Moisture Measurement Methods: Karl Fischer vs NIR Technology

Posted by John Bogart on Wed, Jun 4, 2014

water in measuring cup 1Near Infrared (NIR) technology for moisture measurement is relatively new, compared to traditional moisture measurement methods like Karl Fischer. In some circumstances it does make sense to make the switch from KF to NIR for moisture measurement, but this isn’t the case for all situations. I often still hear about companies using the KF method, which is slow and labor intensive, when they should be switching to NIR technology to increase accuracy, get consistent product quality and reduce costs –it’s for those people I’m writing this article.

Karl Fischer (KF) Moisture Measurement

Originally invented by the chemist whose name it takes, the Karl Fischer Method (KF) of moisture measurement is based on chemical reactions. The product to be tested is combined in some fashion with chemical reagents.  A chemical reaction occurs where the water is separated chemically from the remainder of the sample.  The water is then moved to another cell where it is measured.  That measurement is compared with the initial mass or volume of the sample and the moisture content is calculated.  Karl Fischer tests can be very accurate, testing to the Parts Per Million (PPM) level. 

KF is one of two primary moisture measurement methods - meaning it’s a method that can test “anything” without calibration. 

Certain applications are better suited for primary moisture measurement, such as an independent test lab, a crime scene lab, customs office or within a pure product research facility.  Because samples aren’t available for calibration and may never be seen again after the testing is completed, it doesn’t make sense to calibrate a moisture meter to then be able to perform a rapid and non-destructive secondary moisture test. 

KF Pros

  • It is a primary method and doesn’t need calibration by product (within reason).
  • Can measure moisture content to a very high degree of accuracy.
  • Works very well when testing liquids.
  • Can measure hydrated molecules.
  • Can test very small samples.

KF Cons

  • It’s destructive. meaning the sample is altered and can’t be reused or reintroduced into the main product sample or batch. This can be an issue where the product is very rare and/or expensive.
  • It’s time consuming. In some cases one test can take an hour or more to complete.
  • It requires some degree of expertise. The KF method takes an initial degree of technical expertise to ensure that the chemical reagents are properly selected, the moisture test is properly configured, and the procedure defined for properly dealing with end-products including documentation for disposal.
  • It’s costly. Chemical reagents are used to perform the test – they are expensive to purchase and to dispose.


Industries Using The KF Method

Pharmaceutical companies are large consumers of the KF method. Given the variety of chemicals in their sample and the critical nature of the measurement and regulatory documentation necessary for all aspects of production and measurement, the KF moisture measurement technology is the first method considered. Another standard use for the KF technology is for the measurement of liquid samples.  Since the sample doesn’t need to be broken down from a solid into a liquid (by dissolution) the test is faster and can compete with loss-on-drying systems for throughput. 

Focus Industries

  • Pharmaceuticals
  • Chemicals
  • Flavoring
  • Cosmetics
  • Contract Test Laboratories

NIR TECHNOLOGY

Near infrared (NIR) moisture measurement uses reflectance & absorbance principles for calculating the moisture content of an item. The meter bounces a beam of light off the product (in some cases transmits the light through the sample). The light is filtered to a wavelength (or multiple wavelengths) that excite the moisture molecules. The higher the moisture content, the higher the amount of light absorbed. The instrument measures the light reflected back and an algorithm determines the light absorbed by the sample.

NIR is one of several secondary test methods available for moisture measurement. Secondary means the instrument is product specific, it must be calibrated for the specific requirements before it can be used. So while it make take some initial time to calibrate, once the instrument is set up it’s a much more efficient method for measuring.

Just as there are certain applications that lend themselves to using primary moisture meters, there are other applications where a secondary moisture measurement method would be preferable.

As mentioned, if test time is crucial, an instant moisture reading made by a secondary measurement technology is required. While there are some very unique (and expensive) automated samplers for process line primary measurements, generally if an online or inline measurement is required, a secondary method is used. Also, if destroying or altering the sample is a problem, a non-destructive secondary moisture meter is needed.

The level of expertise of the staff needed to conduct the test may also be a consideration. It’s a lot simpler to point an instrument at the sample and read the moisture content than it is to implement the KF method we mentioned above.

NIR Pros

  • Results are instantaneous.
  • The test is non-contact and non-destructive.
  • Can be used on almost any liquid or solid.
  • Portable, battery-powered units are possible along with online/inline and desktop form factors.
  • Can measure surface moisture to help with optimizing packaging, curing, drying, etc.
  • Can be used with other wavelengths to measure multiple organic concentrations in addition to moisture (fat/oil, protein, sugar, fiber, etc). 

NIR Cons

  • Needs to be initially calibrated (generally against a primary method).
  • Only a surface measurement of moisture. To work properly, there must be a relationship between the surface moisture and total moisture of the product. 

Industries Using NIR Method

NIR applications are wide and varied. Food manufacturers, processors and bulk food companies are large users of NIR moisture and composition analyzers. The tobacco industry has been a traditional large user of this method. The NIR method has started to dominate both the pulp and paper industries and pharmaceutical industries.

Focus Industries

  • Food and grain processors
  • Tobacco
  • Pharmaceutical
  • Pulp and paper
  • Minerals
  • Personal care products
  • Chemicals
  • Textiles

 

Other Resources You May Be Interested In

moisture measurement ebook The purpose of this guide to help you navigate the waters of the various moisture meter technologies, form factors, and companies and assist your efforts to provide your firm with accurate and reliable moisture meter. Learn more here
 different moisture measurement methods ebook If you are interested in pursuing the goal of accurate moisture measurement, including: quality control, quality assurance, production management, design/build engineers, executive management and of course anyone wanting to learn more about this far reaching topic - then this ebook is for you. Learn more here
 
measure moisture case study
Learn how this company used - Kett's Rent-To-Own offer to "test" the benefits of the instrument before making their buying decision. They were able to save time and money, by identifying locations in their production line where the plastic had extra moisture - without touching the raw material or films and without altering the product. Learn more here
 
moisture measurement real time case study
Learn how real-time moisture measurement, during the production cycle, of product development ensured a successful product launch for this client.   Learn more here

 

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