Validation/Standardization: Why Drift Monitoring stays essential in OES

Production engineers rely on their understanding of measurement uncertainty and gauge capability to ensure reliable quality. In optical emission spectrometry (OES), stability and the ability to monitor and correct measurements are crucial for maintaining quality and meeting ISO certification requirements.

Spark OES analyzers generate certain amount of residues/waste material per each measurement and require regular (daily/weekly) cleaning, maintenance and drift control / corrections. Modern Laser OES systems reduce material consumption by a factor of 20, minimize drift, and allow significantly longer intervals (months/quaters) between checks. Nevertheless, drift control and correction samples remain indispensable to comply with ISO standards such as ISO 9001 or ISO/IEC 17025. This is one (amongst others) is one benefit, which makes Laser OES interesting, for an increasing number of applications. There, it  delivers substantial efficiency gains but does not replace the need for rigorous quality assurance.

Measurement Uncertainty and Gauge Capability

Measuring Device capability determines whether a measurement system is suitable in terms of repeatability, reproducibility, and stability for a given measurement task. Simplified:

Measurement device Capability = Tolerance / Measurement Uncertainty

Measurement uncertainty aggregates all potential sources of deviation—operator influence, instrument variability, environmental conditions, and the interval between drift control samples. Each factor should be minimized, considering costs, operator qualifications, and overall efficiency.

Spark OES: Material Loss and Drift

Spark OES spectrometers have been the standard in metal analysis for decades. They generate a plasma of approximately 5 mm³ under the sample via spark discharge. Each measurement causes material loss of around 1–10 mm³, which can deposit on electrodes and lenses, leading to signal deviations. Previously, frequent recalibration was required; today, measuring drift control and correction samples is sufficient to maintain stable calibration curves. For perspective: 10 mm³ of material loss equals about 78 mg of steel—roughly the size of a coarse sugar crystal.

Laser OES: Precision with Minimal Material Loss

Laser OES generates plasma via pulsed laser, offering greater precision, reproducibility, and a significantly smaller plasma volume. Each laser pulse consumes only about 0.000025 mm³ of material. A typical measurement uses hundreds of pulses, totaling 0.2–0.5 mm³ of material loss.

This equals roughly 3.9 mg of material—about the size of a dust particle, or 20 times less than spark OES.

Advantages:

• Minimal sample destruction

• Reduced contamination of electrodes and optical components

• No memory effect due to contactless measurement

Implications for Quality, Costs, and ISO Certification

Laser OES systems are less prone to drift and allow longer intervals between drift control and correction samples. In practice, slag analyzers can deliver stable measurements over months without daily intervention. Weekly monitoring is sufficient to ensure traceability of results—an essential factor for ISO certifications such as ISO 9001 and ISO/IEC 17025.

Business benefits include:

• Reduced downtime

• Lower personnel costs

• Greater audit security

• Minimized risk of ISO non-compliance

Future Outlook

Conventional spark OES spectrometers will remain relevant due to their mechanical design, high spectral resolution, and high light output—particularly for detecting trace elements. However, laser OES provides many advantages for most users: lower material loss, reduced drift, easier operation, and extended measurement intervals.

Conclusion

Laser OES significantly reduces material loss, maintenance, and drift. Nevertheless, regular checks remain mandatory. Quality assurance is not just about using advanced technology—it also requires demonstrating long-term reliability. Drift control and correction samples will continue to be a fundamental part of professional spectrometers, forming the backbone of any quality management system and the basis for ISO certification.