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Use of a Low Resolution Mass Spectrometer to Separately Determine Impurities Having the Same Nominal Mass

IP.com Disclosure Number: IPCOM000019381D
Publication Date: 2003-Sep-12
Document File: 3 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

Quantitative determination of compounds with the same nominal masses has not been possible on a continuous real time basis using a low resolution mass selective detector, like a quadrupole. The classical example of this is nitrogen and carbon monoxide which both have a nominal mass of 28. Another example is carbon dioxide and nitrous oxide which have a nominal mass of 44. The response which is obtained at these masses is due to the presence of both compounds. In order to separate the response from both compounds a high resolution mass spectrometer needs to be used. However, this increases both the expense and the complexity of the analytical instrument. In many instances it is important to obtain the data on a continuous basis using a low resolution mass selective analyzer in order to fully characterize various processes. Another reason for using this type of detector is for the unique high sensitivity achievable with an instrument such as an Atmospheric Pressure Ionization Mass Spectrometer (APIMS).

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Use of a Low Resolution Mass Spectrometer to Separately Determine Impurities

Having the Same Nominal Mass

Quantitative determination of compounds with the same nominal masses has not been possible on a continuous real time basis using a low resolution mass selective detector, like a quadrupole. The classical example of this is nitrogen and carbon monoxide which both have a nominal mass of 28. Another example is carbon dioxide and nitrous oxide which have a nominal mass of 44. The response which is obtained at these masses is due to the presence of both compounds. In order to separate the response from both compounds a high resolution mass spectrometer needs to be used. However, this increases both the expense and the complexity of the analytical instrument. In many instances it is important to obtain the data on a continuous basis using a low resolution mass selective analyzer in order to fully characterize various processes. Another reason for using this type of detector is for the unique high sensitivity achievable with an instrument such as an Atmospheric Pressure Ionization Mass Spectrometer (APIMS).

If the data are obtained in a continuous fashion, then the concentrations are given as an upper bound for each species. In the case of nitrogen and carbon monoxide, the entire signal at mass 28 is attributed to each compound. The response is multiplied by the appropriate response factors for nitrogen and carbon monoxide to yield the maximum concentration of each species which could be present in the sample. This solution gives the worst case scenario and does not necessarily provide accurate concentrations. Another approach to solving this problem is to use a different analytical technique to determine the concentration of one of the two compounds. Then the signal from the mass selective detector contributed by this species is determined by dividing its mass selective monitor calibration response by the concentration determined by the secondary technique. This signal is then subtracted from the total signal to yield the signal from the second compound. This is then multiplied by its mass selective detector response factor to yield its concentration. One limitation to this method is that two instruments are required. Also, the second analyzer is typically a non-continuous detector such as a gas chromatograph. Another disadvantages occurs when an APIMS is used for high sensitivity. Since the secondary analyzer does have the same or better sensitivity than the APIMS, the advantage of the very low limit-of-detection achievable with the APIMS is lost. A third approach is not to use a mass selective detector at all. Disadvantages for this situation include lower sensitivity, non-continuous data, and non-conformational structural data which is typically obtained with a mass selective analyzer.

We report a novel way to simultaneously and continuously monitor compounds with the same nominal masses using a low resolution mass selective detector. In ess...