A derivatization and microextraction procedure with organic phase solidification on a paper template: Spectrofluorometric determination of formaldehyde in milk.

A derivatization and air-assisted dispersive liquid-liquid microextraction procedure with organic phase solidification on a paper template was developed for the first time. The procedure was used for the spectrofluorometric determination of formaldehyde in milk samples. The Hantzsch reaction of formaldehyde with acetylacetone in the presence of ammonia to form a derivative (3,5-diacetyl-1,4-dihydrolutidine) was implemented for the microextraction and detection of analyte. Thymol was investigated as the extraction solvent for the air-assisted dispersive liquid-liquid microextraction for the first time. In the developed procedure, molten thymol was added to the thermostated aqueous sample solution containing reagents for formaldehyde derivatization, and cloudy solution of fine thymol droplets was formed by air bubbling. After separation of phases the liquid extract phase was withdrawn with a dispenser and distributed on the black paper template in a thin layer to be solidified. The solidified extract phase on the template was inserted to a sample holder of a spectrofluorometer and fluorescence intensity was measured without using cuvettes. Under optimal experimental conditions the linear detection range was found to be 45-500 µg L-1 with LOD calculated from a blank test, based on 3σ, 15 µg L-1. The developed procedure does not require the dilution of the solid extract phase in organic solvent to be introduced in an analytical instrumentation and the use of cuvettes for spectrofluorometric detection.