uranium in Sea Thursday, 5th, 2 p.m.: LondonWater,” by W. J. Williams. Joint Pharmaceutical Analysis Group on“The Spectroscopic Examination of Nuclear “Pharmaceutical Applications of NMRMaterials. Part I : ESCA, Auger and XRF Spectroscopy.”Analysis of Unirradiated Fuel Materials,”by G. C. Allen.“Part I1 : Characterisation of Irradiated FuelElements by Micro-y-scanning and XRF,”by D. A. Hilton.Introduction by A. Ferridge.“Application to Aminoglycoside Antibiotics,”by D. H. Calam.[continued inside back coverPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97815BX035

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Vol. 15 No. 9 Proceedings September 1978 of the Analytical Division of the Chemical Society Developments in Pharmaceutical Analysis The following are summaries of three of the papers presented at a Joint Meeting of the North East, North West and Scottish Regions held on March loth, 1978, in Carlisle. Separation Techniques in Pharmaceutical Analysis J. E. Fairbrother and A. Sam Department of Pharmacy, The University of Nottingham, University Park, Nottingham, NG7 2RD Most of the current papers on separation systems in pharmaceutical analysis are concerned with chromatography in one guise or another.However, many of these separations rely on a sample clean-up step prior to chromatography. The design of this step is often difficult and is worthy of greater attention.Not only is it necessary to provide a means of removing sub- stances likely to interfere with the chromatographic determination but the manner in which this is done should be simple and rapid with the introduction of a minimum of error. This separation can sometimes be achieved very simply by partition of the sample between two immiscible solvents. Topical Corticosteroid Formulations Determination of corticosteroids in ointment and cream formulations by either the isonico- tinic acid hydrazide (nydrazid) or blue tetrazolium spectrophotometric procedures can be subject to major interferences by co-formulated excipient materials1 Lengthy clean-up pro- cedures utilising column partition chromatography on diatomaceous earth (Florisil) have been in operation for 25 years2 but they entail many steps and are subject to significant losses and variation.More recently3 the use of column partition chromatography on a column of Florisil impregnated with acetonitrile has been used but this procedure had eight consecutive steps in the clean-up operation alone. In contrast to these laborious methods, partitioning of the sample between immiscible solvents can provide a rapid and simple alternative.For example, for certain ointment formulations containing triamcinolone acetonide and halcino- nide, simple partition of the sample between acetonitrile and hexane or acetonitrile - water (2 + 1) and hexane has provided a most versatile clean-up procedure.* The steroid that partitions into the acetonitrile phase can then be injected directly on to an HPLC column or assayed spectrophotometrically by the nydrazid or blue tetrazolium procedures. These spectrophotometric reactions can be carried out directly in the acetonitrile solvent without loss of colour stability or deviation from Beer’s law.4 Simple partition between other immiscible solvent pairs has been used most effectively for sample clean-up of steroids in topical preparations, allowing the direct injection of an aliquot of the steroid-rich phase on to an HPLC A number of potentially useful pairs of immiscible solvents are shown in Table I.In an attempt to identify a number of alternative solvent - solvent partition systems that might be useful for sample clean-up, the partition coefficients listed in Table I1 were determined.During this work it was also established that the steroids employed could be directly deter- mined by the nydrazid spectrophotometric procedure in either nitromethane or dimethyl sul- phoxide. 263254 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS R o c . Analyt. Div. Chem. SOC. TABLE I SOME SOLVENT PAIRS SUITABLE FOR PARTITION WORK More polar solvent Acetonitrile Acetonitrile - water (2+ 1) Acetonitrile - methanol azeotrope (8 1 + 19) Methanol Methanol - water (5+ 1) Dimethylformamide - water Nitromethane Water (9+1) Less polar solvent Hexane Hexane Hexane 2,2,4-Trimethylpentane C yclohexane C yclohexane Nonane Ox ydipropionitrile Reference 4 4 8 8 9 10 11 TABLE I1 PARTITION OF CORTICOSTEROIDS BETWEEN IMMISCIBLE SOLVENTS Partition coefficient (less polar solvent/ More polar solvent Less polar solvent Steroid more polar solvent) Acetonitrile Hexane Triamcinolone acetonide 6.5 x 10-3 Triamcinolone pentanonide 8.8 x 10-3 Prednisolone 11 x 10-3 Nitromethane Hexane Triamcinolone pentanonide 3.5 x 10-3 Nitromethane Cyclohexane Triamcinolone acetonide 7.4 x 10-4 Betamethasone 17-valerate 6.5 x 10-4 Dimethyl sulphoxide Hexane Triamcinolone acetonide 2.1 x 10-3 Betamethasone 17-valeratc 1.9 x 10-3 Prednisolone 8.4 x 10-4 Dimethyl sulphoxide Cyclohexane Triamcinolone pentanonide 7.4 x 10-3 Just as simple partition between organic solvents is often overlooked in the search for sample It is, however, the basis of several purification procedures, so density also may be forgotten.techniques which, like the partition procedures described above, are both simple and rapid.Flotation A typical problem might be the selection of the sample preparation required for the deter- mination of the content of chloramphenicol palmitate polymorph A by the official BPC pro- cedure12 in a complex suspension formulation. The formulation contains a mixture of two drugs, amphotericin B and chloramphenicol palmitate suspended in a complex vehicle con- taining sugar, tragacanth, sorbitol, Tween 40 and various colours , flavours and stabilising agents.The problem of separating the chloramphenicol palmitate cleanly from this mixture without changing the polymorph ratio can be solved very ea~i1y.l~ The chloramphenicol palmitate and amphotericin B are first separated from the formulation by filtration and re- suspended in distilled water.Centrifugation of this suspension cleanly separates the two solids, the chloramphenicol palmitate being harvested from the upper layer. A more difficult example is the sample preparation required for the determination of the content of the individual granulates in a sustained release capsule formulation. In order to provide the best release profile for the drug the formulation contains three different granulates, based on gelatin, ethyl cellulose and a methacrylate polymer, respectively.It also contains a proportion of lactose. The release profile of the drug from the mixed granulate can be checked by a suitable dissolution test but an assay procedure for the individual granulates is also required. Suspension of the sample in carbon tetrachloride - tetrachlorethylene (3 + 2) allows the separation of the ethylcellulose granules in the lower fraction.The addition of a mixture of chloroform and dibromoethane to the remaining suspension alters the density of the medium and allows the separation of the The granules can be separated by flotation in three simple stages.September, 1978 DEVELOPMENTS I N PHARMACEUTICAL ANALYSIS 255 methacrylate polymer granules leaving a mixture of the gelatin granules and 1act0se.l~ Thus, by a very simple means a difficult problem can be overcome.In considering separation by flotation in pharmaceutical analysis, perhaps greater use could be made of the family of techniques collectively known as the adsubble or adsorptive bubble separation techniques.These techniques, many of which have been most usefully reviewed by Lemlich,15 can be roughly classified as shown in Fig. 1. Adsubble methods I I Foam procedures I 7 Foam fractionation Includes f Dam chromatography and foam countercurrent chromatography Foam flotation Includes Non-foam adsorptive bubble separation I I Solvent sublation precipitate flotation, ion flotation and adsorbing particle flotation Fig.1. Adsorptive bubble separation techniques. I Bubble fractionation In these techniques the analyte can be adsorbed directly on to the surface of a bubble and separated by virtue of its surface activity. Alternatively, the analyte may be given surface- active properties by union with, or physical adherence to, a surface-active collector substance.The product of the analyte and collector