Determining average frequency of series of pulses

Abstract

A method and apparatus for determining an average frequency of a series of ion detection pulses in a spectrometer may be applied to a measurement interval. The method may include determining a duration of an auxiliary interval, where the auxiliary interval overlaps the measurement interval, the auxiliary interval starting at a last pulse (P0) before the measurement interval, and the auxiliary interval ending at a last pulse within the measurement interval. The method may further include determining a number of pulses during the auxiliary interval and dividing the number of pulses by the duration of the auxiliary interval to produce the average frequency. The method can be applied to a series of ion pulses generated by a voltage-frequency converter connected to a Faraday cup.

Description

technical field [0001] The present invention relates to determining the average frequency of a series of pulses, such as detection pulses. More particularly, the present invention relates to a method and an apparatus for determining the average frequency of a series of pulses, such as pulses generated by a voltage-to-frequency converter, in particular in response to a detector signal pulse. The invention further relates to an instrument, such as a mass spectrometer, comprising at least one voltage-to-frequency converter. Background technique [0002] In mass spectrometry, various detectors are known for detecting ions. The detected ions have typically been filtered and / or separated according to the mass-to-charge ratio (m / z) of the ions. In a typical multipole mass spectrometer, multiple rods (eg, quadrupoles or hexapoles) can be scanned across a range of m / z values. For each m / z value (or subrange of m / z values), the number of ions is determined. Therefore, the numbers...

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Problems solved by technology

This means that the measurement interval will not end until the end of the last integration period, creating a dead time during which ion pulses from some detectors may not be counted

This may result in a loss of accuracy

Also, this dead time wastes valuable measurement time

Since multiple consecutive measurement intervals are often used to determine the number of ions, the time penalty can become significant, especially when a detector that receives a large number of ions (and thus pulses at small intervals) is compared to a detector that receives a small number of ions (and thus pulses at large intervals). When the detectors that generate pulses at intervals) are used in parallel

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