Performance Testing For Instrumentation

Timothy J. Alavosus, VHG Labs, Inc.
Tags: oil analysis

In the wear metals testing laboratory, as in all laboratories, significant time is devoted to the quality of the analyses. Laboratory management strives to ensure that the instrumentation is properly calibrated by performing proper routine maintenance, running quality control (QC) standards at regular intervals, training our operators and chemists thoroughly - all to ensure results are as accurate and reproducible as possible.

However, running a sample requires a lot more than simply loading up the autosampler and pressing "Go". Sample preparation (usually dilution), instrument operation and vigilance are necessary to ensure that everything is running properly. While desirable, it would be a difficult task to maintain continuous monitoring of all of the variables involved during an analysis.

Figure 1. Type in your results, then submit.

The use of QC standards, although important, does not illustrate the entire picture. It does, however, answer the question: "Relative to the calibration curve, are the QC results repeatable?" Even if this occurs, it does not prove an analysis is accurate. Some method of monitoring the lab operations is needed to show that all of the lab processes (sample preparation, instrument setup and operation, and analytical methods) are in order and ensure that instrument readings are in agreement with external standards.

Performance Testing
The VHG Labs Inc. Performance Testing Program (PTP) provides benefits, and is designed as an external method of validating laboratory methods for three important analytical techniques: spectrographic elemental analysis (ICP (inductively coupled plasma), and also DCP and RDE), viscosity and particle counting.

Many laboratories rely on their own instrument calibration techniques as their sole method of verifying calibration. This can lead to a near-sighted approach to optimizing laboratory performance. Accordingly, most tribology labs would benefit from a PTP. Tribology is the science of the mechanisms of friction, lubrication, and wear of interacting surfaces that are in relative motion and includes oil analysis.

While the calibration of individual spectrometers is assumed to be accurate based on correlation to known standard reference materials (SRMs), a bias from one instrument to another of the same general type can exist based upon:

  • Design (different manufacturer or model)

  • Operating parameters

  • Methodology

  • Conditions used

  • Environmental factors

  • Operator

It is therefore useful to employ a program that regularly determines the relative correlation of one or more instruments within the same laboratory facility, different facilities or international locations, via the use of a correlation to externally certified standard reference materials (CRMs).

This type of program is often used by large companies with several labs to determine the value and relative validity of data produced. It is also used by individual laboratories to determine any biases or trends in results over time (as well as in correlation with other laboratories using the same techniques). Small or independent labs also utilize these programs to confirm instrument performance over time.

Performance testing should be performed on a quarterly or monthly basis to ensure consistency in the performance and operation of the instrumentation in a laboratory. It is useful to track the performance of instrumentation over extended periods of time because the trends aid in troubleshooting internal or customer-related problems. Routine performance testing can:

  • Confirm instrument performance

  • Confirm proper laboratory methodology

  • Confirm operator competency

  • Demonstrate competitive advantage (via the above)

  • Provide greater customer confidence levels

Old-fashioned performance testing typically uses a round-robin approach, in which a set of samples was sent out (usually) on a quarterly basis, and results were mailed to a central processing facility. After a closed-end evaluation period (typically three months), the submitted values were analyzed and after another month, the data was returned to the laboratories. This method is tedious and counter-productive. The process takes so long that it is a poor method of instrument and/or method evaluation because many parameters change over time. Furthermore, it does not benefit from the use of modern technology nor does it provide instant performance evaluation.

The outdated round-robin method is inadequate for the needs of today's high-volume, multi-instrument oils analysis laboratory. Results must be returned immediately for corrective action to take place, or verification of results may be provided to the laboratory's customers (external or internal). This is where a highly productive use of the Internet can be helpful.

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Figure 2. Validation is automatic and instantaneous.

The PTP from VHG Labs
The VHG Labs PTP was developed for analytical laboratories that measure wear metals in oils by ICP, DCP or RDE, viscosity and particle count. The PTP is designed to provide these laboratories with a method of monitoring and validating their analytical performance as measured against CRMs.

The VHG Labs PTP is currently the only program to provide an instant response to submitted values, with convenient color-coded pass/fail indicators in green (pass), yellow (borderline) and red (fail) formats via a custom-designed, easy-to-use, internet-based user interface.

The PTP from VHG Labs Inc. includes wear metals, viscosity and particle count standards.

Wear Metals
A laboratory may elect to analyze up to 23 common elements, formulated from certified reference materials in the facility at VHG Labs. The lab may enter any or all of the elements. However, the sample provided may contain all 23 elements.

Viscosity
Each viscosity standard has values reportable at 40°C and 100°C.

Particle Count
Each particle count standard allows reporting of values in channels at 4, 6, 14, 21, 38 and 50 µm.

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Table 1

How It Works
The VHG Labs PTP works in the following manner: A lab may order any or all of the tests they desire. Certified testing standards are sent directly to a specified lab with login password. The lab analyzes the samples at the user's convenience and reports the results on-line.

Once reported, the results are immediately available for evaluation, via the Internet in a convenient, easy-to-read format. Data interpretation is easy with the VHG Labs PTP real-time, on-line results evaluation. The user will receive a green, yellow or red value for wear metals* (See Color Label Values at beginning of article.) data interpretation, indicating how closely results compare to the VHG Labs certified values. Validation is automatic and instantaneous; no more waiting weeks or months for results.

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Table 2

The PTP in Action
The following example is an actual issue that arose during a PTP test. An ICP instrument, after running the PTP, produced the following analytical results. As can be seen in Table 1, the results were not desirable. Several results were flagged as yellow and red.

VHG Labs suggested possible sources of error, such as sample introduction, sipper probe, pump tubing, nebulizer, torch (O-rings, fittings and connections), air leaks and more. Typical areas of possible error were examined and it was concluded that the poor results likely had no influence (or at least nothing obvious) on the ICP.

Therefore, if nothing was wrong with the ICP, what was causing the red flags in the analysis? One area that had not been explored was the dilution method. These samples had been diluted with an automated dilution device. The dilutor performed well for years, and was not initially believed to be failing. However, VHG Labs learned that its performance had recently been in question by the lab manager, but not examined. Subsequently, all samples were hand-diluted and were tested again on the ICP. The new results were conclusive (Table 2).

Using the PTP, VHG Labs identified a problem with the dilution system that had never been qualified. It was subsequently repaired, and is now working properly. In addition, with the PTP, VHG Labs confirmed that this ICP unit (instrument) was performing properly, and ensured similar performance among other ICP instruments in the same laboratory and its other labs worldwide. The PTP provided a true evaluation of the laboratory's entire ICP methodology, and in the end, allowed a revalidation of the lab's ICP operations.


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