is termed the sublate. Thus, the technique of solvent sublation can be demonstrated simply by the separation of methyl orange (anionic) from rhodamine B (zwitterionic).16 A dilute aqueous solution of the dye mixture is contained in a cylindrical glass column (45 mm diameter) fitted at the bottom with a porous glass frit and a tap.Nitrogen gas is fed through the tap so that it bubbles through the glass frit and these bubbles travel up the column through the sample solution. If a cationic surfactant is added to the sample solution as a collector and the pH adjusted to 10.5, then the sublate formed by the cationic surfactant and the methyl orange is preferentially adsorbed on to the surface of the bubbles that carry it up and liberate it at the top of the column. If a layer of an organic solvent such as octan-2-01 is placed above the sample solution, the methyl orange will be liberated by the bubbles into this layer.At the selected pH rhodamine B is only slowly transferred into the organic layer and a good separation of the two dyes can thus be achieved. This technique has some considerable potential for sample en- richment and clean-up and has been used effectively in the analysis of sewage effluent.Adsorptive particle flotation uses a more complex sublate structure [see Fig. 2(a) and ( b ) ] . In this technique fine particles carrying a charge (such as bentonite) are incorporated into the sublate and by foam fractionation of the sublate the analyte can be removed in a concentrated form from the sample s01ution.l~ Taking this principle further, Talmon and Rubinls have described a technique they have called foam chromatography.In this technique a bed of foam, created by passage of nitrogen through a pool of anionic surfactant, is made to travel up a vertical glass column. Analytes can be separated after their injection into the foam bed on the basis of their interaction with the surface of the bubbles. The rising foam bed can also be eluted counter-currently by the introduction of eluting solution from the head of the column.Foam chromatography has the added advantage that it can be used as a continuous process. A further development by Ito and Bowman19 utilises foam chromatography in a flow-through coil planet centrifuge providing a technique with great potential for trace sample enrichment. Adsubble techniques would, therefore, seem worthy of some attention in pharmaceutical analysis, especially for sample preparation in instances where very low concentrations of analyte are expected.Solvent sublation might be used simply for the concentration of trace materials present in aqueous solution into a much smaller volume of an organic solvent.Mixed particulates might possibly be separated by precipitate flotation and adsorbing particle flotation may have considerable potential as a tool for the preliminary extraction of low levels256 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc. Analyt. Div. Chem. SOC. (b ) Cationic surfactant Anionic dye I Bentonite Fig.2. Adsorptive particle flotation. Sublate structures with ( a ) , cationic dye and (b) , anionic dye. of drugs from complex biological media, such as body fluids or animal feed extracts. Foam chromatography will doubtless be explored further and may find application in the separation of macromolecules such as enzymes and some of the polyene antibiotics. 1. 2. 3. 4.5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. References Graham, R. E., Williams, P. A., and Kenner, C. T., J . Pharm. Sci., 1970, 59, 1152. Banes, D., J . Am. Pharm. Ass., Sci. Edn, 1953, 42, 669. Graham, R. E., Williams, P. A., and Kenner, C. T., J . Pharm. Sci., 1970, 59, 1472. Fairbrother, J. E., in Reid, E., Editor, “Assay of Drugs and Other Trace Compounds in Biological Fluids, Methodological Developments in Biochemistry,” Volume 5, North-Holland, Amsterdam, 1976, p.141. Bailey, F., and Brittain, F. N., J . Pharm. Pharmac., 1972, 24, 425. Gordon, G., and Wood, P. R., Analyst, 1976, 101, 876. Mollica, J. A., and Strusz, R. F., J . Pharm. Sci., 1972, 61, 444. Bailey, F., Holbrook, A., and Miller, R. J., J . Pharm. Pharmac., 1966, 18, Suppl., 12s.Kassebaum, H., and Sucker, H., Fette Seifen AnstrMittel, 1976, 78, 207. Amin, El S., and Abd El Samad, M., Mikrochim. Acta, 1969, 2, 374. Gal, J. Y., and Persin, M., C.R. Hebd. Se’anc. Acad. Sci., Paris, Ser. C, 1977, 284, 987. “British Pharmaceutical Codex, 1973,” The Pharmaceutical Press, London, 1978, p. 901. Salmon, J. R., Moriau, D. M., and Harrison, M. E., personal communication.Harle, R. K., and Rashid, I. A., personal communication. Lemlich, R., “Adsorptive Bubble Separation Techniques,” Academic Press, London, 1972. Caragay, A. B., and Karger, B. L., Analyt. Chem., 1966, 38, 652. Kobayashi, K., Watabe, N., and Saski, T., Bull. Chem. SOG. Japan, 1976, 49, 2701. Talmon, Y., and Rubin, E., Sep. Sci., 1976, 11, 509. Ito, Y . and Bowman, R. L., Sep.Sci., 1976, 11, 201. Analysis of Drugs and Metabolites by Gas Chromatography - Mass Spectrometry Neville Haskins G. D. Searle and Co., P.O. Box 53, Lane End Road, High-Wycombe, Buckinghamshire The use of any analytical technique for drugs and/or metabolites in biological fluids is generally to answer one of three questions, namely, what is it, how much is present and what propor- tion of the administered dose is that? The increasing use of more specific drugs given in smaller doses has required the development of sensitive and specific techniques capable of measuring concentrations in the low ng ml-l and pg ml-l ranges in plasma, urine and other biological fluids.An important area of development during the last 10 years has been in the field of gas chromatography - mass spectrometry (GC - MS).During this time the advent ofScptember, 1978 DEVELOPMENTS I N PHARMACEUTICAL ANALYSIS 257 new ionisation methods, improved gas chromatograph interfacing, small on-line computer systems and, above all, the development of the mass spectrometer as a sensitive quantitative tool using the technique of selective ion monitoring has led to a rapid expansion in its applica- tion to biomedical and environmental problems. In order to illustrate how mass spectrometry can help in answering the three questions posed above, a number of examples are presented showing some ways in which answers can be found.Propantheline bromide (Ia in Fig. 1) is a parasympatholytic agent used in the treatment of gastric and duodenal ulceration.A recent study in this laboratory1 on the metabolism of propantheline bromide used GC - MS to identify the unchanged drug and a number of meta- bolites. A specimen of the drug containing a 14C-label and a trideuterated analogue was administered. The use of 1% or 3H-labelling to aid in the isolation and identification of meta- bolites has been accepted for a number of years, but even after rigorous isolation procedures a considerable mixture of compounds often remains, including plasticisers and greases introduced into the system by using rotary evaporators, thin-layer chromatographic plates, plastic storage containers, etc.In order to aid the identification of drug-derived materials the use of a mixture of a stable-isotope labelled analogue with the normal drug gives an easily recognised isotopic cluster, owing t o the presence of the stable isotope. When propantheline bromide was used the presence of depropan-2-yl propantheline in the mixture was established by selecting some representative ions (m/e 100, 103, 326) and reconstructing the single ion scans for these Y R C02CH2 CH2 N-+C3 H7 QpJJ ,":-"' I a R=CH3 b R=C2H3 "Site of I4C label a RP = C2H5 II R a = H b R' = CH3 Ill R" = 2 H e R P = H Fig.1. Structures of the compounds referred to. (dl x 10 (6) x 1 0 1 ( a ) x 100 1 I , I I 1 1 00 200 300 400 m/e Selected ion scans (a), m/e = 326; ( b ) , m/e = 103; (d), m/e = 100 and (c), total ion recording for methylated 2-4-h urine extract obtained after administering pro- pantheline bromide to a single subject.Fig. 2.258 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc. AmaZyt. Div. Chern. SOC. from the total ion chromatogram (Fig. 2). The chemical ionisation spectrum obtained for scan 330 clearly shows the doublets for the protonated molecular ion (m/e 326 and 329) and the major fragment ion (m/e 100 and 103) for depropan-2-yl propantheline [Fig. 3(a)]. Ammonia was used as the reagent gas for the chemical ionisation spectra because the trideuteromethyl group is lost by using methane.2 Because propantheline is a quaternary ammonium ion, the presence of depropan-2-yl propantheline may be caused by its formation as a metabolite or by thermal degradation in the gas chromatograph.In order to resolve the alternatives field desorption mass spectrometry was used and the spectrum obtained [Fig.3(b)] shows the extract to contain the intact propantheline ion (m/e 368, 371). A trace of a minor hydroxylated metabolite is also seen (m/e 384, 387). 