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Polishing up on water quality: point-of-use water polishers eliminate background interference and provide optimal water quality for LC.

Water plays a critical role in many analytical methods--particularly in the preparation of samples, standards, blanks, and eluents. It is crucial that water used for these applications does not introduce any impurities that could interfere with analytical results.

As modern analytical instruments become capable of detecting ever increasingly low concentrations of analytes, ensuring the lowest level of back-ground interference has become even more important--and more difficult.

To meet this challenge, laboratory water purification systems have evolved accordingly. Current systems such as the Milli-Q Integral (EMD Millipore) use a sophisticated combination of purification technologies to reduce ions, organics and other potentially background-causing contaminants to extremely low levels (i.e., 18.2 M .cm resistivity and [less than]5 [micro]g/mL of TOC).

However, in order to minimize background interference in certain highly sensitive chromatography applications, such as LC-MS and GC-MS, laboratory water needs to be further purified for the specific application with special point-of-use polishers installed at the outlet of "Type 1" (ultrapure) water purification systems.


A range of point-of-use polishers exist to provide optimal water quality for use in ultra trace organic analysis by LC methods, endocrine disrupter experiments, and in volatile organic compounds (VOC) analyses. Other polishers in the range can provide users with water that is free of pyrogens, nucleases, bacteria and particulates.

The following presents the results of experiments that were carried out to qualify three of these polishers (LC-Pak, VOC-Pak, and EDS-Pak from EMD Millipore), and includes GC-MS and LC-MS data demonstrating their efficiency in eliminating contaminants specific to the application for which they were intended.

Liquid chromatography polisher

* Ultrapure water for analysis of ultra trace organic compounds by LC-MS and UHPLC-MS

* The LC-Pak polisher uses reversed phase C18 granular silica to remove trace organic contaminants from pure water

Endocrine disrupter polisher

* Ultrapure water free of endocrine disrupters

* EDS-Pak (EMD Millipore) contains a specific activated carbon validated by challenge tests using common endocrine disrupters

Volatile organics compounds polisher

* Volatile organic compound-free ultrapure water

* VOC-Pak (EMD Millipore) contains a synthetic activated carbon validated by challenge tests using a range of 25 different VOCs

Liquid chromatography analyses

Developments in HPLC and MS instrumentations have tremendously improved separation efficiency and sensitivity, making detection and measurement of trace amounts of analytes possible. In order to avoid interferences that would make data analysis and interpretation more difficult, reversed phase HPLC methods for trace analysis need to meet stringent requirements for reagent and solvent purity.

For these very sensitive LC-MS applications, LC-adapted polishers produce high quality water that perform as well as, or better than, LC-MS grade bottled water. Based on reversed-phase chemistry, the polisher contains tightly packed C18 silica particles that retain traces of organic contaminants just before water is dispensed.

Ultrapure water further purified by this liquid chromatography (LC) polisher can be used in UHPLC, LC-MS or LC-MS/MS analytical techniques, for preparation of eluents, blanks and standards, as well as for glassware rinsing and sample preparation steps.

The LC-Pak polisher was extensively validated to ensure that water quality at the polisher outlet matches the demanding solvent quality requirements for LC-MS applications. It has been qualified for 500 L of water delivered for the parameters found in Table 1 below.
Parameter         Specification of LC-Pak     Comments
                  ultrapure water

HPLC gradient     At 210 ran < 0.006 AU; At   60 mL of water was
test              254 nm < 0.002 AU           pre-concentrated prior to

Absorbance of     At 210 nm < 0.003 AU; At    No water preconcentration
highest eluted    254 nm < 0.001 AU

Optical           200 nm < 0.05 AU; 205 nm <  According to procedure
properties        0.01 AU                     described in the ISO 3696

Absorbance in UV  210 nm < 0.01 AU; 254 nm <
range             0.005 AU

Fluorescence as   At 254 nm < 1ppb; At 365
Quinine           nm< 1ppb

Compliance with   No peak higher than 10 ppb
suitability for   of reserpine at m/z609 in
LC/MS             ESI+

Reserpine test

Residue after     < 0.0001% w/w               Test performed as
evaporation                                   specified in the ISO 3696

Table 1: Parameters tested for the qualification of an LC polisher
(LC-Pak, EMD Millipore)

The presence of organic contaminants in water that is used to prepare eluents could result in noisy baselines and be a source of ghost peaks that would later show up in chromatograms. To test the capability of the LC-Pak polisher in providing ultrapure water with extremely low organics, it was attached to the outlet of an ultrapure water purification system (Figure 1). Water at the inlet and outlet of the LC-Pak polisher was tested. Water to be analyzed was pre-concentrated on a pre-column for 60 min at 1 mL/min, followed by a gradient run from 100% water to 100% acetonitrile at 0.25 mL/min.


