Rapid Determination of Alkalinity (Ammonia Content) in Para Rubber Latex Using Portable and Fourier Transform-Near Infrared Spectrometers

Abstract

Ammonia (NH 3 ) is the main preservative that is added to field and concentrated latices to prevent the deterioration of properties and, in serious cases, coagulation of latex. Almost all factories monitor NH 3 content or alkalinity during processing, as it is an important parameter for trading purposes. Alkalinity is determined by the standard analytical method, acid-based titration, as detailed in ISO 125:2011(E) Natural Rubber Latex Concentrate – Determination of Alkalinity. This method requires a skilled analyst and also the use of chemicals. In addition, the titration involves the subjective determination of the end-point, which may vary with each analyst. Near infrared (NIR) spectroscopy, a rapid, non-chemical and repeatable method, was used in this work. Calibration equations for predicting alkalinity were constructed from the relationship between the absorbance spectra of latex (measured using a portable NIR and a Fourier transform (FT)-NIR spectrometer) and the alkalinity content of the latex. It was found that the best equation obtained using the portable and the FT-NIR spectrometer could be used to predict alkalinity in latex with a coefficient of determination, standard error of prediction and ratio of standard error of validation to the standard deviation of 0.63, 0.101% and 1.62, and 0.97, 0.027% and 6.07, respectively. From the statistics testing for performance measurement as detailed in ISO12099:2010, NIR-predicted values were no different from actual values at the 95% confident interval. Moreover, the best equation obtained from the more reliable calibration achieved using the FT-NIR spectrometer is attributed to the longer wavelength range.