# Immobilised Humic Substances as Low-Cost Sorbents for Emerging Contaminants
## 2 Materials and Methods
### Sorption Experiments  
Sorption experiments were conducted using the batch system. Na\({}_{2}\)HAsO\({}_{4}\cdot 7\)H\({}_{2}\)O (Sigma-Aldrich) and Cr(NO\({}_{3}\))\({}_{3}\cdot 9\)H\({}_{2}\)O were used for As(V) and Cr(III) stock solution preparation, respectively, while chlorpromazine hydrochloride ((\(\geq\)98% (TLC) Sigma-Aldrich) (Figure 1) was used as an exemplar of pharmaceuticals. A chlorpromazine HCl working standard (5-550 ug/mL) was dissolved in 1% ammonium acetate. A total of 50 mL of an As(V), Cr(III) or chlorpromazine HCl solution was added in each 100 mL glass vessel with 0.05 g or 0.1 g of sorbent for As(V). The vessels were shaken for 24 h at room temperature. The suspensions were then filtered, and arsenic and chromium in the filtrate were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES), while chlorpromazine was analyzed using ultra-high-performance liquid chromatography. All experiments were performed in duplicate, and the average value was calculated. The sorption capacity of the immobilized HS sorbent was evaluated using the following expression:  
\[q_{e}=\frac{(C_{0}-C_{t})*V}{m} \tag{1}\]  
where \(q_{e}\) is the mass of the element adsorbed per unit mass of the adsorbent in mg/g; \(V\) is the solution volume in L; \(m\) is the adsorbent mass in g; and \(C_{0}\) and \(C_{t}\) are the element concentrations in the initial solution and in the solution after adsorption in mg/L. The impact of the pH, dosage of the sorbent and contact time were studied. To investigate the pH impact, either a 0.1 M HCl or a 0.1 M NaOH solution was used. In the glass vessels, the necessary amount of As(V), Cr(III) or chlorpromazine HCl stock solution was added to 0.1 g of immobilized HSs. The varied pH solutions were prepared by adding 0.1 M NaOH or 0.1 M HCl dropwise to achieve pH values of 3-10. After that, the reaction mixture was shaken for 24 h at room temperature and filtered. Finally, the pH scale was measured. The filtrates were analyzed with ICP-OES or with a chromatograph. The point zero charge (pHpzc) of the immobilized HSs was determined with the method outlined by [PERSON] and [PERSON] [25]. The impact of the sorbent dosage was investigated using different dosages of the immobilized HSs (0.05-1.2 g), while the concentration of the sorbate was kept constant. The kinetics of the sorption process was evaluated in the sorption experiments in the same manner as previously described. The initial As(V) and Cr(III) concentrations were 100 mg/L and 8 mg/L respectively, and the sorbate concentration in the solution phase was measured after 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7 and 24 h.  
The concentration of As and Cr in the solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using a Thermo Scientific iCAP7000 spectrometer. The measurement was carried out using argon gas (AGA, 5.0) at a 7000 K temperature, 0.5 L/min plasma gas flow rate and 1.15 kW of applied power. The analyses were performed at a wavelength of 189.042 nm (LOD - limit of detection = 0.02 mg/L, LOQ-limit of quantification = 0.07 mg/L, uncertainty = 3%) for arsenic and a wavelength of 267.716 nm (LOD = 0.04 mg/L, LOQ = 0.12 mg/L, uncertainty = 3%) for chromium. A standard 1000 mg/L arsenic solution (atomic spectroscopy standard in 2% HNO\({}_{3}\), Perkin Elmer, Waltham, MA, USA) and a 1000 mg/L chromium solution (Fisher Scientific, Waltham, MA, USA, high purity reagent) were used to plot the calibration curves. Figure 1: Chlorpromazine hydrochloride. Ultra-Performance Liquid Chromatography (UPLC) analysis of chlorpromazine. Chromatographic separation was carried out using Waters Acquity UPLC H-class equipment (Milford, MA, USA) that consisted of an ultra-high-pressure gradient unit (Quaternary Solvent Manager), an autoinjector (FTN), a column oven (CHA) and a fluorescence detector (FLR). Chromatographic data were collected by means of the Waters Empower chromatography software.