The MBTH method122−124 (3-methyl-2-benzothiazolinonehydrazone) is a nonselective colorimetric method for the determination of aliphatic aldehydes of low molecular weight. MBTH reacts on aldehydes to give an azide. In parallel with this, a reactive cation is formed by oxidation of MBTH with Fe(III). In a further step, a blue ionic dye is formed. Absorbance is monitored at 628 nm. This reaction is less sensitive than that of the pararosaniline method. Other aldehydes undergo an analogous reaction, but the yield is generally lower. The MBTH method quantifies total aldehydes in ambient air in terms of their formaldehyde equivalents. Strong reducing agents can interfere with the determination of aldehydes. An online detection system has been described by Toda et al.(125)