Standardization of sandwich-structured Cu-glass substrates embedded in a flexible diode laser-plasma interface for the detection of cholesterol

This study introduced sandwich-structured copper-glass substrates for standardization of laser desorption and plasma ionization. For standardized quantitative analysis, cavities were constructed which allow better reproducibility in droplet deposition and for laser application. Applying the diode laser, molten substrate material is incorporated into the glass, being trapped inside. Therefore, this method can be separated from laser ablation, achieving high ion signals without ablating material from the surface. Flexible Microtube Plasma (FµTP) was selected as ionization source, being this the first time that laser desorption and FµTP ionization are coupled. This laser-plasma-interface was applied to the detection of cholesterol, which showed a significantly improved limit of detection of 0.4 ng and linear dynamic range of three orders of magnitude in positive ion mode compared to other (ambient air mass spectrometry) methods. The main reason was the change of phase on the copper surface. The dehydrated mo...