An automated analyzer was developed to achieve fast, precise, and accurate measurements of seawater total alkalinity (AT) based on single-point titration and spectrophotometric pH detection. The single-point titration was carried out in a circulating loop, which allowed the titrant (hydrochloric acid and bromocresol green solution) and a seawater sample to mix at a constant volume ratio. The dissolved CO2 in the sample–titrant mixture was efficiently removed by an inline CO2 remover, which consists of a gas-permeable tubing (Teflon AF2400) submerged in a sodium hydroxide (NaOH) solution. The pH of the mixture was then measured with a custom-made spectrophotometric detection system. The analyzer was calibrated against multiple certified reference materials (CRMs) with different AT values. The analyzer features a sample throughput time of 6.5 min with high precision (±0.33–0.36 μmol kg–1; n = 48) and accuracy (−0.33 ± 0.99 μmol kg–1; n = 10). Intercomparison to a traditional open-cell AT titrator showed overall good agreement of 0.88 ± 2.03 μmol kg–1 (n = 22). The analyzer achieved excellent stability without recalibration over 11 days, during which time 320 measurements were made with a total running time of over 40 h. Because of its small size, low power consumption requirements, and its ability to be automated, the new analyzer can be adapted for underway and in situ measurements.

The commercial solid phase microextraction (SPME) fibers are not stable enough in organic solvent and tend to swell and strip off from the silica fiber in the high performance liquid chromatography (HPLC) mobile phase, and therefore the application of SPME coupled online with HPLC is limited. In this study, an SPME fiber coated with single walled carbon nanotubes (SWCNTs), prepared by means of electrophoretic deposition, was coupled on line to HPLC for the determination of four endocrine-disrupting compounds, i.e. bisphenol A (BPA), estrone (E1), 17α-ethynylestradiol (EE2) and octylphenol (OP), in aqueous samples. The results showed that the SWCNTs coating on the prepared fiber did not swell and strip off from the platinum fiber throughout the experiment, thus indicating a high resistance to the HPLC mobile phase, the mixture of water and acetonitrile. The SWCNTs fiber had similar (for OP) or higher (for BPA, EE2 and E1) extraction efficiencies than the commonly used polyacrylate fiber, and had a lifetime of more than 120 operation times. Under the optimized conditions, the linearity of the proposed method was 1.0–30.0 μg/L for BPA and OP and 3.0–90.0 μg/L for E1 and EE2. The limits of detection (LODs; S/N = 3) and limits of quantification (LOQs; S/N = 10) of the method were 0.32–0.52 μg/L and 1.06–1.72 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.3–7.1% and fiber-to-fiber reproducibility (n = 3) was in the range of 1.6–8.4%. The proposed method was successfully applied for the analysis of spiked tap water and seawater samples with recoveries from 81.8 to 97.3%.

A platinum plate coated with single-walled carbon nanotubes (SWCNTs@Pt) was prepared by means of electrophoretic deposition. Using the SWCNTs@Pt plate, an electrosorption-enhanced solid-phase microextraction (EE-SPME) technique was proposed for the extraction of trace anions in water, described as follows: a positive potential was applied to the SWCNTs@Pt plate to extract F−, Cl−, Br−, NO3− and SO42− from water using electrosorption, and then a negative potential was applied to the plate placed in ultra-pure water for the desorption of the absorbed anions, and finally the desorbed anions were analyzed using ion chromatography (IC). The EE-SPME parameters, including extraction potential and time as well as desorption potential and time, were investigated. An analytical method based on the above procedures, i.e., EE-SPME-IC, was established and used for the analysis of trace anions in water. The results showed that the application of potential on the SWCNTs@Pt plate significantly enhanced the ion extraction efficiency, and an enrichment factor of 15–38 was achieved. The SWCNTs@Pt plate could be used more than 50 times without significant decay. The linear range, the limit of detection (S/N = 3), the limit of quantification (S/N = 10) and repeatability (n = 7) of our EE-SPME-IC method were 1.0–150.0 μg/L, 0.06–0.26 μg/L, 0.19–0.85 μg/L and 2.1–8.0%, respectively. The proposed method was successfully applied for the analysis of trace anions in deionized water, and acceptable recoveries between 65.3 and 121.1% were obtained for the spiked deionized water samples.

