Ultraflex 3 tof tof spectrometer

NMR spectra were recorded in CDCl3 on a Bruker DRX (Bruker, Billerica, MA, USA) at 500 MHz. Chemical shifts were reported on the δ scale (ppm) downfield from tetramethylsilane (δ = 0.0 ppm) using the residual solvent signal at δ = 7.26 ppm (1H, CDCl3) as the internal standard. MALDI-TOF mass spectra were recorded on a Bruker Ultraflex III TOF/TOF spectrometer (Bruker, Billerica, MA, USA) using CDCl₃ as the solvent and dithranol/AgTFA as the matrix.
SEC analyses were performed by using a PL-GPC 50 (Agilent, Santa Clara, CA, USA) apparatus equipped with a MIXED-E column (3 µm, 7.5 mm × 300 mm) with a nominal exclusion limit of 30,000 Da and a high resolution for low molecular weights. Sample solutions of approximately 0.1% (w/v) concentration were prepared in THF (stabilized with 200 ppm 2,6-dibutyl-4-methylphenol), which was also used as an eluent at a flow rate of 1 mL·min⁻¹, at 40 °C. A refractive index detector was used, and column calibration was performed with PEG narrow distribution standards. A third-order polynomial equation was obtained from the regression analysis.
DSC thermograms were obtained with a Q200 (TA Instruments, New Castle, DE, USA) calorimeter equipped with a refrigerated cooling system in the temperature range from 0 to 90 °C, using 3–5 mg samples with a scanning rate of 20 °C·min⁻¹, under a 50 mL·min⁻¹ nitrogen flow.

MALDI-ToF MS data were acquired with a Bruker ULTRAFLEX III ToF/ToF spectrometer (Bruker, Billerica, MA, USA), using a NdYAG laser source (355 nm) in reflector mode with a positive acceleration voltage of 25 kV. Samples were prepared as follows: PLA was dissolved in dichloromethane 1.5 mg/mL and mixed with matrix (DCTB 10 mg/mL in dichloromethane) and NaI (2 mg/mL in acetone) in a 20:5:0.5 ratio (matrix:sample:NaI). Before evaporation, 0.5 mL of the mixture solution was deposited on the sample plate. External calibration was performed using Peptide Calibration Standard II + ACTH clip 7–38, ACTH clip 1–39 + INSULINE (covered mass range: 1000–7000 Da).