Importance of ultra pure water for
analytical research and testing techniques
-impact of laboratory water handling and storage
procedures on its purity
Dr Paul Whitehead, Laboratory Manager, ELGA R&D Facility
Objectives
• Define the purity of ultra pure water and compare it to other
solvents used in analytical research and testing applications.
• Study the impact of ultra pure water impurities on the reliability and
reproducibility of ion chromatography.
• Examine the background levels of ultra pure water for ultra-trace
HPLC and ion chromatography analysis.
• Determine the affects that certain general laboratory dispensing and
storage procedures have on the purity of ultra pure water.
Background
• Pure water is crucial for analytical research and testing applications.
• Elements and compounds in the parts per billion (ppb) range or
lower could affect results by interacting with samples or
system components.
• One hundred per cent pure water consists solely of water
molecules in equilibrium with hydroxyl(OH-) and hydrogen
(H+)ions (10-7M at 25ºC)
• Characteristic electrical resistivity of 18.2 Mohm.cm.
• Type 1 ultra pure water is by far the purest substance
used in a laboratory.
Water challenge
• Water has the ability to:
• dissolve almost every chemical compound to some extent
• support nearly every form of life
• Water purity is under continual threat from five types of impurities:
• suspended particles;
• inorganic compounds;
• organic molecules;
• dissolved gases;
• microorganisms including their associated biomolecules
Producing high purity lab water
• High purity lab water is produced from mains drinking water via a
series of purification steps to remove the 5 different types of
impurities.
Maintaining high purity lab water
• A range of techniques maintain the purity of ultra pure water within
the purifier:
• composite vent filter protects the water reservoir from
external contamination
• periodic recirculation of water through the final purification
technologies e.g UV photo-oxidation, adsorption
and ion-exchange
• regularly sanitising the system to minimise bacterial growth
Ultra pure water specification
• Ultra pure water needs to be free from all 5 types of impurities for
the whole range of analytical and experimental applications.
• Measuring the levels of impurities in ultra pure water is
limited by the measurement technique’s sensitivity and the
testing environment.
• Current ultra-trace techniques, ultra pure water is:
• ≥99.99999975 % pure
• Maximum total non-gaseous impurities:
• < 1.5 µg/l (ppb)
• Organic compounds:
• <1.0 µg/l for other elements and ions.
Comparing ultra pure water purity to other analytical
and research testing solvents
ICP-MS Analysis : Comparison of Elemental Impurity Specifications of
Ultra pure Water and Top Grades of Common Solvents for Analytical
Research and Testing.
All non-gaseous elements
were effectively absent
from ultra pure water i.e.
most had detection limits
of less than 1 ng/l (ppt )
which is orders of
magnitude less than all
the other solvents tested.
The impact of ultra pure water contaminants on ion
chromatography, reliability and reproducibility
• Water may be used in many aspects of an analysis:
• preparation of samples,
• dilutions, standards, blanks, eluents
• rinsing instruments
The impact of ultra pure water contaminants on ion
chromatography, reliability and reproducibility
Effects of water impurities on ion chromatography:
(a) on the system and (b) potential impact on experimental results.
The impact of ultra pure water contaminants on ion
chromatography, reliability and reproducibility
Summary of effects of water impurities on ion chromatography:
• The effects of contamination from ions, organics, colloids, bacteria and
gases can all impact on sensitivity and reproducibility to some degree,
thereby compromising and potentially negating results.
• Contaminating ions tend to have a significant but short-term effect,
producing high blanks, high background and chemical interferences that
directly impact results.
• Organics, colloids and bacteria affect background/blanks but also tend to
have a longer-term impact through media fouling and surface coating that
can affect parts of the instrumentation, such as the chromatography column,
the detector or inner surfaces of the system itself.
The impact of ultra pure water on backgrounds for HPLC
and ion chromatography
HPLC analysis: UV detection at 210nm.
Significant improvements in background for HPLC with UV detection at
210nm was obtained using ultra pure water with very low TOC
compared to pure water with higher TOC.
The impact of ultra pure water on background of ion
chromatography
ICP-MS Analysis: Ultra-trace cation analysis by pre-concentrating 20ml
sample.
• Using ultra pure water minimises background levels, enabling highly sensitive
and accurate results in analyses using ion chromatography.
