On Apr 4, 2017, at 12:55 AM, bithika das <[log in to unmask]> wrote:
Hello Isogeochem Members
This mail is regarding a unique problem (to us possibly!), we are experiencing in our bulk organic matter δ13C measurements. Presently, we are analyzing rock samples (Old Oligocene-Miocene marine gray shale) in Flash EA 2000. Analytical conditions are as follows: Carrier flow: 120 ml/min, Reference flow: 80-100 ml/min, Reactor temperature: 1020 °C, Oven temperature: 80 °C. EA 2000 is attached with the DeltaV through a ConFlo IV interface (Dilution 33%). Although ~50 % of the samples are with correct chromatograms (no problem detected), rest are creating some unique problem. The clean samples burn perfectly with no peak widening (i.e., for a ~5V peak we are expecting ~50-55 second peak width, when end slope is set at 4mv/sec). In agreement, both IAEA-C3 and NBS-22 are showing a peak width of ~48 second with the same instrumental setup.
However, problematic samples showing peak widening (~70 second) and followed by an interesting hump (if we really call it) producing peak overlap and non-reproducible delta values. Just after the actual CO2 peak from the sample (identified by retention time) the 46 beam current increases rapidly without much change in 44 and 45 currents. Since, we don’t detect peak unless 44 beam-current is more than 50mV, this unique hump is never detected as peaks. The shape of this following peak is more like a plateau (broad with >300 sec peak width if we try to detect it). We suspected that this is coming from some Sulfur bearing organic matter or elemental Sulfur. We checked it by taking a background scan (intensity vs. magnetic steps) just after the measurement (showing high SO2 compared to clean run or if we take the scan just after the reactor cleaning).
We wonder whether any of you have come across such a problem. If, so please suggest how to get rid of this peak, if possible.
Thanking you in advance
With best regards