automated titrimeter and electrode standardized to pH 2.0, 4.0, 7.0, and 10.0 buffers. Titratable acidity was determined by titrating 0.1 N sodium hydroxide to 6 g of juice diluted with 50 mL of deionized, degassed water to an endpoint of pH 8.2, with
-H refill cartridge (30 × 4.5 mm) was used for a guard column. Columns were maintained at 65 °C by a temperature control unit. Mobile phase consisted of a pH 2.28 solution of sulfuric acid and water with a resistivity of 18 M obtained from a Millipore Milli
a BEH C18 column (Aquity, Waters Co). Each well was injected in triplicate with 5 μL of sample volume. The mobile phases consisted of 5 m m potassium phosphate monobasic (KH 2 PO 4 ), pH 2.65, with 0.1% of formic acid (mobile phase A) and methanol
Instruments, Wilmington, DE) 5 min at 10,000 g n at 4 °C. Supernatant (3 mL) was removed to a test tube, to which 1 mL derivatizing solution, 1,2-benzenediamine dihydrochloride, was added (final Ph, 2.20–2.45), vortexed for 5 s, filtered through a 45-μm
Detector set at 210 nm using an X-bridge C18 column (4.6 × 250 mm, 5 μm, Waters Corporation) operated at 30 °C. The elution solvent was 0.01 mol·L −1 sulfuric acid (pH 2.6) passed at a rate of 0.5 mL·min −1 . The quantity and type of organic acids were
= 0.8780 × Δ pH 3 + 1.3369 × Δ pH 2 + 9.9856 × Δ pH − 0.2569 [1] Plant growth was measured as root and shoot dry weight gain during the experiment. Root and shoot tissue from seedlings and from final replicates was oven-dried for 48 h
with the producers reporting research on nutrient solution formulations (mean = 3.1 ± 1.0) and nutrient solution pH (2.8 ± 1.0) being slightly to very beneficial ( Fig. 6 ). Additionally, with the majority of producers surveyed monitoring and
of 5 m m potassium phosphate monobasic (KH 2 PO 4 ), pH 2.65, with 0.1% of formic acid (solution A) and methanol with 0.1% of formic acid (solution B). The linear gradient of the mobile phase was programmed as follows: 5% to 15% B for 1 min, followed
was carried out on a 250 × 4.6-mm, 5-μm column (Diamonsil C18; Dikma Technologies, Foothill Ranch, CA). Detection was operated at 214-nm wavelength with 0.1 mmol·L −1 KH 2 PO 4 (pH = 2.6) as mobile phase passed through a 0.45-μm membrane filter. The
(pH 2.0, using 6 M HCl). With a separatory funnel, the free phenolic compounds were extracted with diethyl ether (5 × 20-mL portions). The extractant was composed of acetone, water, and acetic acid. The organic phase (acetone) was removed using the