A Guide to Achieving Top Accuracy with an OES Spectrometer

A quick and accurate way for foundries to measure the exact chemical composition of the materials during their melt processes is Optical Emission Spectrometry (OES), but this speed and accuracy mean that spectrometers are also extremely sensitive.

The performance of an OES can start to suffer without frequent maintenance, verification, and recalibration. When a business relies on maintaining tight control over the exact chemical composition and the quality of their end products, inaccurate analysis is an issue that must be combated quickly.

Spark spectrometers use relative instead of absolute measurements, so it is crucial to get the quantity or concentration of the analyzed substance correct. This is where certified reference materials (CRMs) and calibration come in. For various reasons, the standard calibration of the instrument may not fulfill your accuracy requirements. A Type Standardization may be needed to get the accuracy of your OES analyzer to the level you need.

Is a Type Standardization Required?

If deviations are still being seen despite being calibrated to a lot of CRMs then there are a number of reasons why this could be occurring:

  • Alloys on the more exotic end of the spectrum can often deviate strongly from the matrix material.
  • The majority of CRMs are manufactured synthetically. This means it is not guaranteed that they will correspond to the composition or structure of the sample being analyzed.

The status of an analyzer could also be the problem, too much could be asked of an OES by wanting a level of accuracy that is actually above the calibration of the instrument. The effect of drift, which is the slow change in instrument sensitivity, can also distort results over time.

Hitachi High-Tech’s range of optical omission spectrometers has a total wavelength coverage of between 130 and 800 nm, meaning it is really easy to detect the early indicators of potentially disruptive drift. So that correction occurs during each analysis, monitoring the spectral positions of all relevant channels is also automated.

Whilst such measures increase the stability of their OES analyzers greatly, even they are not immune to the requirement for an occasional type standardization. This can be identified quickly so that operational disruption is kept to a minimum if daily control samples are used to keep a detailed eye on a spectrometer’s performance.

The Benefits of Type Standardization

Type Standardization can help you attain a bigger improvement in the accuracy of OES results on top of a standard calibration if your OES is affected by any of the factors outlined above. Though it is important to remember that it is only valid for the correction of unknown materials which are still similar in composition to the standardization sample.

To really fine-tune the calculation, the process should be carried out just before running one or more samples of an alloy type. After the right kind of samples are obtained, the optimal level of accuracy of the basic calibration with the CRMs should be checked before beginning. The user must be sure that there are a lot of recently prepared and easy to measure materials ready to go, as would be normal when utilizing control samples for a recalibration.

For all its advantages, Type Standardization should not be utilized as a global correction technique to analyze materials with significantly different chemical composition (hence it is named Type Standardization).

Understanding how an analyzer works and the factors that can affect it over the long term is crucial to achieving the optimum performance from an OES. An OES analyzer’s sensitivity is one of its key strengths, but if an operator is not careful it can also lead to distorted results.

Hitachi High-Tech OES analyzers are built to be durable and stable. If control samples are used to monitor the performance of your spectrometer regularly, the underlying stability should mean that any imbalances can be corrected before they get to the stage where complete Type Standardization is needed. With over 45 years of expertise, the Hitachi High-Tech range of OES analyzers is made to add value to industrial operations instead of slowing them down.

This information has been sourced, reviewed and adapted from materials provided by Hitachi High-Tech Analytical Science.

For more information on this source, please visit Hitachi High-Tech Analytical Science.

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