Moisture Detection in Medical Device Resins

The requirement of specialized medical devices has led to the development of new resins and polymers to provide high quality care at a low cost. The resins utilized for medical devices are subjected to stringent analysis, which includes detecting the presence of moisture, as this largely affects the final product's service life, consistency, and rigidness, in addition to the quality of care that will be offered to the consumers.

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

Moisture Determination

The advent of the Computrac® 3000 Moisture Analyzer from Arizona Instrument enabled the use of Relative Humidity (RH) sensor moisture detection as an alternative solution to the Coulometric Karl Fisher titration to determine water in materials. This technique employs a thermoset polymer capacitor that shows a selective response in the presence of water like many RH sensors working in conventional settings such as dry boxes and laboratory controlled environments.

The process involves sealing medical device resins in a sample vial and transporting them into an oven chamber circulated with inert gas. When the material becomes hot, water molecules evolve off and are carried through the carrier gas towards the sensor to be detected. The reduced use of solvents makes this method an environmentally friendly alternative to conventional chemical titration. The Computrac® 3000 Moisture Analyzer’s ability to yield in-situ moisture measurements facilitates real-time performance monitoring by users.

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

With major technological developments, the medical device community is using new rapid loss on drying techniques for moisture analysis. These devices apply the same principle of conventional loss on drying methods, but tackle their drawbacks. Heating of sample is performed on a balance and moisture concentration can be determined immediately with real-time measurements.

Arizona Instrument’s Computrac® MAX® 4000XL offers a parameter development expert program, which enables users to optimize testing parameters, including temperature rate, idle temperature, testing temperature, test ending criteria and sample size. The steel chassis of this device prevents case cracking and cool air entry into the testing chamber, which would 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 used in this analysis was a medical grade TPU, which was stored wet in a one gallon plastic Ziploc bag before analysis. An initial analysis was performed for determining the water content in the material, followed by drying in the Dri-Air HP4-X 25 plastics drying hopper for 6hr before testing.

The material remained in the dryer during analysis because of the hygroscopic properties of the material. Reference testing was performed utilizing a Karl Fischer titrator. The Computrac® Vapor Pro® 3100L was used to perform 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 are summarized in Table 1, showing the correlation between the results obtained from the two different devices under similar testing conditions. Although the Vapor Pro® showed an improvement in the relative standard deviation, it took slightly longer analysis time compared to the Karl Fischer. Furthermore, the Vapor Pro® yielded real time data points, which could be used to plot the total moisture curve (Figures 1 and 2). This enables better product monitoring or diagnosing potential problems with the device. The Karl Fischer titrators do not have 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 6hr at 200°F.

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


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

The reduced use of harmful organic solvents makes this analyzer an eco-friendly alternative to current Karl Fischer moisture analyzers. The results of water content in TPU obtained from the two different instruments strongly agree with each other. The Vapor Pro® 3100L yields real-time data, which can be applied to obtain a comprehensive profile of the TPU.

Arizona Instrument

This information has been sourced, reviewed and adapted from materials provided by AMETEK Brookfield Arizona

For more information on this source, please visit AMETEK Brookfield Arizona


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