Sensitive Detection of PAHs Using the Agilent 1290 Infinity III Fluorescence Detector

Sensitive Detection of PAHs Using the Agilent 1290 Infinity III Fluorescence Detector — Summary

Significance of the topic

Polycyclic aromatic hydrocarbons (PAHs) are persistent, hydrophobic environmental contaminants with several members known to be mutagenic or carcinogenic. Their occurrence in water, soil, food, and industrial streams at trace levels requires analytical approaches combining high sensitivity, selectivity, and speed. Fluorescence detection after chromatographic separation is advantageous because many PAHs are strongly fluorescent, allowing selective, low-background measurements and wavelength-specific optimization for individual analytes.

Objectives and study overview

• Demonstrate the analytical performance of the Agilent 1290 Infinity III Fluorescence Detector (FLD) for a 16‑component PAH standard mixture under UHPLC conditions.
• Optimize excitation and emission wavelengths for individual PAHs using online spectral scans and exploit the FLD’s fast wavelength switching to measure each compound at its fluorescence optimum within high‑speed separations.
• Evaluate chromatographic precision, linear dynamic range (LDR), limits of detection (LOD) and quantification (LOQ), and the system’s ability to achieve ultrahigh sensitivity (sub‑fg level on column for anthracene).

Methodology and instrumentation

• Chromatography: UHPLC separations using Agilent ZORBAX RRHD Eclipse Plus PAH columns (2.1 × 50 mm and 2.1 × 100 mm, 1.8 µm). Gradient and fast short‑column methods were developed to separate 16 PAHs within a 4‑minute UHPLC run and a longer 12‑minute gradient for LDR studies.
• Detector and acquisition: Agilent 1290 Infinity III Fluorescence Detector with capability for rapid excitation/emission spectral scans, fast wavelength switching, selectable PMT gain (Standard/High), and two flow cell options (standard 2 µL low‑dispersion cell and a high‑volume 13 µL cell for maximum sensitivity). Data rates up to 80 Hz were used to secure sufficient points per peak in UHPLC mode.
• Hardware: 1290 Infinity III High‑Speed Pump, Multisampler, Multicolumn Thermostat; Low Dispersion Kit to minimize extra‑column volume.
• Standards and solvents: 16‑PAH mixture standard and anthracene reference; Agilent InfinityLab acetonitrile and water for HPLC.
• Wavelength optimization: Online emission scans (e.g., excitation at 250 nm, emission 270–800 nm) followed by excitation scans (e.g., emission fixed at compound optimum) to select per‑compound Ex/Em pairs used during fast switching.
• Calibration and sensitivity testing: Serial dilutions across wide ranges to determine LDR, LOQ (S/N = 10) and LOD (S/N = 3). Special anthracene dilution series (down to sub‑fg on column) to probe ultimate sensitivity with the 13 µL cell and high PMT.

Instrumentation

• Agilent 1290 Infinity III High‑Speed Pump (G7120A)
• Agilent 1290 Infinity III Multisampler (G7167B)
• Agilent 1290 Infinity III Multicolumn Thermostat (G7116B)
• Agilent 1290 Infinity III Fluorescence Detector (G7123B)
• Agilent ZORBAX RRHD Eclipse Plus PAH Columns (2.1 × 50 mm and 2.1 × 100 mm, 1.8 µm)
• Agilent OpenLab CDS software (v2.8); Agilent Low Dispersion Kit and two FLD flow cells (2 µL, 13 µL)

Main results and discussion

• Wavelength optimization: Online emission/excitation scanning provided optimal Ex/Em settings for each PAH; these values were implemented as timed wavelength switches during UHPLC runs to maximize sensitivity for each analyte.
• Fast wavelength switching: The FLD demonstrated switching times around 120 ms, sufficient to apply individual Ex/Em pairs to closely eluting PAHs without loss of chromatographic fidelity. An 80 Hz data rate produced adequate points per peak for UHPLC separations.
• UHPLC performance: A fast 4‑minute separation of all 16 PAHs was achieved using the short 2.1 × 50 mm column at 0.9 mL/min and 30 °C. Retention time RSDs were typically below 0.05% and peak area RSDs generally below 0.9%, indicating excellent run‑to‑run precision suitable for quantitative workflows.
• High sensitivity: Using the 13 µL flow cell and high PMT gain, anthracene produced a calibration linear down to sub‑fg on column with R² = 0.99971. Calculated LOD (S/N = 3) was below 1 fg on column, demonstrating ultrahigh sensitivity potential for targeted analytes.
• Linear dynamic range and LOQs: For the 16 PAHs, linear dynamic ranges exceeded five decades for most compounds and reached over six decades for several (e.g., anthracene, pyrene, fluorene). Typical LOQs fell into the low ng/L region; benzo(a)pyrene—an important regulatory marker—exhibited an LDR of ~5.5 decades, LOQ ~19 ng/L, and R² ≈ 0.99987.

Practical benefits and applications

• High sensitivity and selectivity: Fluorescence detection with per‑compound Ex/Em optimization minimizes matrix interference and achieves trace‑level detection suitable for environmental monitoring and food safety testing.
• Speed and throughput: Sub‑5‑minute UHPLC separations combined with fast wavelength switching permit high sample throughput without compromising resolution or quantitative precision.
• Method development support: Online spectral scans simplify identification of optimal excitation/emission pairs, accelerating method setup for new PAH targets or matrices.
• Versatility: Exchangeable flow cells and adjustable PMT gain allow the same platform to be tuned for routine quantification (standard cell, standard gain) or extreme sensitivity tasks (13 µL cell, high gain).

Future trends and potential applications

• Expanded targeted panels: The approach can be extended to broader PAH panels or other fluorescent contaminants by leveraging automated spectral scans and timed wavelength lists.
• Environmental and regulatory monitoring: The combination of low LOQs and wide LDR supports regulatory compliance testing where both trace detection and quantitation across orders of magnitude are required.
• Coupling with sample preparation automation: Integration with automated extraction and concentration workflows (e.g., SPE, SPME) will enhance throughput while maintaining low LODs for complex matrices.
• Data analytics and unattended operation: High data rates and reproducible switching enable robust algorithms for peak deconvolution, compound ID, and automated quality control in high‑throughput labs.

Conclusion

The Agilent 1290 Infinity III Fluorescence Detector, combined with UHPLC‑compatible low‑dispersion hardware and optimized Ex/Em settings, delivers rapid, precise, and highly sensitive PAH analysis. Fast wavelength switching and high data rates support quantitation of closely eluting compounds at their fluorescence optima. The system achieves exceptional analytical figures of merit: retention time RSDs <0.05%, peak area RSDs typically <1%, linear dynamic ranges exceeding five decades for most PAHs, and ultralow LODs (sub‑fg on column for anthracene using the high‑volume cell and elevated PMT gain). These attributes make the platform well suited for environmental surveillance, industrial process control, and high‑sensitivity research applications.

References

1. Agilent ZORBAX Rapid Resolution High Definition Eclipse PAH Threaded Columns. Agilent Technologies data sheet, publication number 820210-018, 2011.
2. Wiese S.; Teutenberg T.; Hoffmann B.; Naegele E. High Throughput Method Development for PAHs using the Agilent 1290 Infinity LC system and a ZORBAX Eclipse PAH column. Agilent Technologies application note, publication number 5990-5007EN, 2009.