Nanotof instrument

Surface distributions of lubricant were mapped using time-of-flight secondary-ion mass spectrometry (ToF-SIMS, nanoToF instrument, Physical Electronics Inc., Chanhassen, MN, USA) at 30 kV. For mapping purposes, signals were collected from an area of approximately 90 μm × 90 μm for each sample. Characteristic peak fragments were identified to effectively distinguish ciprofloxacin from lubricant materials: for ciprofloxacin, m/z ~ 332, corresponding to the fragment [C₁₇H₁₉FN₃O₃⁺]; for MgSt, m/z 24 corresponding to the fragment [Mg⁺]; and for L-leucine, m/z 132 corresponding to the fragment [C₆H₁₄NO₂⁺].

Surface composition of the composite formulations was characterized using Time-of-flight secondary ion mass spectrometry (nanoToF instrument, Physical Electronics Inc., Chanhassen, Minnesota, USA) as described elsewhere with slight modifications (51 (link)). Data were obtained from 4 areas (75 × 75 μm each) per sample. Characteristic peak fragments for azithromycin and L-leucine were identified. For azithromycin, the peaks at m/z ~98 atomic mass unit (amu) and ~158 amu were selected corresponding to [C₆H₁₂N⁺] and [C₈H₁₆NO₂⁺] fragments, respectively. For L-leucine, the fragment at m/z ~ 132 amu corresponding to [C₆H₁₄NO₂⁺] was selected as the characteristic peak. A WincadenceN software (Physical Electronics Inc., Chanhassen, Minnesota, USA) was employed to construct high-resolution surface composition overlays.

Surface composition of the composite formulations was characterized using Time-of-flight secondary ion mass spectrometry (nanoToF instrument, Physical Electronics Inc., Chanhassen, Minnesota, USA) as described elsewhere with slight modifications (Q. Zhou et al., 2011 (link)). Data were obtained from 4 areas (100 × 100 μm each) per sample. Characteristic peak fragments for azithromycin and L-leucine were identified. For colistin, the peaks at m/z ~30 atomic mass unit (amu) and ~86 amu, corresponding to [CH₄N⁺] and [C₅H₁₂N⁺] fragments, respectively, were selected. For meropenem, the fragment at m/z ~ 68 amu corresponding to [C₄H₆N⁺] was selected as the characteristic peak. Sample spectra were processed using the WincadenceN software (Physical Electronics Inc., Chanhassen, MN, USA) to construct high-resolution surface composition maps.