MS is fast, Very, Very fast ! analyse in just 10ms, make multiple component analyses in seconds, monitor multiple components on multiple inlets in just 4 minutes, try doing that with your GC!
Mass spectrometer analysers are fast, with a capillary inlet system, 5 to 95% transient steps have a response time of <120mS. A single mass may be analysed in just 10mS making MS one off the fastest analytical techniques available.
No need to sacrifice stability !
The Speed advantage can be used in a number of ways:
Since the capillary inlet offers a rapid response to step changes and the acquisition time for a signal is very short, it is possible to trend a number of individual masses in a very short acquisition phase. For example, 10 individual masses could be acquire in just 100mS per sample. This high speed acquisition allows close analogous trends to be displayed for very rapid reactions.
Many process control loops are very time critical, examples of this include Syn.Gas generation in Ammonium Nitrate production and Polyethylene Reactor gas phase control.
Both of these applications can be tackled by GC but require a sampling time of between 10 and 20 minutes respectively. The equivalent cycle time on MS would be just 2 seconds ! This means that gas phase control is very accurate and reactors or processes are not "Flying Blind" wasting resources whilst the process awaits the next GC update.
Since MS analysis is so fast, it is easily possible to have the instrument switch around a number of sample points taking a short analysis on each one. Addition of our Navigator™ multiple gas stream selector unit allows the MS to automatically sample from up to 20 different inlet points.
Since up to 64 individual masses can be measured on any given sample point and the type of analysis at any given sample point is able to change as the sample point switches, a single MS analyser can replace large numbers of discreet analysers with no loss of time resolution.
Example:
In a typical polyethylene reactor, the gas phase control may require monitoring of ten analytes. This could be achieved over 8 reactors with each reactor being fully updated every 4 minutes.
It is also possible to switch inlets in any sequential order or an order of priority which places a higher monitoring requirement on a particular inlet. Thus, all inlets are updated with certain "priority" inlets being sampled more frequently.
In order to provide ultra-low detection levels for Brewery Gas and Ambient Monitoring applications, we employ a linked technique Thermal Desorption-Mass Spectrometer system .
The TD pre concentrates a batch of sample gas for a fixed period, this increases the volume of any trapped sample available for analysis at the MS inlet. Since a given trapped volume will result in a given volume increase for any trapped component, there is a direct relationship between trapped volume, concentration of sample within the trapped volume and the intensity at the MS inlet.
In practice, a total cycle time of around 8 minutes produce a sufficient sample step to give ppt detection. This is much faster than GC without pre-concentration at around 15 to 20 minutes per sample. Since it is also unlikely that a straight GC could achieve these detection limits, it would be necessary to run TD-GC with a cycle time of around 25 to 30 minutes. These techniques are too slow to pick up short emission profiles which are "smoothed out" by the long cycle time.
| System | Cycle Time | Samples per Hr./ Day | Detection Limit | |
| UniSys-A TD-MS | 8 mins | 7.5 / 180 | PPT | |
| GC Only | 15-20 mins | 4 or 3 / 96 or 72 | PPB | |
| TD-GC | 25-30 mins | 2 / 48 | PPT |
