The dual-layer LpDNPH sorbent tube is an air sampling device designed for sampling carbonyls (e.g. formaldehyde) in ambient, indoor, and industrial atmospheres. Carbonyls are trapped on our high-purity silica gel adsorbent coated with 2,4-dinitrophenylhydrazine (2,4-DNPH) where they are converted to stable hydrazone derivatives. The derivatives are eluted from the tube in acetonitrile and analyzed by HPLC. The results indicate that under the sampling conditions employed, there was no reakthrough of formaldehyde, acetaldehyde, acetone, or hexanal.