Theory And Application Of Calculational Titrimetric Analysis

Calculational Titrimetric Analysis(simplified as CTA)is the resultant of titrimetry combined with mathematical methodology and computative technology.Compared with the traditional titrimetry CTA has its own inherent regularity and thus has more applications.The research into the CTA is of significance both in the academic approaches and practical applications.The following focuses mainly on CTA study and its applications.First,the viewpoint is proposed here that CTA is to be divided into two categories, that is,Controlled Volume Titration(CVT)and Controlled Potential Titration(CPT).Of the two the former includes Linear Titration,Single Point Titration and Double Point Titration while the latter deals mainly with Controlled Single Potential Titration and Controlled Multiple Potential Titration.And further introduction to CTA is made such as the basic principles,specificities of CVT and CPT as well as their differences and interrelationship.Second,according to the error transfer theory the regularities are studied affecting the determination error of the potential on CVT and the controlled error of the potential on CPT and thereby the nature of the regularities is found.The determination error of potential on the accuracy of CVT is related to the titration percentage.The closer the titration percentage is to stoichiometdc point(SP),the less its influence is.And the controlled error of the potential on the accuracy of CPT is connected to the proportional coefficient in the computational model and the shape of titration curve.The bigger the coefficient in the computational model and the change rate of titration curve are,the less their influence are.Besides the factors and their influences are considered that how to select suitable titration reaction and titration modality and under the guidance of the above theory amino acids were successfully determined.Thirdly,the stable performance and the good reproducibility of fluoride ion selective electrode make it possible to determine Al³⁺,Fe³⁺and Ga³⁺using fluorin-metal complexometric titrations of CTA.The high accuracy is achieved taking advantage of only three kinds complexes forming in water-alcohol solution for F^- and Al³⁺,that is,AlF²⁺, AlF₂⁺ and AlF₃.Thus the high ligancy complexes of F-Al are prevented from forming.The three order accumulative formation constants of F-Al complexs are determined first and then the concentration of Al³⁺in test solution is detected in water-alcohol solution using Linear Titration.The determination of single ion such as Fe³⁺,Al³⁺or Ga³⁺and the mixtures of ions such as Al³⁺and Fe³⁺or Al³⁺and Ga³⁺were carried out in water solution using CPT.A brand-new viewpoint is proposed that under non-equilibrium state the determination could be carried out with CPT.In addition the preliminary exploration is probed into the determination of Al³⁺with Kinetic Potentiometry in low pH condition.Fourthly,The CTA was used in acid-base,precipitation and redox titrations.In the case of the argentimetry in precipitation titration of CTA when pK_sp＜9 the concentration of test solution and K_spcan be got simultaneously provided the concentration of the titrant is known.When pK_sp＞9 and after SP the concentrations of both test solution and titrant could be known at the same time even though K_spis unknown.In precipitation titration both Single Point Titration and Double Point Titration only can be used in the system where the SP is passed and pK_sp＞9.As to the acid-base titration of CTA the concentration of the tested acid and the titrant could be acquired at once using any of the three means,Simplified Optimization Method,Non-Linear Least Squares Method or Linear Least Squares Method.The simplified Single Point Titration or Double Point Titration can be used to the monoacids whose protonation constant K_HA＜10^-7and to the points whereα＞1 while both titrations can be used to the polyprotic acids whose m multiple protonation constants K_HAjare less than 10^-7and to the points whereα＞m.The factors affecting the accuracy of determination in the case of Single Point Titration are the determination error of potential,the error of conditional protonation constants of acids as well as the error of proton transfer constant of water,fortunately the combined effect of the above factors reaches its minimum in the vicinity of SP.As to the cerimetry in redox titration of CTA Fe(â…¡)and Ce⁴⁺can be analyzed simultaneously if Fe(â…¢)exists. And Fe(â…¢)and Fe(â…¡)also can be done if the concentration of Ce⁴⁺is known.If the concentration of Fe(â…¢)is 20 times more than that of Fe(â…¡)the concentration of Fe(â…¡) can be got using Single Point Titration or Double Point Titration.At last,as a practical application the analyses of amino acids and medicines were studied.Single amino acid or mixtures of amino acids can be determined by CPT such as acidic and alkaline,alkaline and alkaline,acidic and neutral,and alkaline and neutral amino acids,but the different object should be dealt with different titrant or different titrating modality.The muriate medicines can be done with Double Point Titration in the precipitation titration and the weak acid or base medicines with CPT in the acid-base titration.