50 100 150 200 250 300 350 400 100 150 200 250 300 350 400 m/e Fig. 3. (a), Ammonia chemical ionisation and (b), field desorption spectra of propantheline ion obtained from a urine extract.A minor hydroxylated metabolite is also visible in the field desorption spectrum. In the instance of propantheline, therefore, the identity of the minor metabolites was estab- lished by using a mixture of hot and cold labelling. The hot label eased the problem of tracing the metabolites through the extraction procedures while the cold label acted as a marker for the mass-spectrometric identification.As an example of the question “How much?” the quantification of diphenoxylic acid (IIc in Fig. 1) [the major metabolite of diphenoxylate hydrochloride (IIa)] in urine and plasma illustrates the use of a stable isotope labelled analogue (IIIc) that acts as a carrier and internal standard. The extraction procedure isolates the free and conjugated diphenoxylic acids and these are derivatised to form the methyl esters (IIb, IIIb in Fig. 1 ) .These esters are chroma- tographed but require harsh conditions (1 yo OV-1 at 270 “C) and considerable losses caused by absorption and thermal degradation occur. By adding a large excess of the tetradeuterated analogue of diphenoxylic acid these losses are reduced because the deutero analogue acts as a carrier. Despite the large excess a good assay for diphenoxylic acid down to 20 ng ml-l in plasma3 has been obtained.The assay gives a straight calibration line over the range 20- 400 ng ml-l (Fig. 4). The assay has been used to measure the plasma concentration at various times after oral dosage with diphenoxylate hydrochloride (Fig. 5). A more recent develop- ment in this area is the use of a computer to control an automatic liquid injector.In this way completely automated GC - MS runs of 24 h can be carried out, enabling the fullest use to be made of a GC - MS system. We have recently used such a system (Finnigan Instruments Ltd.) to carry out an assay for diphenoxylic acid in urine, and the results appear promising, giving straight calibration lines.The autosampler used requires a relatively large volume of sample (150-200 pl) for operation and this precludes its use for plasma extracts. However, relatively large volumes of urine are readily obtained so that it can A number of drawbacks exist.September, 1978 DEVELOPMENTS I N PHARMACEUTICAL ANALYSIS 259 be used for urine analysis. Such intensive use of the mass spectrometer also leads to the source becoming dirty more rapidly, leading to more time being required for cleaning. Nonetheless, these minor problems are surmountable and this totally automated approach will find greater application with the use of GC - MS for routine clinical studies.10.00 8.75 7.50 a“ 6.25 0 p 5.00 9 .- w m ; 3.75 2.50 1 0 200 400 600 800 1000 1200 Diphenoxylic acid concentratiodng mi-’ Fig.4. Calibration graph for di- phenoxylic acid in plasma obtained by using a stable iosotope dilution assay. V , Points nos. 1-32; 0, points nos. 33-64. Is) $ 150 0 m .- + 100 a, C 8 50 Is) 3 n 0 5.0 10.0 15.0 20.0 : 1.0 Time after administration/h Plot of drug concentration in plasma a t various times after oral dosage with diphenoxylate hydrochloride (10 mg) .v , Tablets administered ; 0, standard solution administered. The tablets had poor dissolution characteristics. Fig. 5. The final question “What proportion?’’ means just how available is an orally administered drug to the system. In the past these studies have been accomplished by using lengthy cross- over clinical trials involving the administration of a number of formulations of the drug, in- cluding an intravenous form, and leaving several weeks between each dose in order to clear the system of drug before the next dose is administered.The use of a stable isotope labelled analogue can greatly simplify this procedure, enabling the simultaneous administration of labelled and unlabelled drug by differing routes of administration. Use of a second labelled analogue to quantify both the administered forms enables one to build up a picture of the plasma concentration of the drug, and more importantly, the proportion of the drug derived from each route of administration. The first report of a study using this technique was by Strong et aL4 on N-acetylprocainamide in man.We have also used this technique with an experimental antidiarrhoeal agent, SC-27 166.5 By administering SC-27166 (IVa in Fig.1.) orally to a baboon, and co-administering the tetradeuterated analogue (IVb) intravenously at the same time, it was possible to obtain a series of plasma samples post-dosage containing SC-27166 from both routes of administration. By using a second deuterated analogue, hexadeutero SC-27166 (IVc) , straight calibration lines were obtained for mixtures of both SC-27166 and its tetradeuterated analogue in plasma.Analysis of the plasma samples obtained post-dosage enabled the construction of two graphs of plasma concentration zleysus time, one for the intravenous component and one for the oral. The ratio of the areas under these traces is a measure of the oral availability and in this instance this was 76% (Fig.6). The more serious are the occurrence of isotope effects in metabolism, the inhibition of absorption by a high circulating concentration of the drug after intravenous administration and the problems of obtaining a suitable intravenous formulation for administration. These three examples show that the combination of stable isotope labelled compounds and gas chromatography - mass spectrometry can be a powerful tool in the field of drug metabolism and pharmacokinetics.With the advent of stricter laws governing the use of radiolabels in man, and the need to obtain pharmacokinetic data from people (e.g., children, pregnant women) There are some drawbacks to this technique that limit its applicability.260 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc.Analyt. Div. Chem. SOC. 1000 - 800 I - E .- 5 600 P m C -. + + C 0, C 8 400 m 6 200 0 I, \ 5 10 15 20 25 Time after administratiodh Fig. 6. Concentrations of drug in plasma of baboon a t various times after simultaneous dosage with SC-27166 orally (trace A) and tetradeuterated SC-27166 intra- venously (trace B). The oral availability was approxi- mately 76 yo. where the use of radiolabels is not permissible means a search for sensitive and specific methods for non-radiolabelled drugs.The GC - MS approach is one method which can, and is, being used to a greater extent in this area. The author thanks G. C. Ford, S. J. W. Grigson and K. A. Waddell for their invaluable technical assistance, and the other members of the metabolic studies department for their encouragement. References 1.2. 3. 4. 5. Vose, C. W., Prout, M., Haskins, N. J., Ford, G. C., Palmer, R. F., Fellows, I., and Tidd, M. J., Biomed. Ford, G. C., Grigson, S. J., and Haskins, N. J., Biomed. Mass Spectrom., 1976, 3, 230. Ford, G. C., Haskins, N. J., Palmer, R. F., Tidd, M. J., and Buckley, P. H., Biomed. Mass Spectrom., Strong, J. M., Dutcher, J. S., Lee, W.-K., and Atkinson, A. J., Clin.Pharmac. Ther., 1975, 18, 613. Haskins, N. J., Ford, G. C., Grigson, S. J. W., and Palmer, R. F., in Baillie, T. A., Editor, “Proceedings of the Symposium on Stable Isotopes, Applications in Pharmacology, Toxicology and Clinical Research,” Macmillan, London, 1978, p. 127. Mass Spectrom., in the press. 