Citation: Schäfer, S.H.; van Dyk, K.;
Warmer, J.; Schmidt, T.C.; Kaul, P. A
New Setup for the Measurement of
Total Organic Carbon in Ultrapure
Water Systems. Sensors 2022, 22, 2004.
https://doi.org/10.3390/s22052004
Academic Editor: Sergi
Garcia-Segura
Received: 21 January 2022
Accepted: 2 March 2022
Published: 4 March 2022
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Article
A New Setup for the Measurement of Total Organic Carbon in
Ultrapure Water Systems
Sara H. Schäfer
1,
* , Katharina van Dyk
2
, Johannes Warmer
2
, Torsten C. Schmidt
3
and Peter Kaul
1
1
Department of Natural Science, Safety and Security Research Institute, Bonn-Rhein-Sieg University of
Applied Science, 53359 Rheinbach, Germany; peter.kaul@h-brs.de
2
Innovatec Gerätetechnik GmbH, 53359 Rheinbach, Germany; k.vdyk@innovatec-rheinbach.de (K.v.D.);
j.warmer@innovatec-rheinbach.de (J.W.)
3
Department of Instrumental Analytical Chemistry, University of Duisburg-Essen, 45147 Essen, Germany;
torsten.schmidt@uni-due.de
* Correspondence: sara.schaefer@h-brs.de; Tel.: +49-2241-865-521
Abstract:
With the increasing demand for ultrapure water in the pharmaceutical and semiconductor
industry, the need for precise measuring instruments for those applications is also growing. One
critical parameter of water quality is the amount of total organic carbon (TOC). This work presents a
system that uses the advantage of the increased oxidation power achieved with UV/O
3
advanced
oxidation process (AOP) for TOC measurement in combination with a significant miniaturization
compared to the state of the art. The miniaturization is achieved by using polymer-electrolyte
membrane (PEM) electrolysis cells for ozone generation in combination with UV-LEDs for irradiation
of the measuring solution, as both components are significantly smaller than standard equipment.
Conductivity measurement after oxidation is the measuring principle and measurements were
carried out in the TOC range between 10 and 1000 ppb TOC. The suitability of the system for TOC
measurement is demonstrated using the oxidation by ozonation combined with UV irradiation of
defined concentrations of isopropyl alcohol (IPA).
Keywords: TOC; ultrapure water; ozonation; AOP; O
3
/UV
1. Introduction
The quality of ultrapure water is of particular importance in the pharmaceutical and
semiconductor industry. Due to its unique properties, it serves as a solvent or starting
product for the preparation of injection solutions, and it is also used to clean surfaces in
the production of high-precision components in semiconductor manufacturing. Contami-
nation of any kind leads to considerable loss in the quality of the manufactured products
in semiconductor industry, and impurities in water for injections would have a direct
impact on human health [
1
,
2
]. For this reason, water quality is of utmost importance and
requires monitoring.
An important parameter for the quality of ultrapure water is the total organic carbon
(TOC). TOC is defined as the carbon content of dissolved (DOC) and non-dissolved (NDOC)
organic carbon present in water. DOC is furthermore defined as the sum of organically
bound carbon after membrane filtration with a filter of 0.45
µ
m pore size [
3
]. Because
water is filtered in an ultrapure water system, the influence of the NDOC is irrelevant for
this work and, consequently, no further distinction is made here between TOC and DOC.
TOC is a sum parameter that serves as an indicator for the extent of organic pollution in
water. Organic substances are the most common contaminants in water [
4
], thus the TOC
is a key criterion for the water quality of ultrapure water and the measurement of TOC
allows an estimation of the degree of pollution of water in general. As ultrapure water
has only trace amounts of organic pollution, a very sensitive method is needed for water
analysis. Thresholds and standards for the analysis of TOC are defined by the European
Sensors 2022, 22, 2004. https://doi.org/10.3390/s22052004 https://www.mdpi.com/journal/sensors
