Teledyne 6200T - Sulfides Analyzer - Manual (Page 188)

Calibration Procedures Model 6200T Total Sulfur Analyzer
Teledyne Analytical Instruments 188
standard charcoal scrubber that supplies zero air for the diluter assembly. The second
scrubber is located inside the analyzer behind the sample filter. This scrubber uses a
specially impregnated charcoal (TAI Part# CH_52) which is especially effective in
scrubbing TS gases. This filter is used to scrub TS from the inlet sample gas for use in
zero calibrating the analyzer.
Make sure that the charcoal is replaced at the 3-month interval suggested in the
6400T maintenance schedule. Also be sure not to mix charcoal between the inner
and outer scrubber canisters, they are different materials.
CO
2
Source:
A common application for this instrument is to analyze CO
2
sample gas for sulfur
containing impurities. Typically the impurities should be at low levels; therefore it is
especially important that the zero calibration of the analyzer is done accurately so that
even small levels of impurities can be detected.
In this type of application, a source of CO
2
that is free of sulfides is required for accurate
zero calibration of the instrument. If the ‘zero gas’ used to zero the instrument is
contaminated, the process gas will read artificially low, sometimes even showing a
negative TS concentration. Standard CO
2
bottles can have unacceptably high levels of
sulfur compounds in them. Beverage grade CO
2
should be used as a diluent as well as
the ‘zero gas’ source for calibration of the 6200T.
Since CO
2
strongly quenches the SO
2
fluorescence reaction, the instrument sensitivity
will be greatly reduced when using CO
2
as the balance gas. Therefore it is imperative
that the 6200T be calibrated using CO
2
as the balance gas when it will be measuring TS
in a gas matrix that is primarily CO
2
.
CO
2
liquefies when compressed, and sulfur compounds do not stay dissolved in liquid
CO
2
. Therefore it is not practical to use compressed gas bottles of H
2
S in CO
2
for
calibration purposes. TAI strongly recommends that H
2
S in N
2
bottles be used for
calibration of the 6200T, and that a calibrator be used to mix zero gas (CO
2
) into the cal
gas stream, making the final calibration gas mostly CO
2
.
9.1.1.2. Span Gas
Span gas is specifically mixed to match the chemical composition of the gas being
measured at about 80% of the desired full measurement range. For example, if the
measurement range is 500 ppb, the span gas should have an SO
2
concentration of about
400 ppb.
Span gases should be certified to a specific accuracy to ensure accurate calibration of the
analyzer. Typical gas accuracy for SO
2
gases is 1 or 2 %. SO
2
standards should be mixed
in nitrogen.
Teledyne Analytical Instruments offers an IZS option operating with permeation
devices. The accuracy of these devices is about ±5%. Whereas this may be sufficient for
quick, daily calibration checks, we strongly recommend using certified SO
2
span gases
for accurate calibration.
I MPORTANT I MPACT ON R EADINGS OR D ATA
Applications requiring US-EPA equivalency do not allow permeation
devices to be used as sources of span gas for calibration of the analyzer.