104
Model 5380 PFPD Operator’s Manual
Rev. 3.1
Sulfur Mode
The minimum detectability for sulfur is the mass flow rate of sulfur atoms in the
carrier gas that gives a detectable signal equal to twice the peak-to-peak noise level
and is calculated from the measured sensitivity and noise level. Since the sulfur
response frequently obeys a square law, the minimum sulfur detectability is usually
calculated as follows.
D
S
= (2N
S
/ S
S
)
Q/w
[4]
where: D
S
= minimum detectability for sulfur [pgS/sec]
N
S
= peak-to-peak noise level in sulfur mode [Amp]
S
S
= sulfur sensitivity (response) [Amp/(pgS/s)
2
]
Since there is generally a nonlinear quadratic relationship between the PFPD
response and the mass flow rate of sulfur atoms into the flame, the sulfur sensitiv-
ity can be determined as follows.
S
S
= (A
i
/ m
S
) * (1 / m
S
)
[5]
where: S
S
= sulfur sensitivity (response) [Amp/(pgS/s)
2
]
A
i
= integrated peak area [Amp×sec]
m
S
= mass of sulfur atoms in the sample [pgS]
m
S
= mass flow rate of sulfur atoms in the sample at ¼ height of peak
[pgS/sec]
and
m
S
= m
S
/h
Q/r
[6]
where: h
Q/r
=
Q/r
height of the peak [Amp]
Substituting equations [5] and [6] into equation [4] yields an expression for calcu-
lating sulfur detectivity:
[7]
Since the sulfur response often obeys the square law, the square root of the re-
sponse can be calculated to obtain a linear relationship between sulfur concentra-
tion within the analyte and the PFPD signal output. The dual channel capability of
the Model 5380 allows both the direct quadratic sulfur response and the linear
square root response signals to be output simultaneously.
D
S
=
2N
S
* m
S
2
A
i
* h
Q/r
Q/w
Summary of Contents for 5380
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