Analytical balance

To determine the fresh weight (crop yield, g plant⁻¹), the lettuce were harvested and weighed on an analytical balance (Ohaus Corporation, Pine Brook, NJ, USA).

The Association of Official Analytical Chemists (AOAC) method [30 ] was used to determine the nutritional compositions and energetic values of LCD and HCD. Samples were weighed and dried at 105 °C for 24 h for moisture content determination. Ash content was measured by using a muffle furnace (Nabertherm GmbH, Lilienthal, Bremen, Germany) at 550 °C for 5 h. Total protein content was determined by the Kjeldahl method and calculated by multiplying the nitrogen content by 6.25. Fat content was determined by using the Soxhlet method, with hexane as a solvent. Carbohydrate content was estimated by the difference of mean experimental values, i.e., 100 − (sum of percentages of moisture, ash, protein and fat) [31 (link)]. The sample weight was measured by an analytical balance (Ohaus Corporation, Parsippany, NJ, USA) having a precision of ±10⁻⁴ g. Energetic values (EV) of LCD and HCD were estimated on the basis of protein, fat and carbohydrates content as follows [32 (link)]: $$EV \left(\frac{kcal}{g}\right)=4\times Protein content+4\times Carbohydrate content+9\times Fat content$$

Water, ACN, or MeOH were employed as solvents to prepare the standard solutions of the selected pharmaceuticals. First, an accurately weighed (±0.1 mg) amount of pharmaceutical, 10 or 20 mg measured with an analytical balance (Ohaus, Greifensee, Switzerland), was transferred into a 25 mL amber volumetric flask. The final concentration of each stock solution depended on each pharmaceutical’s solubility. The different stock solutions were mixed to obtain a 5 µg/mL working standard solution of each pharmaceutical. All solutions were stored at −20 °C for a minimum period of one month.
Mobile phases A and B were prepared by adding 500 μL of formic acid to ~400 mL of Milli-Q water (mobile phase A) or acetonitrile (mobile phase B), respectively. The volume was finally set to 500 mL with the corresponding solvent to achieve a final formic acid concentration of 0.1% in each case.
A McIlvaine buffer solution was prepared by mixing citric acid (615.4 mL at 0.1 M) with disodium hydrogen phosphate (385 mL at 0.2 M). NaOH or HCl was used to adjust the pH. Once the pH was 4, EDTA (37.2 g) was added to a 1 L McIlvaine buffer solution and stored at 8 °C for one month. The final extraction solution was a mixture of methanol and McIlvaine–EDTA (70:30), which was prepared for each day of extraction.