Transmittance Turbidimetry

Determining Concentration by Turbidimetry In turbidimetry the measured transmittance, T, is the ratio of the transmitted intensity of the source radiation, fy, to the intensity of source radiation transmitted by a blank, Iq. 

Spectroscopic measurements may also involve the scattering of light by a particulate form of the analyte, fn turbidimetry, the decrease in the radiation s transmittance through the sample is measured and related to the analyte s concentration through Beer s law. fn nephelometry we measure the intensity of scattered radiation, which varies linearly with the analyte s concentration. 

Turbidimetry is ideally suited to detect the temperature at which a transparent polymer solution turns opaque. The temperature corresponding to the onset of the increase of the scattered light intensity is usually taken as the cloud-point temperature, TcP, although some authors define the cloud point as the temperature for which the transmittance is 80% (or 90%) of the initial value. This technique is commonly known as the cloud-point method [199]. Turbidimetry was employed, for instance, to show that the cloud-point temperature of aqueous PNIPAM solutions does not depend significantly on the molar mass of the polymer [150]. 

In a comparative study, we assessed the average values of PLA domain diameters in IPNs by turbidimetry using UV-visible spectroscopy. The turbidity r of an IPN sample was determined from the measurement of its transmittance Tr at 460 nm, and calculated according to the Beer-Lambert law as follows r = -In (Tr) / e, where e is the sample thickness (2 mm). Then, following Blundell s pioneering study on a system constituted of domains of PMMA embedded in a polyurethane matrix (19), we applied his theoretical expression to our IPN systems to estimate the average size of PLA microdomains dispersed within the PMMA matrix. Thus, the t value led to the calculation of the parameter Bfy) as shown in eq 1 ... 

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