Nahco3

Six experimental primers each containing 10 wt %
MDP (DM Healthcare Products, Inc., San Diego, CA, USA) were prepared
using ethanol, acetone, water, or their mixtures as solvents with
different pH values. Sodium bicarbonate (NaHCO₃, Macklin,
Shanghai, China) was used to adjust the pH of the E-W-MDP₂ to 5 (E-W-MDP_2/5) or 7 (E-W-MDP_2/7). The pH
values of different primers were measured using an electronic pH meter
(FE28, Mettler Toledo, Zurich, Switzerland). Prior to measuring the
primers, the pH electrodes were calibrated with buffer solutions at
pH 7.00 and pH 4.01. Three specimens were prepared for the measurements
for each primer and the mean was calculated. The compositions and
pH values of these six experimental primers are listed in Table 3.

l-Trp, l-Glu, NaCl, sodium acetate, KH₂PO₄·3H₂O, acetic acid, 2,4-dinitrofluorobenzene, and NaHCO₃ were purchased from Shanghai Macklin Biochemical Technology Co.,
Ltd. (Shanghai, China). NaOH was provided by Tianjin Jinbei Fine Chemical
Co., Ltd. (Tianjin, China). Hydrochloric acid was purchased from China
Pingmei Shenma Group Kaifeng Dongda Chemical Co., Ltd. All the above
reagents were analytically pure. Acetonitrile (chromatographic pure
reagent) was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.
(Tianjin, China).