1976, 3, 45. Analysis of Pharmaceutical Dosage Forms by Second Derivative Ultraviolet - Visible Spectrophotometry Anthony F.Fell Department of Pharmacy, Heriot- Watt University, 79 Grassmarket, Edinburgh, EH1 2HJ The quality control of drugs and excipients before and after formulation often involves the use of ultraviolet - visible spectrophotometry for qualitative and more probably quantitative analy- sis. Unless the drug components are separated selectively from the formulation matrix, their spectra can be subject to serious interferences by those formulation components which also absorb in the same part of the spectrum.Spectral overlap and non-specific irrelevantSeptember, 1978 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS 261 absorption adversely affect the interpretation of data for even the simplest single-component drug systems, leading to variable intercepts on the absorbance axis and systematic errors in the graphs of absorbance ueYsus concentration.Classically, the problem of determining drugs in the presence of variable spectral interferences has been approached in a number of ingenious ways. Morton and Stubbsl proposed a method for correcting irrelevant absorption (presumed to be linear) based on the selection of three observation wavelengths centred on the analyte’s absorption maximum. This procedure has been extensively modified by many workers and has found wide use in drug analysis.In 1960 Glenn2 proposed a modified Vierordt method for the analysis of mixtures of two well defined components. This method was based on criteria for selecting the two best observation wave- lengths for absorbance measurement.Glenn3y4 and Agwu and Glenn5 went on to demonstrate the use of orthogonal functions for correcting irrelevant absorption and this work was contin- ued by Wahbi and co-workers.6-8 All of these published methods and their variants make simplifying assumptions about the nature and extent of band overlap, and may be tedious and lengthy in their application to real problems. Another approach has been to employ difference or differential spectrophotometry, where the analyte absorbance in the formulation matrix is measured at its Amax.against a reference solution of the matrix. Clearly, the concentration of matrix in the reference cell should be identical with the matrix concentration in the sample cell.This condition limits the viability of the method, since the matrix can vary from one batch or from one manufacturer to another. Liquid preparations can contain variable amounts of absorbing impurities leached from the container or its closure, or the composition of the solution may be changed by sorption of solutes at the container interface or by permeation of solvent through the container wall.One elegant approach to the problem of resolving spectral overlap that has received little attention in pharmaceutical analysis is derivative spectroscopy, whereby the first, second or higher derivative of spectral band absorbance or intensity is generated with respect to wave- length at all points in the spectrum. ,lo explored theoretic- ally by Giese and French,ll by Martin12 and more recently by O’Haver and Green,13 spectral derivatives can be computed for most types of spectra : ultraviolet - visible,14 fluorescence,15 infrared,16 nuclear magnetic resonance,17 Mossbauer18 and mass spectra.lg Published applications of derivative spectroscopy have been intermittent and usually limited to first derivative enhancement of qualitative features and semi-quantitative studies.Derivative methods have not so far been applied seriously to the quantitative assay of drugs in mixtures. This paper describes some of the first applications of second derivative ultra- violet - visible spectrophotometry for the quantitative assay of drugs in their dosage forms. Proposed more than 25 years Principles of Derivative Spectrophotometry The first derivative spectrum is simply the gradient dA/dA of the absorption envelope and features a maximum and a trough; the vertical distance between these is the amplitude, pro- portional in principle to the analyte concentration, provided that the Beer - Lambert law obtains in the zero order spectrum.The ideal Gaussian peak in Fig. 1 shows the first derivative spectrum passing through zero at a point corresponding to the band’s Amax., illustrating a method for accurate measurement of Amax.values. By contrast, the second derivative spectrum d2A/dh2 is inverted with respect to the zero order spectrum and features two satellite maxima S and L and one minimum coinciding with the Amax. for the normal absorption band. In principle both peak height amplitude measurements D, and D, are proportional to analyte concentration.A key feature of the second derivative spectrum is the considerably reduced band width (depending on band shape), which immediately points to the possibility of im- proved resolution of overlapping bands with increased sensitivity. As shown by Martin20 the next even derivative (d4A/dX4) would be expected to give a further reduction in band width and increased sensitivity.This has recently been shown to be the casea1~22 and is discussed below. Considering a narrow peak for analyte X overlapped by a constant broad interfering peak I (Fig. 2), quantitation of X by absorbance measurement of the zero order spectrum, even employing the tangent base-line method, would be expected to lead to considerable systematic errors.It is apparent that the second derivative spectrum yields two well resolved peaks, the amplitudes D,, D, being related to X concentration, with D, constant and reflecting the level262 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc. AnaZyt. Div. Chem. Soc. 1 S L Fig. 1. (a), Ideal Gaussian peak, zero order spectrum; ( b ) , first derivative spectrum ; and (G), second derivative spectrum. of I.Low levels of X obscured in the zero order spectrum are readily detected in the second derivative spectrum and may be quantified. Various graphical measurements are available for the amplitude of the second derivative of analyte X in matrix I, the most convenient being D,, D, and the vertical distance between the trough and the base line D,.In practice, that measurement is selected which exhibits the best linear response to analyte concentration, which gives a zero or near zero intercept on the absorbance axis of the analytical growth curve and which is least affected by the concentration of any other components. Thus, at h nm, then Atooral = A& + A? . . .. .. .. - - (1) The best amplitude measurement for quantitation is that for which the last term in (2) is zero.For the type of systems illustrated in Fig. 2 it has been found that this is often D,. It should perhaps be stressed that the selection of an appropriate amplitude measurement for a multi- component mixture is an empirical process. First derivative measurements have been found to be useful only for quantitating the simplest systerns14923.Their potential contribution in analysis is discussed below. Fig. 2. ( a ) , Typical peak overlapped by an interfering peak (I) and ( b ) , graphical measurement of the second derivative of the analyte X, overlapped by interfering peak I.September, 1978 DEVELOPMENTS I N PHARMACEUTICAL ANALYSIS 263 The main parameters that appear to determine the usefulness of the derivative approach for resolving two overlapping spectra have been identified theoretically by O’Haver and Greed3 as the wavelength separation of the Amax.values for the two components, their relative band width and their relative spectral intensities. They have evaluated detailed and complex data based on the numerical simulation of two overlapping Gaussian bands characterised by these three parameters in various combinations.The systematic and random-noise errors for these overlapping peak combinations were deter- mined for all possible amplitude measurements for zero order, first and second derivative spectra. Derivative measurements were generally found to give the lowest systematic errors in instances where the analyte band width was less than that of the interfering band.Much work remains to be carried out to translate O’Haver and Green’s interesting theoretical projections into practically useful guidelines for assessing the potential feasibility of derivative measurements for real analytical systems. Instrumental methods for generating derivative spectra have been summarised elsewhere.24 925 Two groups of methods can be identified.The first and hitherto most widely used group includes those methods operating directly on the radiation beam itself. Thus, the wavelength modulation technique, where the wavelength is oscillated rapidly over an interval