The invention is directed to an imidazole derivative represented by formula : wherein each of R1 and R2 represents an aryl group, a heteroaryl group, etc. The filament is coated with a resilient material. The diaphragm and flange define a balancing chamber that is in fluid communication with a leveling port. When the electric motor is in the speed control state, the allowable current passing through the over-temperature protection circuit of the DC electric tool cannot exceed a preset second current value less than the first current value. These determined principal components may be compared with known principal components corresponding to known analytes.