Do we need to rethink collaborative trials?

The currently recommended design of collaborative trials (interlaboratory method performance studies) is examined in relation to the usefulness of the resulting statistics. It is suggested that larger experiments, without duplicate analysis, would be more informative.

Do we need to accredit proficiency testing schemes?

 Proficiency testing (PT) is being increasingly used as an important quality assurance tool for laboratories. The subject of quality of the providers of PT schemes has been discussed increasingly in recent years. Some countries have implemented systems for the accreditation of PT schemes. This paper looks at the background to the accreditation of PT schemes, the likely mechanisms which could be employed for accreditation, and some of the practical aspects.     

On the use of the ‘uncertainty budget’ to detect dominant terms in the evaluation of measurement uncertainty

In the evaluation of measurement uncertainty, the uncertainty budget is usually used to identify dominant terms that contribute to the uncertainty of the output estimate. Although a feature of the GUF method, it is also recommended as a qualitative tool in MCM by using ‘nonlinear’ equivalents of uncertainty contributions and sensitivity coefficients. In this paper, the use of ‘linear’ and ‘nonlinear’ parameters is discussed. It is shown that when and only when the standard uncertainty of the output estimate is nearly equal to the square root of the sum of the squares of the individual uncertainty contributions, will the latter be a reliable tool to detect the degree of contribution of each input quantity to the measurand uncertainty.     

Achieving traceability in chemical measurement—a metrological approach to proficiency testing

ISO/IEC 17025 requires that testing laboratories establish the traceability of their measurements, preferably to the SI units of measurement. The responsibility for establishing traceability lies with each individual laboratory and must be achieved by following a metrological approach.The results of measurements made in such a way are traceable to the standards used in method validation and to the calibration standards used during the measurement process. If these standards are traceable to SI then the measurements will also be traceable to SI.Participation in appropriate proficiency studies (an ISO/IEC 17025 requirement) enables laboratories to demonstrate the comparability of their measurements. If the materials used for the studies have traceable assigned values, then proficiency testing also provides information about measurement accuracy and confirms, or otherwise, that appropriate traceability has been established. This paper will report on a new approach for the establishment of traceable assigned values for chemical testing proficiency studies. The work is conducted at a "fit for purpose" level of measurement uncertainty, with costs contained at a level similar to previous "consensus" based proficiency studies. By establishing traceable assigned values in a cost effective way, NARL aims to demonstrate the added value of the metrological approach to participant laboratories.     

Do we really need to account for run bias when producing analytical results with stated uncertainty? Comment on 'Treatment of bias in estimating measurement uncertainty' by G. E. O'Donnell and D. B. Hibbert

Treatment of bias is an important issue relating to analytical quality. Recently, G. E. O'Donnell and D. B. Hibbert (Analyst, 2005, 130, 721) recommended to always correct analytical results for 'run bias' determined by a single analysis of a certified reference material (CRM) in each analytical run. In the authors' opinion, this is necessary for the results obtained to be comparable from run to run. It is argued here that such a recommendation is logically inconsistent and stems from misinterpretation of measurement uncertainty as being estimated under repeatability conditions. The fundamental principle underlying the measurement uncertainty methodology is that all relevant sources of error should be taken into account, which results in overall uncertainty assessment and thus provides a means for a global comparability of measurement and test results. The local, i.e. run-to-run, comparability is not a factor if analytical results are interpreted on the basis of their associated uncertainty.     

Future of high pressure liquid chromatography: do we need porosity or do we need pressure?

Making a theoretical study supported by experiments of the kinetic advantages of increased inlet pressures versus increased external porosity using impedance plots of analysis time versus required plate number, it is found that both approaches more or less have the same effect on the kinetic performance. The need to change a given system to one with an increased inlet pressure or with an increased external porosity can best be assessed from the optimal plate number (N(opt)) of the system. When the pursued application requires a plate number that is larger than N(opt), any increase in inlet pressure and external porosity is beneficial. When the required plate number is smaller than N(opt), any increase in inlet pressure and external porosity should preferentially be accompanied by an overall reduction of the feature sizes of the support. The degree to which this feature size reduction can be realized in practice will to a large extent determine which of the two approaches will be the dominant system of the future.     

