Varian 450-GC, User Manual

Page: 167 / 205

Pulsed Flame Photometric Detector (PFPD) - Detectors
Varian, Inc. User Manual 450-GC Page: 407
Emission Timing
Tin emission is somewhat longer delayed than phosphorus and emission
duration is intermediate between phosphorus and sulfur. Use the phosphorus
gate delay and width for best sensitivity; use the sulfur gate delay and width for
best selectivity against carbon interference.
Flame Composition
Tin emission is optimized in hydrogen rich conditions similar to those used for
phosphorus or sulfur. Increasing Air1, Air2 and hydrogen by 50 - 100% each
will help to reduce peak tailing. Either the 2 or 3 mm combustor may be used,
with a slight preference for the 3 mm.
Filters
Tin may be detected using either the BG12 (sulfur) or the OG590 filter. Best
detectivity, ~100 fg/second Sn, is achieved using the BG12 filter, but this also
gives the most interference from high levels of sulfur compounds. Detectivity
with the OG590 filter is ~1 pg/second Sn, but sulfur response is considerably
reduced. Response with the OG590 filter is best with the red sensitive R5070
photomultiplier tube. A 610 nm interference filter has also been found useful in
conjunction with the R5070 PMT.
Linearity and Dynamic Range
Preliminary results indicate that the tin response is linear and extends over
more than three orders of magnitude.
Other Consid erations
Tin compounds exhibit tailing in the PFPD, probably due to limited volatility of
the tin combustion products. This tailing can be reduced by using higher gas
flow rates and by raising the detector temperature to 350
°
C to help volatilize
the tin compounds. You may also find it helpful to insulate the detector tower
using the PFPD tower cover, or by wrapping the tower with fiberglass cloth,
being careful not to cover the outlet.
An alternative approach to tin tailing is to reduce the detector temperature as
much as possible without impairing the chromatography. This reduces the “tail”
amplitude, but spreads it out in time. Several minutes may be required for the
detector to clean itself of tin deposits. Refer also to: J. A. Jacobsen, F. Stuer-
Lauridsen and G. Pritzl, Organotin Speciation in Environmental Samples by
Capillary Gas Chromatography and Pulsed Flame Photometric Detection
(PFPD), Appl. Organometallic. Chem. 11, 737-741 (1997).
Manganese Selective Detection
The following recommendations are based upon work reported by Prof. Aviv
Amirav and Hongwu Jing and are accurate to the best of our knowledge. This
is an area of ongoing research, so you may find that your application requires
modification of some parameters.