How to Detect Moisture in Device Resins

The development of new polymers and resins to supply high quality care at a low cost is a result of a growing need for specialized medical devices. The resins employed for medical devices are put through stringent analysis, which includes detecting the presence of moisture. This moisture largely affects the consistency, service life, and rigidness of the final product, plus the quality of care that will be provided to the consumers.

To establish the effectiveness of the instruments and consistency of the final product standard, the quality control of medical device resins is monitored closely with testing devices described in installation qualification/operational qualification/performance qualification (IQ/OQ/PQ).

Moisture Determination

The emergence of the Computrac® 3000 Moisture Analyzer from Arizona Instruments has permitted the utilization of Relative Humidity (RH) sensor moisture detection as a viable solution to the Coulometric Karl Fisher titration to establish water in materials.

This method uses a thermoset polymer capacitor that shows a selective response if water is detected like many RH sensors working in conventional settings such as laboratory controlled environments and dry boxes.

The technique entails sealing medical device resins in a sample vial and transporting them into an oven chamber which is circulated with inert gas. Water molecules evolve off and are transported through the carrier gas towards the sensor to be detected once the material becomes hot. The decreased utilization of solvents make this technique an environmentally friendly alternative to conventional chemical titration.

To facilitate real-time performance monitoring by users, the Computrac® 3000 Moisture Analyzer has the ability to yield in-situ moisture measurements.

The detection limit of the Computrac® 3000 Moisture Analyzer is extremely low compared to Karl Fisher titrators, it is in the range of 10 ppm, making it the ideal device for moisture analysis in inspection laboratories, quality control, and manufacturing facilities. The analyzer also meets the high performance demands outlined in IQ/OQ/PQ.

The medical device community is utilizing new rapid loss on drying methods for moisture analysis because of major technological developments. These devices use the same principle of conventional loss on drying methods, but address their drawbacks. Heating of the sample is carried out on a balance and moisture concentration can be established instantly with real-time measurements.

Allowing users to optimize testing parameters, including idle temperature, temperature rate, test ending criteria, testing temperature, and sample size, Arizona Instrument’s Computrac® MAX® 4000XL provides a parameter development expert program. The steel chassis of this device stops cool air entry into the testing chamber and case cracking, which can affect the results. Like the Vapor Pro® 3100L, the MAX® 4000XL fulfills the performance requirements outlined in typical IQ/OQ/PQ testing.

Moisture Analysis

The sample utilized in this analysis was stored wet in a one gallon plastic Ziploc bag before analysis and was a medical grade TPU. An initial analysis was carried out for establishing the water content in the material, followed by drying in the Dri-Air HP4-X 25 plastics drying hopper for 6 hours before testing.

The material stayed in the dryer throughout analysis due to the hygroscopic properties of the material. Reference testing was carried out using a Karl Fischer titrator. The Computrac® Vapor Pro® 3100L was utilized to undertake corollary testing.

Table 1. Analysis Results

  Karl Fischer Vapor Pro 3100L
  Result (ppm) Test time Result (ppm) Test time
  47 6:53 51 12:32
  58 7:30 74 14:36
  67 7:04 53 12:20
  79 7:46 78 15:08
      69 13:18
Average 62.75   65  
S.D. 13.57387196   11.00908716  
RSD 21.63166846   16.93705716  


The results can be observed in Table 1, it shows the correlation between the results gathered from the two different devices under similar testing conditions. The Vapor Pro® exhibited an improvement in the relative standard deviation but the analysis time was slightly longer compared to the Karl Fischer.

In addition, the Vapor Pro® yielded real time data points, which could then be utilized to plot the total moisture curve (Figures 1 and 2). This permits improved product monitoring or diagnosing potential problems with the device. The Karl Fischer titrators do not possess this feature.

Total Moisture Curve of pre-dried TDU

Figure 1. Total Moisture Curve of pre-dried TDU.

Total Moisture Curve of TPU Dried for 6 hr at 200 °F.

Figure 2. Total Moisture Curve of TPU Dried for 6 hr at 200 °F.


The successful application of the Relative Humidity sensor technology by the Computrac® Vapor Pro® 3100L moisture analyzer is clearly shown for accurate and selective measurement of moisture content in medical device grade resins.

This analyzer is an eco-friendly alternative to current Karl Fischer moisture analyzers because of the decreased utilization of harmful organic solvents. The results of water content in TPU gathered from the two different instruments agree strongly with each other. The Vapor Pro® 3100L yields real-time data, which can be used to gain a comprehensive profile of the TPU.

About AMETEK Arizona Instrument

Initially known as the Quintel Corporation, Arizona Instrument LLC was founded in 1981 by a group of engineers breaking away from The Motorola Corporation who were dedicated to the idea of providing precision moisture analysis instruments that were accurate, reliable, and easy to use.

The first instrument released was the MA Moisture Analyzer, but the company quickly expanded its Computrac® moisture analysis line and became an accepted leader in moisture analysis, setting a standard that has been adopted by many Fortune 500 companies. Today the Computrac® line is comprised of three technologies: rapid loss-on-drying, high temperature loss-on-ignition, and moisture specific analysis using polymer capacitance sensor, GREEN alternative to Karl Fischer.

In 1986, Arizona Instrument acquired Jerome Instrument Corporation the manufacturers of the Jerome® toxic gas analyzers. At the time of purchase the corporation had an established reputation for accuracy and durability, which complemented and added depth to the Arizona Instrument’s offerings; and these traditions continue today. The Jerome® line is comprised of instruments used for detecting low-level mercury and hydrogen sulfide gases. Both portable detection and fixed position monitoring solutions are available, using gold film sensor and atomic fluorescence spectroscopy technologies as the method of detection.

Through the years Arizona Instrument has pursued and maintained a total quality management system, being certified initially as ISO 9001:1994 then ISO 9001:2000 and most recently ISO 9001:2008. Though the company is located in Chandler, Arizona, its distributors and service centers located around the world provide consistent, dependable service to its many customers worldwide.

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Last updated: Sep 29, 2020 at 7:58 AM


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