V SUMMARIES OF PAPERS I N THIS ISSUE July, 1979Summaries of Papers in this IssueSimplification of the Mathematical Evaluation of Titration Resultsby Regarding Complexes of the Type A,B as n Complexesof the Type ABWhen titration results are evaluated mathematically, the calculations can besimplified and generalised by regarding complexes of the type A,B as n complexesof the type AB. For example, a diprotic acid can be replaced by two mono-protic acids, each of the same molarity as thc diprotic acid but with otherequilibrium constants. The conditions to be fulfilled if such simplificationsare to give correct results are discussed in detail.Keywovds : Titration results ; mathematical evaluationSTEN JOHANSSONDepartment of Analytical Chemistry, The Royal Institute of Technology, S-10044 Stockholm 70, Sweden.Analyst, 1979, 104, 593-600.Automatic Titration by Stepwise Addition of Equal Volumesof TitrantPart IV.General-purpose Program for Evaluating PotentiometricAcid - Base TitrationsA computational procedure for evaluating titration results is described. Itutilises non-linear regression techniques to solve the equations for titrationgraphs from acid - base titrations. The procedure is based on the fact thatthe titration of an n-protic acid can usually be treated as a titration of nmonoprotic acids of the same molarity as the n-protic acid.In principle, the composition of an unknown mixture of acids can be deter-mined by non-linear regression if a sufficient number of measurements(millilitres of titrant uersus pH) are available.However, this assumes thatthe measured values are known with adequate accuracy, an assumption thatis not correct in practice. All measured values (especially the pH values)are imperfect, hence a conventional non-linear regression can give a largenumber of mathematically equivalent solutions. This approach may there-fore, by chance, produce a result that is mathematically correct but chemicallyimpossible. This problem is avoided by setting boundary conditions andcarrying out calculations in an appropriate sequence. Dominating termsare dealt with first, then the effects of the remaining terms are included. Acomputer program TITRA, capable of handling such a calculation scheme, ispresented. No preliminary estimates of the required concentrations orequivalence volumes are necessary in the program.The general equation for the titration graph derived is applicable to samplesthat may contain monoprotic acids (strong or weak), polyprotic acids,mixtures of acids, ampholytes, salts of weak acids and “abnormal” acids(acids with an abnormal sequence of stability constant, values).Byexchanging hydrogen-ion concentrations for hydroxide-iorr concentrationsand vice versa the equation is applicable to the titration of bases.Keywords : Acid - base titrimetry ; evaluation programAXEL JOHANSSON and STEN JOHANSSONDepartment of Analytical Chemistry, The Royal Institute of Technology, S-10044 Stockholm 70, Sweden.Analyst, 1979, 104, 601-612July, 1979 SUMML4RIBS OF PAPERS IX THIS ISSUEPyridine-2-carbaldehyde 2-I4ydroxybenzoylhydrazone as a SelectiveReagent for the Extraction and Spectrophotometric Determinationof Iron( 11)VPyridine-2-carbaldeliyde 2-h ydroxybenzoylhydrazone reacts with iron( 11) toproduce a green 2 : 1 complex ( A m a x .= 620 nm, E = 3.64 x lo3 1 mol-l cm-lin aqueous ethanolic solution, and A,,,. = 640 nm, E = 3.67 x 10”1 molk1 cn-l in chloroform). The grcen complex, extracted into chloro-form, has been used for tlie spectropliotometric determination of traceamounts of iron. The method has a high selectivity and has been appliedto the detcrniination of iron in different samples, such as industrial wastewatcr, non-ferrous materials and minerals.Keywovds I von detevnzination ; s~ectvo~JzotonzetvyM. GALLEGO and M.GARCIA-VARGASDcpartnient of Analytical Chemistry, I7aculty of Sciences, l’niversity of Seville,Scvillc, Spain.and M. VALCARCELDepartment of Analytical Chcmistry, 1;aculty o f Scicnccs, Iiniversity of Cdrdoba,C6rdoba, Spain.A n a l y s t , 1979, 104, 613-619.Spectrophotometric Determination of Acetaminophen, Salicylamideand Codeine Phosphate in Tablets,in accuratc and simple method is proposed for the analysis of a threc-coniponent mixture composed of acetaminophen, salicylamide and codeinephosphate, without the necessity for the previous separation of any com-poncnt. ‘L’he first two coniponcnts arc determined directly by independentspectropliotometric ~neasure~ncmts, based on the pH-induced spectral changes.Codcine phosphate is assayed by the formation of an ion pair with methylorange.The procedure has been applied successfully to the analysiso f known mixtures and commcrcial tablets.Keywovds 1 A cetaiizinoplien ; salicylamide ; codeine PJzospJiate ; spectvopJLoto-iizetvyM. ABDEL-HADY ELSAYED, SAIED F. BELAL, ABDEL-FATTAH M.ELWALILY and HASSAN ABDINEDcpnrtnicnt oi T’harniaceutical Analytical Chemistry, Faculty of I’harmacy, l - n i -a-crsity of Alexandria, Alexandria, Egypt.A n a l y s t , 1979, 104, 620-025J d y , 19 79 SUMMARIES OF PAPERS I N THIS I S S U EDetermination of Vitamin D, in Multivitamin Tablets byHigh- performance Liquid ChromatographyA procedure is described for the determination of vitamin D, in multi-vitamin tablets.The vitamin is released from the tablets by enzymicdigestion, which is followed by solvent extraction and chromatography on amicroparticulate silica column. Other fat-soluble vitamins do not interferewith the assay. The problem of defining and quantifying vitamin D, in orderto correlate results with biological potency is discussed. The procedure issuitable for stability studies.Keywords : Vitamin D, ; five-vitamin D, ; multivitamin tablets ; high-pevformance liquid chronzatogvaphyCHRISTEEN MACKAYDepartment of Chemistry, Loughborough Cnivcrsity of Technology, Loughborough,Leicestershire, LE11 3TU.J. TILLMANFisons Limited, Pharmaceutical Division, Research and Devclopment Laboratories,Bakewell Road, Loughborough, Leicestershire, LE 11 OQY.and D.THORBURN BURNSDepartment of Analytical Chemistry, The Qucen’s University of Belfast, Belfast,BT9 5AG, Northern Ireland.Analyst, 1979, 104, 626-636.Modified Fluorimetric Procedure for the SimultaneousDetermination of Thiamin and Riboflavin in CowpeaThe fluorimetric methods for the assay of thiamin and riboflavin have beenmodified so that the same sample extract may be used for the simultaneousanalysis of the two B vitamins. The procedure eliminates acid hydrolysisand specific pH adjustment for either vitamin; the sample extract is obtainedafter enzymic hydrolysis only with Clarase and has a pH of 4.5-4.8. Astandard additions method for thiamin determination is introduced. Acowpea sample analysed by this procedure gave mean recoveries andstandard errors of 103.9 -J= 1 and 100.5 & 2% for added thiamin and ribo-flavin, respectively; the detection limits for the aqueous solutions taken forfluorescence measurement according to the described procedures for these twovitamins are 0.002 5 and 0.0020 pg ml-l, respectively.Keywords : Thiamin detevmination ; Yibojlinvin determination ; Juovinzetvy ;Clavase ; cowpeaJ. K. EDIJALADepartment of Food Science and Nutrition, University of Strathclyde, 131 AlbionStreet, Glasgow, G1 ISD.Analyst, 1979, 104, 637-644.vi