TECHNOLOGY NOTE 26

PureSure® System used inPURELAB® Chorus 1
Ensures removal of weakly ionized impurities

Organic compounds and silica are among the species least
strongly held by the ion exchange resins. After a period of use,
the ion exchange capacity of a purification pack starts to be
used up and these compounds are released first, even before
the resistivity has fallen much below 18.2 MΩ-cm. This is shownin Figure 1 where the TOC and silica content of the water rises
rapidly as the product water resistivity starts to fall. Theseproblems are avoided in the PURELAB Chorus 1 as any organics
and silica released from the primary purification pack as it
exhausts, are retained on the second, polishing pack which is still
highly regenerated.

Increased security

Figure 1:

PURELAB Chorus 1 product water purity is not dependent on
accurate resistivity and temperature measurements. Even thebest meters are only accurate to ± 0.2 MΩ-cm and those used in
the laboratory water purifiers are more typically ± 0.4 MΩ-cm.
A conventional water purifier relies on changing the purification
packs as soon as the output resistivity drops below 18.2 MΩ-cm
in order to maintain the highest water purity.
Table 1
Impurity
Na +CIFe2+
Na + + CI- + SO42NaCl

Volume (liters)

18.2 MΩ-cm
0.8
<0.1
2.0
<0.1
<0.1

Any error in the resistivity or temperature will seriously
threaten the water purity from the unit. This could result inorganics or silica release as shown in Figure 1 above, or thepresence of other ions as in Table 1. In the PURELAB Chorus 1
any minor errors in the measurements will only affect thechange-over point of the packs and have no effect on theoutput water purity.

Impurity Levels in Purified Water of Different Resistivities
Concentrations in µg/l which could be present at resistivity of18.0 MΩ-cm17.5 MΩ-cm
1.3
1.8
0.15
0.5
2.4
3.0
0.3
1.1
0.2
0.9

Advanced warning of usable purification pack life
A further advantage lies in the security provided by the PURELAB
Chorus 1 system. If the ‘Intermediate Purity’ alarm warning isignored, the PURELAB Chorus 1 will continue to produce 18.2
MΩ-cm water for another 1000 liters or more with a 35 µS/cm
feed. This is due to the polishing pack which is virtually unused
when the primary purification pack needs to be changed.
Where regular logging of water purity is required the security
provided by the PURELAB Chorus 1 system offers the advantage

15.0 MΩ-cm
3.6
2.1
5.4
5.4
5.0

that, even with very heavy usage, daily recording is sufficient toguarantee that the product water will be maintained at ultrapure
purity, 18.2 MΩ- cm, throughout the whole day. This would be
the case even if the intermediate purity fell below 1 MΩ-cm
early in the day.
In a conventional water purifier, if the resistivity drop is notdetected or ignored, serious contamination can result as shownin Table 1 and frequent logging and validation of resistivity
monitors would be needed.

ELGA LabWater
Tel: +44 (0) 203 567 7300 Fax: +44 (0) 203 567 7205 Email: info@elgalabwater.com Website: www.elgalabwater.com
ELGA® is the global laboratory water brand name of Veolia Water Technologies. VWS (UK) Ltd. Registered in England & Wales No. 327847 © Copyright 2014 ELGA LabWater/VWS (UK) Ltd.
All rights reserved. As part of our policy of continual improvement we reserve the right to alter the specifications given in this technology note. Technology Note TN26.