An automated viscometer based on high-precision flow injection analysis. Part I. Apparatus for high-precision flow injection analysis

Abstract

The development of an automated viscometer is described. It is a modified Ostwald viscometer in which the sample to be determined is injected into a suitable carrier stream flowing along a narrow-bore tube. The time taken for the sample to traverse a fixed distance is directly proportional to the viscosity. The sample size is typically 50 µl and the time of determination 30 s, with a precision of 0.2–0.3%, for samples of viscosity 0.2–190 cP (a greater range is attainable in principle by minor alteration of the tube parameters). It may be operated in the reverse mode by using a carrier stream of unknown viscosity and injecting a sample of known viscosity. In this way it way it may be used for continuous monitoring. A number of detectors have been devised and evaluated and several microcomputer systems have been employed in the development and these are described and discussed.

In order to obtain high precision, numerous theoretical and practical factors that affect the dispersion of the sample have been investigated. It is shown that it is critically dependent on chemical factors, such as hydrogen bonding between the sample and carrier, which is discussed in Part II. The instrumental factors that most critically affect the precision are shown to be as follows: the use of two detectors to measure the timing of flow-rate and the sample profile, thereby circumventing the role of the inlet valve as a timing device; the rate of data collection, about 100 points per peak being the optimum, together with a good data processing algorithm and control of the temperature to within ±0.1 °C.