Introduces the measurement methods of signal, noise, and detection limits in high and low background noise conditions.
This document is a technical note from Agilent Technologies addressing the challenges of determining detection limits in modern mass spectrometry. It defines key terms such as instrument background signal, noise, analyte signal, and signal-to-noise ratio. The text highlights that traditional methods based on single signal-to-noise measurements can be difficult or impossible in ultra-low noise modes like high resolution mass spectrometry or tandem MS.
The document further distinguishes between the Instrument Detection Limit (IDL) and the Method Detection Limit (MDL). It explains that while IDL relates to the signal distinguishable from system noise, MDL accounts for additional errors introduced by sample preparation steps like extraction and concentration. The note also discusses the Limit of Quantification (LOQ) and Practical Limit of Quantification (POL), noting that POL is often practically defined as 5-10 times the MDL.
IDL is the analyte concentration required to produce a signal distinguishable from the noise level of a blank, whereas MDL includes all steps of the analysis, such as extraction and concentration, which can increase the measured detection limit.
The POL is often practically defined simply as about 5-10 times the MDL.
Modern mass spectrometers can operate in modes with very low background noise, sometimes resulting in essentially zero noise, which makes the traditional comparison of performance based on signal-to-noise increasingly difficult or impossible.