Photometric titrations advantages

One of the major advantages of photometric titrations is the ease with which the sensitivity of the measurements can be changed simply by changing... 

Photometric titrations are advantageous because the data from several measurements are used to determine the end-point, which results in a more accurate analysis. As only a change in absorbance is being measured, the presence of any other absorbing species will not interfere with the result obtained. Photometric titrations are popular for determining the amount of a metal ion in solution. 

Lippi et. al (87) and Dirstine (88) circumvented titration by converting the liberated fatty acids into copper salts, which after extraction in chloroform are reacted with diethyldithio-carbamate to form a colored complex which is measured photometrically. While the end point appears to be more sensitive than the pH end point determination, the advantages are outweighed by the additional steps of solvent extraction, centrifugation and incomplete extraction when low concentrations of copper salts are present. Other substrates used for the measurement of lipase activity have been tributyrin ( ), phenyl laurate (90), p-nit ro-pheny1-stearate and 3-naphthyl laurate (91). It has been shown that these substrates are hydrolyzed by esterases and thus lack specificity for lipase. Studies on patients with pancreatitis indicate olive oil emulsion is definitely superior to water soluble esters as substrates for measuring serum lipase activity. 

The prime advantage of polarisation titrations is the ability to handle reactions of poor equihbrium constant. This stems from the location of the endpoint by extrapolation to intersection from either side of the endpoint zone. This ability renders the method capable of carrying out titrations not easily possible by the potentiometric method. This characteristic is shared with other titration techniques (e.g., conductometric, photometric). 

There are numerous automatic titrators that employ potentiometric end-point detection. They usually can automatically record the first or second derivative of the titration curve and read out the end-point volume. The sample is placed in the titration vessel, and the titrant, drawn from a reservoir, is placed in a syringe-driven buret. The volume is digitally read from the displacement of the syringe plunger by the electronic driver. Titrators may also employ photometric detection of indicator color changes. An automatic titrator is shown in Figure 14.7. Automatic titrators make volumetric analyses rapid, reproducible, and convenient. While instrumental methods provide many advantages, classical volumetric analyses are still widely used and are very useful, especially for major constituents, for example, in the pharmaceutical industry. 

The photometric end point has been applied lo many types of reactions. For example, most standard oxidizing agents have characteristic absorption spectra and thus produce photometrically detectable end points. Although standard acids or bases not absorb, the introduction of acid-base indicators permits photoineiric neutralization titrations. The photometric end point ha.s also been used to gicat advantage in titrations with F.DTA (cthylenediaiiiinetciraacetic... 

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