Agilent Single Quad 5975 GCMS CI Installation Video
Introduction
In this video we will go over CI installation and tuning of the single quad. We will first cover a hardware overview including the CI installation kit, then we will cover the CI tunes and checkout samples. Lastly we will cover common problems and solutions.
CI Hardware
To setup CI you must first install the CI hardware. The next item is to hookup and purge the gas connections and then condition the system before autotuning and running the checkout sample.
Here is the cut out of the CI source. Please see the source video for more in depth information. Special note is the installation of an interface tip seal for CI mode.
CI setup requires the CI flow module. The flow module is a self contained assembly that is easily installed on the top of the manifold. After mounting the CI flow assembly, connections to the CI tranferline and CI gas supply will need to be made.
CI operation
CI gas first enters the back of the CI flow module. it then goes through a two way selection valve. Two valves are present to allow for the setup of 2 different CI gasses. The Gas then goes through a mass flow controller that regulates the CI gas flow between 1 and 5 milliliters a minute.
Introduction of the CI gas into the mass spectrometer is controlled by an isolation valve that allows the CI gas to flow into the one eighth inch tube contained in the Ci transferline. Addition of tuning compound into the flow path is done by opening the Calibration valve contained in the flow module.
The CI gas exiting the flow module goes through a one eighth inch tube here. The gas flow flows into the MS through the tip seal and into the source. The tip seal is spring loaded to help seal the transferline to the source.
CI gas flows are set as a percentage of the maximum flow in the chemstation or mass hunter software. In the case of PCI and methane, the default flow rate of 20 percent is used. Since the maximum flow rate is 5 milliliters a second, this translates to a flow rate of approximately 1 milliliter a minute.
CI Calibrant
Because the PFTBA that is used to calibrate the Mass spectrometer in EI mode is not ideal for CI mode, a special calibrant is used. It is abbreviated PFDTD and it's chemical structure is shown in this slide. Unlike PFTBA, it has a strong ion response below mass 302 and pumps away quickly when the calibrant valve is turned off.
CI Startup and Tuning
Typical CI startup procedure is to first qualify the Mass Spectrometer using EI first. Then vent the system and install the CI source including the tip seal. After allowing adequate time to both pump down and purge the CI lines, the PCI or NCI tune is run.
The file PCICH4 dot U is the tuning file used for PCI. When this method is loaded in chemstation, the system will automatically configure the method for CI. When the method is first loaded in the chemstation or mass hunter software, the system goes through an automatic purge of the CI lines. The system should always be checked out using CI with methane before switching to another type of CI gas.
Here is a profile of the reagent gas of methane. Note the strong peaks at 17, 29 and 41. Also note the presence of water in the system at mass 19. It will normally be present when the system is first pumped down but should slowly decrease with time.
Here is a table showing the different reagent ions used with three diffent common CI gasses. For Isobutane the reagent ions observed will be 39, 43 and 57. Flow can be adjusted by increasing the flow and observing the ratio of mass 57 to 43. When the flow is properly adjusted the ratio should be between 5 and 15. When using ammonia, ions at 18, 35 and 52 should be observed. Adjusting the ratio of 18 to 35 from .03 to .1 will result in proper flow.
Here is the absolute pressures as measured when the flow rate is optimized. Note that for PCI methane, the typical flow is around 20 to 30 percent. For NCI methane, the typical optimum flow rate is at 60 percent.
Troubleshooting CI
A common problem in CI can be leaks. It is important to first make sure that the system shows acceptable air water values in EI before switching to CI. Also, failure to install the Interface seal will result in inadequate source pressure and failure to create CI ions. It is important to make sure that the inlet pressure on the back of the flow module is correct for the type of CI gas being used. For methane, a pressure of 20 PSI is recommended. A dirty source can also be a problem, resulting in poor peak shapes and weak signals during the tuning processes.
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