Photometric and turbidimetric

TITRATIONS FOR COMPARISON OF METHODS. The automated photometric and turbidimetric methods were compared using 30 cm3 samples of surfactant solution containing a nominal 20 mol SDBS to give an equivalence volume of 5 cm3. The effect of salinity on the titrations was studied using samples prepared containing sodium chloride concentrations of 0.0, 0.14, 0.70 and 1.46 wt%. The influence of the choice of filter (580 or 620 nm) was also investigated. 

Titrimetry may also be classified by the nature of the endpoint measurement. The use of electrical measurements gives rise to potentiometric, ampero-metric, and coulometric titrations. Measurement of heat changes is used in thermometric titrimetry, and of absorbance in photometric and turbidimetric titrations. Radiometric titrations measure changes in radioactivity during the titration. All of these techniques are dealt with in other articles in this Encyclopedia. This article discusses only those titrations that use visual indicators. 

The dried gummy exudate from the stems and branches of Acacia Senegal and other A. species. Used as protective colloid to prevent settling of ppts. in some photometric and turbidimetric detns. Yellowish-amber lumps. Dissolves slowly in H2O. 

A typical photometric titration of SDBS against hyamine at low salinity is shown in Figure 3. It was noted, however, that the titration curve was "V" shaped and not the anticipated step curve. The turbidimetric titration of SDBS against hyamine afforded a curve, Figure 4, very similar to that for the photometric titration. 

Turbidimetric measurements are easily performed on photometers or spectrophotometers and require little optimization. The principal concern of turbidimetric measurements is signal-to-noise ratio. Photometric systems with electro-optical noise in the range of 0.0002 absorbance unit or less are useful for turbidity measurements. ... 

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