AX by one of several methods, produces a modulated intensity of the spectrophotometer beam which can be decoded to give first or higher derivatives at stationary wavelength.If the monochromator is scanned simultaneously, the derivative spectrum is obtained. In another approach the dual wavelength spectrophotometer generates first derivative spectra when there is a sufficiently small interval, AX, between the two monochromators scanned synchronously. The compara- tive expense and complexity of these two types of instrument probably explains why derivative spectrophotometry has for years been relegated to the spectroscopic wilderness by practising analysts.However, the second group of methods, where the spectrophotometer output is processed in some way to give a higher derivative (computer differentiation, electronic differentiation), are now being explored in many fields of analysis, thanks to the recent development of inexpensive electronic derivative modules.26 927 These modules are simply connected in series between the recorder and the spectrophotometer output. The zero order spectrum is presented to one or two resistance - capacitance circuits in series (Fig. 3) to produce the first or second derivative spectrum, respectively, as the spectrum is scanned.The time constant of the derivative circuit is readily changed by selecting different values of R, and R, and this determines the recorded amplitude of the derivative spectrum. Of necessity, the output voltage A is differen- 1 tiated with respect to time to giveithe derivative signal. Since scan speed ($ = S nm min-l is normally held constant, the derivative with respect to wavelength is readily related to the time derivative signal as follows : dA dA dX - dt - dt therefore the first derivative is dA dA 1 - d h - d t x s d X 2 - a F X S z and the second derivative is d2A d2A 1 - and so on for each higher derivative.The performance of the derivative unit depends on excellent scan speed linearity and reproducibility as any variations in the scan speed are reflected in the observed time derivative amplitude.The finite time interval required for the computation of derivatives increases with each higher derivative and introduces a spectral shift between the analogue derivative output and the zero order spectrum. This shift is an easily calibrated constant for given instrumental conditions and can be corrected automatically in microprocessor-controlled spectrometers, where the derivative circuit is integrated with the instrument.264 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc.Analyt. Div. Chem. Soc. Applications Enhancement of detection sensitivity is illustrated by the second derivative spectrum of 20 p.p.m. aqueous benzalkonium chloride solution, where measurement of the peak - trough amplitude D,,, at 262 nm permits rapid quantitation.At the trace amount level this analyte is barely detectable in the zero order spectrum. Tablets of caffeine extracted with 95% ethanol can be assayed for content of caffeine by measurement of the peak - trough amplitude of the broad second derivative spectrum between 270 and 290 nm (Fig. 4). The calibration graph is linear, passes through the origin and has 95% confidence limits of & 0.2 pg ml-l at the 10 pg ml-l level. Experiments in which pure caffeine was added to the tablet extracts gave recoveries of 98-102%.Any irrelevant absorption caused by formulation components extracted from the tablets makes little, if any, contribution to the derivative spectrum. 0.6 a, 6 0.5 e % 2 0.4 d 3 0.3 dt2 0.2 - dA d t 0.1 Fig.3. Simplified electronic derivative circuit. 0 - I --A 2 50 300 Wavelengthhm Fig. 4. Zero order (below) and second derivative ultraviolet spectra (above) of caffeine tablet extract in 95% ethanol. Derivative condi- tions with Hitachi derivative module: scan speed 120 nm min-l; spectral slit width 2.0 nm; and mode (time constant) No. 5. As an example of a two-component system, hyoscine hydrobromide eyedrops (o.25-2y0 m/ V ) containing O .O l ~ o m/V of chlorhexidine acetate as preservative presents a difficulty in con- ventional spectrophotometry. Although the concentration of hyoscine hydrobromide is 25- to 200-fold greater than the preservative, its absorptivity (Aizi) at the A,,,. of 257 nm is only 4.5, some 100-fold less than that for chlorhexidine acetate at this wavelength (A:$ = 460).In the zero order spectrum, therefore, hyoscine hydrobromide is almost completely obscured by the broad band spectrum of the preservative (Fig. 5). However, the amplitude of the second derivative spectrum at 257 nm (D25, measured to the long-wavelength satellite) is linearly related to hyoscine hydrobromide concentration, and passes through the origin.The 95% confidence limits for the calibration graph are typically & 10 pg ml-l at the 1000 pg ml-l level. Furthermore, D25, for 500 pg ml-l of hyoscine hydrobromide is robust to %foldSeptember, 1978 DEVELOPMENTS I N PHARMACEUTICAL ANALYSIS 265 changes in chlorhexidine acetate concentration. This is all the more remarkable when it is considered that in 30 pg ml-l chlorhexidine acetate the hyoscine hydrobromide has an absorbance of only 0.2 unit in a total absorbance of 1.7 units.This second derivative method22 has been used routinely for the quality control of batches of the eyedrops since March 1977, the coefficient of variation being 1-2y0. Pilocarpine and Eserine Eyedrops BPC containing 0.01 yo m/V benzalkonium chloride as a preservative represents a three-component system.Studies with pilocarpine hydrochloride (2.0% m/V) and benzalkonium chloride alone, and with eserine sulphate (0.5% m/V) and benzalkonium chloride, have established that the preservative exerts no detectable influence on the second derivative spectra for these components at these concentrations. In the zero order spectrum of the mixture of pilocarpine hydrochloride and eserine sulphate the pilocarpine hydrochloride peak a t 215 nm is subject to severe interference by eserine sulphate absorption.The eserine sulphate peak at 246 nm, however, is not interfered with by pilocarpine hydro- chloride and could be used directly for the assay of eserine, were it not for the possible presence of irrelevant absorption at this wavelength.The second derivative spectrum for the mixture displays two minima (Fig. 6). The amplitude at 218 nm is linearly related to pilocarpine hydrochloride concentration while that at 246 nm is linearly related to eserine sulphate concentration. Both calibration graphs show zero intercept on the absorbance axis, and have 95% confidence limits of & 0.3 pg ml-1 at the 20 pg ml-1 level.Interaction studies for a¶ ; 0.9 I] & 0.8 2 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 200 250 300 Wavelengthhm Fig. 5. Zero order (below) and second derivative ultra- violet spectra (above) of A, hyoscine hydrobromide (250 pgml-1) ; B, chlorhexidine acetate (10 p g ml-1) ; C, binary mixture of A in B; and D, distilled water. Derivative conditions with Hitachi derivative module : scan speed 120 nm min-l; spectral slit width 2.0 nm; and mode (time constant) No.5. 