ASTM D7593—Analysis of Diesel for In-Service Motor Oils

Importance of Topic

Diesel fuel intrusion into engine lubricants serves as an early warning of component wear and impending failure. Reliable quantification of diesel in used lubricating oils is essential for maintenance planning, cost control, and prevention of catastrophic breakdowns. ASTM D7593, based on capillary gas chromatography with backflush, delivers rapid and accurate diesel contamination measurements.

Objectives and Study Overview

This study evaluates the analytical equivalence between two Agilent gas chromatographs—the Intuvo 9000 and the 7890 series—when applying ASTM D7593. Key goals include comparing backflush timing, calibration linearity, precision across replicate injections, and overall method robustness without modifying established parameters.

Methodology and Instrumentation

The method requires no sample pretreatment: standards and in-service motor oil samples are injected directly. A backflush timing standard containing 10 mg/mL eicosane in carbon disulfide defines the ejection point for heavy oil components.

• Instrumentation (Intuvo 9000):
• Syringe: 0.5 µL autosampler type
• Inlet: split/splitless with ultra-inert liner (glass wool)
• Flowpath modules: Inlet Flow Chip, Guard Chip, post-column backflush chip
• Analytical column: DB-1UI, 15 m × 0.25 mm, 0.25 µm
• Carrier gas: Helium, 47.6 psig (3.5 mL/min)
• Detector: Flame ionization at 350 °C
• Temperature program: Column oven held at 225 °C; backflush initiated at 1.49 min

Key Results and Discussion

Backflush timing on both systems was effectively identical (Intuvo at 1.49 min vs 7890 at 1.45 min), demonstrating comparable fluidic performance despite different hardware. Calibration using three diesel-oil standards (2 %, 5 %, 10 % w/w) yielded linearity coefficients of R² = 1.000 (Intuvo) and R² = 0.9992 (7890), well above the 0.998 requirement.

Five in-service lubricants were analyzed in ten consecutive injections on each GC. Mean diesel contents and relative standard deviations for each sample were virtually indistinguishable between instruments, confirming precision and accuracy equivalence.

Benefits and Practical Applications

Introducing the Intuvo 9000 for ASTM D7593 analysis offers:

• Unchanged method conditions and validated performance versus an established GC platform
• Simplified backflush module installation and maintenance through smart flowpath design
• Rapid turnaround and minimal carryover, enabling high-throughput routine monitoring

Future Trends and Opportunities

Advancements may include full integration of automated flowpath diagnostics, real-time data analytics for trend monitoring, adaptation to alternative fuel blends, and field-deployable GC units for on-site oil surveillance.

Conclusions

The Agilent Intuvo 9000 GC reliably replicates the 7890 series performance for diesel contamination analysis in motor oils under ASTM D7593. Equivalent backflush timing, calibration linearity, and measurement precision were achieved without modifying the established method, underscoring Intuvo’s fitness for routine engine oil diagnostics.

References

1. ASTM D7593-14, Standard Test Method for Determination of Fuel Dilution for In-Service Engine Oils by Gas Chromatography, ASTM International, 2014
2. Beard K.; McCurry J., Gas Chromatographic Analysis of Diesel Fuel Dilution for In-Service Motor Oil Using ASTM Method D7593, Agilent Technologies Application Note 5991-9278EN, 2018