Final answer:
Thin-layer chromatography (TLC) is the least sensitive chromatographic technique compared to HPLC, LC/MS, GC/MS, and GC due to its simpler qualitative approach and less sophisticated detection capabilities.
Step-by-step explanation:
The chromatographic technique that is the least sensitive is the thin-layer chromatography (TLC). This is because TLC is a simpler method that involves a stationary phase applied to a flat, inert carrier sheet and a mobile phase that moves up the sheet by capillary action, separating components of a mixture based on differences in affinity to the stationary phase. This method provides qualitative information but is generally less quantitative and less sensitive compared to techniques like high-pressure liquid chromatography (HPLC), liquid chromatography combined with mass spectrometry (LC/MS), gas chromatography combined with mass spectrometry (GC/MS), and gas chromatography (GC) that can provide more sensitive and quantitative analyses due to their more sophisticated detection methods and instrumentation.