Signal Drift in Liquid Chromatography Tandem Mass Spectrometry and Its Internal Standard Calibration Strategy for Quantitative Analysis

Abstract

The present project studied the signal drift in liquid chromatography tandem mass spectrometry (LC-MS/MS) and proposed a strategy for compensating such drift. In the study, four 4-component groups were repeatedly run on different LC-MS/MS systems for over 12 h to investigate the dependence of signal drift on time and hardware systems. The 4-component groups each consisted of (1) an analyte, (2) a stable isotope labeled analyte, (3) a compound with similar structure to the analyte, and (4) a compound with dissimilar structure. All of the species showed significant signal drift, generally more than 25% over 12 h. The analyte and its stable isotope labeled analog always have the same drifting pattern including the trends and direction from one LC-MS/MS system to another. Signal drift was also found to be concentration dependent. Our experiments further proved that a conventional stable isotope labeled internal standard in LC-MS/MS quantification would not compensate the variations caused by concentration-dependent signal drift. An ideal internal standard for LC-MS/MS has both identical structure and similar concentration to the analyte. For that, we proposed a new internal standard strategy, pseudo internal standard (Pseudo IS), for LC-MS/MS quantification. Pseudo IS could effectively compensate signal drift in spite of its significant time, system, and concentration dependencies.

Equilibration for Electrospray Ionization Mass Spectrometry in Quantitative Analysis

“…The reason is that the response drift can be significantly concentration dependent. At this time, due to the concentration difference between the internal standard and the analyte, their response drift will be inconsistent, and the calibration may fail . Therefore, even with the use of isotope internal standards, analysts still need to consider reasonable measures to avoid the impact of response variation on quantitative analysis.…”

“…At this time, due to the concentration difference between the internal standard and the analyte, their response drift will be inconsistent, and the calibration may fail. 12 Therefore, even with the use of isotope internal standards, analysts still need to consider reasonable measures to avoid the impact of response variation on quantitative analysis. ESI-MS equilibration matching the instrument state and compound is obviously easier and more practical.…”

“…Of even greater concern is that the instability of electrospray ionization is more pronounced during the initial stages of instrument operation. Response drift caused by electrospray ionization variation can affect the validity of raw data and may ultimately affect the correctness of conclusions, setting a challenge for ESI-MS quantification. , …”

“…Response drift caused by electrospray ionization variation can affect the validity of raw data and may ultimately affect the correctness of conclusions, setting a challenge for ESI-MS quantification. 11,12 As a general rule, before high-performance liquid chromatography with UV (HPLC-UV) is used, the column requires a specific equilibration time. Besides, the deuterium lamp needs to be preheated for 30−60 min until the baseline is stable.…”

Guide to Semi-Quantitative Non-Targeted Screening Using LC/ESI/HRMS

“…Additionally, QC samples, i.e., analysis of samples spiked with known concentrations of analytes, can be used to evaluate the stability of the instrument, both the within-day and day-to-day performance, and can also account for drift in signal. [62,63] This is especially important during long analyzes, as signal have been shown to drift over ±25% during a 12 h run [64]. For more details on quality control in non-targeted screening see recent reviews by Knolhoff et al [65] and Schultze et al [66].…”