Teledyne 6200T - Sulfides Analyzer - Manual (Page 73)

6200T Total Sulfur Analyzer Getting Started
Teledyne Analytical Instruments 73
For analyzers without an IZS or external zero air scrubber option, a zero air generator
such as the Teledyne Analytical Instruments Model 701 can be used (Figure 3-16).
Calibration (Span) Gas
The most common application of 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 these types of applications, 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
.
For other applications not involving CO
2
, TAI recommends a calibration gas
specifically mixed to match the chemical composition of the type of gas being measured
at near full scale of the desired measurement range. In this case, SO
2
measurements
made with the Teledyne Analytical Instruments 6200T UV Fluorescence SO
2
Analyzer,
it is recommended that you use a span gas with a SO
2
concentration equal to 80% of the
measurement range for your application.
EXAMPLE: If the application is to measure between 0 ppm and 500 ppb, an appropriate
span gas concentration would be 450 ppb SO
2
.
Cylinders of calibrated SO
2
gas traceable to NIST-Standard Reference Material
specifications (also referred to as SRM’s or EPA protocol calibration gases) are
commercially available. Table 3-12 lists specific NIST-SRM reference numbers for
various concentrations of SO
2
.
Table 3-12: NIST-SRM's Available for Traceability of SO
2
Calibration Gases
NIST-SRM Type Nominal Concentration
1693a Sulfur dioxide in N
2
50 ppm
1694a Sulfur dioxide in N
2
100 pp
1661a Sulfur dioxide in N
2
500 ppm
2659a 1 O
2
in N
2
21% by weight
2626a CO
2
in N
2
4% by weight
2745 2 CO
2
in N
2
16% by weight
1 Used to calibrate optional O
2
sensor.
2 Used to calibrate optional CO
2
sensor.