The UV and mass chromatograms of ultra-pure water obtained at the inlet and the outlet of the LC-Pak polisher are shown in Figure 2. Cleaner chromatograms are obtained when the water is purified with the LC-Pak, demonstrating the efficiency of the polisher in removing traces of organics that could interfere with sensitive HPLC methods.

Volatile organics compounds analyses

Scientists performing VOC analyses require a source of VOC-free ultrapure water that can be obtained with a VOC polisher such as the VOC-Pak (EMD Millipore).


To test the efficiency of this VOC polisher, high purity water was spiked at 1 [micro]g/L levels with various VOCs. Three hundred liters of this VOC-spiked water was made to pass through the cartridge and the concentrations of the VOCs at the outlet were measured by GC-MS. Figure 3 and Table 2 show the results for five of the 25 VOCs tested (chloroform, carbon tetrachloride, bromoform, benzene, toluene). The VOCs were no longer detected in the high purity water after passing through the VOC-Pak cartridge.

Volume  Chloroform (ppb)  Carbon         Bromoform  Benzene  Toluene
                          tetrachloride  (ppb)      (ppb)    (ppb)

100              <0.05 *        <0.05 *     <0.5 *  <0.05 *   <0.1 *

200              <0.05 *        <0.05 *     <0.5 *  <0.05 *   <0.1 *

300              <0.05 *        <0.05 *     <0.5 *  <0.05 *   <0.1 *

* Values below the limit of quantification of the analytical method.
Initial concentrations before passing through the VOC-Pak cartridge
were about 1 ppd

Table 2: VOC concentrations after different amounts of spiked water
are passed through a VOC polisher (VOC-Pak, EMD Millipore)

Endocrine disruptor analyses

As concerns for the presence of endocrine disrupters in the environment mount, many researchers are focusing their work on the effect(s) of these compounds on wildlife and humans. Endocrine disrupter-free water is needed for use in experimental tests, as well as for the analytical methods used to measure endocrine disrupters and monitor their presence in water, food, and other products.

The EDS-Pak (EDS polisher developed by EMD Millipore) contains a specific type of activated carbon carefully selected for its ability to remove the small organic molecules suspected of being endocrine disruptors.

To test the efficiency of this polisher in retaining endocrine disrupter compounds, high purity water was spiked with known endocrine disrupters (EDs) at the [mu]g/L TOC level: bisphenol A, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DnBP), nonylphenol. The EDs-spiked water was made to pass through the EDS-Pak and the concentrations of the EDs at the outlet were measured by GC-MS. None of the endocrine disrupters tested were detected in the spiked water after it passed through the polisher (Figure 4 and Table 3).

Volume (L)  Bisphenol A (ppb)  DEHP (ppb)  DnBP (ppb)  n-Phenol (ppb)

100                  <0.005 *      <0.2 *     <0.02 *          <0.1 *
200                  <0.005 *      <0.2 *     <0.02 *          <0.1 *
300                  <0.005 *      <0.2 *     <0.02 *          <0.1 *

* Values below the limit of quantification of the analytical method.
Initial concentrations of EDs were from 1.5 to 4 ppd.

Table 3: Result of the challenge test after different amounts of
spiked water are passed through an EDs polisher (EDS-Pak, EMD

Application match

A range of point-of-use polishers exists to meet the high purity water requirements of specific applications. Scientists should take advantage of the range of available point-of-use polishers and select the device that best matches their research needs to be sure they obtain the highest purity water adapted to their work.

Additional information on point-of-use water polishers can be found at:

by Cecilia Devaux, Coralie Monferran, Maricar Tarun, Estelle Riche, Daniel Darbouret, Laboratory Water Business Field, EMD Millipore, Saint-Quentin-en-Yvelines, France, and Billerica, Mass.
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Title Annotation:Cover Story
Author:Devaux, Cecilia; Monferran, Coralie; Tarun, Maricar; Riche, Estelle; Darbouret, Daniel
Publication:Laboratory Equipment
Date:Dec 1, 2010
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