Direct-injection methods were found in combination with ion-mobility spectrometry (IMS). Conventional IMS injection relies on wiping suspected surfaces for residues or particulates using a swab, or withdrawing air through the filters. Neither of these methods is sensitive enough for trace-compound analysis because there is no preconcentration step. Replacing the swab or the filter by a piece of thin film to enrich the compounds is a good approach to enhance the method sensitivity [39,40,55].