Near vs. Mid-IR: pick your poison

Is there a simple answer?

Of course not! When it comes to the debate regarding which infrared spectroscopy reigns superior, near-infrared (NIR) or mid-infrared (IR), the answer should be a reflect the merits of the technology in light of the application of interest. It’s like asking whether a knife is better than a spoon. Well, are you trying to cut an apple or eat ice cream? You see my point.

Basic theory

Put simply, infrared spectroscopy is the study of the interaction of infrared light with matter, where infrared light is characterized by wavenumber range spanning from 12,800 to 10 cm^-1 (or wavelengths of 0.78 to 1000 micron). Mid-IR is typically defined as light between 4000 and 400 cm^-1, and NIR as light between 10,000 and 4,000 cm^-1, give or take. Mid- and near-IR are included under the umbrella of molecular spectroscopy.

Imagine your sample at the molecular level, with carbon, hydrogen, oxygen and nitrogen atoms coordinated by chemical bonds in such a way as to produce the water, fat and protein content in that sample. The relative positions of the atoms in the molecules of your sample are not fixed; they fluctuate continuously as a consequence of a multitude of different types of vibrations (i.e. stretching and bending) and rotations about the bonds in the molecule. Check out this page for some nice illustrations and more in-depth theory. When the frequency of a specific vibration is equal to the frequency of the IR radiation directed on the molecule (*and the molecule undergoes a net change in dipole moment as a consequence of the vibrational or rotational motion), the molecule absorbs the radiation. A plot of the measured infrared radiation intensity versus wavenumber is known as an infrared spectrum.

Consider the difference in the wavenumber range (and hence, energy) of mid- and near-IR radiation. The higher-energy mid-IR is exciting fundamental vibrations; that is, when energy is absorbed by the molecule in its ground state to the first vibrational state. NIR spectroscopy is comprised of combination bands of overtones of those fundamental vibrations.  The latter are of much lower intensity than their fundamental analogs, owing to their lower transition probabilities. This can be an advantage OR disadvantage – depending on what you’re trying to do (keep reading!).

The bonds defining functional groups (structural fragments within the molecule, like C=O, N-H or C-H), tend to absorb IR radiation at predictable wavenumber ranges, regardless of the rest of the molecule’s structure. Organic functional groups have characteristic and well-delineated absorption bands in the mid-IR, lending the technique to structural elucidation and compound identification, especially when paired with other analytical methods like NMR. While the broad peaks and overlapping of the overtone and combination bands strongly decrease the specificity of NIR spectroscopy for spectral interpretation, low absorptivity and efficient light scattering by NIR radiation can be advantageously exploited. In other words, because the absorption intensity is low, NIR samples do not need to be diluted (as with mid-IR) to avoid saturation at the detector; sample thickness interrogated by NIR light can be extended from millimeters up to centimeters, depending on the sample composition. This large sampling volume is valuable for quantitative analysis of samples with some degree of heterogeneity.

Let’s now consider a common application where both mid-IR (FT-IR) and NIR methods are commonly employed: raw material identification.

Mid-IR Advantages

  • Characteristic and well-delineated absorption bands  for organic species in the mid-IR lend the technique to structural elucidation and compound identification; detailed tables of characteristic group frequencies facilitate structural elucidation efforts

Mid-IR Disadvantages

  • The need for sample dilution (e.g. KBr pellets, salt plates) is common, requiring extra time for material evaluation, as well as effective “destruction” of the sample (i.e. the sample cannot be used beyond the mid-IR measurement)
  • The small sampling volume of mid-IR when using attenuated total reflectance (ATR) is small, thus limiting method repeatability for less homogeneous samples

NIR Advantages

  • NIR spectra are impacted by both chemical and physical attributes of the sample; therefore, NIR can be used to discriminate between grades of the same chemical substance
  • NIR radiation achieves more sample penetration; increased sampling volume may increase sensitivity to contaminants
  • No sample preparation  (i.e. no pellets or salt plates), nor purge gas is required, thus reducing the sampling efforts and costs
  • Spectra are collected in seconds (typically 4 to 30s)

NIR Disadvantages

  • Some functional groups having both fundamental and first order (or higher) overtones in the mid-IR region will not appear in the NIR region, potentially limiting the discriminatory power of NIR for certain sample sets
  • Due to the more complex (i.e. broad and overlapping) signal of NIR spectroscopy, chemometric procedures are required for qualitative discrimination.  The superposition of bands However, software capable of handling these procedures is widely available and quite capable when paired with solid experimental design

Conclusion

What’s the moral of the story? If you have a label on a bag of white powder and you want to quickly see if that label is correct, then NIR is likely to be the right choice for you. You’ll complete your analysis quicker and be able to retain or use the NIR sample as you see fit. However, if you are synthesizing compounds in the lab and you want to know what you brewed up, mid-IR is the clear choice.

