INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 46)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
CRYSTALS, HOLDERS AND FLOW CELL 4-8
4.2.1 CRYSTAL CLEANING
The surface properties of the sensor crystal determine the interaction of sample material with the
surface. Therefore, the developments of proper procedures for cleaning are required to obtain
meaningful and reproducible measurements. This section provides the basic information you need
to develop a cleaning procedure suited to your sample/surface preparation.
CAUTION
– When developing a cleaning procedure, always perform
a test run on a crystal before committing to a larger batch cleaning.
Follow the crystal handling guidelines throughout the cleaning process
to protect the crystal quality. Avoid using high pH cleaners since they
will etch the crystal surface.
4.2.1.1 General Cleaning
For general purpose applications such as electrochemistry and liquid or viscoelastic film
experiments, it is usually sufficient to clean the crystals in a solution of non-basic detergent
in deionized water. Immediately rinse liberally with deionized water and dry in a gentle flow
of filtered nitrogen gas.
4.2.1.2 Organic (hydrocarbon contaminants)
UV/ozone treatment 12 is a powerful tool for removing hydrocarbon impurities which have been
adsorbed from the ambient air. This method utilizes irradiation with ultra violet light that breaks
up the organics on the surface of the sample being cleaned. A flow of air or a weak vacuum
carries off the organics. This method does not affect the quartz surface; it is low cost and is very
efficient.
Oxygen plasma cleaning is another effective method that will remove organic matters. In this
method, the plasma reaction breaks up organic matters at the surface of the sample being cleaned
into smaller molecules and a vacuum pump removes them from the surface of the sample.
4.2.1.3 Biomaterials (lipids, proteins and similar biomolecules)
Start by treating the crystal in an UV/ozone chamber for 10 minutes, then immerse it into a
1:1:5 solution of hydrogen peroxide (30%), ammonia (25%) and deionized water heated
to a temperature of about 75°C for 5 minutes
22
. Immediately rinse liberally with
deionized water and dry in a gentle flow of nitrogen gas. Immediately before
measurement, treat the crystal with UV/ozone for 10 minutes.
4.2.1.4 Lipid vesicles on SiO
2
surfaces
Treat the crystal in an UV/ozone chamber for 10 minutes, then immerse it into water with
2% of sodium dodecyl sulfate (SDS) at room temperature for 30 minutes
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. Rinse
generously with deionized water and blow dry with filtered nitrogen gas. Immediately before
measurement, treat the crystal with UV/ozone for 10 minutes.
4.2.1.5 Polystyrene removal
To clean polystyrene (PS) off a crystal, immerse the crystal into a 1:1 solution of hexane
and deionized water. Rinse thoroughly with deionized water and blow dry with filtered
nitrogen gas.
4.2.1.6 Polymer Removal
To clean polymers from the crystals a combination of plasma cleaning with O2 plasma and
piranha solution is recommended. However, it is best to remove the bulk of the material with