Direct quantitative determination of cyanamide by stable isotope dilution gas chromatography-mass spectrometry

Cyanamide is a multifunctional agrochemical used, for example, as a pesticide, herbicide, and fertilizer. Recent research has revealed that cyanamide is a natural product biosynthesized in a leguminous plant, hairy vetch (Vicia villosa). In the present study, gas chromatography-mass spectrometry (GC-MS) equipped with a capillary column for amines was used for direct quantitative determination of cyanamide. Quantitative signals for (N-14(2))cyanamide, (N-15(2))cyanamide (internal standard for stable isotope dilution method), and m-(trifluoromethyl)benzonitrile (internal standard for correcting errors in GC-MS analysis) were recorded as peak areas on mass chromatograms at m/z, 42 (A(42)). 44 (A(44)), and 171 (A(IS)), respectively. Total cyanamide content, (N-14(2))cyanamide plus (N-15(2))cyanamide, was determined as a function of (A(42) +A(44))/A(IS). Contents of (N-14(2))cyanamide and (N-15(2))cyanamide were then calculated by multiplying the total cyanamide content by A(42)/(A(42) + A(44)) and A(44)/(A(42) + A(44)), respectively. The limit of detection for the total cyanamide content by the GC-MS analysis was around 1 ng. The molar ratio of (N-14(2),)cyanamide to (N-15(2))cyanamide in the injected sample was equal to the observed A(42)/A(44) value in the range from 0.1 to 5. It was. therefore, possible to use the stable isotope dilution method to quantify the natural cyanamide content in samples, i.e., the natural cyanamide content was derived by subtracting the A(42)/A(44) ratio of the internal standard from the A(42)/A(44) ratio of sample spiked with internal standard, and then multiplying the resulting difference by the amount of added (N-15(2))cyanamide (SID-GC-MS method). This method successfully gave a reasonable value for the natural cyanamide content in hairy vetch, concurring with the value obtained by a conventional method in which cyanamide was derivatized to a photometrically active compound 4-cyanimido-1,2-naphthoquinone and analyzed with reversed-phase HPLC (CNQ-HPLC method). The determination range of cyanamide in the SID-GC-MS method was almost the same as that in the CNQ-HPLC method, however, the SID-GC-MS method was much simpler than the CNQ-HPLC method. (c) 2005 Elsevier B.V. All rights reserved.