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Electrochemical anodization has been applied to grow porous shell layers of 300 nm (30 nm pores) in 5 μm diameter pillar array columns (PACs) with a spacing of 2.5 μm. Using turn structures preceded and followed by the flow distributor structures recently introduced by our group and filled with radially elongated pillars, columns with quasi unlimited channel lengths could be conceived. The uniformity of the porous PAC was assessed by determining local plate heights along the channel, which appeared to be constant. Minimal (absolute) plate heights (H) between 4 and 6 μm were obtained at optimal flow rates when imposing increasing retention factors. Upon measuring the surface area involved in chromatographic retention as an indicator of the available surface area, an increase in the surface area by a factor of about 30 compared to that of non-anodized pillars was found. On reconfiguring a commercial HPLC instrument to enable on-chip injections, 90% of the performance (expressed in theoretical plates) could be maintained for a 1 m column, while for a 25 cm column severe losses were still observed. As the corresponding pressure drop for optimal operation of retained components is on the order of 10 bar per m only, portable and cheaper HPLC devices with high efficiencies become realistically conceivable.

Proper hydration of the stratum corneum, the skin’s outermost layer, is essential for healthy skin. Water-soluble substances called natural moisturizing factors (NMF) are responsible for maintaining adequate moisture in the skin and are closely associated with a variety of the skin’s functions. Therefore, quantitative analysis methods for NMF are indispensable when attempting to clarify one of the mechanisms of hydration and its effect on the skin. This study sought to develop a quick and simple analytical technique, which can quantify NMF from the skin without the need for extraction or separation, using direct analysis in real time-mass spectrometry (DART-MS). The goal was to deliver a high quantitative capability, so a unique inkjet printing technique was employed to evenly coat a stable isotope-labeled internal standard (SIL-IS) on tape-stripped skin. This technique allowed for the quantification of 26 NMF with established calibration curves and comparatively high linear correlations. The speed of measurement was found to be advantageous as 100 strips of tape can be measured in roughly 2 hours. The effectiveness of the inkjet coating was also verified by comparing its precision with that of conventional pipetting. This new technique can be an alternative method to quantify NMF rapidly and perhaps allow for a clearer elucidation of their function in skin.

Analyzing the natural moisturizing factor (NMF) in the stratum corneum (SC), such as amino acids, pyrrolidone carboxylic acid, and urocanic acid, is important in dermatology research.

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