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Ms-NoVentTM5 minute GC/MS Column Changeover
Overall Oven Layout of the ms-NoVentTM Changing a capillary column connected to a mass spectrometer normally requires shutting down the MS, cooling the ion source and venting the vacuum system. This is necessary to avoid damaging the MS system. After the column has been changed, the system must be pumped back down to low vacuum and the system allowed to stabilize for several hours. The entire process can take from 3 hours to overnight in order to remove water and achieve the optimum MS performance.
In the normal operating mode, the purge gas is turned OFF. In the change over mode, a purge gas of 3 psi is applied to the system with a purge leak rate to atmosphere of approximately 30 ml/min. The ms-NoVentTM allows a capillary column to be changed without venting the MS and the mass spectrometer can be operational almost immediately. The ms-NoVentTM is simple to install and operate. The ms-NoVentTM consists of an oven interface fitting connected directly to the existing transfer line interface on the MS. A fused silica transfer line (specific in length and inside diameter for the vacuum system of the particular MS) fits inside the interface. This transfer line is designed to restrict the gas flow that can be pulled into the ion source, allowing a low pressure to be maintained in the system. On the oven side of the fused silica restrictor, a "Flow Director Orifice" ensures that there is a flow in only one direction, preventing air from being drawn into the MS vacuum system. The result is that only pure helium can enter the MS while the column is being changed. With ms-NoVentTM, installing a new capillary column simply involves turning "ON" the helium purge gas via a convenient ms NoVentTM control module, then disconnecting the column. There is no time limit on how long the MS vacuum system can be left open. A new capillary column could then be conditioned ready for use, while the ms- NoVentTM continually purges the MS transfer line inlet with helium. After reconnecting the GC column the helium purge gas to the ms-NoVentTM is turned "OFF".
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