sample presentation; NIR; spectroscopy

Chapter 26

Eggcule Poirot presents sample presentation options for NIR

📁 Case overview: The detectives take a deserved break from their case load for a quick tutorial on sample handling options for the NIR method. Eggcule Poirot attempts to explain different sample presentation and sample cup possibilities to his colleagues. But will the sun shine on their understanding or will their minds cloud over with confusion? Read on to find out.

Eggcule Poirot walks into the office and the other detectives stare at him in surprise. His usual shiny white eggshell has turned brown. He is now one very brown egg! The detective was on a week-long vacation and admits that he had spent a good chunk of time lying on the beach. But he assures them that he did not forget about them. In fact, he read a good deal on one of his favorite techniques, near-infrared spectroscopy (NIR).

Shallot Holmes notices the summery mood and suggests that they also take a break from the cases but have a quick NIR tutorial over a couple of virgin cocktails the next day. The others are more than happy with the break in routine and take the idea in stride. Eggcule Poirot is very happy to share his knowledge with his colleagues.

The following morning finds the detectives dressed in various beach hats, sipping on yummy cocktails, comfortably leaning back in loaned lounge chairs and listening to Eggcule Poirot’s exciting NIR knowledge exchange. It has been a long while since their last workshops on how to develop NIR calibrations, as well as how NIR compares to IR spectroscopy and Raman spectroscopy.

Today, he has decided to review with his colleagues different sample presentation and sample cup possibilities and how to decide which option is better suited to a particular NIR application.

Sample presentation: Up View and Down View

Firstly, Eggcule Poirot discusses different sample presentation options with the team. A good NIR system typically offers Up View and Down View options, which are suitable for different applications. As Miss Mapple is looking confused, Eggcule Poirot draws out what he means with these two sample presentation options, where his yellow arrow indicates the direction of light:

sample presentation; NIR system

Now that they have a clear idea of what these two sample presentation options are, the food detective goes on to discuss benefits of each view.

Benefits of sample presentation with Up View:

  • More consistent sample presentation to achieve highly reproducible results with minimal effort
  • Nearly complete exclusion of stray light from the measurement
  • Possibility to measure liquids in transflectance mode

Benefits of sample presentation with Down View:

  • Larger measurement spot and large sample carrier option resulting in averaging over a larger amount of sample
  • Measurements without interference in plastic sample cups or other NIR-absorbing materials to avoid glass dishes

Taking these advantages into consideration, Eggcule Poirot recommends using:

Up View for analysis liquids, as well as for any samples where highest precision is required and Down View for measuring inhomogeneous samples, as well as for work in glass-free environments.

The food detectives are excited about this information and quietly discuss that they can hardly wait for a new NIR case on which to try out these findings.

Eggcule Poirot is happy with their reaction, lets them chitchat briefly and brings their attention back to the second part of the tutorial.

Sample cups

There are various sample cups suitable for different measurement applications with an NIR system. Eggcule Poirot decides to list three types of sample cups. These may not be offered by every company, but still represent the three most frequently encountered options for Up View sample presentation:

  • High-performance sample cups – these are frequently distinguished by their higher quality, optically tested glass windows. These sample cups should be used in applications where optical performance is essential
  • Robust cups – these are protected by a rubber rim and offer improved resilience in rough environments
  • Standard glass petri dishes – as the most economical option; these are also useful when multiple sample cups are required for highest sample throughput
NIR samples; NIR system; spectroscopy

Similarly, for Down View sample presentation, sample cups often come in variations such as:

  • Large sample cups – most suitable for inhomogeneous samples, as a larger sample area is passed under the measurement spot
  • Small plastic petri dishes – mainly recommended for limited sample amounts of homogenous samples, which are insufficient to fill larger sample cups, for use in glass-free environments
NIR system; sample cup

And with this, Eggcule Poirot concludes the quick training. The detectives raise their own cups in the air and decide to head out to the park for the rest of the day where they continue their beach-vacation-themed day. Nancy Beef does not like being roasted, and Miss Mapple believes the sun rays give her wrinkled skin, so the two hang out in the shade. Shallot Holmes decides he is naturally tanned unless you peel him, Lieutenant Cornlumbo doesn’t mind getting a shade of yellow darker and Eggcule Poirot is already a brown egg, so they relax on a picnic blanket in a sunny spot. All members, naturally engrossed in a deep conversation on visible light and infrared light, of course!