Seven compact s210k

The establishment of the acidifying system was based on the methods of our previous study (Hu et al., 2017 (link); Sun et al., 2017 (link)). Three pH levels were evaluated in the present study: pH 8.1 (present ambient seawater pH, pCO₂≈390ppm), pH 7.6 (predicted pH in 2100, pCO₂≈1,000ppm), and pH 7.4 (predicted pH in 2300, pCO₂≈2000ppm), obtained by gentle bubbling with 0.22-μm filtered ambient air and air/CO₂ mixtures. The air/CO₂ mixtures were generated by plant CO₂ chambers (HP400G-D, Ruihua Instrument & Equipment Ltd., Wuhan, China) with a variation of less than 5%. The pH values and salinity of the seawater in the flasks were measured by a pH meter (Seven Compact™ S210k, Mettler Toledo, Switzerland) and a handheld salinometer (WY028Y, HUARUI, CHN).

The pH value and dissolved inorganic carbon (DIC) were determined prior to and after the daily dilution. The concentration of DIC in the culture medium was measured using a total organic carbon analyzer (TOC-V_CPN, Shimadzu). The samples were filtered onto brown glasses via 0.45 μm cellulose acetate membranes and stored in a refrigerator (4°C). The pH was measured using a pH meter (SevenCompact^™ S210k, Mettler Toledo, Switzerland), which was calibrated daily with standard National Bureau of Standards (NBS) buffer system. The other relevant parameters of carbonate system were determined with the CO₂SYS software [35 ], based on the known parameters (pH, DIC, salinity and temperature).

The investigation of the halochromic properties of the flavylium dye involved measurements of the UV-VIS spectra of the flavylium dye solutions (7 × 10⁻⁵ M in methanol:water 1:14) over time at pH values ranging from 2 to 12. The buffer solutions were prepared by following a previously described procedure [42 (link)], and the pH values were measured with a Mettler Toledo Seven Compact S210-K (Mettler Toledo, Columbus, OH, USA) at 25 °C.
The colorimetric response to pH changes was assessed by recording the UV-VIS spectra of 1 × 1 cm polymeric films after they had been immersed for 1 h in buffer solutions ranging from 2 to 12, then washed with distilled water and dried at 40 °C for 4 h.