Evaluation of Mass Accuracy Robustness for the Agilent InfinityLab Pro iQ Plus

Significance of the topic

Reliable detection and accurate mass assignment of small-molecule toxicology targets are essential in high-throughput clinical, forensic, and QA/QC laboratories. Single‑quadrupole LC/MS systems are widely used because of their cost, robustness, and throughput, but they are limited by unit mass resolution and systemic mass biases. Demonstrating sustained instrument robustness and practical strategies to improve mass accuracy on such platforms supports confident compound identification across large sample batches without frequent recalibration or maintenance.

Objectives and overview of the study

The study evaluated the long‑term robustness and mass accuracy of the Agilent InfinityLab Pro iQ Plus single‑quadrupole mass detector coupled to an Agilent 1260 Infinity II LC system. Key goals were to:

• Assess chromatographic signal stability across 1,150 sequential injections without intermediate cleaning or retuning.
• Monitor raw mass accuracy and quantify improvements achievable by postacquisition spectral calibration using Cerno Bioscience MassWorks software.
• Demonstrate a practical workflow for periodic infusion‑based calibration during a long injection sequence.

Methodology

Samples and standards: A commercial toxicology checkout mix was prepared at two concentrations (10 pg/µL and 100 pg/µL) in 60:40 water:methanol. Mobile phases were water with 2 mM ammonium formate/0.1% formic acid (A) and methanol with 0.1% formic acid (B).

Chromatography and acquisition: Separations used an Agilent ZORBAX RRHD Eclipse Plus C18 (2.1 × 50 mm, 1.8 µm) with a 6 min gradient, 0.5 mL/min flow, 1 µL injection, and 60 °C column temperature. The method combined full scans (m/z 100–1,000) and selected ion monitoring (SIM) for nine target compounds. Two isomeric targets (phentermine and methamphetamine) could not be baseline differentiated by mass and were consolidated for reporting.

Mass spectrometry and calibration protocol: The Pro iQ Plus with Agilent Jet Stream source operated in positive polarity. During the robustness sequence, 1,150 low‑concentration injections (10 pg/µL) were performed; after each block of 50 low‑conc injections, a single 100 pg/µL standard was injected followed by a 0.5 min infusion of an ESI‑L tuning solution to provide calibrant ions. Cerno MassWorks TrueCal was used postacquisition to compute spectral/mass corrections using four selected calibrant ions across m/z 100–1,000. A total of 23 calibration infusions were applied across the dataset and corrections were propagated to corresponding runs.

Instrumentation used

• Agilent 1260 Infinity II LC system (Clinical Edition): binary pump, multisampler, and multicolumn thermostat.
• Agilent ZORBAX RRHD Eclipse Plus C18 column (2.1 × 50 mm, 1.8 µm).
• Agilent InfinityLab Pro iQ Plus single‑quadrupole mass detector (G6170A) with Agilent Jet Stream (AJS) ion source.
• Data systems: Agilent OpenLab CDS v2.8 and Agilent MassHunter Quantitative Analysis v12.0.
• Postacquisition calibration software: Cerno Bioscience MassWorks v7.0.0.3, using Agilent ESI‑L LC/MS tuning solution as calibrant.

Main results and discussion

Chromatographic stability: Across the full 1,150 injections, peak areas for the monitored toxicology components showed low variability. Most compounds exhibited %RSDs in the range of ~4–7% after blocks of 50 injections; overall the study reported peak area RSDs below 10% for analyzed components, indicating minimal signal drift for high‑throughput sequences. Some gradual loss of signal for a subset of analytes was attributed to column aging rather than MS instability.

Raw mass performance: Before postacquisition correction, calibrant ions (e.g., m/z 622.0290 and 922.0098) showed average mass errors of approximately 14.6 and 16.2 mDa (≈23–26 ppm), with %RSDs below 12% and no systematic increase of error over the injection series. This indicates consistent mass bias but limited absolute accuracy typical of unit‑resolution quadrupoles (~±0.1 Da nominally).

Improvement with MassWorks calibration: Applying MassWorks TrueCal reduced observed mass errors substantially. For example, diazepam error decreased from ~42.3 mDa (uncorrected) to ~8.39 mDa after correction (≈5‑fold improvement). Across analytes, corrected average mass errors were commonly sub‑25 mDa, representing roughly a threefold enhancement relative to raw data. Importantly, corrected mass errors remained stable across the 1,150 injections, supporting the practicality of periodic infusion calibration during long runs.

Benefits and practical applications of the method

• High‑throughput toxicology screening: The workflow supports many consecutive injections with stable response and reliable mass assignment, reducing downtime and retuning frequency.
• Cost‑effective mass accuracy enhancement: Postacquisition spectral calibration enables single‑quadrupole platforms to approach mass accuracies useful for confident compound confirmation without upgrading to high‑resolution hardware.
• Operational simplicity: Using periodic postrun infusion of a tuning mix automates tracking of mass bias across batches and enables batch‑specific correction.

Future trends and possibilities for use

Anticipated directions and opportunities include:

• Tighter integration of real‑time lock‑mass or continuous calibrant infusion in routine LC/MS workflows to minimize postprocessing needs.
• Wider adoption of spectral‑calibration software to extract higher confidence identifications from unit‑resolution instruments, combined with curated spectral libraries tailored to forensic/toxicology targets.
• Combining improved software correction with modest hardware advances (e.g., enhanced source stability, drift compensation) to further close the gap to high‑resolution platforms for routine screening.
• Machine‑learning approaches for automated detection of instrument drift, column degradation, and adaptive calibration schedules to maximize uptime and data quality.

Conclusion

The Agilent InfinityLab Pro iQ Plus single‑quadrupole detector demonstrated robust, repeatable performance across 1,150 sequential injections with low chromatographic variability and consistent mass bias. Applying Cerno MassWorks postacquisition calibration significantly reduced mass error (commonly to sub‑25 mDa, with examples <10 mDa), enabling improved confidence in compound identification on a unit‑resolution system. The reported infusion‑based calibration workflow provides a practical, low‑cost route to enhanced mass accuracy suitable for high‑throughput toxicology and routine analytical laboratories.

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