Introduction
The Health Care industry has increased its needs for
specialized devices over the past decade, which has led to a new frontier of
resin and polymer development designed to keep the quality of care high while
minimizing cost. With these goals in
mind, the resins being used for medical devices are scrutinized more thoroughly
than other resins that require less regulatory compliance. Analyzing a product for outgassing,
deformation, and reactivity, among other things, has become part of the daily
routine for manufacturers, molders, and final inspection personnel before an
item can be shipped or used. This
additional testing and control also includes the amount of water that is allowed
in the resins, since this will greatly influence the final product's rigidness,
consistency, and lifetime, as well as the quality of care that will be provided
to the customer. Oftentimes the quality control
of the materials is closely monitored using testing equipment defined in an IQ/OQ/PQ:
installation qualification (IQ), operational qualification (OQ), and performance
qualification (PQ) to ensure that the instruments are effective, and the
quality of the product is consistent.
Moisture
Determination
As an alternative to the Coulometric
Karl Fisher titration, Relative Humidity (RH) sensor moisture detection was
first used as a method for determination of water in materials in 1997, with
the introduction of the Computrac® 3000 Moisture Analyzer by Arizona Instrument
LLC. This method uses a thermoset polymer
capacitor that has a selective response when in the presence of water, the same
way that many RH sensors work in traditional settings such as houses,
laboratory controlled environments, and dry boxes.
Medical device resins are sealed in a sample vial, and then transported into an oven chamber with inert gas blown through it. As the material gets hot, water molecules evolve off and are carried to the sensor via the carrier gas. The sensor is exposed to the water molecules and a measurable change in the electronic activity takes place. This method requires no solvents, making it an environmentally friendly alternative to traditional chemical titration. The instrument provides in-situ moisture measurements, which allows users to monitor performance in real time. Additionally, it has a lower detection limit of 10ppm, and is more rugged than Karl Fisher titrators, making it a suitable instrument for moisture analysis in manufacturing facilities, as well as Quality Control and inspection labs. This technology is now being adopted as the standard test method and is described by ASTM D7191, Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor. This instrument also meets the high demands of performance given in an IQ/OQ/PQ.
Medical device resins are sealed in a sample vial, and then transported into an oven chamber with inert gas blown through it. As the material gets hot, water molecules evolve off and are carried to the sensor via the carrier gas. The sensor is exposed to the water molecules and a measurable change in the electronic activity takes place. This method requires no solvents, making it an environmentally friendly alternative to traditional chemical titration. The instrument provides in-situ moisture measurements, which allows users to monitor performance in real time. Additionally, it has a lower detection limit of 10ppm, and is more rugged than Karl Fisher titrators, making it a suitable instrument for moisture analysis in manufacturing facilities, as well as Quality Control and inspection labs. This technology is now being adopted as the standard test method and is described by ASTM D7191, Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor. This instrument also meets the high demands of performance given in an IQ/OQ/PQ.
With major advances in technology, the medical device community is also taking advantage of new RAPID loss-on-drying methods for moisture determination. These instruments use the same principle as traditional loss-on-drying techniques, but address the shortcomings of the method. Sample material is heated on a balance and real time measurements are providing immediate feedback and moisture concentration. The Computrac® MAX® 4000XL instrument, manufactured by Arizona Instrument LLC, provides a parameter development expert program that allows users to optimize testing conditions, such as sample size, test ending criteria, testing temperature, idle temperature, temperature rate, etc. The chassis of this instrument is made of steel, which prevents cracking in the case and cool air from entering the testing chamber, which would influence the results. These new techniques are being adopted as standard testing methods and are described by ASTM D6980-12, Standard Test Method for Determination of Moisture in Plastics by Loss in Weight. Like the Vapor Pro® 3100L, the MAX® 4000XL meets the performance standards set forth in typical IQ/OQ/PQ testing.
Testing
Sample
Prep – A medical grade TPU was selected for analysis. The material was stored wet in a 1 gallon
plastic Ziploc bag prior to testing. An
initial analysis was conducted to determine the water content prior to
drying. The material was then dried in
the Dri-Air HP4-X 25 plastics drying hopper for 6 hours prior to testing. The material remained in the dryer during
testing due to the hygroscopic properties of the material.
Test
Conditions - Reference testing was conducted using the Mitsubishi CA-100
Coulometric Karl Fischer titrator. The
parameters were: sample size – 0.5g +/- 0.1g, temperature – 90°C,
purge/preheat/cooling – 1/2/2, ending sensitivity – 0.1µg/sec.
Corollary testing was conducted
using the Computrac® Vapor Pro® 3100L. The
parameters were: sample size – 2g +/- 0.2g, temperature – 105°C, purge – 50
sec., ending criteria – rate < 0.1µg/sec.
Results
Graph 1.
Total moisture curve of pre-dried TPU
From the table, the results using
the two different instruments with similar testing conditions correlate to each
other. The Vapor Pro® did show an
improvement in the relative standard deviation, but did require a slightly
longer test time than the Karl Fischer.
Additionally, the Vapor Pro® provided real time data points that could
be used to graph the total moisture curve.
This allows for better monitoring of the product, or diagnosing possible
problems with the instrument. This
feature was not available for Karl Fischer titrator.
Conclusion
The development of an alternative
to Karl Fischer moisture analyzer has been achieved, and can be used for
moisture specific analysis of medical device grade resins. The Computrac® Vapor Pro® 3100L moisture
analyzer successfully uses Relative Humidity sensor technology for selective
and accurate moisture measurement. The instrument
reduces the use of hazardous organic solvents makes it an environmentally
friendly alternative, when compared to current Karl Fischer technology. The results between the two methods of
detection of H2O content in TPU strongly correlate, with the Vapor
Pro® 3100L providing real-time data that can be used to provide a complete
profile of the TPU.
James Moore, Chemist
Arizona Instrument LLC • 3375 N. Delaware St., Chandler, AZ 85225 • www.azic.com
(800) 528-7411 • sales@azic.com
(800) 528-7411 • sales@azic.com
