The Cecil range of UV/visible spectrophotometers includes models designed for student teaching, routine analysis, quality control applications and cutting-edge research.
Its instruments are widely used across a huge range of industry sectors, water analysis to food and beverage analysis, and from life science analyses to the determination of chemicals, as well as for pharmaceutical product development.
Spectrophotometers operate on the principle of UV or visible light absorption to measure levels of chemicals present in a liquid sample.
Cecil's spectrophotometers offer the advantage of an automated sipper system to transfer a discrete amount of liquid under investigation from its sample container to the sample beam ready for testing.
Accurate delivery
The instruments can draw in samples at regular, pre-set intervals, delivering accurate and consistent amounts of liquid to the sample beam without any human intervention.
With the instruments often working with very low volumes of sample, frequently involving harsh and aggressive chemicals, the accuracy and reliability of the pump is critical to the effectiveness of the instrument.
“In many applications, the amount of sample available for testing can be very small. For example, it is not untypical in hospital or clinical testing, for the instruments to be working on samples of just a few hundred microlitres.
“For the results of comparative tests to be meaningful, we have to be able to guarantee that consistent volumes of sample are delivered every time. In addition, we have to consider that many of the chemicals under test can be very aggressive. Our instruments have a reputation for quality and reliability, so the ability of the pump to operate under demanding conditions is paramount,“ said a spokesman.
High precision, low flow
To meet these requirements, the company employs Watson-Marlow 100 Series OEM pumps in its spectrophotometers.
These high precision, low-flow peristaltic pumps have become almost a de facto standard across the world for applications such as fermentation systems and scientific equipment, and for Cecil Instruments they combine the required accuracy and good chemical resistance with extreme reliability and ease of use (Fig. 1).
In peristaltic pumps, liquid is drawn into a tube and pushed through by the action of rollers squeezing and releasing the tube.
Because nothing but the tube is ever in contact with the fluid, there is no risk of the fluid contaminating the pump, or of the pump contaminating the fluid.
Preventing backflow
The design also prevents backflow, so eliminating the need for check valves when the pump is not running.
Accuracy of the delivered volume and flow rate are parameters which can be fully tailored through the size of the pump, the speed of the rotating rollers and the tube diameter.
The 102R pumpheads used by Cecil Instruments accept, without adjustment, all Watson-Marlow tubing from 0.5 mm to 4.8 mm internal diameter, with 1.6 mm wall thickness.
They have a spring-loaded, two-roller rotor and are suitable for continuous use up to 65 rpm to provide flow rates up to 106 ml/min, or for intermittent use up to 130 rpm for flow rates up to 212 ml/min.
All 102R pumpheads have a choice of mounting points and a shatterproof clear polycarbonate guard which is hinged to allow easy access for tube changing.
The 102R may be driven in either direction: clockwise rotation will give a longer tube life but anticlockwise rotation can be used for working against greater pressures. It is available with a choice of track material and rotor springs and is suitable for either a 6mm or 8mm drive shaft if mounted on users' own drive.
Snap-in connectors can be supplied in place of the sprung tube clamps.
“The accuracy of flow rate and sample delivery are extremely good, whilst the operating principle of the pumps negates the effects of any precipitation that might take place is the liquid vessels.
“At the same time, the 100 Series pumps are very reliable, easy to maintain and easy to control, which is essential as our typical users are chemists and biologists, not engineers,“ added the spokesman.
Cecil's options for its spectrophotometers extend to complete tablet dissolution systems. For example, a pharmaceutical company developing a new controlled release product would want to test the rate of release of the drug over time.
The tablet would be released into a vessel of chemicals that mimic the human stomach, and at predetermined intervals a sample of the vessel would be drawn into the spectrophotometer to measure the absorbance of the drug.
These tests could run over a period of several hours or more, so an automated process is of real benefit.
Minimising alteration
In this application, accurate control of flow rate is vital. A fast flow minimises any alteration of the drug whilst the sample is in transit to the test station, whilst consistent flow from sample to sample ensures that any alteration that does take place is a constant rather than an unknown variable. Thus the flow rate accuracy of the Watson-Marlow pumps is of real benefit.
Further, the norm with such controlled release investigations is to run multiple dissolution channels at once, often using up to eight vessels.
Watson-Marlow offers an eight-channel version of the pump that is ideal for this. With a single pump operating on eight channels, the overall package is extremely compact, whilst offering consistent flow across all channels.
A typical experiment would use six vessels, each containing a tablet, a seventh vessel as a control, and the eighth would be empty, meaning that the pump was running dry on one channel. This ability to run dry without any implications for reduced lifespan is another key benefit.
