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

Abstract

Ammonia (NH3) 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 NH3 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.