Until recently freeze-dried (lyophilised) vials were checked for vacuum using a spark test which would make the glass glow if a vacuum is present. Due to the relatively long testing time required for energising the vial (especially amber) this method of test became unsuitable as production speeds increased. A revolutionary method has now been developed by analysing the head space pressure inside a vial using laser absorption spectroscopy. Laser absorption spectroscopy is an optical measurement method for rapid and non-destructive gas analysis.
Light from a near-infrared semiconductor laser is tuned to match the internal vibrating frequency of the moisture molecule. The rays are passed through the headspace region of a container. Energy from the laser is absorbed by the target molecules and thus begin to vibrate. The light is then scanned in frequency and detected by a photo detector. Using spectroscopy the absorption curve is analysed whereby information about the headspace gas concentration and total headspace pressure is calculated. If no energy was absorbed then it would mean that the target molecule was not present. The amount of energy absorbed depends on the amount of target molecules present in the container under test.
The LVA machine utilises one laser head and may achieve outputs of up to 500cpm depending on the type of container. The colour or glass type of the vial under test does not influence the result. An indication of the actual vacuum level is also detemined and displayed. The LVA machine is fully computerised utilising a SCADA platform. The software is easy to operate and includes utilities such as a products database, statistical reports, etc. A printer is also installed for printing test results and parameters. The machine includes an auto self-test system using calibrated check vials whereby the machine is self-challenged as frequently as desired to assure 100% reliability.