Characterization and Improvement of Signal Drift Associated with Electron Ionization Quadrupole Mass Spectrometry

Abstract

Quadrupole mass spectrometry with electron ionization (EI-QMS) is a very popular detection technique in combination with gas chromatography. It is deployed for the analysis of volatile and semivolatile analytes in many industry domains. Although a very important factor for quantitative analysis, little is known about the stability of ion source performance. Only a few papers and patents report possible signal instabilities due to sample adsorption, degradation, or insulating deposits on the hot stainless steel surface of the ion source. In this study, a conventional stainless steel ion source was used to investigate possible signal drifts. It was observed that the EI-QMS instrument indeed suffered from continuous signal instability. It was found that the key parts which are responsible for the signal instabilities are those that regulate the ion beam toward the mass analyzer: the repeller, exit plate, and focusing lenses. The voltage of the repeller was found to have a major influence on the signal stability. The surface of the repeller, exit plate, and focusing lenses was modified by applying a gold coating. It was demonstrated that the signal stability of the MS dramatically improved when using the gold-coated parts. The contribution of each part to the stability improvement was quantitatively determined and compared with the standard stainless steel source performance. It was assumed that the signal drift observed with the stainless steel EI source originated from charge buildup on the surfaces. This hypothesis was supported by software simulations.

Separating $${^{39}\hbox {Ar}}$$ from $${^{40}\hbox {Ar}}$$ by cryogenic distillation with Aria for dark-matter searches

“…Indeed, a small offset in the measured isotope ratio to the natural isotopic composition of nitrogen at the start of the run, on the order of 1 × 10 −3 , was observed, together with a linear decrease in time of 1.6 × 10 −6 h −1 . We attribute the latter effect to a signal drift of the mass spectrometer (an effect which can partly be explained by the instrument sensitivity to atmospheric conditions, which is also observed in other quadrupole mass spectrometers; see for instance [16]). For this calibration, since we did not fully understand the ori-gin of the signal drift, we used two correction methods, one based on the ratio and one on the difference between the natural and the measured isotopic ratio values.…”

Quantitative mass spectrometry methods for pharmaceutical analysis

“…Because most GC-MS experiments are performed using electron ionization (EI) and many analysts are not aware of the signal drift that can occur using this type of ionization, the reliability of some results may be questionable. D'Autry et al [85] demonstrated that when stainless steel was used in the EI source, the MS signal decreased in consecutive runs. This error could be countered with an internal standard, but experiments showed a various drift pattern for different homologous compounds.…”

“…The use of isotopically labelled internal standards therefore seems insufficient to correct for signal drift when high accuracy levels are required to perform quantitative analysis. It was demonstrated that conventional EI sources should rather be modified by applying a gold coating to obtain reliable data [85]. Alternatively, a different ionization source can be used.…”

Boosting the Detection Potential of Liquid Chromatography-Electron Ionization Mass Spectrometry Using a Ceramic Coated Ion Source

“…In fact, it has been reported that certain surface activities and contamination can induce anomalies in EI mass spectra, depending on matrix complexity, ion source temperature and cleanliness, analyte concentration, and other factors. Adsorption and thermal degradation on the metal surface of the ion source can cause peak tailing and reduce the chromatographic response as well, especially for low-volatility, thermally sensitive, and polar compounds [1][2][3]. This phenomenon is often underestimated, though it has a dramatic impact on sensitivity and reproducibility.…”