“Quality of a measurement result” is established by means of metrological criteria

Accreditation and Quality Assurance -     

The way to AI-controlled synthesis: how far do we need to go?

Chemical synthesis always plays an irreplaceable role in chemical, materials, and pharmacological fields. Meanwhile, artificial intelligence (AI) is causing a rapid technological revolution in many fields by replacing manual chemical synthesis and has exhibited a much more economical and time-efficient manner. However, the rate-determining step of AI-controlled synthesis systems is rarely mentioned, which makes it difficult to apply them in general laboratories. Here, the history of developing AI-aided synthesis has been overviewed and summarized. We propose that the hardware of AI-controlled synthesis systems should be more adaptive to execute reactions with different phase reagents and under different reaction conditions, and the software of AI-controlled synthesis systems should have richer kinds of reaction prediction modules. An updated system will better address more different kinds of syntheses. Our viewpoint could help scientists advance the revolution that combines AI and synthesis to achieve more progress in complicated systems.

It is still a long march for AI-controlled synthesis to enter into general laboratories. Flaws in the architecture of AI-controlled synthesis systems must be overcome.     

Status of uncertainty assessment in k 0-NAA measurement: anything still missing?

Several approaches to quantifying measurement uncertainty in k ₀-based neutron activation analysis (k ₀-NAA) are reviewed, comprising the original approach, the spreadsheet approach, the dedicated computer program involving analytical calculations and the two k ₀-NAA programs available on the market. Two imperfectness in the dedicated programs are identified, their impact assessed and possible improvements presented for a concrete experimental situation. The status of uncertainty assessment in k ₀-NAA is discussed and steps for improvement are recommended. It is concluded that the present magnitude of measurement uncertainty should further be improved by making additional efforts in reducing uncertainties of the relevant nuclear constants used.     

Do we have to explicitly model the ions in brownian dynamics simulations of proteins?

Brownian dynamics (BD) is a very efficient coarse-grained simulation technique which is based on Einstein's explanation of the diffusion of colloidal particles. On these length scales well beyond the solvent granularity, a treatment of the electrostatic interactions on a Debye-Hu?ckel (DH) level with its continuous ion densities is consistent with the implicit solvent of BD. On the other hand, since many years BD is being used as a workhorse simulation technique for the much smaller biological proteins. Here, the assumption of a continuous ion density, and therefore the validity of the DH electrostatics, becomes questionable. We therefore investigated for a few simple cases how far the efficient DH electrostatics with point charges can be used and when the ions should be included explicitly in the BD simulation. We find that for large many-protein scenarios or for binary association rates, the conventional continuum methods work well and that the ions should be included explicitly when detailed association trajectories or protein folding are investigated.     

“Demonstration” vs. “designation” of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. “traceable” to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be “external” to the measurement laboratories which are being evaluated. This is realized in IRMM’s International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using “metrology”, the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be “demonstrated” rather than just “designated” and this can be shown to both customers and regulators. It inspires more confidence.     

Experimental sensitivity analysis applied to sample preparation uncertainties: are ruggedness tests enough for measurement uncertainty estimates?

It has been suggested that typical ruggedness tests might lead directly to uncertainty estimates. This assertion is tested using simple experimental studies of uncertainties associated with sample grinding and oven-drying operations. The results are used to predict the outcome of typical ruggedness tests on the same systems. It is concluded that uncertainty estimation from ruggedness tests is appropriate only where a strong effect can be observed. Since current practice in ruggedness testing is predisposed to confirming insignificance, typical ruggedness tests are not likely to lead to reliable uncertainty estimates; instead, lack of statistical significance in ruggedness tests is better interpreted as reason to leave an effect out of the uncertainty budget. Only where the ruggedness study is modified in order to achieve statistically significant change is it useful for uncertainty estimation. Received: 27 November 2000 Accepted: 13 February 2001