For instance, Fig. 3 illustrates this difference with typical image of both devices with and without sulfur emission present under normal operating conditions. As seen in Fig 3A, the quartz tube FPD exhibits a notable orange glow at the burner tips of the SS capillaries, while a dim background emission is also seen at the analytical flame. Fig 3B then demonstrates the same during sulfur analyte emission. Here again, even though blue S2* chemi-luminescence can be clearly seen, the dominant orange background emission persists. As noted above, this results from incandescent glowing of the cement used to hold the flame burners in place