G20 compact titrator

The CO₂ loading and the amine concentration of 60% L92/10% were determined by titration. The absorbed CO₂ was determined following the procedure described by Weiland et al. [31 (link)]. A loaded sample weighing 0.6 g was added to 25 mL of 1 N BaCl₂ and 50 ml of 0.1 N NaOH in an Erlenmeyer flask. The mixture was stirred until the sample was fully dissolved. The flask was covered with a stopper equipped with a vapor tube, and was heated until the reaction mixture started boiling. A BaCO₃ white precipitate was formed. After 4 min of boiling, the heating was stopped and the flask was cooled down. The solution was filtrated using a 0.45 μm HA MF-Millipore membrane filter. The precipitate was transferred to a beaker and dissolved in 50 ml of deionized water and 40 mL of 0.1 N HCl solution. After BaCO₃ was completely dissolved, the sample was titrated with 0.1 N NaOH in a Titrando autotitrator (Metrohm, Herisau, Switzerland). Following the same procedure, a blank sample was prepared to account for CO₂ present in air. In this case, 10 mL of HCl was added prior to the titration. The concentration of amine groups was determined by alkaline titration according to the procedure described by Ma’mun et al. [32 (link)]. A sample weighing 0.2 g was dissolved in 50 mL of deionized water, and the sample was titrated with 0.1 M H₂SO₄ in a G20 Compact titrator (Mettler Toledo, Oslo, Norway).

Abbe refractometer ORT1RS and Mettler Toledo G20 Compact Titrator equipped with a combined platinum electrode (Mettler Toledo DMI140-SC, Schwerzenbach, Switzerland) were used to measure refractive index and peroxide value, respectively. Molecular UV absorptivities values were measured using an Agilent 8453 spectrophotometer. An oil monitor electrochemical probe FOM320 Ebro device was employed to quickly measure total polar compound (%TPC). Technical data provided by the device supplier ensure good correlation with the recognised chromatographic method for the most common oils running in the ‘semiliquid’ equipment mode [16 ], and its performance was periodically checked with a suitable reference oil (Testo 05542650). An Agilent 7820A gas chromatographer equipped with an autosampler (7693) and a mass spectrometer (5977B MSD), using Rtx-65TG (30 m × 0.25 mm i.d., 0.1 μm) capillary column was applied for chromatographic analyses.

The pH of the culture samples obtained during the incubation was measured using a pH meter (Seven Compact^™ S220, Mettler Toledo, United States). The cultures were then centrifuged for 10 min at 3,900 g (Allegra X-22R, Beckman Coulter, United States). The supernatant obtained after centrifugation was analysed for total alkalinity (TA), anions, cations, and total nitrogen concentrations. In brief, TA was measured using a G20 compact titrator (Mettler Toledo, United States); 40 ml of supernatant was taken in a beaker and titrated with 0.2N H₂SO₄ until the samples reached an endpoint of pH = 4.3 (Vadlamani et al., 2019 (link)). Bicarbonate and carbonate concentrations were calculated using the measured pH and total alkalinity (TA) (Vadlamani et al., 2017 (link); Vadlamani et al., 2019 (link)).
The nitrate concentration was measured using an ion chromatograph equipped with an IonPac AS18 anion and a conductivity detector (DIONEX ICS 2000; Thermo Fisher, United States) (Vadlamani et al., 2017 (link); Vadlamani et al., 2019 (link)). The ammonium concentration was determined colorimetrically as previously described (Sims et al., 1995 (link)). The total nitrogen concentration was assessed using a scaled down version of the Persulfate Digestion method (Hach Method 10071, Hach, United States) (Vadlamani et al., 2017 (link); Vadlamani et al., 2019 (link)).