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Chemical Industry QC with NIR

 

Read this post, or watch the webinar instead!

Quality control for many labs involves a heavy dose of wet chemistry methods, things like titration and separation techniques that take skill, time and (even more) chemicals to execute. Luckily, some of these traditional testing methods can be replaced by simple, fast and safe NIR spectroscopy.

While this blog title indicates applicability to the Chemical Industry, “chemical” is one broad umbrella. There are myriad products and processes that fall under the chemicals category, from natural products like wood and pulp to personal care products to standard bulk chemicals. Reaching all of these audiences with one blog post seemed a little daunting until we broke it down to some common key themes for implementation of NIR for the chemical (or any!) industry:

  • Raw material qualification
  • Intermediate/in-process testing
  • Finished product testing

Of course, the typical applications that might fall into any one of these categories will differ based on the products being produced. Some of the more common applications include:

  • Material identification
  • %-Moisture or %-solvent quantification
  • Reaction extent or %-polymerization
  • Hydroxyl and acid number determination

As with many other industries, the raw materials used for production of chemical products are often non-discrete, sourced from various parts of the galaxy, and labeled–sometimes correctly, sometimes not.  If you follow product recalls, you’ll find that millions of dollars have been lost due to mislabeled containers being poured into mixers, placed on trucks for distribution to other producers, or stocked on store shelves.

NIR is one quick tool used for identity testing of routinely received materials. There is potential to differentiate isomers, crystalline forms, chemical analogs, fatty acids, and even contaminated materials. Because identity testing with NIR takes seconds and can be done in the warehouse, more frequent testing can be accomplished without backlogging the QC guys and gals.

On the quantitative side, there is plenty to measure keeping in mind the inherent sensitivity of NIR to particular molecular bonds, including O-H, C-H, N-H and C-O bonds. So, if those bonds are changing in type or in number, NIR could be a great fit. This is the case in the typical chemical application of determining hydroxyl number, where we observe a decrease in NIR signal attributed to O-H bonds as those O-H end groups are consumed during polymerization. In fact, determining hydroxyl number of polyols by NIR is a standard practice per ASTM and ISO.

BUCHI Market Manager and former BUCHI NIR Applications Specialist Ryanne Palermo produced a short webinar on these topics, including a fiery example of tracking nitrogen substitution in nitrocellulose. Tune into the webinar by clicking here.

Find more free, streaming content on our BUCHI Webinar On-Demand page, including information about preparative chromatography, laboratory and industrial evaporation, drying, encapsulation and more.

 

Be a Champion of Final Goods Inspection

Max won’t let a pile of untested final goods (or third wheel) stand between him and a coffee date with his lady love. Check out the newest and last installment of the Food Quality Champion Series animated videos, then download the Guidebook and become a Final Goods Inspection Champion, yourself!

The Final Goods Inspection Guidebook is ripe with information to understand or expedite quality control operations in the food and feed industry. Topics include:

  • Regulations impacting final product quality control
  • Representative sampling & sample preparation
  • Tips for optimizing Kjeldahl workflow for protein determination
  • Tips for optimizing extraction and hydrolysis workflow for fat determination
  • Tips for optimizing NIR methods for proximate determination in food and feed products

Download the guidebook for helpful insights, then start a conversation with your local BUCHI Application Specialists to see how you can be a Champion!

 

 

Champion saves the day: Volume 2 Production

In-process and at-line NIR for production

Beat the costs in production! Download Volume 2 of the Champions’ Guidebook and find out how to save money while monitoring production lines.

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Our determined (and love-struck) food champion, Max, is back at it. Check out the newest animated video to see how NIR can avoid costly production errors (and increase profitability) after googly-eyed Max’s big goof-up.

One of the greatest assets of on-line and at-line NIR is having a second set of (focused) “eyes” on production operations. The NIR can be trained to measure critical material properties for in-process or finished products, or even do simple identification procedures to confirm questions like: is Product A is actually being produced?

Max may be a little distracted at times, but NIR can still make him a champion!

Be a Food Analysis Champion!

Save time with efficient incoming goods inspection

New BUCHI campaign delivers 3 e-booklets to create Food Analysis Champions!

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Every day, food producers undergo myriad processes and procedures designed to achieve a quality product and (hopefully) a profitable business.

