Naphthalene (NAP), 1-naphthol (1-NAP) and 2-naphthol (2-NAP) are bicyclic hydrocarbons (Figure 1) used in the production of dyes, synthetic rubber, pesticides and pharmaceutical industries. Since naphthalene and its derivatives are toxic at high concentrations, the widespread use of these compounds (e.g., tar, asphalt, etc.) means that they may be present in the environment as pollutants. Naphthalene has also been shown to occur naturally in volcanic gases. In addition, it has been shown that NAP, 1-NAP and 2-NAP are formed by thermal degradation of 1,5-naphthalenesulfonate, a common tracer used in the geothermal industry. There are many methods for detecting 1-NAP and 2-NAP, including spectrophotometry, HPLC and electrochemical methods.

Determination of naphthalene, 1-NAP, and 2-NAP in saline water by HPLC-fluorescence detector

NAP, 1-NAP, and 2-NAP were determined from saline water (up to 1.00 mol kg-1 NaCl) using HPLC-fluorescence detector combined with SPE method. Among different tested SPE cartridges, Discovery-C18 (100 mg) cartridge was the most effective. Ethanol was selected as the best eluent. Although salinity in the range of 0.00 - 1.00 mol kg-1 NaCl had no effect on the analytical quality.

Determination of 1-NAP and 2-NAP based on electrochemical sensor

Fe3O4@prGO-CNT/CPE is a simple, cost-effective electrochemical sensor based on magnetite (Fe3O4 nanoparticles) porous reduced graphene oxide/carbon nanotube (Fe3O4@prGO-CNT) nanocomposite for the simultaneous detection of 1-NAP and 2-NAP. The voltammetric responses showed that the electrocatalytic performance of naphthols was significantly improved by the addition of Fe3O4@prGO-CNT on the carbon paste electrode (CPE). Differential pulse voltammetry (DPV) measurements showed a large potential separation of about 200 mV between naphthols, allowing their simultaneous determination from a binary mixture. Under the optimized conditions, Fe3O4@prGO-CNT/CPE exhibited a linear relationship with 1-naphthol and 2-naphthol in the range of 0.5–30 and 0.7–40 μM, with detection limits (S/N = 3) of 76 and 82 nM, respectively. In addition, Fe3O4@prGO-CNT/CPE showed satisfactory responses for the determination of 1-NAP and 2-NAP concentrations in wastewater and river water.

Determination of 1-NAP and 2-NAP by fluorescence spectrophotometry

A simple and sensitive fluorescence spectrophotometric method for the simultaneous determination of trace 1-NAP and 2-NAP was established by taking advantage of the different excitation and emission wavelengths of 1-naphthol and 2-naphthol. The influencing factors such as pH, temperature, and surfactant were comprehensively considered, and the interference of similar organic matter and inorganic ions was considered. Compared with the traditional method, this method does not require complex pretreatment and expensive equipment, is convenient, fast, and inexpensive, and has satisfactory precision and accuracy. When the concentration ratio (CR) of 1-NAP and 2-NAP is in the range of 1:19 to 19:1, the accuracy and precision of the results are satisfactory. The detection limits (DL) of the two naphthols are both 8.6×10(-3)ng·mL(-1); the relative standard deviations (RSDs) of 1-NAP and 2-NAP are 1.26% and 1.45%, respectively; the recoveries (RR) of the two naphthols are between 95% and 105%. The method was applied to the simultaneous determination of trace 1-naphthol and 2-naphthol in artificial water samples and environmental simulated water, and satisfactory results were obtained.