Titrimetric methods

Titrimetric methods with potentiometric end point location can be applied when an electrode with the needed selectivity is not available. The precision and accuracy of potentiometric titrations are superior comparing it with the properties of direct potentiometry. However, the concentration range where potentiometric titration can be used effectively is narrower. A solution with analyte concentration below 1 mM seldom is determined by potentiometric titrations. Potentiometric end point location is most often employed in the case of acid-, base-, precipitate-, redox-, or complexometric titrations. 

The amount of an evolved gas can be determined by a continuous titration method. A carrier gas removes the evolved gas from the furnace chamber and transports it to an aqueous-absorbing solution where it is continuously titrated. The titrant used will depend on the type of evolved gas to be determined. For example, ammonia is titrated with dilute hydrochloric acid, whereas water is determined by the Karl Fischer method. Compounds that can be determined include water, hydrogen chloride, ammonia, sulfur dioxide, carbon dioxide, and chlorine (80). 

Infrared spectroscopic techniques have long been used to analyze gas streams in industrial chemical processes. Recently, with the advent of fastscan infrared spectrometers, they have been used as gas chromatograph detectors. One requirement of their use, needless to say, is that the compound must possess one or more infrared absorption band. By means of a carrier gas. the evolved gas sample from a pyrolysis chamber can be readily passed through an infrared cell for analysis. Infrared systems that can be employed include (1) nondispersive analyzers, (2) dispersion spectrometers. 3) band-pass filter-type instruments, and (4) interference spectrometers all these techniques have been adequately reviewed by Low (87). 

Kiss (88.89) coupled a Chevenard-type thermobalance with a type DR 10 spectrophotometer the evolved gases from ihe thermobalance were passed through a 10-cm-long infrared cell. A meihod was developed in which either 

A standard method for determining solution kinetics of compounds that evolve gaseous products is to measure the amount of gas given off at constant pressure as a function of the amount of liquid displaced from a volumetric buret. Alternatively, it is possible to monitor the change in pressure at constant volume. Timberlake and Martin (125) have described an apparatus that 

The systems illustrated permit dissociation pressure measurements in the l-10(a)and 1CT3 - 10 s Torr (b) pressure ranges. In the former, the pressure 

---

For this class of thiazoles most of the chemical and physicochemical studies are centered around the protomeric equilibrium and its consequences. The position of this equilibrium may be determined by spectroscopic and titrimetric methods, as seen in each section. A simple HMO (Hiickel Molecular Orbitals) treatment of 2-substituted compounds however, may, exemplify general trends. This treatment considers only protomeric forms 1 and 2 evidence for the presence of form 3 has never been found. The formation energy reported in Table 1 is the energy difference in f3 units. 

Almost any chemical reaction can serve as a titrimetric method provided that three conditions are met. The first condition is that all reactions involving the titrant and analyte must be of known stoichiometry. If this is not the case, then the moles of titrant used in reaching the end point cannot tell us how much analyte is in our sample. Second, the titration reaction must occur rapidly. If we add titrant at a rate that is faster than the reaction s rate, then the end point will exceed the equivalence point by a significant amount. Finally, a suitable method must be available for determining the end point with an acceptable level of accuracy. These are significant limitations and, for this reason, several titration strategies are commonly used. 

Although each acid-base titrimetric method has its own unique considerations, the following description of the determination of protein in bread provides an instructive example of a typical procedure. 

An acid-base titrimetric method for determining the amount of nitrogen in organic compounds. 

---