罗丹明B溶液在激发波长（λ_ex）为365 nm时，在发射波长（λ_em） 580 nm处有最大荧光发射强度。如向罗丹明B溶液中加入碘溶液（I₃^-），由于两者之间反应生成缔合物而使其荧光猝灭，但罗丹明B发射荧光的峰位未变。如在此猝灭反应之前加入一定量的抗坏血酸（AA），则上述猝灭作用由于I₃^-被AA还原而失效，使荧光得以重现。进一步试验表明，在总体积为50 mL中，1×10^-3mol·L^-1碘溶液为2.0 mL，1.0×10^-4mmol·L^-1罗丹明B溶液为5.00 mL，pH 4.7的乙酸-乙酸钠缓冲溶液为5.0 mL，在常温下反应10 min的条件下，抗坏血酸的浓度在40 μmol·L^-1内与其对应的荧光强度之间呈线性关系（注：抗坏血酸反应在碘溶液及罗丹B溶液之前加入），其检出限（3s/k）为5.6×10^-9mol·L^-1。根据以上事实，提出了应用上述荧光猝灭法间接测定维生素C片剂及注射液中抗坏血酸的含量。分析时取片剂样品5片，研磨混匀后称取25.0 mg溶于水中，并定容至250.0 mL，取1.00 mL溶液按上述方法测定。注射液样品则取0.10 mL，加水定容至250.0 mL，取1.00 mL溶液进行测定。在实际样品基础上进行加标回收试验，测得回收率为97.4%（片剂）和98.4%（注射液），测定值的相对标准偏差（n=6）依次为2.3%，1.7%。还应用此方法测定了3种果汁饮料，所测得结果与用碘量法校对的结果相符。

Rhodamine B (RB) solution when excited at (λ_ex) 365 nm shows fluorescence emission at its maximum at (λ_em) 580 nm. And the fluorescence will be quenched or weakened by addition of iodine (I₃^-) to the solution due to association of RB with I₃^-, but site of the fluorescence peak is not changed. However, if a definite amount of ascorbic acid (AA) is added before the quenching reaction, due to reduction of I₃^- by AA, the quenching effect will be ceased to a definite extent or completely eliminated as related to the amount of AA added, and re-appearance of the fluorescene emission will happen. Optimum conditions for the fluorescence quenching reaction were found as follows:in a total volume of 50 mL, an amount of AA was added to the solution before addition of 2.0 mL of 1×10^-3mol·L^-1 iodine solution, 5.00 mL of 1.0×10^-4mmol·L^-1 RB solution and 5.0 mL of pH 4.7 acetic acid-sodium acetate buffer solution. The solution was kept under normal temperature for 10 min. Linear relationship between values of fluorescence intensity and concentration of AA was obtained in the range within 40 μmol·L^-1. Detection limit (3s/k) found was 5.6×10^-9mol·L^-1. Based on these facts, it was proposed to use this indirect fluorescence quenching method to determine AA in Vitamin C tablets and injections. For the analysis, 5 tablets were taken, powdered and mixed thoroughly by grinding, and an aliquot of 25.0 mg was taken and dissolved in water, and its volume was made up to 250.0 mL with water. 1.00 mL of the solution was taken and its content of AA was determined by the method described above. For injection sample, 0.10 mL of the drug was taken and diluted to 250.0 mL with water. 1.00 mL of the solution was taken and analyzed in the same way. Test for recovery was made by addition of standard solutions of AA to substantial samples of VC tablets and injections, results of recovery found were 97.4% (for tablets) and 98.4% (for injections). Values of RSDs (n=6) found were 2.3% and 1.7% respectively. The proposed method was also used to determined AA in 3 fruit juice drinks, and the results obtained were found to check quite well with the results found by iodimetry.