U.S. Patent 7,700,913
The DART® source utilizes inert carrier gas containing either metastable atoms or molecules to ionize molecules present in close proximity to the exit of the DART® gun. The flow of this carrier gas is perturbed as it strikes the surface. Due to vacuum restrictions, most LC/MS instruments collect only a small fraction of this carrier gas. We designed VAPUR® to collect more of the desorption gas containing ions and transfer it to the API inlet region where the ions can enter the mass spectrometer.
We have designed and implemented the VAPUR® atmospheric pressure interface to improve collection of ions desorbed from the surface by collimating them for transfer into the MS. The VAPUR® has significantly improved performance of our Direct Analysis in Real Time (DART®) desorption ionization sources.
In the VAPUR®, a relatively large open tube, the entrance tube, is placed between the desorption ionization region and the API-inlet of the LC/MS. The outlet of this tube is placed in close proximity to the API-inlet. A small gap is provided between the entrance tube and API-inlet so that suction from a low capacity vacuum pump can be used to evacuate the region.
The function of the pump is to suction more of the gas containing ions and molecules desorbed from the sample into closer proximity to the instrument API inlet. The pumping strips away the carrier gas so that the pressure of the mass spectrometer can be kept in its normal operating range. The VAPUR® also collects ions and carrier gas while reducing the volume of oxygen present in the atmosphere around the sample, reducing the loss of ions that might otherwise interact with oxygen, becoming neutrals.
In practice, the VAPUR® interface has improved the quantitative capability of the DART® ionization system. Evidence of this is shown in the following figures where the repeat injection of rat plasma containing the drug compound Verapamil was used to demonstrate the reproducibility of sampling and overall sensitivity and quantitative capability.
Significant improvement in overall sample to sample reproducibility.
The VAPUR® interface has reduced the consumption of the DART® carrier gas, which is most commonly helium, from 4 - 6 L/min to 1 - 2 L/min allowing the end user to save on operating costs.