The invention is directed to a non-destructive method of detecting whether a coating or deposit (30, 34) of (a) SiOxCy or SiNxCy and/or (b) of SiOx is present on or near a surface of an article (12), such as a disposable thermoplastic medical article. The method includes impinging infrared light (216) having a wave number in at least a portion of a desired range onto at least a first surface being examined for the presence of the one or more coatings or deposits. At least a portion (224) of the infrared light impinged on the first surface is collected (at 222) and the response output, which may include for example the maximum intensity and/or peak area of the collected infrared light at an infrared spectroscopy peak, is used to indicate the presence of the one or more coatings or deposits.
