Determination of Lead and Cadmium in Food by Hydride Generation Atomic Fluorescence Spectrometry Based on Outer Tube Injection Enhanced Signal Technology

Considering that the carrier gas of the commercially available hydride generation atomic fluorescence spectrometer was loaded into the inner tube of the quartz atomizer with a small flow (300-600 mL·min^-1 for the determination of lead and cadmium), resulting in smaller lead and cadmium fluorescence intensities, the flow paths of the carrier gas and auxiliary gas in the quartz atomizer of this instrument had been modified, and the inner tube injection had been changed to the outer tube injection. Meanwhile, the additives and carrier current had been optimized, and methodological validation had been conducted. After being treated with acid solution, the sample was analyzed using the modified hydride generation atomic fluorescence spectrometer. It was shown that compared to the inner tube injection, the outer tube injection could increase the carrier gas flow to 1 000-1 400 mL·min^-1, carrying more hydrogenated gas. The mixture of hydrogenated gas and hydrogen gas could come into contact with the heating furnace wire at the upper end of the quartz sleeve faster and beignited. The auxiliary gas (argon) input from the inner tube would moderately lift the hydrogen flame upwards, resulting in more stable and larger volume of the flame. Using potassium ferricyanide and cadmium sensitizer as additives, the fluorescence intensities of lead and cadmium could significantly be enhanced. Replacing traditional dilute acids with water as carrier current, RSDs (n=7) of fluorescence intensities of lead and cadmium in the reagent blank during alternating injection were less than 3.0%, suitable for small batch sample detection. Linear ranges of lead and cadmium standard curves were within 10.00 μg·L^-1 and 0.50 μg·L^-1, with detection limits (3s/k) of 3.5 μg·kg^-1 (lead in puffed food) and 0.74 μg·kg^-1 (cadmium in rice). The sensitivity (standard curve slope k) of lead, cadmium was 1.3-13 and 2.8-99 times those of similar methods reported in literatures, respectively. Test for recovery was made according to the standard addition method, giving recoveries in the range of 86.0%-118%, and RSDs (n=6) of the determined values were found in the range of 2.6%-5.8%.