How do you rate your analytical chemistry data - good, bad, or just a number on a spreadsheet?

ISO 17025 Collage

A recent thought-provoking blog in the LCGC Journal* reviewed current practice in accredited laboratories highlighting concerns that many current analytical methods have not kept pace with recent developments in technologies. The authors commented that the fact that an organisation’s analytical procedures are well documented, does not always mean that their analytical data is credible.

Unreliable measurements can affect patient safety, have an environmental impact, affect product quality and manufacturing efficiency, impacting competitiveness and profitability.

Analytical instruments able to routinely measure ppm and ppb levels have become more sensitive over the years, in line with changes in food, beverage, environmental, clinical, research & manufacturing compliance.

How can we know analytical laboratories are producing reliable data?

ISO 17025 accreditation is intended to indicate reliable data production because a series of compliance training, proficiency testing, and validations is required to achieve compliance. However, current procedures may not have kept pace with technological advances. 

Many laboratories realise good levels of precision, although accuracy is often questioned. Certified Reference Material (CRM) quality has become more important to assure traceability, precision, and accuracy. If the metrological quality of the standards used in different laboratories is unclear, discrepancies will be inevitable when different labs analyse the same sample. The data is only meaningful if it is underpinned by the use of reliable ISO 17034 standards used to calibrate instruments that validate and verify data.

How can specialist suppliers add value?

ESSLAB’s Application Specialists have the required skills and experience to work with clients to review current sample preparation, and precision liquid handling techniques employed for Certified Reference Materials and samples, in addition to advising on suitable CRMs used to calibrate instruments and verify analytical performance.

How confident are we in the data produced by analytical measurements?

Technological advances in analytical systems and techniques have improved significantly over the past 10 years.  However, we should ask, are current workflows still “fit for purpose” assuring precision, accuracy, and process efficiency?  Three key questions that need to be considered:

  1. Have we introduced new instruments where modified sample preparation methods should be considered?
  2. Do we regularly monitor individual analysts’ performance?
  3. Have we reviewed our calibration and verification protocols and materials in line with regulatory and customer demands?

Follow this comprehensive checklist to ensure confidence in analytical data

  1. Is there a total reliance on instrument software to identify drift?

Technological developments have seen major improvements in instrument software simplifying setup, running, and validation of methods supportive of industry compliant protocols. Whilst instrument software often provides options to correct for background and spectral interferences, ESSLAB still advocate the inclusion quality standards to identify possible background signal under the analyte peak.

In addition, more frequent performance testing of the instrument will verify that performance criteria satisfies agreed metrics. Poor instrument setup is often the cause of performance problems or instrument failure.

  1. Would using internal standards improve data reproducibility?
  1. Are the sample and Certified Reference Material matrices qualified?
  • Is the matrix to be dictated by the sample preparation method, and what will the stability of the standard solution(s) be in this matrix? 
  • Are there inter-element or matrix incompatibilities that need to be avoided?
  • Will the blend be stable, or should the elements be split into two or more solutions?
  • Also - has the order of addition and content been ratified to consider measurand interactions?
  1. Are calibration standards analysed periodically to verify the accuracy of the existing calibration for those analytes?
  2. Are laboratory fortified blanks used?
  3. Is there a quality control sample in the analysis batch?
  4. Has accuracy been demonstrated using the same set of replicate data, with average percent recovery for each analyte meeting the specified QC requirements?
  5. Are instrument performance (determination of linear dynamic ranges and analysis of quality control samples) and laboratory performance (determination of method detection limits) verified prior to samples being analysed by the method?
  6. Are standards used correctly?

The stability of the Certified Reference Material once it has been opened is entirely dependent on the frequency and how it is used. Observing the following recommendations will assure confidence in the certified value.

