Functionality of turbidity measurement under changing water quality and environmental conditions.

Turbidity is one of the key water quality parameters in environmental monitoring, water treatment or industrial process operation. Turbidity is however very challenging to measure reliably due to the many factors affecting the reading and functionality of the measurement device. In this paper, the results of the experiments to study the effects of changes in water quality and environmental condition to the readings of turbidity measurement devices are presented. The experiments were carried out in stable laboratory conditions where controlled changes were made to water pH, the temperature, salinity, colour, environment brightness and the mixing speed of the water. The study showed that even though the actual turbidity of the water remained constant the changes in other variables caused in the worst-case significant disturbances to the turbidity measurements. This knowledge is vital, for instance in monitoring or developing a robust model for forecasting regional turbidity in natural waters.

Continuous direct tablet compression: effects of impeller rotation rate, total feed rate and drug content on the tablet properties and drug release.

CONTEXT: Continuous processing is becoming popular in the pharmaceutical industry for its cost and quality advantages. OBJECTIVE: This study evaluated the mechanical properties, uniformity of dosage units and drug release from the tablets prepared by continuous direct compression process. MATERIALS AND METHODS: The tablet formulations consisted of acetaminophen (3-30% (w/w)) pre-blended with 0.25% (w/w) colloidal silicon dioxide, microcrystalline cellulose (69-96% (w/w)) and magnesium stearate (1% (w/w)). The continuous tableting line consisted of three loss-in-weight feeders and a convective continuous mixer and a rotary tablet press. The process continued for 8 min and steady state was reached within 5 min. The effects of acetaminophen content, impeller rotation rate (39-254 rpm) and total feed rate (15 and 20 kg/h) on tablet properties were examined. RESULTS AND DISCUSSION: All the tablets complied with the friability requirements of European Pharmacopoeia and rapidly released acetaminophen. However, the relative standard deviation of acetaminophen content (10% (w/w)) increased with an increase in impeller rotation rate at a constant total feed rate (20 kg/h). A compression force of 12 kN tended to result in greater tablet hardness and subsequently a slower initial acetaminophen release from tablets when compared with those made with the compression force of about 8 kN. CONCLUSIONS: In conclusion, tablets could be successfully prepared by a continuous direct compression process and process conditions affected to some extent tablet properties.