The effect of exposing ultra pure water to air over time,
with and without stirring
Results
• Within seconds the ultra pure water starts to absorb CO2 from the air forming carbonic acid. This
procedure occurs more rapidly with stirring and reduces the resistivity of the water from 18.2
Mohm.cm to a minimum of about 1.3 Mohm.cm.
•
Though this carbon dioxide does not degrade the water for most applications,
its effect on resistivity can mask the contamination of the water by other ions.
Contamination from the atmosphere due to different
water collection methods
Negative ion chromatography analysis:
(a) water collected with splashing;
(b) water collected by flowing it along the vessel i.e no splashing
•
Analysis clearly showed that negative ions, particularly nitrite ions, were
detected at higher concentrations when splashing had occurred.
•
When ultra pure water is dispensed impurities in the air can also reduce the
water’s purity therefore it is important that air entrainment is minimised.
Plasticizer contamination from passing ultra pure water
through plastic tubing
GC-MS analysis of ultra pure water: effect of plasticizer in tubing.
•
GC-MS scans show that ultra pure water passed through flexible PVC tubing can be contaminated with
N-butyl-benzene sulphonamide plasticiser illustrating that tubing organic release agents or plasticisers
can leach into the water.
•
A pharmaceutical company survey showed that the average total viable bacterial
count in water from 22 water purifiers without tubing was 0.7 CFU/ml. This
increased to 26 CFU/ml for 7 units with dispense tubing.
Assessing ultra pure water contamination after storage
in glass v plastic bottles
LC-MS Analysis: comparison of phthalate ester contamination from glass
versus plastic wash-bottles* after 2 days storage.
References A) Suzuki, Kawaguchi, Enami and Kuroki: Abstract of Proceedings of 15 th Environmental Chemistry Forum, 2006, 182-183. (3). B) Clinical and Laboratory
Standards Institute. Preparation and Testing of Reagent Water in the Clinical Laboratory; Approved Guideline-Fourth Edition. CLSI document C3-A4, 2006. C) Kuroki:
Chromatography, 2006, 27(3), 125-9. D) Kuroki: Industrial Water, 2003, 541, 24-30. (2). E) Horikiri S., Fujita N., Kuroki Y. and Enami T. Abstracts of Proceedings of
54th Mass Spectrometry Analysis General Forum, 2006, 458-459.
Assessing ultra pure water contamination after storage
in glass v plastic bottles
LC-MS Analysis: comparison of phthalate ester contamination from glass
versus plastic wash-bottles* after 2 days storage
• For trace organic analyses glass bottles are preferable for storing water to plastic
wash-bottles i.e. in addition to other impurities, di-n-octyl phthalate was present in the
water from the plastic wash-bottle at ppb levels but at much lower levels in glass bottle
water.
• To maximise its purity, ultra pure water should be used soon after it is dispensed. In a
survey of wash-bottle use, Kuroki et al., found that over 80% of users did not refill their
wash-bottles every day with ultra pure water.
• Similar contamination problems can occur if bottled purified water for high sensitivity
analysis is stored and reused after opening.
*Horikiri S. et al . Abstracts of Proceedings of 54th Mass Spectrometry Analysis General Forum, 2006, 458-459.
References A) Suzuki, Kawaguchi, Enami and Kuroki: Abstract of Proceedings of 15 th Environmental Chemistry Forum, 2006, 182-183. (3). B) Clinical and Laboratory
Standards Institute. Preparation and Testing of Reagent Water in the Clinical Laboratory; Approved Guideline-Fourth Edition. CLSI document C3-A4, 2006. C) Kuroki:
Chromatography, 2006, 27(3), 125-9. D) Kuroki: Industrial Water, 2003, 541, 24-30. (2). E) Horikiri S., Fujita N., Kuroki Y. and Enami T. Abstracts of Proceedings of
54th Mass Spectrometry Analysis General Forum, 2006, 458-459.
Conclusion
• The extremely high purity of ultra pure water enables accurate
results to be obtained from high sensitivity analyses such as ion
chromatography and HPLC.
• The analytical accuracy of ion chromatography and HPLC is
dependent, on the use of water from a well designed water
purification system to maintain and monitor the ultra pure water’s
purity within the system.
• Easy to use ultra pure water dispensing and good laboratory
practise during collection and use are essential to maintain the
purity of ultra pure water and prevent results being compromised.
Thank You
Presentation prepared by:
Dr Paul Whitehead
Laboratory Manager, ELGA R&D Facility
Lane End Industrial Park, High Wycombe, HP14 3BY, UK.
www.elgalabwater.com