  1. Never put solution transfer devices into the standard solution, this avoids possible contamination from the pipette or transfer device.
  1. Always pour an aliquot from the standard solution to a suitable container before pipetting and do not add the aliquot removed back to the original standard solution container to avoid contamination of the stock standard solution.
  1. Pipette solutions at room temperature, aqueous solutions stored at lower temperatures will have a higher density (consider this if standards are stored under refrigeration). Gravimetric solution transfers avoid this problem, provided the density of the standard solution is known or the concentrations units are in wt./wt. rather than wt./volume.
  1. Never use glass pipettes or transfer devices with standard solutions containing HF. Free HF attacks glass but it is sometimes considered safe to use glass when the HF is listed as trace and/or as a complex. However, many fluorinated compounds will attack glass just as readily as free HF.
  1. Uncap stock standard solutions for the minimum time possible to avoid transpiration concentration of the analytes as well as possible environmental contamination.
  1. Replace stock standard solutions on a regular basis.

(Regulatory bodies recommend or require at least annual replacement.) 

This is due to the changing concentration of the standard through container transpiration mentioned earlier, and the possibility of an operator error through general usage. A mistake may occur the first time a stock standard solution is used, or it may never occur with the probability increasing with use and time.

In addition, the transpiration concentration effect occurs whether the standard solution is opened / used or not and increases with use and increased vapour space (transpiration rate is proportional to the ratio of the circumference of the bottle opening to vapour space).

Using a standard for longer than a year is a risky proposition.


Further potential issues worth considering to improve precision, accuracy, and efficiency in the laboratory:

  1. Liquid handling - are all analysts’ pipetting techniques producing accurate and precise analytical results, or is further training required?
ESSLAB Pipetting Academy

Find out more about ESSLAB’s Pipetting Academy here…
  1. Are all Certified Reference Materials currently in use fit for purpose and, are Certificates of Analysis (CoA's) always examined before use?

CoA’s contain critical technical information on each Certified Reference Materials use and suitability for a given application. They provide clear information of the traceable value of the measurands and the trace metal impurities’ (TMI’s) concentration levels.

Trace metal impurity levels may not be used as certified values; however, they should always be taken into account when considering use for specific applications. Just knowing that impurities are low is insufficient, TMI analysis data detailed on the Certificate of Analysis gives analysts a much greater understanding of the CRM purity. Although not required by ISO, Trace Metal Impurity data provides a complete picture for the analyst.

The CoA should specify exactly how the CRM manufacturer accomplished traceability, for example NIST traceability requires the Uncertainty of Measurement to be stated. Error Budgets must be carefully defined for every CRM and all significant errors are factored into the Uncertainty of Measurement.

Certified Reference Material storage conditions are also detailed on each Certificate of Analysis together with lot shelf life and expiration date. There is a difference between shelf life and expiration date: shelf life is the period the product satisfies its certified value assuming it is unopened and stored under appropriate conditions, expiration date is the period it should remain in use after opening.

 

The use and preparation of reliable Certified Reference Materials, with traceability to international standards has proven to be key to realising analytical performance targets.

If results obtained from different laboratories are to be comparable, it is essential that all results are based on reliable Certified Reference Materials with full traceability to recognised international standards. Any differences between the quality of the CRMs used in different laboratories can result in large inter-laboratory variability for the same samples.

When reviewing analytical method modifications, only method performance improvement and not cost should be considered. As with original validated methods, any alteration should outline how quality is assured (e.g., calibration and quantitation using internal standardisation, comparison of acquired mass spectra and retention times to reference spectra and retention times for calibration standards acquired under identical conditions.

Whilst many laboratories often make material changes to manage costs, they are often more reticent to change the factors which affect the reliability of results, which require investment in time, bringing efficiencies to performance and to deliver real benefits to health, manufacturing process and costs.

- maybe now is the time for a more in-depth review?

If you believe you may benefit from technical input from ESSLAB, please contact our Application Specialist Team

*LCGC and the American Chemical Society Analytical Division Subdivision on Chromatography and Separations Chemistry (Vol 18, issue 3*)

More information:

Download 'Factors Influencing Precision When Measuring Natural Samples Using ICP-MS'  PDF

Contact Us

ESSLAB Resource Centre