Mercury 400 mhz spectrometer

Sweat samples collected in conjunction with measurements with the wearable electronic tongue (Device 3) were also prepared for ¹H nuclear magnetic resonance (NMR) spectroscopy. Fifty µL of sweat was dried under a flow of N₂ gas to minimize the amount of water in the sample. Afterwards the samples were resuspended/diluted in 350 µL D₂O. The resuspended samples were transferred into 5 mm NMR tubes. The spectra were collected on a Varian Mercury 400 MHz spectrometer at a resonance frequency of 400.41 MHz using a 5 mm Varian 400 ASW 1H/13C/31P/15N/4NUC PFG 40–162 MHz (SN40P5A910) probe at 25 °C. The spectra were acquired using a 90 °C pulse (12.3 µs pulse width), a relaxation delay of 2 s, an acquisition time of 2.6 s, a spectral width of 6406.1 Hz (−3.3 to 12.7 ppm), with 16,384 complex data points and a 20 Hz spin. The residual water signal was suppressed by using a PRESAT pulse sequence available in VnmrJ version-4.2, using a presaturation delay of 10 s and a power of 36 Hz at 4.65 ppm. All spectra were Fourier transformed using MestReNova (version 14.1.2, Mestrelab Research, Escondido, CA, USA) with zero filling to 64k data points. All spectra were phased and baseline corrected. The area of the peaks was calculated by fitting Lorentzian–Gaussian peaks to the regions of interest.

Structural analysis of the PLGA-PEG-PLGA copolymer, initial determination of its molecular weight and estimation of the lactide:glycolide ratio, was carried out via NMR spectroscopy. The copolymer was dissolved in deuterated acetone and analysis was done using NMR spectroscopy (Varian Mercury 400 MHz spectrometer, Varian Inc., Palo-Alto, CA, USA) operating at 400 MHz [35 ]. Subsequently, the molecular weight was calculated by comparing the integral of the signal for PEG protons chemical shift at 3.6 ppm with the integrals of glycolide at 4.8 ppm and those of lactide at 1.6 and 5.2 ppm.

All reagents, solvents, and chemicals were purchased from POCH (Gliwice, Poland), Merck (Darmstadt, Germany), and Sigma-Aldrich (Munich, Germany) and were at analytical grade. Dimethyl sulfoxide (DMSO), molecular biology grade used as a solvent for all stocks of the chemical agents was obtained from Roth (Karlsruhe-Rheinhafen, Germany). The reactions were monitored by TLC aluminum plates with silica gel Kieselgel 60 F₂₅₄ (Merck, Darmstadt, Germany, 0.2 mm thickness film) using UV light as visualizing agent. Column chromatography was performed using Kieselgel 60 (Merck, 0.040–0.063 mm). Melting points were determined in open glass capillary tubes. IR spectra were taken on a Specord M80 instrument (Carl Zeiss, Jena, Germany). HRMS spectra were recorded on a Micro-mass ESI Q-ToF Premier instrument (Micromass UK Limited, Manchester UK). ¹H (400 MHz) and ¹³C NMR (100 MHz) spectra were recorded on a Mercury 400 MHz spectrometer (Varian, California, USA) in CDCl₃ solution; chemical shifts (δ) are reported in ppm; coupling constants (J) are given in hertz (Hz).