Varian 450-GC, User Manual

Page: 168 / 205

Detectors – Pulsed Flame Photometric Detector (PFPD)
Page: 408 User Manual 450-GC Varian, Inc.
Emission Wavelengths
Manganese exhibits a strong atomic emission line at 403 nm, along with other
weaker lines and bands in the 380 - 600 nm range. The 403 nm line is the only
emission of analytical interest with the PFPD.
Emission Timing
Manganese shows no delayed emission, as expected for atomic emission. Use
the minimum delay time and a gate width of 2 to 4 msec, depending on your
flame propagation rate.
Flame Composition
Manganese emission is favored by a hot flame, which is achieved by a
stoichiometric or slightly air rich air1/hydrogen mixture and minimum dilution of
the flame by carrier gas flow. The manganese emission is not very sensitive to
the exact gas composition, so you may vary the composition somewhat to
enhance selectivity against other elements. Emission is enhanced by t he use of
the 3 mm ID combustor.
Filters
Because the manganese emission is not separated in time from the flame
background emission, a narrow band interference filter is required to provide
adequate selectivity against hydrocarbons and other interfering elements. A
404.7 nm interference filter with 10 nm bandwidth was used in Prof. Amirav’s
work. This filter is commonly available as part of a set of filters for the isolation
of mercury emission lines and may be obtained from many sources of
interference filters. Using this filter, detectivity of ~100 fg Mn/second and a
selectivity against hydrocarbons of ~104 have been observed by Prof. Amirav.
Linearity and Dynamic Range
Manganese response is linear. No information is available on linear dynamic
range, although it is expected to exceed 103.
Other Consid erations
Manganese containing peaks show some tailing due to incomplete clearance of
the manganese from the combustor. This tailing is minimized using near-
stoichiometric flame conditions. It may be further reduced by using a detector
temperature below 225
°
C, but this may result in long term buildup of
manganese deposits in the combustor, although this was not observed by Prof.
Amirav.