200 250 300 Wavelengt h/n m Fig. 6. Second derivative spectrum of ternary mixture of pilocarpine hydrochloride (20 pg ml-l), eserine sulphate (5 p g ml-l) and benzalkonium chloride (0.1 pg ml-l) . Deriva- tive conditions with Hitachi derivative module : scan speed 120 nm min-l ; spectral slit width 1.0 nm; mode (time constant) NO.5.266 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS Proc. Analyt. Div. Chem. SOC. constant pilocarpine hydrochloride in varying eserine sulphate concentration, and for constant eserine sulphate in varying pilocarpine hydrochloride concentration, reveal that, as expected, the eserine sulphate derivative measure is independent of pilocarpine hydrochloride concentra- tion.However, the pilocarpine hydrochloride derivative amplitude is dependent on eserine sulphate concentration. A 50% increase in eserine sulphate concentration introduces a syste- matic error of 4% in the assay for pilocarpine hydrochloride. For routine quality control analyses, where concentrations are usually controlled to +5y0 of nominal label strength or better, the systematic error introduced is less than 1% and can be further reduced if a com- posite reference standard is used containing both analytes at their anticipated label strengths.The second derivative method22 enables both components to be assayed rapidly, the coefficient of variation being typically 2-3y0. Oily phenol injection is usually prepared in almond oil, which absorbs strongly in the ultra- violet region.Variability in batches of this natural product invalidates the difference spectro- scopic method, unless the original almond oil is available as a reference. The second derivative spectrum of samples diluted in cyclohexane yields several useful peaks for phenol, the ampli- tude at 277 nm (to the long-wavelength satellite) giving an excellent calibration graph with 95% confidence limits of &0.4 pg ml-l at the 25 pg ml-l level.Varying the proportion of almond oil in the cyclohexane dilution exerts no effect on this derivative measurement for phenol. Typical coefficient of variation values for routine quality control2* are better than 2%. Monitoring the level of preservatives by ultraviolet - visible spectrophotometry in nutrient broth seeded with Staphylococcus auyeus is complicated by high matrix absorbance.3- Phenylpropan-1-01 can be determined in this medium by measuring the second derivative spectrum amplitude at 266 nm after simple dilution. This amplitude is independent of the proportion of nutrient broth and bacterial concentration and gives 95% confidence limits of & 3 pg ml-l at the 100 pg ml-l level.This method can be applied to a number of aromatic alcohols used as preservatives.28 Discussion These selected applications illustrate the relative ease and simplicity offered by second derivative spectrophotometry for the assay of complex mixtures of spectrally interfering com- ponents. It should be emphasised that the selection of a suitable amplitude measure for the analyte is to a large extent empirical in that the magnitude of the interfering component’s second derivative should be close to zero at this wavelength.Work at Hitachi21 has shown that recording the next even derivative (d4A/dh4) not only improves sensitivity and sharpens band width, but may also reduce the spectrum of a broad interfering component to a horizontal line.Work in our laboratory has shown that the fourth derivative spectra of chlorhexidine acetate, almond oil and several other components that interfere spectrally in polypharmaceuti- cal systems are zero, although this will not necessarily hold for interferences in other systems. Fourth derivative spectrophotometry has been shown to yield linear analytical growth graphs independent of formulation matrix for diphenhydramine hydrochloride in expectorants,22 and offers an additional approach for de-convoluting spectra.There is, however, a concomitant decrease in signal to noise ratio in higher derivative spectrophotometry. The implications of fourth derivative spectrophotometry for improved resolution and quantitative accuracy are currently being explored in our laboratory with regard to drugs in their formulations and in systems of clinical and biological interest.First and second derivative spectrophotometry are potentially useful for the assay of analytes in suspension and in turbid solutions, provided that the absorptivity of the analyte is sufficiently high to withstand the large dilution required to reduce the apparent total absorb- ance to less than 1.5 absorbance units.In systems where the absorbance is changing with time (e.g., in enzymatic reactions, in elevated temperature stability tests and in tablet dissolu- tion studies) the first and second derivatives can be monitored continuously at fixed wave- length by using a flow cell and peristaltic pump. This technique can provide accurate and stable parameters that are readily related to reaction or dissolution rate, with a potential increase in precision and reduction in analysis time.Higher derivative methods can potentially make significant contributions in other branches of analytical chemistry. In high-performance liquid chromatography ultraviolet - visible and fluorescence spectrophotometers used as detectors can be linked with a derivative unit toSeptember, 1978 DEVELOPMENTS IN PHARMACEUTICAL ANALYSIS 267 de-convolute overlapping peaks in chromatograms, differentiating with respect to time at fixed wavelength or, if stop-flow scanning is carried out, with respect to wavelength at a given retention time.Milano and co-w~rkers~~ 93O have already demonstrated the feasibility of the latter approach when using the rapid scanning diode array spectrometer to generate first derivative spectra in liquid chromatography.The second derivative should prove to be a use- ful extension of this idea. In gas - liquid chromatography, too, optimisation of the derivative unit’s time constant should offer a simple method for improving the resolution of overlapping peaks.Second derivative spectrophotometry generates inverted, sharpened spectra with improved resolution of overlapping peaks. This enables sensitive detection and identification at the trace amount level. The amplitude of carefully selected peaks may be quantitatively related to analyte concentrations in mixtures. Depending on the relative band shapes, interference by irrelevant absorption or by other spectrally active components can be eliminated, thus reducing systematic errors in quantitative determination.Our work has shown that the signal to noise ratio in higher derivative spectra can be improved by careful optimisation of scan speed, spectral slit width and derivative time constant, so that coefficients of variation better than 2% are readily achieved for routine quality control applications. Continued research into the error sources and applications of higher derivative spectroscopy, particularly in relation to drugs and enzymes in biological matrices, should contribute potentially rapid, accurate and sensitive analytical methods for the medical sciences.The author acknowledges the advice and encouragement of the late Dr. A. L. Glenn in the early stages of this work. The generous loan of a Model 200 ultraviolet - visible spectrophoto- meter and a Hitachi derivative attachment by Perkin-Elmer Ltd. and helpful discussions with Dr. Brian P. Chadburn (Perkin-Elmer Ltd.) are also acknowledged. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27 28. 29. 30. Morton, R. A., and Stubbs, A. L., Analyst, 1946, 71, 348. Glenn, A. L., J . Pharm. Pharnaac., 1960, 12, 595. Glenn, A. L., J . Pharm. Pharmac., 1963, 15, Suppl., 123T. Glenn, A. L., Proc. SOC. Analyt. Chem., 1967, 4, 116. Agwu, I. U., and Glenn, A. L., J . Phavm. Pharmac., 1967, 19, Suppl., 76s. Abdine, H., Wahbi, A. M., and Korany, M. A., J . Phavm. Pharmac., 1971, 23, 444. Wahbi, A. M., and Ebel, S., J . Phavm. Phavmac., 1974, 26, 317. Wahbi, A. M., and Unterhalt, B., 2. Analyt. Chem., 1976, 282, 31. Hammond, V. J., and Price, W. C., J . Opt. SOC. A m . , 1953, 43, 924. Morrison, J . D., J . Chem. Phys., 1953, 21, 1767. Giese, A. T., and French, C. S., A p p l . Spectrosc., 1955, 9, 78. Martin, A. E., Nature, Lond., 1957, 180, 231. O’Haver, T. C., and Green, G. L., Analyt. Chem., 1976, 48, 312. Wahbi, A. M., and Ebel, S., Analytica Chim. Actn, 1974, 70, 57. Green, G. L., and O’Haver, T. C., Analyt. Cheun., 1974, 46, 2191. Collier, G. L., and Singleton, F., J . Appl. Chew.., 1956, 6, 495. Horsfield, A., Morton, J. R., and Whlffen, D. H., Molec. Phys.. 1961, 4, 425. Bressani, T., Brovetto, P., and Chiavassa, E., Nucl. Instrum. Meth., 1967, 47, 164. Beynon, J. H., Clough, S., and Williams, A. E., J . Scient. Instrum., 1958, 35, 164. Martin, A. E. Specfrochim. Acta, 1959, 14, 97. “Hitachi Technical Data Sheet hTo. 12,” Perkin-Elmer Ltd., Norwalk, Conn., 1978. Fell, A. F., to be published. Shibata, S., Angew. Chew., Int. E d n . Engl., 1976, 15, 673. Gunders, E., and Kaplan, B., J . Opt. SOC. Am., 1965, 55, 1094. O’Haver, T. C., and Green G. L., Am. Lab., 1975, March, 15. Schmitt, A4., “Derivative Spectroscopy,” Perkin-Elmer Applications Data Bulletin ADS 103, Perkin- Botten, D., Honkawa, T., and Tohyama, S., “Second Derivative Spectroscopy,” Perkin-Elmer Fell, A. F., J . Pharm. Pharmac., 1978, 30, in the press. Milano, M. J., Lam, S., and Grushka, E., J . Chromat., 1976, 125, 315. illilano, M. J., and Grushka, E., J . Chromat., 1977, 133, 352. Elmer Ltd., Norwalk, Conn., 1077. Applications Data Bulletin ADS 104, Perkin-Elmer Ltd., Norwalk, Conn., 1977.

