Determination of small amounts of formaldehyde in acetaldehyde

Two methods are described for the determination of formaldehyde in acetaldehyde based on gas-chromatographic separation of mixtures before, or after, the reduction of formaldehyde to methanol with borohydride. The latter technique is capable of determining 400 p.p.m. of formaldehyde in acetaldehyde but the presence of methanol and methyl formate will interfere. The former technique, in which a borohydride reactor reduces formaldehyde after separation, will determine down to 10 p.p.m. of formaldehyde in acetaldehyde in the presence of methanol and methyl formate.