| Two parts are included in this thesis. Part one, the principles of optical fibre and liquid core waveguide are introduced in detail, the progress of liquid core waveguide (LCW) during the recent ten years and the application of LCW in analytical chemistry are reviewed mainly. Part two, the principle of high sensitivety of light intensity technique (LIT) or light intensity difference technique (LIDT) must be conbined with LCW, and its analytical applycation in food safety, including organophosphorus pesticides, antiseptic and bleacher, are investigated.The major content was described as follows:1. Trace organophosphorus pesticides (OPs) was determined by LCW and LIT with bismuth phosphomolybdenum blue (BPMB) method, and ultra bright red light emitting diode (LED) worked as spectroscopic source. OPs were degradated into phosphate with UV light, potassium peroxydisulphate as oxidant and nanosized titanium dioxide as catalyst. BPMB can be formed in 10 min with phosphate, perchloric acid, ammonium molybdate, bismuth nitrate oxide and ascorbic acid. The linearity range low limit and detection limit were lower over 1000 times than classical spectrophotometry, the linearity range and detection limit were 2.0×10-11～8.0×1010 g/mL, 7×10-12 g/mL, respectively. The relative standard derivation for 1.0×10-10 g/mL was less than 1.0％(n=11).2. Trace nitrite in food was determined by LCW and LIDT with GB/T 5009.33-2003, and an ultra bright green LED worked as spectroscopic source. The linearity range low limit and detection limit were lower 1000 times than classical spectrophotometry, the linearity range and detection limit were 4.0×10-11～4.0×10-9 g/mL, 2×10-11 g/mL, respectively. The relative standard derivation for 8.0×10-10 g/mL was less than 1.0％(n=11).3. Trace sulfite in food was determined by LCW and LIDT with GB/T 5009.34-2003, and ultra bright green LED worked as spectroscopic source. The linearity range low limit and detection limit were lower 1000 times than classical spectrophotometry. The linearity range and detection limit were 1.6×10-11～1.6×10-9 g/mL, 5×10-12 g/m, respectively. The relative standard derivation for 1.6×10-10 g/mL was less than 1.0％(n=11).4. Trace formaldehyde was determined by LCW and LIDT with GB/T 18204.26-2000, and ultra bright red LED worked as spectroscopic source. The linearity range low limit and detection limit were lower over 1000 times than classical spectrophotometry. The linearity range and detection limit were1.0×10-11～1.0×10-9 g/mL, 7×10-12 g/mL, respectively. The relative standard derivation for 1.0×10-10 g/mL was less than 1.0％(n=11).
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