Lambda 40p spectrophotometer

Absorption spectra were registered in the range of 200–450 nm in a 10 mm quartz cell by means of a PerkinElmer Lambda 40P Spectrophotometer (PerkinElmer, Waltham, MA, USA) under the following conditions: scan rate: 1 nm s⁻¹, time response: 1 s, and spectral band: 1 nm. Light exposure was simulated in a light cabinet, Suntest CPS+ (Heraeus, Milan, Italy), equipped with a Xenon lamp (Atlas Material Testing Technology, Mt Prospect, IL, USA), compliant with the ICH rules. The apparatus was fitted with an electronic device for irradiation, temperature measurement, and control inside the box. The system was able to closely simulate sunlight and appropriately select spectral regions between 300 and 800 nm through the interposition of filters. In particular, the application of the ID65 standard filter limits radiation to about 320 nm.
Chromatographic equipment consists of a HP 1100 pump fitted with a DAD G1315B (Agilent Technologies, Santa Clara, CA, USA) and a Rheodyne 7725 manual injector. The LC column was a C18 Gemini (Phenomenex, Bologna, Italy), 250 × 4.6 mm × 5 μm.

NA, propylene glycol, microcrystalline cellulose, Brij^® 97, and isopropyl myristate were purchased from Sigma-Aldrich (Milan, Italy). Ethanol and methanol were from J.T. Baker (Deventer, Holland).
UV spectra were recorded by using a Perkin-Elmer Lambda 40P Spectrophotometer by setting the following instrumental conditions: λ range 200–450 nm, scan rate 1 nm/s; time response 1 s; spectral band 1 nm. Spectral acquisition and elaboration were made by using the dedicate software UV WinLab^® (Perkin-Elmer, Waltham, MA, USA). A light cabinet Suntest CPS+ (Heraeus, Milan, Italy) equipped with a Xenon lamp was used to perform the photodegradation experiments. The ID65 standard filter was set to simulate sunlight in a spectral range between 300 and 800 nm. Multivariate analysis was performed by the software Matlab^® computer environment (Mathwork Inc., version 7, Torino, Italy).