Fe20 fiveeasy plus ph meter

One milliliter of unstimulated saliva was mixed with 20 ml normal saline for use in further experiments. All saline-saliva samples were centrifuged at 12,000 rpm for 5 min. Ten milliliters of supernatant was used for measurement of the pH with a calibrated FE20 FiveEasy Plus pH meter (Mettler-Toledo, Schwerzenbach, Switzerland). Two milliliters of supernatant was used for measurement of the iron concentration with a Thermo elemental atomic absorption spectrometer (Thermo Scientific, East Lyme, CT). Briefly, standards containing known concentrations of iron were prepared by serial dilutions. The standards and samples then were dried at 80°C and 130°C for 20 s and 10 s, respectively, ashed, and atomized at 1,200°C and 2,100°C for 10 s and 5 s, respectively. Spectrophotometric measurements of the samples were performed at a wavelength of 243.8 nm. A calibration curve was generated using the measurements for the standards and was then used to quantify the iron levels in the samples and blank (normal saline only); the difference between the sample and blank was the final value. The samples used for measurement of the pH and iron concentration were analyzed in triplicate. The entire pellet was used to extract salivary DNA, and salivary DNA extraction was performed using a Qiagen Stool minikit (Qiagen, Valencia, CA) as previously described (7 (link)).

The human cancer cell lines including AGS, HGC27, HeLa, Panc-1, HCT116, A549, and U2OS were purchased from the Cell Resource Center, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences (Shanghai, China). MKN45 was purchased from the Cell Resource Center, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences (Beijing, China). Hucct1 were obtained from the Japanese Collection of Research Bioresources (JCRB) (Tokyo, Japan). The cell lines were originally authenticated in China Center for Type Culture Collection (CCTCC) by Short Tandem Repeat (STR) profiling and passaged less than 6 months in the lab. These cells are routinely maintained in the laboratory of our group.The acid cell culture medium (pH 6.5) was obtained by the addition of 1 M HCl solution as previously reported^{23 (link),24 (link)}. The pH was estimated by the use of a FE20 FiveEasy Plus pH Meter (METTLER TOLEDO Instruments (China), Shanghai, China).