Measuring Veterinary Drugs in Meat Using Matrix Calibration and Standard Additions

Importance of the topic

Quantitative LC–MS analysis of veterinary drug residues in complex food matrices (e.g., meat) is challenged by matrix effects that can suppress or enhance analyte ionization, causing biased results. Reliable calibration strategies and automation of calibration/standard-addition procedures improve accuracy, throughput, and reduce operator error. This application note evaluates automated matrix‑matched calibration and standard addition using an Easy Injector workflow to mitigate matrix effects in the analysis of 25 veterinary drugs in meat extracts.

Objectives and overview of the study

The study aimed to demonstrate the Easy Injector workflows implemented in Agilent MassHunter for automated preparation of calibration dilutions and standard-addition samples on the 1290 Infinity III Multisampler, and to compare quantification performance for veterinary drugs using: (1) external calibration in solvent, (2) matrix‑matched calibration, and (3) automated standard addition. Key performance metrics included accuracy (recoveries) at 10 ppb and 1 ppb spiking levels and the capacity of automated workflows to simplify routine analysis.

Methodology

The workflow combined automated dilution and spiking by the Multisampler (Easy Injector) with LC–MS/MS detection on a triple‑quadrupole instrument. Calibration series were prepared automatically from a 500 ppb stock by 1:4 serial dilutions to yield points at 125, 31.25, 7.81, 1.95, and 0.488 ppb. For standard addition, individual samples were spiked in‑needle with two standard levels to give +1 and +10 ppb. A blank meat matrix extract was produced and used both for matrix‑matched calibration and as the sample background for spiking experiments. Data processing and quantitation (including automatic calculations for standard addition) were done in MassHunter Quantitative Analysis.

Used instrumentation

• Agilent 1290 Infinity III LC system components: High‑Speed Pump, Multisampler (G7167B), Multicolumn Thermostat.
• Agilent Ultivo triple quadrupole LC/MS with Agilent JetStream source; Dynamic MRM acquisition in positive polarity; instrument tuning provided unit resolution (0.7 amu).
• Software: Agilent MassHunter acquisition (v12.2), Qualitative Analysis (v12.0), Quantitative Analysis (v12.1) with Easy Injector workflow enabled.
• Column: Agilent InfinityLab Poroshell 120 Phenyl‑Hexyl, 2.1 × 150 mm, 1.9 µm at 40 °C.
• Solvents and reagents: 5 mM ammonium formate/0.1% formic acid in water (A) and methanol (B); ACN; DMSO; Na‑EDTA; Captiva EMR—Lipid cartridges for cleanup.
• Typical LC conditions: 0.5 mL/min, gradient 5% to 60% B at 6 min then to 100% B at 6.1 min, 7 min stop time, 3 min post time; injection volumes 1.0 µL (0.9 µL for standard addition).

Sample preparation (concise)

1. Weigh 2 g minced pork into a 50 mL tube; add 2 mL 0.1 M Na‑EDTA and shake.
2. Centrifuge; transfer supernatant. Extract residue with ACN/2% formic acid/2% DMSO; combine extracts and centrifuge.
3. Perform lipid removal with Captiva EMR—Lipid cartridge by gravity elution and a secondary 80:20 ACN/water elution; apply vacuum and combine aliquots with water before analysis.

The final blank matrix was post‑spiked to generate the test samples.

Main results and discussion

• Solvent calibration produced significant matrix biases: example sulfanilamide exhibited strong ion suppression (measured at ~20% of expected when using solvent calibration). Some analytes showed ion enhancement (~+20%).
• Matrix‑matched calibration largely compensated for these effects: for a 10 ppb spiked meat sample quantified with matrix calibration, recoveries were typically 95–105% across the 25 compounds, indicating accurate correction for matrix-induced suppression/enhancement.
• At low concentration (1 ppb), matrix effects became more pronounced. Matrix‑matched calibration improved quantification compared to solvent calibration, but some variability remained for certain analytes.
• Automated standard addition (in‑needle spiking to produce +1 and +10 ppb calibration points per sample) further improved accuracy at low levels; recoveries from automated standard addition were typically within 90–110% for the 1 ppb spiked samples.
• The Easy Injector workflow enabled fully automated generation of dilution series and per‑sample standard additions within the injection sequence, reducing manual handling and potential for error while accelerating setup.

Benefits and practical applications of the method

• Automation of calibration and standard addition reduces operator time and error, enabling higher sample throughput in routine monitoring of veterinary drug residues.
• Matrix‑matched calibration and standard addition provide robust strategies to mitigate matrix effects common in food matrices like meat, yielding reliable recoveries at regulatory-relevant levels.
• The approach is adaptable to multiclass residue analysis and integrates directly with existing LC–MS/MS platforms and data‑processing pipelines.

Future trends and possibilities of use

• Broader adoption of integrated injector workflows and on‑instrument sample manipulation can extend automation to more complex sample‑prep tasks and real‑time quality checks.
• Combining automated calibration/standard addition with isotopically labeled internal standards and advanced MRM scheduling could further improve sensitivity and precision at sub‑ppb levels.
• Application to other challenging matrices (dairy, plant, processed foods) and multiclass panels will expand utility for food safety laboratories and regulatory testing.
• Integration with laboratory information management systems (LIMS) and instrument orchestration will streamline compliance documentation and method traceability.

Conclusion

Automating calibration and standard addition using the Easy Injector workflows in conjunction with matrix‑matching substantially improves quantitative accuracy for multiclass veterinary drug analysis in meat by compensating for matrix effects. Matrix‑matched calibration delivered accurate recoveries at 10 ppb, while automated standard addition provided reliable results at low‑ppb levels. The workflow reduces manual preparation time and error potential, supporting robust routine residue testing.

References

1. Cakar A. Easy and Fast Automation of Sample Preparation. Agilent Technologies application note, publication number 5994-7703EN, 2025.
2. Zhao L., Lucas D. Multiclass Multiresidue Veterinary Drug Analysis in Beef Using Agilent Captiva EMR—Lipid Cartridge Cleanup and LC/MS/MS. Agilent Technologies application note, publication number 5991-8598EN, 2017.