Dual-Mode SEM Calibration Check Using Non-Analyte Ions
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Solution Overview
Problem
Dual-mode secondary electron multiplier (SEM) detectors in mass spectrometers experience drift in amplification factors due to aging effects, leading to inaccurate calibration and cross-calibration between counting and analogue modes, which affects the reliability of quantitative measurements over a wide dynamic range.
Innovation Solution
A method for checking and recalibrating the SEM detectors using non-analyte ions, such as argon ions, to ensure accurate calibration and cross-calibration without requiring user input, involving curve-fitting and adjustment of supply voltages to maintain the working point within an acceptance range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual-mode SEM detectors are used to achieve wide dynamic range, then measurement capability is improved, but calibration drift occurs due to aging effects
Solution Approach 1:
The patent applies preliminary action by performing rapid calibration checks at the beginning of measurement cycles using non-analyte ions (argon ions). This preliminary calibration establishes a baseline before actual sample analysis, allowing the system to detect and correct drift early in the measurement process rather than waiting for significant degradation to occur.
Solution Approach 2:
The patent implements feedback by continuously monitoring the calibration status using non-analyte ions and comparing measured values against reference values. When drift exceeds predetermined thresholds, the system automatically triggers recalibration procedures. This closed-loop feedback mechanism maintains calibration accuracy throughout extended measurement periods without requiring frequent manual intervention.
2Reliability
If frequent full calibrations are performed to maintain accuracy, then measurement reliability is improved, but instrument downtime increases
Solution Approach 1:
The patent applies partial action by implementing rapid calibration checks that use only non-analyte ions (argon ions) rather than performing complete calibrations with multiple standards and analytes. These partial calibration checks take only seconds to complete compared to minutes or hours for full calibrations, yet they are sufficient to detect drift and trigger full recalibration only when necessary, thereby maintaining instrument availability.
Solution Approach 2:
The patent enables self-service by automating the calibration check process using readily available argon ions from the plasma source itself. The system automatically performs calibration checks, compares results against stored reference values, and triggers recalibration procedures without requiring user intervention. This self-monitoring capability eliminates the need for manual calibration scheduling and reduces instrument downtime.
3Productivity
If calibration checks are performed without calibration samples, then productivity is improved, but measurement precision may be compromised
Solution Approach 1:
The patent uses non-analyte ions (argon ions) as an intermediary substance for calibration checks. These argon ions serve as a proxy standard that can be rapidly introduced and measured without requiring physical calibration samples. The argon signal provides a stable reference that correlates with detector performance, enabling quick calibration assessments that maintain sufficient accuracy for drift detection while avoiding the time-consuming process of preparing and analyzing actual calibration standards.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and reliable calibration and cross-calibration of SEM detectors, reducing downtime and ensuring accurate quantitative measurements over a wide dynamic range, even in the absence of a calibration sample, thereby enhancing the instrument's performance and reducing the need for frequent full calibrations.
Implementation Method 1
A secondary electron multiplier (SEM) detector is a type of detector which has surfaces coated with a secondary-emissive material. When an electron strikes the secondary-emissive material, secondary electrons are emitted.
Implementation Method 2
If multiple such structures are cascaded one after the other, then the generation of secondary electrons is repeated and the number of electrons can be increased many times such as by a factor of a million.
Implementation Method 3
Some systems have an additional electrometer mode that provides a further 3 to 4 orders of magnitude dynamic range, which is achieved by measuring the ion beam directly using a Faraday cup.
Data Source
AI summary
Methods of checking calibration of a dual-mode secondary electron multiplier (SEM) detector of a mass spectrometer using non-analyte ions comprise: recording, using a counting mode detector of the dual-mode SEM detector, a first count signal related to the number of non-analyte ions incident at the SEM detector at a working point voltage; offsetting the working point of the counting mode detector and recording second count signals related to the number of non-analyte ions incident at the SEM detector at respective two or more offset working point voltages; fitting a non-linear function to the first and second recorded count signals and values corresponding to the working point voltages; and determining that the calibration is valid if a rate of change of the non-linear function at the calibrated working point is within an acceptance range. A mass spectrometer configured to perform the method is also described.