Yes, technology is taking over. How are these NASA instruments calibrated?
I ask as in other fields such as geotechnics, on site survey and analysis is still usually backed up by lab testing, with good reason. Ground truthing is used to verify results and demonstrate that field instruments have been calibrated properly.
Does/should the same principle apply?
Strategic Planning and Infrastructure
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From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Colin Green
Sent: 06 July 2018 18:59
To: [log in to unmask]
Subject: Cost of on site analysis - Triad approach
I do not want to be seen selling products, so I will try to be generic in giving the current costs of using on site analysers
On site analysis has come a long way since the fiddly, semi-quantitative test kits of earlier times. I have to confess to being partly responsible for that because I was involved in some way in the development/commercialisation of most of them, but especially the immunoassay and turbidity based kits. Mea Culpa.
The newer systems are really miniaturised full chemical analysers, capable of producing very accurate and reproducible data that matches the best accredited laboratories. NASA and the other space agencies use these on their space probes. In fact XRF was taken to the moon in 1975 on the Apollo mission. The Mars rover uses several instrumental X ray and spectroscopy techniques in its search for water and potential life forms. UV fluorescence will be used on other Mars missions. A good indicator of even simple carbon based life forms are specific UV fluorescence fingerprints. Crude oil, the residue from decayed plant matter several million years old is fluorescent. It is reasonable to believe similar metabolic and geochemical processes will have occurred on planets within our solar system, so hunting for the same compounds found in petroleum hydrocarbons would be a sensible option. They naturally escape to the surface and can be found in minute quantities in the atmosphere. NASA would not consider using these technologies if they were not certain high quality data can be produced.
Several terrestrial on site analysers available use UV fluorescence as their methodology, some such as the QED, use the same micro spectrometers as used by the Mars and the Rosetta/Philae missions. These solid state spectrometers are very robust, having to withstand the extremes of temperature, shock of rocket launch and subsequent landing while retaining their initial calibration set up and accuracy. They run on artificial intelligence software systems that provides all the required QA/QC needed to give reliable results. Adapting these systems for TPH and PAH analysis for terrestrial applications means you get easy to use yet reliable and accurate analysis for 99% of the hydrocarbon parameters needed for site investigation or remediation projects.
The analysers themselves are in the same price range as XRF at around £21,000 - £25,000. The reagents are however low cost. Compared to a test kit that would typically cost between £20 and £50 per sample, the instrumental on site analysers use reagents/consumables that can cost less than £4 per sample. Test kits also had a "hidden" cost, Exceeding or being lower than the calibration range meant repeating the entire test at another £20 - £50. The user also needed to know what the hydrocarbon type was in the sample to get the right calibration. This caused a lot of inaccuracy because the response factors for even fresh diesel and degraded diesel could be as much as x5 different. If kerosene fuels or highly degraded fuels or coal tars were present, but the test kit was calibrated with a diesel calibrator, the concentration reported could be as much as x20 too high or too low. Another "gotcha" cost was where the user made a mistake during the analysis. This required running the entire sample analysis again at the £20 - £50 cost. As test kits were often run in batches, a single mistake could get quite costly and because they were time consuming, cause another hour or so of your life to be wasted.
The latest on site hydrocarbon analysers identify the hydrocarbon type first and then apply the correct calibration automatically. This makes sure the reported concentration is accurate. The QED hydrocarbon analyser holds as many as 18 different hydrocarbon types in its calibration library, including most fuel types, oil types and coal tars, creosotes and bitumen based road binders, so should be able to find a match. If a mistake is made or the sample is over or under the calibration range, the AI system in the analyser tells the user to repeat the analysis and provides the correct dilution to use to get within range. A repeat only costs a few pence in reagent. A typical analysis takes about 3 minutes from sample collection, through extraction and final analysis. A repeat analysis is less than a minute.
Calibration is very simple for fluorescence based systems. Fluorescence is a quantum effect. This means for a given range of concentrations for a specific atom (such as arsenic) or a given hydrocarbon molecule (phenanthrene, a PAH) they always give the same ratio of input to output energy at specified wavelengths under defined conditions. Ensure the conditions meet the requirements, measure the input energy and you can predict the output energy. That's how both XRF and UV Fluorescence calibration is set up. The instrument manufacturer works out the energy input/output ratios for all the heavy metals or hydrocarbon types for a given input energy. In the field, the input energy is measured and so the factory calibration curves can be re created. In the case of XRF, certain wavelengths are measured during analysis to measure the X Ray energy input. For the hydrocarbons analysis a single fluorescent compound in solution is used to measure the input energy before samples are analysed. This makes on site calibration very simple and robust and removes the need for expensive and time consuming field calibration. The stability of the sensors in the analysers ensures the factory calibrations remain very stable, showing less than 5% drift over 12 months. The annual service ensures this stability is retained over many years.
These features actually bring the cost of on site analysis down to significantly lower than conventional lab costs. The capital cost of the analyser can be amortised over 5 years (yes, they easily last that long if looked after. Just look at how long the sensors in the Mars rover have lasted under extreme conditions), which means most of the sample cost is the reagent/sample prep.
The AI in the analysers allows anybody to use them and still get valid results. Internal QA/QC in both the XRF and hydrocarbon analysers is very good at spotting user error and flagging it up.
I hope that answers your questions and I hope I have not been too blatantly commercial. All I can say is that these latest generation analysers makes TRIAD a very sensible and cost effective way of doing things. I wonder when it will be adopted.
Finally, a cautionary note. The cost of laboratory analysis has come down significantly, but this may be at the expense of overall quality. There comes a price point where it just cannot be possible to make money and provide high quality analysis and service the high overhead costs of the staff, equipment, accreditation and buildings. The oil industry laboratories cannot run even simple TPH analysis for less than £70/sample. Maybe this is why so many of our environmental labs are closing or merging. We as an industry need good quality high resolution chemical analysis for risk assessment data. Reporting of alkyl PAH, not just parent PAH is a very powerful diagnostic tool. Effective and demonstrable removal of interfering background organics from TPH analysis should be routine, not a requested (or barely mentioned) option. Knowing the oxidation states of metals is again very useful (actually essential) for proper, scientifically defendable risk assessment. Perhaps we should be prepared to pay more for this type of analysis to keep our laboratories alive and let on site analysis provide the routine TPH, hydrocarbon identification, simple PAH and total heavy metals analysis
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