Thermo Scientific 43iQ, Instruction Manual

Page: 148 / 284

Calibration
Equipment Required
4-2 43iQ Instruction Manual Thermo Scientific
An SO
2
-free (< 0.0005 ppb) air supply is required for the proper calibration
and checkout of the instrument. There are several methods that are
acceptable to generate this zero air.
Commercial heatless air dryers filled with a mixed bed of activated charcoal
and a 13X molecular sieve have been found effective in removing SO
2
from
compressed air. The use of this type of zero gas system is recommended
when minimum maintenance is of prime importance. This system requires
a source of compressed air. Refer to the manufacturer’s recommendations
for installation of such a system.
An absorbing column packed with activated charcoal is acceptable for
scrubbing SO
2
from ambient air. Ambient air is forced through a
laboratory gas absorption column packed with the charcoal and the SO
2
is
removed to acceptable levels (<0.0005 ppb). The charcoal should be
changed at a minimum of every six months. It may be necessary to change
the charcoal more frequently depending on local conditions.
A cylinder of SO
2
in air containing an appropriate concentration of SO
2
suitable for the selected operating range of the analyzer under calibration is
necessary. The assay of the cylinder must be traceable either to a National
Institute of Standards and Technology (NIST) SO
2
in Air Standard
Reference Material (SRM) or an NIST/EPA approved gas manufacturer's
Certified Reference Material (CRM).
A recommended protocol for certifying SO
2
gas cylinders against a SO
2
,
SRM or CRM is given in the Quality Assurance Handbook
1
. The SO
2
gas
cylinder should be recertified on a regular basis determined by the local
quality control program.
A calibration gas system capable of providing accurate levels of SO
2
calibration gas between zero and 80% of the full-scale range is required.
The calibration system must provide a flow rate of at least 0.5 LPM for an
instrument with the standard flow (instruments with higher flow rates will
require a higher minimum calibration system flow rate). All calibration gas
should be derived from local or working standards (such as cylinders of
compressed gas or permeation devices) that are certified as traceable to an
NIST primary standard.
Zero Air Generation
Commercial Heatless Air
Dryers
Absorbing Column
SO
2
Concentration
Standard
Calibration Gas
Generation