Matters needing attention in the use of FPD in gas chromatograph

Abstract: The principle of FPD is based on the sample burning in a hydrogen-rich flame, so that the sulfur and phosphorus compounds are combusted and then reduced by hydrogen, resulting in excited states S2 * (S2 excited state) and HPO * (HPO excited state ), When these two excited substances return to the ground state, they emit a spectrum of about 400nm and 550nm. The intensity of this spectrum is measured with a photomultiplier tube. The light intensity is proportional to the mass flow rate of the sample.

structure

FPD is a structure that combines FID and photometer. It started as a single flame FPD. After 1978, a double flame FPD was developed to compensate for the shortcomings of single flame FPD. It has two air-hydrogen flames separated from each other. The lower flame converts the sample molecules into combustion products, which contain relatively simple molecules, such as S2 and HPO; the above flame produces luminous excited fragments, such as S2 * and HPO *, there is a window aiming at the flame above, the photoluminescence tube is used to detect the intensity of chemiluminescence, the window is made of hard glass, and the flame nozzle is made of stainless steel.

performance

FPD is a selective detector for determining sulfur and phosphorus compounds.

The flame is a hydrogen-rich flame, and the air supply is only sufficient to start a combustion reaction with 70% of hydrogen, so the flame temperature is low so as to naturally generate excited sulfur and phosphorus compound fragments.

The flow rates of carrier gas, hydrogen and air have a great influence on FPD, and the gas flow control should be very stable.

The flame temperature of sulfur-containing compounds should be around 390 ℃, and S2 * can be generated in an excited state; the ratio of hydrogen and oxygen for phosphorus-containing compounds should be between 2 and 5.

According to different samples, the hydrogen-oxygen ratio should be changed, and the amount of carrier gas and make-up gas should be adjusted appropriately in order to obtain a better signal-to-noise ratio.

Use matters needing attention

1. FPD can also use hydrogen flame, so the safety issue is the same as FID.

2. FPD's hydrogen, air and makeup gas are different from FID. Generally, hydrogen is 60 ~ 80ml / min, air is 100 ~ 120ml / min, and the sum of makeup gas and column flow is 20 ~ 25ml / min.

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