The sampling interface—A critical Theory of Sampling success factor in process sampling and PAT

Abstract

In the process industry arena, analytical endeavors are today well served by the Process Analytical Technology (PAT) framework, offering a plentitude of on-line analytics, mostly spectroscopic: UV-VIS, NIR, RAMAN, NMR, “acoustic chemometrics” a.o. This context is generally considered satisfactory, but there is a major catch. The present paper focuses on a fundamental feature in process sampling, the link between an on-line analytical technique and a moving stream of matter, which is to be characterised, monitored, and analysed. A process sampling operation can serve many objectives; process regulation, product or interim product characterisation, optimisation of raw material consumption, maximizing energy efficiency, pollution, and environmental impact management ‒ or process, plant, company, corporation decision making at supervisor and management levels concerning economics and risk management. All these objectives can only be meaningfully undertaken if based onrelevant information, that is, if based on reliable analytical data, which in turn is 100% dependent upon representative samples, or representative sensor signals. The singular common element in all of this is the process sampling interface. This paper develops a critique of most current interfaces, with a scathing verdict: the dual role of the process sampling interface as both delineating an appropriate aliquot volume while facilitating the specific analytical technique, has largely been overlooked, with a significant negative effect that is spelled out in full detail across implemented solutions across widely different application sectors. Most current process sampling interfaces do not comply with TOS’ demands, putting representativity severely at risk for heterogenous materials.

Before reliable near infrared spectroscopic analysis - the critical sampling proviso. Part 2: Particular requirements for near infrared spectroscopy

“…The sampling cell interface actually determines the very possibility for representative PAT process analysis or not; full treatment of these issues can be found in 3,[5][6][7]12 ; this topic was recently treated in depth at the 10 th World Conference on Sampling and Blending (WCSB10). 22 Question 4: Rotating versus fixed cell? Some NIR devices use a fixed sample cell, while others make use of a rotating cell, and the latter can measure over a larger field-of-view (FoV); although this does come at a minor additional instrument cost.…”

“…This is a potentially immense area only indicated here; the avid reader is strongly recommended to consult. 2,6,22 Question 6: For process monitoring: are two en suite NIR spectrometers better than one?…”

“…Intelligent application of TOS' process sampling principles will suffice in most cases; good examples can be found in. 2,[5][6][7]22 A simple rationale will clarify TOS' point of view regarding sample support (volume/mass).…”

“…The critical issue is the distinction between a traditional sample cell and a sampling cell 22 -and willingness to identify and modify inferior and faulty designs and installations where needed. Process sampling (PAT) is fully treated elsewhere 2,5,6,22 and further references herein. 6.…”

“…The sampling cell interface actually determines the very possibility for representative PAT process analysis or not; full treatment of these issues can be found in 3,5–7,12 ; this topic was recently treated in depth at the 10 th World Conference on Sampling and Blending (WCSB10). 22…”