37
Experimental Instrumentation:
In both experiments the instrumentation used was a Thermo Scientific TRACE GC with DSQII Mass Spectrometer detector (Austin, USA).
Experiment 1 – Removing the front part of the column
Column(s):
1. Thermo Scientific TraceGOLD TG-5SILMS 30m x 0.25mm x 0.25µm (ThermoScientific, Runcorn, UK)
2. Thermo Scientific TraceGOLD TG-5SILMS 30m x 0.25mm x 0.25µm with SafeGuard (10m)
The experimental conditions used were as follows;
Carrier gas: Helium, set at a constant flow rate of 1.2mL/min.
The injection mode was splitless at a temperature of 300°C, with a splitless time of 1.5 minutes, after which the split valve was opened at a ratio of 100:1. The injection volume used was 1µL.
The oven temperature was initially held at 80°C for 1 minute, then ramped at 40°C/min to 200°C where the ramp rate was reduced to 15°C/min until the temperature reached 325°C where it was finally held for 3 minutes.
To determine the effect of cleaning the column by removing the front end, 13 metres was removed from both configurations. This is clearly an excessive amount of column removed in one go, however it replicates what would happen in many laboratories where over a period of time the column will be gradually reduced in length by removal of the front part of the column. The performance of both columns was then compared to identify which approach would give the better data, either using just the column or using the column and the column with integrated guard.
Method 2 – Integrated vs press fitted Experimental Columns:
1. Thermo Scientific TraceGOLD TG-WAXMS 30m x 0.25mm x 0.25µm with SafeGuard 5m
2. Thermo Scientific TraceGOLD TG-WAXMS 30m x 0.25mm x 0.25µm
with TraceGOLD capillary guard column 5m x 0.25mm connected with a column union
The experimental conditions used were as follows;
Figure 1 & 2:The effect of cutting the top of the column to simulate removing contamination with and without an integrated guard column.
Carrier gas: Helium set at a constant flow rate of 1.0 mL/min.
The injection mode was split, using a ratio of 20:1, with the injector temperature set at 250°C. 1 µL of sample was injected onto the system for each arrangement of columns used.
The oven temperature was initially held for 1 minute at 100°C and then increased at 10°C/min until the temperature reached 250°C where it was held for a further 4 minutes.
Results Experiment 1
Figures 1 and 2 show the resultant chromatograms obtained after 13 metres of each column had been removed. Initially the column performance was exactly the same, as was to be expected. However, once a substantial part of the columns had been removed there was a difference in the performance of the two columns. The actual amount of column removed is equivalent to more than 40% of the initial 30 metre
Experiment 2
Figure 3 shows the resultant chromatogram obtained from analysing the toothpaste sample using the two different columns under investigation. It can be seen from these chromatograms that the performance of the integrated column is better than that obtained using the separate guard column as there is a significant improvement in the signal to noise ratio, by almost a factor of two.
column. In this experiment a 21% loss in resolution was observed when monitoring the critical pair of phenanthrene and pyrene (Figures 1, 2).
However, when the same amount of column length was removed from the column with the integrated guard there was only a 9% loss in resolution between the critical pairs. It is worth noting that removing 13 metres of the integrated column actually removed all of the guard column and 3 metres of the active part of the column that is coated with stationary phase.
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