Jenway 6715 - Manual (Page 166)

148
Good Practice Guidelines
Sample Size - the cuvette must be filled with solution. If sample volume is limited, the two-stage
uptake cycle can be used, i.e; sufficient sample is taken up to ultimately fill the cuvette, followed by air
during the second part of the uptake cycle. The sample will be drawn into the cuvette and only air will
occupy the tubing dead space leading to the cuvette.
Sample Characteristics – viscous samples may cause high levels of carryover. A simple test going
from a blank to a standard solution and back to a blank, will determine the degree of carryover.
With normal aqueous solutions it should be possible to keep this figure below 1%. If this cannot be
achieved and it is critical to the test, it may be necessary to include a wash cycle between samples.
System Cleaning – at the end of a sample run it is important to leave the system clean. This can
usually be achieved by pumping deionised water through the system. If the nature of the sample is
such that water will not adequately clean the system, other solvents may be used, providing they are
compatible with the components that will be contacted during cleaning, i.e; PTFE, glass and silicon
rubber tubing.
Pump tubing – the tubing has a finite life and will need to be changed when pumping rates decrease
to unacceptable levels, or the walls of the tubing stick together.
note: If left under roller pressure for prolonged periods, the pump tubing may not pump. In such
cases the tubing should be removed from the roller assembly and be reformed by hand. Normal
operation should be restored. This is not a sign of tube wear.
It is recommended that the tubing should be removed if the sipper pump is not being used for a
prolonged period.
Setting Up the Sipper Pump
There are three modes of operation:
1. independent 2. Segmented 3. Bi-Directional
1. independent
This is similar to the old continuous mode. Here operation of the sipper pump is via the switch on
the front of the accessory module. It can be switched on and off independently of the measurement
functions of the spectrophotometer.
This is the simplest mode of operation and can be used to take up samples from bulk containers or as
a bypass from a flow or pipeline.
Measurements may be made on the flowing sample using the auto-log function or the pump switched
off and measurement on the stopped flow be made manually on the instrument.
This mode is also useful for checking the cuvette and tubing for correct and leak free connection.
No other options are available with this mode selected.
2. Segmented
This mode uses the programmability feature to take up a controlled volume of each sample in a
sequential manner. This chain of sample segments can be broken up, by inserting an air (or wash)
segment between each. If air (or wash) is not needed, this option is set to zero during calibration.
This can be controlled by using the switch on the front of the accessory module or the touch screen
of the instrument, depending on the
Automatic Sip setting and the instrument measurement mode
selected. The sample always moves forward from the container to the waste receptacle.
3. Bi-Directional
This is identical to the segmented mode, but here the sample is returned to the original container, i.e;
pump direction is reversed during the drain sequence.