ISSN:0306-1396    

DOI:10.1039/AD9781500253

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

268 EQUIPMENT NEWS Proc. Analyt. Div. Chem. SOC. Equipment News Laser Raman System The Spex Ramalog 5M has four slits and two 1 800 grooves mm-l holographic gratings fitted to produce a resolution of better than 0.15 cm-l. The system incorporates a high light gathering power f/l lens system with variable working distance, a photomultiplier which has a guaran- teed low dark count and a photon counter to give an excellent signal to noise ratio.A pro- grammable data handler with calculator is also available. Glen Creston Instruments Ltd., 16 Carlisle Road, London, NW9 OHL. Auto Sampler for Flame Atomic Absorption The Model AS-50 Auto Sampler for flame atomic absorption is operable with all Perkin- Elmer atomic-absorption spectrophotometers ; it can automatically present up to 50 samples to the instrument for analysis, and activate the “Read” cycle of instruments with signal integra- tion capabilities.When combined with either the Model 460 or 603 spectrophotometer, the AS-50 initiates automatic instrument calibra- tion as well as re-calibration up to three times during an analysis. Automated analysis is possible with other instruments. Perkin-Elmer Ltd., Beaconsfield, Bucking- hamshire, HP9 1QA.Dosimeter The Swedtool Dosimeter is designed for the rapid and repeated measurement of specific quantities of liquids. The required volume of liquid is transferred to the measuring head by squeezing the bottle after adjusting the movable pipe, any surplus draining back. C-0 Witte AB, Box 5006, 40221 Goteborg 5, Sweden. Gas Monitoring Systems A modular remote control and indication system compatible with existing automatic gas monitors is announced.Systems range in size from a single channel to 100 monitored points, with remote control and indication panels giving considerable flexibility. Common modules con- tain audible alarms and alarm mute and re-set switches for the complete system. The modular concept enables any component within the system to be quickly changed without affecting the operation of other monitoring points.Neotronics Ltd., Building 102, FSTS Site, Stansted Airport, Stansted, Essex, CM24 8QX. Toxic Gas Monitor A carbon monoxide alarm system is announced to monitor the level of this toxic gas. It in- corporates an integral, self-checking system, which triggers an alarm in the event of either power failure or circuit malfunction.The standard scale range is 0-150 p.p.m. of carbon monoxide and the accuracy is to 2 p.p.m. or better. The carbon monoxide alarm can be set to monitor levels in accordance with BS 4275: 1973. Theta Pneumatics Limited, 9 Hazel Road, Mytchett, Camberley, Surrey. Bacteriological Filter A bacteriological filter is available for use in in- line and vent-guard situations.The filter has a minimum retention of 99.95% for particles of 0.3 pm and withstands an operating line pressure of 1.41 kgf cm+. A. Gallenkamp and Co. Ltd., P.O. Box 290, Technic0 House, Christopher Street, London, EC2P 2ER. Particulate Analysis Millipore membrane collection techniques, well known in the laboratory, are now available in a range of kits for field or site testing.Kits to monitor contamination levels in fuels, hydraulic fluids, oils and waters (raw or purified) use either 47 or 37 mm diameter membranes, the latter being incorporated in field monitor form if required. Field monitors consist of trans- parent, disposable filter holders, pre-assembled with the filter in place, with a cellulose pad be- neath the membrane in order to allow the sample to flow evenly over the filter surface.For gravimetric analysis, matched-weight filters can be incorporated in place of the single membrane type normally used. The degree of discoloration of the white membrane can also be used for “patch testing.” Millipore (UK) Ltd., Millipore House, Abbey Road, London, NWlO 7SP. Membrane Filter A membrane, Tuffryn HT, composed of a high- temperature aromatic polymer possessing high tensile strength, compatibility with live steam and excellent thermal stability at elevated temperatures, is announced. In addition to its high thermal stability and high tensile strength,September, 1978 EQUIPMENT NEWS 269 the membrane is non-protein binding, non-toxic and resistant t o most acids, bases, alcohols, oils and glycols.It is not compatible with esters, some ethers, aromatic and halogenated hydro- carbons and ketones. This membrane shows low moisture pick-up and is low in trace metals. Bacteriological recoveries are comparable with cellulose nitrate membranes. Gelman Hawksley Ltd., 12 Peter Road, Lancing, West Sussex, BN15 8TH. Filter An improved filter, Type 92E, is designed for use in coalescing applications where the filter tube gives 99.99% removal efficiency of oil and water aerosols at flow-rates up to 56 normal m3 h-1 (33 standard f t 3 min-I) at 10-bar line pressure.The filter element is now sealed independently of the filter bowl to enable it to be removed without disturbing the element seal. Balston Ltd., Springfield Mill, Maidstone, Kent.Battery-powered pH Meters A series of hand-held, battery-powered digital pH meters is announced. The Model LTD60, which measures pH over the range 0-14 to an accuracy of 0.1 pH f the last digit, incorpor- ates automatic temperature compensation over the range 0-100 "C, this being effected by a high accuracy, platinum resistance element which can also operate as a platinum resistance thermometer with auto-polarity.In this way, the LTD6O enables direct temperature measure- ment within the range from -30 to +150 "C. The Model LTD80 has a resolution of 0.01 pH and provides accurate pH measurement from 0 to 14 with fast response. Fully automatic temperature compensation from 0 to 50 "C is achieved by a platinum resistance element similar in design to Model LTD60.The LTD80 combines a steel-bodied temperature compensa- tion measurement probe with either a plastic- bodied pH electrode for liquid applications or a plastic-bodied combination electrode with a pointed, toughened-glass tip for pH measure- ment in semi-solids such as meats, cheeses, soils, etc. A specially designed temperature measure- ment probe can also be supplied when forcible insertion into frozen materials is required.MN1500 batteries are fitted as standard, with Type AA rechargeable batteries and a charger also available. Lenton Thermal Designers Ltd., 68 Cannock Street, Leicester, LE4 7HR. Monochromator for Ultracentrifuge The new system, which can be fitted to Centri- scans already in the field, has the ability to use the wavelength of choice between 240 and 580 nm.It reduces stray light to negligible amounts, thus increasing the range over which the relationship between concentration and absorption is linear. MSE Scientific Instruments, Manor Royal, Crawley, West Sussex, RH 10 2QQ. Gas Chromatograph A simple, heated-column gas chromatograph, designed for teaching but equally suitable for many types of routine analysis purposes, is now available.The column, filled with silicone oil on Celite, is heated by a 750-W heater with a temperature range of 25-150 "C. Signals from the flame-ionisation detector system are fed to a pair of 4-mm sockets, which can be connected to an external chart recorder. A. Gallenkamp & Co. Ltd., P.O. Box 290, Technico House, Christopher Street, London, ECBP 2ER.Micropipetting System A universal sampler, the P7000, is available for micropipetting requirements in the range 1-1 000 p,l with high accuracy and reproduci- bility. Two sizes of removable tip are required. Boehringer Corporation (London) Ltd., Bell Lane, Lewes, East Sussex, BN7 1LG. Oscilloscope Camera The Shackman 7000 is available for both permanent and hand-held mounting.It is developed from the CT-9 withf/3.5 lens and an 8-speed shutter. It is available with'a range of hoods for hand-held operation and of oscillo- scope adaptors for permanent mounting. Quick-loading Polaroid black and white 8-exposure film packs are used. Shackman Instruments Ltd., Mineral Lane, Chesham, Buckinghamshire, HP5 1NU. Safety Modification for Centrifuge The CFC-300 Centrifuge has been modified to improve its operational safety by incorporating an interlock between a latch on the lid and the motor, which ensures that when the lid is not secured shut no power is supplied to the motor.A. Gallenkamp & Co. Ltd., P.O. Box 290, Technico House, Christopher Street, London, ECSP 2ER.270 EQUIPMENT NEWS Proc. Analyt.Div. Chewz. SOC. Humidity Incubator An incubator with continuous monitoring and automatic control of carbon dioxide levels is now available. The carbon dioxide content is regulated by a katharometer controller, injecting as necessary to maintain the required level. A Compenstat solid-state thermostat provides for accurate temperature control up to a maximum temperature of 60 "C.The liner and shelves are constructed of stain- less steel, the working volume is 180 1 and an inner glass door permits sample observation without loss of incubator atmosphere. A. Gallenkamp & Co. Ltd., P.O. Box 290, Technico House, Christopher Street, London, EC2P 2ER. Microbalances The range of Cahn Series-20 automatic micro- balances is now available, with four balances in the range and giving 3.5-g capacity.The Cahn 25 has four weighing ranges of 2, 20, 200, and 1000 mg. All of the microbalances are fully automatic within their ranges, with the weight automatically shown on the large, easy-to-read, digital display readout. Full-range push- button tare is a feature found only on these microbalances. The user can tare &l20% of the weighing range simply by pushing the tare button and still retain full use of the range for sample weighing.Oertling Ltd., Cray Valley Works, St. Mary Cray, Orpington, Kent, BH5 2HA. Quick- Connects Swagelok Quick-Connects, with $-in female nominal pipe thread ends, designed for maxi- mum flow and fast, leak-tight connections on rigid or flexible tubing, piping lines and hy- draulic hose assemblies, are now available.The new QF4 Series Quick-Connects are available in both brass and 316 stainless-steel barstock construction, and include a full &in orifice with no restriction, 360" swivel action and standard size O-rings which can be changed without disassembling the body unit. Service ratings are 5 000 lb in-2 in brass and 10 000 lb in-2 in 316 stainless steel.Maximum flow capacity (C,) is 1.8. Techmation Ltd., 58 Edgware Way, Edgware, Middlesex, HA8 SJP. Roller Mixer The rocking and rotating action of this roller mixer makes it suitable for blending a wide range of blood, plasma and powder specimens. Five plastic-coated rollers, each 320 mm long and 30 mm in diameter, will accept stoppered test-tubes, universal containers and McCartney and Bijou bottles.A 36-W motor rotates up to speeds of 50 rev min-I, and each roller has a built- on spiral of 100-mm pitch, which causes the vessel to be rocked as well as rotated. A. Gallenkamp & Co. Ltd., P.O. Box 290, Technico House, Christopher Street, London, EC2P 2ER. Polythene Bag Sealer A sealer for polythene bags, designed to be mounted either on a bench or a wall, can be used to make seams by heat fusion.The sealer will close up to a thickness of 0.5 mm and up to a maximum width of 300 mm. Welding time can be controlled by a 12-position click-stop switch. A. Gallenkamp & Co. Ltd., P.O. Box 290, Technico House, Christopher Street, London, EC2P 2ER. New Materials High-performance Liquid Chromatography Solvents A range of 17 HPLC solvents with extremely tight specifications, coupled with superior product definition, is announced.All of the solvents have a controlled, low ultraviolet light absorbance and a low water content. The residue after evaporation is equal to or less than 0.000 5% and a controlled refractive index assures reproducibility of performance in units with refractive index detectors. J. T. Baker Chemicals B.V., P.O.Box 1, 7400 AA Deventer, Holland. Deactivating Material Material for deactivating gas chromatography columns, Deacticol, is intended to complement, not to replace, the usual silanisation treatment of non-polar columns and is stable a t column temperatures up to 275 "C. Scientific Glass Engineering (UK) Ltd., 657 North Circular Road, London, NW2 7AY. Liquid Chromatogram Absorbent Ultrafine is a general purpose absorbent for use in polar and non-polar solvents as an alternative to silica gel. Designed for semi-analytical, laboratory and industrial-scale separation of a wide range of substances, including aldehydes, ketones, aromatics, nucleotides, steroids, lipids, vitamins, etc., and compounds containing hydroxyl or amino groups, the material is stable over a wide pH range (2-12) and is catalytically inactive.September, 1978 CORRESPONDENCE 27 1 The rigid porous bead form allows for fast Pharmacia (Great Britain) Ltd., Paramount flow-rates and pressures in excess of 1 400 lb i r 2 have been used. House, 75 Uxbridge Road, London, W5 5SS.

