PURE LABWATER GUIDE - Veolia

Spectroscopy
& spectrometry
Spectroscopy was historically the study of the interaction between radiation
and matter as a function of wavelength (l), and it referred to the use of visible
light dispersed according to its wavelength, i.e. by a prism. Later the concept
was further expanded to comprise any measurement of a quantity as a function
of either wavelength or frequency. Thus it also can refer to interactions with
particle radiation or a response to an alternating field or varying frequency
(v). Once the very close relationship between photon energy and frequency
(E=hv) was realised, where h is the Plank constant, a further extension of the
definition added energy (E) as a variable. A plot of the response as a function of
wavelength — or more commonly frequency — is referred to as a spectrum.
Spectrometry is the spectroscopic technique that is employed to assess the
concentration or amount of a given substances and the instrument that
performs such measurements is a spectrometer or spectrograph.
Techniques Include:
Flame Atomic Absorption
Spectrophotometry (F-AAS)
Although somewhat eclipsed by
ICP-MS and ICP-ES for multielement
analyses, the relatively modest cost
of AAS ensures its use in smaller
laboratories or for specific analyses.
Depending on the element, detection
limits vary from low ppb to ppm levels.
Type II water is usually pure enough
for most routine AAS and there is no
requirement for low levels of organic
compounds or bacteria.
Gas Chromatography – Mass
Spectrometry (GC-MS)
For GC, purified water is used to
prepare blanks, standards and sample
pretreatments, e.g. solid phase
extraction. Since high sensitivity can
be achieved in GC-MS, the requirement
for water purity is extremely stringent.
Very low TOC levels, i.e. less than 3
ppb, are required and this can best be
achieved by using a top-of-the-range
polisher that is fed with water that has
been pre-treated by Reverse Osmosis
for removal of ions and organic
compounds.
Graphite Furnace Atomic Absorption
Spectrophotometry
(GFAAS) also known as Carbon
Furnace Atomic Absorption
Spectrophotometry (CFAAS)
This variant of AAS in which the flame
is replaced with an electrically heated
graphite tube or rod can achieve very
high sensitivity in elemental analysis.
A top of the range Type I water polisher
is required that ensures ppt levels of
elemental impurities, 18.2 MΩ-cm
resistivity water and low TOC, while
multi-stage monitoring (as delivered by
the ELGA PureSure system – see right)
provides the best guarantee of purity.
Ultimate performance is achieved when
enhanced pre-treatment is followed
by continuous recirculation and repurification
of the polished water.
Mass spectrometry
This highly sensitive technique permits
trace analysis of complex mixtures
and therefore requires high purity
water. All sample pretreatments such
as solid phase extraction and sample
preparation steps require Type I (ultra
pure) water, which is produced by a top
of the range water ‘polisher’ system.
This gives ppt levels of elemental
impurities, 18.2 MΩ-cm resistivity water
and an extremely low TOC, typically