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What kind of purity gas to choose for a second-hand gas chromatograph is indeed a more complicated issu.
In principle, the choice of gas purity depends primarily on the object of analysis; the packing in the column; the detecto.
We recommend that the gas with higher purity be selected as much as possible under the premise of meeting the analysis requirement.
This will not only improve (maintain) the high sensitivity of the instrument, but also prolong the life of the chromatographic column and the entire instrument (gas control components, gas filters.
Adverse effects of low purity of auxiliary gas on second-hand gas chromatographs According to the analysis object, the type of chromatographic column, the gear of the operating instrument and the specific detector, if the low-purity gas that does not meet the requirements is used, the adverse effects may be as follows: 1) Chromatographic column failure: H2O and CO2 deactivate the molecular sieve column, H2O gas decomposes the polyester fixative, and O2 breaks the PEG chai.
2) Distortion or disappearance of the sample: For example, H2O gas hydrolyzes the chlorosilicon sample; 3) Influence on the retention characteristics of the column: For example, the retention index of H2O on hydrophilic fixatives such as polyethylene glycol will increase, and in the carrier gas When the oxygen content is too high, the retention characteristics of the polar or non-polar stationary liquid column will change, and the longer the use time, the greater the impac.
4) Sometimes some gas impurities interact with the stationary liquid to generate false peaks; the impact on the detector FID: especially when operating at Dt≤1Ⅹ10ˉ⒒/sec, organic impurities such as CH4 will cause the base flow to surge, and the noise will increas.
Microanalysis is not possibl.
TCD: The signal-to-noise ratio is reduced, zero adjustment is impossible, the linearity is narrowed, the correction factor in the literature cannot be used, and the oxygen content is too large, which will accelerate the aging of the components at high temperatures and reduce the lifespa.
ECD: The oxygen and water in the carrier gas have a great influence on the normal operation of the detecto.
In different power supply working modes, the pulse power supply has a greater impact than the DC voltage power supply, and the fixed base current pulse modulation power supply has a greater impact than the pulse power suppl.
This is the reason why the carrier gas purity selector switch must be turned from "standard nitrogen" to "normal nitrogen" when the carrier gas purity is low when operating a fixed base flow pulse-modulated EC.
You will find that in this case, not only the sensitivity becomes lower, but also the linearity becomes narrowe.
Practice has proved that when the ECD is operated, the water content in the carrier gas is lower than 02ppm, and the ideal performance can be achieved when the oxygen is lower than 1pp.
It is worth pointing out that we have found many times that the secondary pollution of the carrier gas caused by the contamination of the regulating gas circuit system of the instrument greatly increases the fundamental frequency of the ECD and reduces the signal-to-noise rati.
Commonly used detectors such as FPD and NPD, because they are selective detectors, should be operated according to the analysis requirements, and special attention should be paid to the removal of impurities in the detected sensitive substance.
6) During the temperature-programmed operation, some impurities in the carrier gas will remain in the chromatographic column at low temperatur.
When the temperature increases, it will not only cause the baseline drift, but also may appear wider "false peaks" on the spectru.
.Effects on other parts of the gas phase .
All kinds of filters are accelerated to fail; .
The gas circuit system is pollute.
To restore the instrument to operate under high sensitivity, sometimes it needs to be purged for a long time (maybe more than a week) when the pollution is serious Sometimes it can't be recovered anymor.
.
The regulating valve (pressure-stabilizing valve, steady-flow valve, needle valve) is polluted, the air resistance is blocked, the adjustment accuracy is reduced or fails; .
The life of the detector, practice shows that it has a significant impact on the life of ECD and TCD, and should be draw the user's attentio.
In principle, the choice of gas purity depends primarily on the object of analysis; the packing in the column; the detecto.
We recommend that the gas with higher purity be selected as much as possible under the premise of meeting the analysis requirement.
This will not only improve (maintain) the high sensitivity of the instrument, but also prolong the life of the chromatographic column and the entire instrument (gas control components, gas filters.
Adverse effects of low purity of auxiliary gas on second-hand gas chromatographs According to the analysis object, the type of chromatographic column, the gear of the operating instrument and the specific detector, if the low-purity gas that does not meet the requirements is used, the adverse effects may be as follows: 1) Chromatographic column failure: H2O and CO2 deactivate the molecular sieve column, H2O gas decomposes the polyester fixative, and O2 breaks the PEG chai.
2) Distortion or disappearance of the sample: For example, H2O gas hydrolyzes the chlorosilicon sample; 3) Influence on the retention characteristics of the column: For example, the retention index of H2O on hydrophilic fixatives such as polyethylene glycol will increase, and in the carrier gas When the oxygen content is too high, the retention characteristics of the polar or non-polar stationary liquid column will change, and the longer the use time, the greater the impac.
4) Sometimes some gas impurities interact with the stationary liquid to generate false peaks; the impact on the detector FID: especially when operating at Dt≤1Ⅹ10ˉ⒒/sec, organic impurities such as CH4 will cause the base flow to surge, and the noise will increas.
Microanalysis is not possibl.
TCD: The signal-to-noise ratio is reduced, zero adjustment is impossible, the linearity is narrowed, the correction factor in the literature cannot be used, and the oxygen content is too large, which will accelerate the aging of the components at high temperatures and reduce the lifespa.
ECD: The oxygen and water in the carrier gas have a great influence on the normal operation of the detecto.
In different power supply working modes, the pulse power supply has a greater impact than the DC voltage power supply, and the fixed base current pulse modulation power supply has a greater impact than the pulse power suppl.
This is the reason why the carrier gas purity selector switch must be turned from "standard nitrogen" to "normal nitrogen" when the carrier gas purity is low when operating a fixed base flow pulse-modulated EC.
You will find that in this case, not only the sensitivity becomes lower, but also the linearity becomes narrowe.
Practice has proved that when the ECD is operated, the water content in the carrier gas is lower than 02ppm, and the ideal performance can be achieved when the oxygen is lower than 1pp.
It is worth pointing out that we have found many times that the secondary pollution of the carrier gas caused by the contamination of the regulating gas circuit system of the instrument greatly increases the fundamental frequency of the ECD and reduces the signal-to-noise rati.
Commonly used detectors such as FPD and NPD, because they are selective detectors, should be operated according to the analysis requirements, and special attention should be paid to the removal of impurities in the detected sensitive substance.
6) During the temperature-programmed operation, some impurities in the carrier gas will remain in the chromatographic column at low temperatur.
When the temperature increases, it will not only cause the baseline drift, but also may appear wider "false peaks" on the spectru.
.Effects on other parts of the gas phase .
All kinds of filters are accelerated to fail; .
The gas circuit system is pollute.
To restore the instrument to operate under high sensitivity, sometimes it needs to be purged for a long time (maybe more than a week) when the pollution is serious Sometimes it can't be recovered anymor.
.
The regulating valve (pressure-stabilizing valve, steady-flow valve, needle valve) is polluted, the air resistance is blocked, the adjustment accuracy is reduced or fails; .
The life of the detector, practice shows that it has a significant impact on the life of ECD and TCD, and should be draw the user's attentio.