ISSN:0306-1396    

DOI:10.1039/AD9781500268

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

September, 1978 CORRESPONDENCE 27 1 Analytical Division Distinguished Service Award Nominations are invited for the Division’s Distinguished Service Award, the Rules for which are as follows: 1. The aim of the Award is to recognise exceptional service over a period of years to the Analytical Division of the Chemical Society (including that to the Society for Analytical Chemistry). 2. The Award shall normally be in the form of an illuminated address which may be accompanied by such additional recognition as Council of the Division shall agree. 3.Nominations for the Award will be invited annually from members of Council of the Division, and may be received from any member of the Division. They shall be made in writing, with supporting evidence, to the President of the Analytical Division. 4. Nominations shall be considered by the Honours Committee of the Analytical Division, which shall recommend to Council of the Division (a) to whom an award should be made, (b) the nature of the award or (G) that no award should be made. 5. The Award shall be made by the Council of the Analytical Division, which must ap- prove any alteration of these Rules. Nominations for the Award should be sent to the President of the Analytical Division before September 30th, 1978.

ISSN:0306-1396    

DOI:10.1039/AD978150271b

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

272 CONFERENCE Proc. Analyt. Div. Chem. SOC. Publications Received A History of Analytical Chemistry. Edited by Herbert A. Laitinen and Galen W. Ewing. Pp. xvi + 358. Washington, D.C.: Division of Analytical Chemistry of the Ameri- can Chemical Society. Available from Dr. F. Guthrie, Department of Chemistry, Rose- Hulman Institute of Technology, Terre Haute, Indiana 47803, USA. 1977. Price $11.Developments in Food Analysis Techniques -1. Edited by R. D. King. Developments Sevies. Pp. x + 323. London: Applied Science. 1978. Price i25. Fourier Transform Infrared Spectroscopy. Applications to Chemical Systems. Volume 1. Edited by John R. Ferraro and Louis J. Basile. Pp. viii + 311. New York, San Francisco and London: Academic Press. 1978. Price $25; i16.25. Viruses of Vertebrates. Fourth Edition. Sir Christopher Andrewes, H. G. Pereira and P. Wildy. Pp. x + 421. London: Ballikre Tindall. 1978. Price A13.50 (hardback).

ISSN:0306-1396    

DOI:10.1039/AD978150272c

出版商:RSC    

年代:1978

数据来源: RSC