The present invention provides a method for the detection of a material comprising ammonium nitrate and a sugar, the method comprising sensing for the presence of hydrogen isocyanate (HNCO). The present invention further provides an apparatus suitable for the examination of a material suspected of comprising ammonium nitrate and a sugar, the apparatus comprising heating means in thermal communication with a sample holder suitable for the containment of the material, the sample holder being in gaseous communication with sensing region, the apparatus being further provided with a means for inducing flow of gas from the sample holder to the sensing region and a means for sensing the presence of hydrogen isocyanate in the sensing region.