Optical Characterization of Ciprofloxacin Photolytic Degradation by UV-Pulsed Laser Radiation

Abstract

Ciprofloxacin is one of the most prescribed antibiotics in treating bacterial infections, becoming an important pollutant of the wastewaters. Moreover, ciprofloxacin is hard to be destroyed by conventional water treatment processes; therefore, efficient treatments to destroy it are needed in water decontamination. This study offers insights into the performance of 266 nm laser beams on the photodegradation of ciprofloxacin. An Nd:YAG laser was used that emitted 266 nm at an energy of 6.5 mJ (power of 65 mW) and ciprofloxacin water solutions were irradiated up to 240 min. The irradiated solutions were investigated by UV-Vis and FTIR absorption spectroscopy, pH assay, and laser-induced fluorescence. An HPTLC densitometer was used to characterize the laser-induced fluorescence and fluorescence lifetime of photodegradation products. The UV-Vis absorption, FTIR, and laser-induced fluorescence spectra showed the degradation of ciprofloxacin. Moreover, HPTLC densitometry offered the fluorescence and fluorescence lifetime of ciprofloxacin and its three photoproducts as well as their relative quantification. From the FTIR spectra, the molecular structure of two out of three photoproducts was proposed. In conclusion, the laser irradiation method provided the efficient photodegradation of ciprofloxacin, whereas the analytical techniques offered the proper means to monitor the process and detect the obtained photoproducts.

Keywords: FTIR; HPTLC densitometry; absorption spectroscopy; ciprofloxacin; fluorescence; laser degradation.

Figure 1

Absorption spectra of unirradiated and irradiated CIP for 1, 15, 30, 60, 120, 180, and 240 min, diluted to 0.2 mg/mL and recorded between (a) 200–400 nm, (b) 300–400 nm, (c) 200–240 nm.

Figure 2

Stability studies over a 4-week time interval performed by recording UV-Vis absorption spectroscopy for CIP (a) unirradiated, (b) 1 min irradiated, (c) 15 min irradiated, (d) 30 min irradiated, (e) 60 min irradiated, (f) 120 min irradiated, (g) 180 min irradiated, (h) 240 min irradiated; the spectra were recorded at the initial concentration of 2 mg/mL.

Figure 3

(a) LIF spectra of CIP, recorded in real-time during irradiation, in the 350–750 nm spectral range; (b) the fluorescence intensity of the 458 nm fluorescence band as a function of the laser irradiation time interval.

Figure 4

IR spectra of 2 mg/mL CIP unirradiated and irradiated between 1 min and 240 min in (a) 3600–700 cm⁻¹, (b) 1800–1560 cm⁻¹, (c)1560–1380 cm⁻¹, (d) 1380–1200 cm⁻¹ spectral range.

Figure 5

Calibration curve for CIP solutions at concentrations between 2 and 64 µg/band. The parameters of the fitting curve (red line) are indicated in the figure.

Figure 6

(a) Horizontal chromatogram resulting from point-by-point scanning of the plate before development in the mobile phase. (b) Fluorescence spectra of CIP and each irradiated CIP solution applied on the HPTLC plate. (c) Evolution of fluorescence peak wavelength with the irradiation time.

Figure 7

(a) Developed HPTLC plate, containing unirradiated CIP and the separated photoproducts of CIP, visualized at 254 nm and photographed. (b) Vertical (oy) chromatogram of the plate, (c) Horizontal (ox) chromatogram of the plate.

Figure 8

Time evolution of fluorescence spectra of CIP and its photoproducts for (a) 10 s, (b) 1 min, (c) 15 min, (d) 30 min, (e) 60 min, (f) 120 min, (g) 180 min, (h) 240 min irradiation. The right coloured oy axes correspond to the fluorescence curves of the compounds P3 (red), P1 (green).

Figure 9

The time-resolved fluorescence signal of CIP, P1, P2, and P3 when excited at 375 nm.

Figure 10

Fluorescence intensity peak evolution of CIP and its photoproducts during laser irradiation resulted from the HPTLC densitometry measurements.

Figure 11

Absorption spectra for CIP exposed one week to sunlight and exposed 240 min to 266 nm laser radiation.