Conversely, however, the respective images taken in the SS mFPD (Fig. 3C and D) are very different by comparison. For example, no background emission can be visually detected at either the analytical or worker flame positions with or without sulfur present. As a result, the strong S2* emission generated (Fig. 3D) occurs on a much darker background, which should improve detector perfor-mance. Also interesting is that the analytical flame profile (Fig. 3D)assumes the channel shape, and appears rectangular relative to the typical spherical flame seen in the counter-current mode (Fig. 3C).This is presumably because the gas flow (and hence emission) can more freely flow upward and fill the central channel without the opposing flow of the conventional counter-current flame mode . Thus, the SS mFPD can significantly reduce background emission and interference relative to the original quartz tube mFPD.