Glp 31 conductivity meter

The characterization of the obtained black liquors was determined using different laboratory analyses. The pH was analysed using a Crison GLP 21 pH meter (Crison Instruments, Barcelona, Spain). The density was determined by dividing their total mass by its total volume. The total dry solids (TDS) of these liquors was determined by drying samples in porcelain crucibles at 105 °C for 24 h. Afterwards, the samples were heated in a muffle at 575 °C for 3 h to measure the ash content [39 (link)]. A simple mass balance was performed to determine the lignin content of these spent liquors. Additionally, electrical conductivity was analysed with a Crison GLP 31 conductivity meter (Crison Instruments). All analytical measurements were performed in triplicate.
An aliquot of the different liquors was subjected to quantitative posthydrolysis with 4% H₂SO₄ at 121 °C for 60 min to determine its monosaccharides, acetic acid, furfural and hydroxymethylfurfural (HMF) content. Afterwards, the resulting supernatant was filtered through a 0.45-µm membrane filter before high-performance liquid chromatography (HPLC) analysis. HPLC analyses were performed using an Aminex HPX-87H column (Bio-Rad, Berkeley, CA, USA) at 30 °C eluted with 0.01 M H₂SO₄ at a flow rate of 0.6 mL∙min⁻¹ using a refractive index (RI) detector to quantify glucose, xylose, arabinose, acetic acid, HMF and furfural [49 (link)].

Cell Membrane Stability (CMS) was evaluated as previously reported (Rampino et al., 2020); 3.5 cm long leaf segments were rinsed in distilled water, placed in a closed tube with 2 mL of distilled water, and incubated at 50 °C for 1 h (T1), while controls were kept at 10 °C (C1). 8 mL of distilled water were then added to each tube and the tubes were incubated at 10 °C for 24 h. When samples reached room temperature, conductivity of the solution was measured using a Crison GLP 31 conductivity meter (Crison Instruments, Barcelona, Spain). Samples were autoclaved at 100 °C/0.10 MPa for 15 min (T2, C2) and the conductivity was measured again. Ten replicates for each cultivar (cv) were analyzed, and CMS was calculated as follows:

The electrical conductivity of the samples was measured by means of a Crison GLP 31 conductivity meter, which works with an alternating current of 500 Hz and a voltage of 4.5 V. The measuring cell Hach 52 92 connected to it operates in a range from 0.2 µS·cm⁻¹ to 100 mS·cm⁻¹. It also allows a working temperature range from −30 to 80 °C with a repeatability of 0.5%, it being possible to measure at higher temperatures as long as these are very stable. A Julabo F25 thermostatic bath controlled the temperature with an uncertainty of 0.1 °C.