取69.8 mg·L^-1氰化钠溶液0.50 mL，用0.25 mol·L^-1氢氧化钠溶液调节其酸度至pH 12，减压蒸发至干。加入二甲基亚砜（DMSO）0.5 mL溶解残渣，随后加入2，2，2-三氟苯乙酮（TFAP）10 μL和乙酸酐20 μL，室温下反应45 min，使氰根衍生为1-氰基-2，2，2-三氟-1-乙酸苯乙酯（CTPA）。取0.30 mL上述溶液，加入7.78 mmol·L^-1乙酸-3-氟苄酯-氘代三氯甲烷（CDCl₃）溶液0.2 mL为内标，按仪器工作条件进行¹⁹F-核磁共振（NMR）分析。试验表明该衍生方法的检出限为0.7 mg·L^-1。方法不受其他干扰离子（如CO₃^2-、B₄O₇^2-、Cl^-、SO₄^2-等）的影响，具有良好的专属性。选用3种不同水源的水样（自来水、河水、纯水）按所提出方法衍生化并测定，三者的回收率依次为74.0%，74.0%，75.0%，并无大的差别，3种水样测定值的相对标准偏差（n=6）依次为2.1%，2.4%，3.0%。方法曾用于天津8·12爆炸区采集的水样中氰根的测定，获满意结果。

An aliquot of 0.50 mL of 69.8 mg·L^-1 NaCN solution was taken and its acidity was adjusted to pH 12 with 0.25 mol·L^-1 NaOH solution. The solution was then evaporated to dryness under reduced pressure. The residue was taken up with 0.5 mL of DMSO, and then CN^- in the solution was derivatized with 10 μL of TEAP and 20 μL of acetic anhydride at room temperature for 45 min to form 1-cyano-2,2,2-trifluoro-1-phenylethyl acetate (CTPA). An aliquot of 0.30 mL of the solution was taken and used for ¹⁹F-NMR analysis under the specified instrumental condition after 0.2 mL of 7.78 mmol·L^-1 3-fluoro-benzyl acetate-CDCl₃ solution was added as internal standard. As shown experimentally, the detection limit of CN^- after derivatization was found 0.7 mg·L^-1. The method was found to be highly specific, as interferences of many co-existing anions, e.g., CO₃^2-, B₄O₇^2-, Cl^-, SO₄^2- and etc. were avoided. Three water samples of various origins (i.e., tap water, river water and pure water) were derivatized and determined by the present method, giving values of recovery of 74.0%, 74.0% and 75.0% respectively, showing no significant difference. Values of RSDs (n=6) found for the 3 samples were 2.1%, 2.4% and 3.0% respectively. The present method has been used satisfactorily for determination of CN^- in some water samples taken from the incidental site of the 8·12 explosion in Tianjin.