Hplc grade ethyl acetate

The analytical standards for glufosinate ammonium (99.2%), MPP (97.9%), and MPA (99.4%) were obtained from Beijing Perfect Technology Co., Ltd. (Beijing, China). The glufosinate ammonium formulation (200 g L⁻¹ aqueous solution (AS)) was purchased from Hebei Veyong Bio-Chemical Co. Ltd. (Hebei province, China). Standard solutions of glufosinate ammonium, MPP, and MPA were prepared with methanol (1.0 g L⁻¹). Working standard solutions for calibration were prepared by dilution with methanol to concentrations of 0.05 to 5.0 mg L⁻¹.
Trimethyl orthoacetate (analytical reagent grade) was purchased from Sigma-Aldrich (USA). Acetic acid and ammonium hydroxide (both analytical reagent) were purchased from Sinopharm Group Chemicals Co., Ltd. and Beijing Chemical Reagent Company (Beijing, China), respectively. Ethyl acetate (HPLC-grade) was purchased from Fisher Scientific (Fair Lawn, NJ, USA). Water (HPLC-grade) was prepared using a Milli-Q water purification system (Millipore, USA).

All glassware was prepared as described previously (Johnson et al., 2011). The internal standard was 4‐phenylbutanoic acid (Acros Organics) (10 mg) dissolved in 0.1 M NaOH (final concentration 2 mg l⁻¹) and added to each culture immediately prior to extraction. Samples were acidified to pH 2 using concentrated HCl, and the diamondoid carboxylic acids were extracted from the supernatants three times using 15 ml of ethyl acetate (HPLC grade; Fisher Scientific, Loughborough, UK) as previously described (Johnson et al., 2011). Solvent extracts were pooled, dried with 5–10 g anhydrous Na₂SO₄ (Fisher Scientific), and concentrated by rotary evaporation (Buchi) at 40°C. Samples were transferred to a gas chromatography vial (Chromacol) and stored at −20°C. Samples were injected with a 1 µl splitless injection (injector temperature 250°C) onto a 30 m x 250 µm x 0.25 µm Rtx – 1MS column using helium as the carrier gas at a constant flow of 1 ml min^‐1. Oven temperatures were as follows: an increase from 40 to 250°C at 10°C min^‐1 followed by a final hold at 250°C for 10 min. The transfer line was held at 230°C onto a source for the MS which was in full‐scan mode (scan range 50–650 Da). Data were analysed and integrated using ChemStation for GC‐MS (Agilent, Stockport, UK).

Indomethacin (γ polymorph)
was purchased from Baoji Guokang Bio-Technology Co. Ltd. (China).
Poloxamer 407 (Kolliphor P407) was sourced from BASF (Germany). The
solvents used were acetone (≥99.8%) and ethyl acetate (HPLC
grade) obtained from Fisher Chemicals (Ireland). Carbon dioxide (99.98%)
was supplied by BOC (Ireland).