Numbers are the name of the game

When your shopping is weighed at the till, have you ever given it a second thought? Have you ever wondered how the balance knows it weighs that much? Or why?

And what if it’s wrong. That’s another 12p please, says the assistant – not earth shattering news but what if that balance was a particulate monitor and that extra little bit of particulate pollution failed the legal emissions limit and caused the shut down of your manufacturing plant? Downtime may not be earth shattering but it could cost the earth.

It is therefore much better and far more cost-effective to check that the monitor works. Calibrate it against reference standards and if the particulate in question is still over the limit, then so be it, but at least the measurement is right.

In brief, it’s a series of labs and services which ensure that users can be confident that their measurements are consistently traceable back to nationally and internationally accepted reference standards – and are therefore both valid and fit for purpose. These standards may then be subsequently integrated into regulation.

The Department of Trade & Industry (DTI) is responsible for the NMS and has a portfolio of programmes within it that covers the range of measurements used in society,

for example, time and frequency, optical radiation, acous-tics, length, mass and biotechnology.

Industry measures

One of these deals exclusively with analytical measurements, the Valid Analytical Measurement (VAM) Programme, run jointly by the National Physical Laboratory (NPL) and LGC, an independent science-based provider of chemical and biochemical analysis and diagnostic services.

Peter Bedson, the VAM Programme Manager at LGC, explains, “Measurements are very important to industry within the UK and absolutely vital to global trade. In order to be a successful trading nation, we need a measurement system that enables accurate measurements and the international acceptance of test results. This is particularly important where measurement data is used to provide evidence of product specification or compliance with regulation.

“Measurements must be traceable to international standards if the principle of ‘once measured, accepted everywhere’ is to be achieved.”

Analytical measurements are carried out widely by industry to assure the composition of manufactured products and raw materials; to control and optimise processes; in research and development; and to monitor emissions.

Research into human health has shown that poor air quality accelerates about six per cent of deaths in the UK. Vehicles and industry are the main source of this air pollution, which is not only composed of the well-known evils such as carbon dioxide, sulphur and nitrogen oxides, but carbon monoxide, particulates and ozone as well.

This has led to air quality being increasingly regulated with national and European laws dictating emissions limits. Limits which must be tested throughout industry to ensure compliance. In fact, the UK spends approximately £7b per year making measurements which are indispensable in enforcing legislation and for environmental protection.

“In order to provide a basis for accurate and reliable measurements, the NMS supports the maintenance, development and dissemination of measurement standards in the UK,” says Bedson, “The VAM programme develops calibration standards and valid measurement techniques for those air pollutants subject to current regulation, and research is underway to provide similar methods and standards for upcoming national and EU standards.” This process is accredited by UKAS, as required by EU legislation.

Direct intercomparison

But how are accurate and comparable measurements of pollutants actually achieved? Bedson explains that historically the comparability of chemical measurements was achieved by adopting ‘standard’ methods of analysis, which were often embedded within the regulation they support.

Although in some cases standard methods will remain fit for purpose, their long development time and the advent of new technology means that such methods are becoming obsolete very quickly. The trend nowadays is towards setting ‘performance-based’ methods, but in turn this requires a measurement system that provides the reference points against which the performance of a method can be validated.

“Under the direction of the International Committee on Weights and Measures (CIPM), LGC is working with National Measurement Institutes (NMIs) in other countries to establish a measurement system to enable traceable chemical measurements, similar to the system which exists for physical quantities such as mass, length and time,” says Bedson.

“This will provide internationally accepted reference points for chemical measurements. Work to date has focused on developing high accuracy measurement capabilities in areas that are particularly important for trade and regulation, such as sulphur in fuel, determining environmental pollutants such as tributyl tin and PCBs in sediment, and measuring contaminants in food such as lead in wine – which probably has its source in air pollution,” says Bedson, “If we can use our high accuracy techniques at LGC for the more complex analyses and do it well, then the best practice we learn can be adopted by other labs.”

The results of high level intercomparisons between NMIs in these areas are then entered into the international database at the Bureau International des Poids et Mesures (BIPM) (International Centre for Weights and Measures, www.bipm.fr) in France and this provides the basis for demonstrating the equivalence of measurement capabilities in different countries.

The problem with air pollutants, or any pollutant for that matter, is that they are not as straightforward to measure as, say, a kilogram of tomatoes. Pollutants are usually embedded quite securely in a matrix of some sort, whether it be air or effluent gas or soil.

Bedson: “Chemical measurements are often quite complex. If you want to look at lead in soil you may have to use a completely different procedure to measuring lead in petrol or lead in plastic. The first problem is getting the lead out of what we call ‘the matrix’ – the substance it’s in – before it can be measured, whereas if you measure the weight of something, you don’t have to extract it.”

This brings us onto another important part of the VAM programme – the application of high accuracy measurement facilities to assigning reference values that can be used by anyone and everyone.

“Another of the difficulties we face in chemical measurement is linking the small number of very high accuracy measurements done by the NMIs with the large number of routine measurements done everyday by the field labs,” says Bedson, “In addition to providing calibration services, we do this through the certification of hundreds of Certified Reference Materials (CRMs).”

LGC produces a small number of CRMs which can be divided into two types: matrix reference materials and pure reference materials. The matrix materials are literally the matrix that the compound of interest is likely to be found in, for example, the sediment sludge or effluent. These are then used by laboratories to validate the performance of their methods. The pure materials are the compound of interest, but in an ultra pure form. These are diluted to a known concentration and used to calibrate measuring instruments.

Knowledge transfer

However, the VAM programme is not only about the development of methodology and the applications of that methodology to assigning reference values. A very valuable part of it is the transfer of knowledge gained through the programme.

LGC works with industry and academia, schools, and regional networks to disseminate that knowledge and ensure that the information is made available in a form that will have a significant impact on UK business.

In addition to a library of technical reports, the VAM product portfolio includes a range of best practice guides, books, videos and software. Many of the products can be freely downloaded or ordered on-line through the VAM website (www.vam.org.uk).

Three sectoral networks have also been set up to develop training materials and to deliver training in environmental chemistry, clinical chemistry and specialist organic chemicals. A key focus for training materials is the development of procedures and protocols to enable laboratories to carry out efficient method development and validation.

Evolution

Programmes evolve as time goes on. This VAM programme was started in 1988 and the programmes are renewed on a three year cycle by the DTI.

“Before 1997, a significant proportion of work carried out under the programme concentrated on communicating best practice to labs. Since then, it has become much more of a technical programme,” explains Bedson, “Now we are focussing on developing the infrastructure of those technical activities.”

And the future?

“One of the key issues facing environmental laboratories is the extension of the MCERTS scheme to cover chemical testing of soils. In the next VAM programme we will be looking at using our high accuracy facilities to produce and certify reference materials and calibration standards to enable help laboratories to validate the performance of their methods and comply with MCERTS. We are currently discussing requirements with the Environment Agency and labs throughout the UK.”