A solid-phase microextraction (SPME) fiber coated with single walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition and treated at 500 °C in H2 stream. In order to evaluate the characteristics of the obtained fiber, it was applied in the headspace solid-phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water sample and quantification by gas chromatography with flame ionization detection (GC-FID). The results indicated that the thermal treatment with H2 enhanced the extraction of the SWCNTs fiber for BTEX significantly. Thermal stability and durability of the fiber were also investigated, showing excellent stability up to 350 °C and life time over 120 times. In the comparison with the commercial CAR–PDMS fiber, the SWCNTs fiber showed similar and higher extraction efficiencies for BTEX. Under the optimized conditions, the linearity, LODs (S/N = 3) and LOQs (S/N = 10) of the method based on the SWCNTs fiber were 0.5–50.0, 0.005–0.026 and 0.017–0.088 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.5–5.6% and fiber-to-fiber reproducibility (n = 3) was in the range of 4.2–8.3%. The proposed method was successfully applied in the analysis of BTEX compounds in seawater, tap water and wastewater from a paint plant.

A novel solid-phase microextraction (SPME) Pt fiber coated with single-walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition (EPD) and applied to the determination of phenols in aqueous samples by direct immersion (DI)-SPME-HPLC-UV. The results revealed that EPD was a simple and reproducible technique for the preparation of SPME fibers coated with SWCNTs without the use of adhesive. The obtained SWCNT coating did not swell in organic solvents nor strip off from substrate, and possessed high mechanical strength due to the strong Van der Waals attractions between the surfaces of the SWCNTs. The prepared SPME fiber was conductive since both SWCNT coating and Pt wire were conductive. Using Pt wire as substrate, the fiber was unbreakable. Owing to the presence of oxygenated groups on SWCNTs and the high surface area of SWCNTs, the SWCNT fiber was similar to or superior to commercial PA fiber in extracting the studied phenols from aqueous sample. A durability of more than 80 analyses was achieved for one unique fiber. Under optimized conditions, the detection limits for the phenols varied between 0.9 and 3.8 ng/mL, the precisions were in the range of 0.7–3.2% (n = 3), and linear ranges were within 10 and 300 ng/mL. The method was successfully applied to the analysis of spiked seawater and tap water samples with the recoveries from 87.5 to 102.0%.

The development of new sorbents, which are able to trap polar compounds, is a growing research field in solid-phase extraction (SPE). In this study, multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were oxidized in air at 600 °C and 500 °C, respectively, for 2 h. MWCNTs, SWCNTs, air oxidized MWCNTs (OMWCNTs) and SWCNTs (OSWCNTs) (200 mg of each) were packed in SPE cartridges. The four cartridges obtained, together with a commercial Oasis HLB cartridge, were used to extract six polar organophosphorous pesticides (OPPs), i.e., dichlorvos, methamidophos, acephate, omethoate, monocrotophos and dimethoate, from an aqueous sample. The results showed that the oxidation process significantly enhanced the adsorption abilities of both SWCNTs and MWCNTs for polar OPPs. A comparative study indicated that OSWCNTs were more effective than Oasis HLB for the extraction of methamidophos and acephate and as effective as Oasis HLB for the other four OPPs from aqueous samples. When 100 mL of a natural sample was spiked with OPPs and extracted with OSWCNTs, the recoveries of five of the six polar OPPs (methamidophos excepted) ranged from 79.1 to 101.9%. The detection limits of the method based on OSWCNTs was found to be 0.07–0.12 µg L−1.

The development of new sorbents, which are able to trap polar compounds, is a growing research field in solid-phase extraction (SPE). In this study, multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were oxidized in air at 600 °C and 500 °C, respectively, for 2 h. MWCNTs, SWCNTs, air oxidized MWCNTs (OMWCNTs) and SWCNTs (OSWCNTs) (200 mg of each) were packed in SPE cartridges. The four cartridges obtained, together with a commercial Oasis HLB cartridge, were used to extract six polar organophosphorous pesticides (OPPs), i.e., dichlorvos, methamidophos, acephate, omethoate, monocrotophos and dimethoate, from an aqueous sample. The results showed that the oxidation process significantly enhanced the adsorption abilities of both SWCNTs and MWCNTs for polar OPPs. A comparative study indicated that OSWCNTs were more effective than Oasis HLB for the extraction of methamidophos and acephate and as effective as Oasis HLB for the other four OPPs from aqueous samples. When 100 mL of a natural sample was spiked with OPPs and extracted with OSWCNTs, the recoveries of five of the six polar OPPs (methamidophos excepted) ranged from 79.1 to 101.9%. The detection limits of the method based on OSWCNTs was found to be 0.07–0.12 µg L−1.