[Determination of boric acid and silicic acid in mineral water by nonsuppressed ion chromatography].

Boron and silicon are widely distributed in nature; in water, these compounds typically present in the forms of boric acid and silicic acid, respectively. The maximum allowable levels of silicic acid and boric acid in water are stipulated in relevant national and industry standards, such as GB 8538-2022. Quality changes in water, which are of great significance in water-quality evaluations, can be understood in terms of its silicic acid and boric acid contents. Boric acid content is usually determined by ion exclusion chromatography, whereas silicic acid content is usually determined by postcolumn derivatization. Therefore, traditional methods cannot achieve the simultaneous determination of silicic acid and boric acid contents in water. Modern ion chromatography has been widely used in the detection of ionic compounds, such as anions, cations, organic acids, organic amines, amino acids, and sugars. Boric (pKa=9.24) and silicic (pKa=9.77) acids are weak acids that dissociate into ionic states under alkaline conditions. Although these compounds cannot be tested using suppressed ion chromatography, they can be retained on ion chromatography columns. In this study, a method based on nonsuppressed conductance detection was established for the simultaneous determination of boric acid and silicic acid in water. The contents of boric acid and silicic acid were detected by nonsuppressed ion chromatography using a Dionex IonPacTM AS20 analytical column. The chromatographic conditions were as follows: flow rate, 1.0 mL/min; column temperature, 30 ℃; eluent, 6 mmol/L sodium hydroxide solution and 60 mmol/L mannitol; and sample injection volume, 50 µL. The effective separation of silicic acid and boric acid was achieved within 8 min. SiO32- and boric acid demonstrated good linear relationships in the concentration ranges of 0.25-100 and 0.5-100 mg/L (correlation coefficients, 0.9999), respectively. The method detection (MDL) and quantification (MQL) limits were 0.078 and 0.26 mg/L for SiO32-, and the MDL and MQL limits were 0.18 and 0.60 mg/L for boric acid. The average recoveries of boric acid and SiO32- (n=6) were 97.3%-105.3%. Moreover, the relative standard deviations were less than 0.9% for boric acid at four spiked levels and less than 0.30% for SiO32- at three spiked levels. Thus, the method meets detection requirements. The pretreatment method is very simple, and the sample can be directly injected through a 0.22 µm water filtration membrane and into the column. The boric acid and silicic acid contents in nine mineral drinking water samples were determined under the optimized analytical conditions. Boric acid was not detected in these nine samples, but silicic acid was detected in six samples. The silicic acid contents detected were between 18.70 and 62.08 mg/L, which was consistent with the concentration ranges marked on the manufacturers' packaging. The proposed method can be used for the determination of boric acid and silicic acid in mineral drinking water and laboratory water, and provides a reference for the simultaneous detection of boric acid and silicic acid in ultrapure water used in the semiconductor industry.

[A polymer resin surface polymerization-based hydroxide-selective anion exchange stationary phase].

A polystyrene-divinylbenzene (PS-DVB) microspheres-based hydroxide-selective anion exchange stationary phase is described. This stationary phase is obtained by the surface polymerization of an allyl glycidyl ether (AGE) and the pendant vinyl groups onto the surface of PS-DVB, followed by open-ring of the epoxy groups using an alkylol amine (abbreviated as P@A-M). Both alkylol amines were compared in terms of separation performance of the stationary phase. Scanning electron microscopy, infrared spectroscopy, and elemental analyses were carried out to characterize the stationary phase. The results indicated that the quaternary amine group was successfully introduced onto the surface of the PS-DVB microspheres, and that there was no obvious change in the physicochemical properties of the resin during the surface polymerization reaction. The P@A-M phase showed high hydroxide-selectivity and good separation performance (resolution>1.5) as well as high running stability (relative standard deviation of retention times<1.13%). The utility of the P@A-M phase was demonstrated by using it for the determination of inorganic anions in the tea.

A poly(glycidylmethacrylate-divinylbenzene)-based anion exchanger for ion chromatography.

An anion exchanger has been described by grafting dimethylaminoethyl methacrylate methylchloride (DMC) onto the poly(glycidyl methacrylate-divinylbenzene) (GMA-DVB) subtract. The grafting was performed by coupling of DMC with the pendant double bonds of DVB. Prior to grafting, a hydrolysis treatment to free epoxide groups associated with GMA-DVB substrate enables an improved hydrophilic surface of the obtained anion exchanger. The capacity of the obtained anion exchanger can be manipulated by controlling DMC amount to a great degree. Common seven inorganic anions onto the anion exchanger could be well separated within 20 min and high separation efficiency was obtained, e.g. 46,500/m of the plate count for chloride.

A novel hydrophilic polymer-based anion exchanger grafted by quaternized polyethyleneimine for ion chromatography.

A novel hydrophilic polymer-based anion exchanger has been described for ion chromatography (IC). It is prepared by grafting polyethyleneimine (PEI) onto the poly(glycidylmethacrylate-divinylbenzene) (GMA-DVB) substrate, followed by hydrolytic treatment to convert the residual epoxide groups onto the surface of GMA-DVB substrates to hydroxyl groups, finally quaternized PEI by a molecule containing epoxide group. Hydrophobic surface of GMA-DVB substrate can be converted to hydrophilic, aiming to reduce unwanted non-ionic interaction from the substrate. After optimizing the reaction conditions, the obtained anion exchanger showed good separation towards standard inorganic anions under the suppressed mode and complete elution of seven common inorganic anions could be achieved in less than 16 min by using potassium bicarbonate eluent. It also demonstrated fast dynamic kinetic and enabled the separation of 7 anions within 3 min at the isocratic mode. Column efficiency of the anion exchanger was up to 34,000 /m.

Low-Bleed Silica-Based Stationary Phase for Hydrophilic Interaction Liquid Chromatography.

Bleeding of hydrophilic interaction liquid chromatographic (HILIC) phases is a major problem. A hydrophobic silica surface exhibits low bleeding but does not behave as a HILIC phase. A hydrophilic coating, such as that of poly(vinyl alcohol) (PVA) on a hydrophobic particle should result in a low-bleed hydrophilic phase. However, a silica particle functionalized in a hydrophobic manner is not wetted by PVA and cannot be coated with it. Coating with PVA becomes possible if one region of the hydrophobic functionality is polar. We describe a low-bleed HILIC stationary phase, PVA-coated benzylthioethyl-silica. The benzyl groups shield the silica from water erosion, while the thiol group provides sufficient local polarity for PVA to wet the material. The new stationary phase demonstrated good chromatographic performance and typical HILIC retention behavior. The measured silica concentration in the effluent was ∼80-fold lower than that from a bare silica column. The new stationary phase exhibited a lower background level, lower background noise, and lower background drift under gradient conditions than benchmark commercial columns.