The loading docks and warehouse serve as initial points of contact for ingredients and foodstuffs that will become integrated into delicious (and sometimes nutritious) food products. It is the obligation of the producer to ensure that they are obtaining the highest quality and correctly priced goods prior to feeding those ingredients into the production process.

Our first booklet provides insight into challenges and opportunities related to incoming goods inspection, including:

  • Typical slow-downs in incoming goods receiving
  • Tips to meeting incoming goods inspection requirements efficiently
  • Benefits of using fast, non-destructive NIR analysis for testing incoming goods
  • Improving time-to-result for classical reference methods (i.e. extraction and Kjeldahl)
  • Sample NIR and classical testing applications to help you save time!

Download this complimentary resource, and stay tuned for future additions to the series, including: production and finished goods control!

For some nice (and enlightening) lunch break entertainment, watch our Food Analysis Champion, Max, save the day when production is halted due to QC backlog in the BUCHI animated video short series for “Beat the Clock.”

 

Next at bat: BUCHI @ PROCESS EXPO

Summer might be coming to a close, but our PROCESS EXPO pre-game is just heating up!

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The global food equipment and technology show PROCESS EXPO is being held in Chicago, home of the defending World Series Champions. You can catch us there September 19-22. In the spirit of the game and in anticipation for the Fall Pennant Races, the BUCHI Booth will be hosting a Wii Sports Home Run Derby competition! Be sure to stop by and take a swing for a chance to win some swag.

While you wait to step up to the plate, check out the NIR-Online, our in-line near-infrared sensor that will help you hit a Grand Slam in process control!

Not into baseball? BUCHI has something for you industry, including classical Kjeldahl reference methods and near-infrared spectroscopy (NIRS) for food analysis, in addition to spray-drying, encapsulation and freeze-drying.

Looking for a way around those long QC queues? Check out our NIRSolutions for the PROCESS EXPO industry sectors: 

Confectionery, Baking and Snack

We already blogged about some of the sweet stuff BUCHI can do in the chocolate industry, but our products can provide quantitative measurements for much more:

  • Whole & ground cereals (e.g. wheat, semolina, barley, rice, corn/maize)
  • Hulls & bran
  • Oil seed meals
  • Fats & oils (e.g. vegetable oils and animal fats)
  • Egg &  milk derivatives (e.g. egg powder, liquid egg, milk powder)
  • Dry pasta & noodles
  • Ready-meals (e.g. lasagna, frozen pizza)
  • Confectionary (e.g. chocolate, cocoa & derivatives)

Meat, Poultry and Seafood

Protein builds muscle, and BUCHI has flexed some muscles in the QC of many meats and meat products, including:

  • Animal meat (e.g. beef, pork, turkey, wild animals)
  • Fish meat
  • Sausage
  • Animal flour
  • Fish meal
  • Pig adipose tissue

Dairy

Our BUCHI NIR products are used to make sure that the stuff that goes into milk and milk products are in-spec, including:

  • Milk
  • Yogurt and fresh cheese
  • Hard, semi-hard and soft cheese
  • Processed cheese
  • Butter
  • Milk creams
  • Milk powders

Frozen and Prepared Foods

When you don’t have time to cook or time for long lab turn-around times, BUCHI NIR has methods developed for:

  • Dry pasta/noodles
  • Ready-meals (e.g. lasagna, meat pie, meat & fish ready noodles, frozen pizza)

Beverage

Drink up! BUCHI NIR can be used for quality control of beverages:

  • Distillers grains
  • Milk powders
  • Chocolate (e.g. cocoa & derivatives)

Getting hungry for more information?

Check out our Application Finder on the BUCHI website or Contact us to talk about your specific application needs.

 

Webinar! Best Practices in NIR Method Sample Planning

Missed our summer web-training series? Scratching your chin about how to get started on your next NIR project? Looking for something to do other than Farmville on your lunch hour?

Whether you are a dedicated BUCHI NIR power user or just looking to dip your toe in the NIR waters before taking the plunge, you are cordially invited to attend our September 27 webinar on NIR Method Sample Planning, part of our BUCHI Best Practices webinar series.  Use this link to register for the event!

During this webinar, you will receive tips and tricks on:

  • Identifying variables impacting method performance
  • Learning how to maximize calibration “learning” with fewer samples
  • Navigating calibration project workflow

Both qualitative and quantitative methods will be discussed.

Can’t wait til September 27? Contact us to discuss your upcoming/ongoing projects, or check out our BrightTALK Channel or blog archives for existing content to support your efforts.