The development of a simple and sensitive analytical approach that combines multiple monolithic fiber solid-phase microextraction with liquid desorption followed by high-performance liquid chromatography with diode array detection is proposed for the determination of trace levels of seven steroid sex hormones (estriol, 17β-estradiol, testosterone, ethinylestradiol, estrone, progesterone and mestranol) in water and urine matrices. To extract the target analytes effectively, multiple monolithic fiber solid-phase microextraction based on a polymeric ionic liquid was used to concentrate hormones. Several key extraction parameters including desorption solvent, extraction and desorption time, pH value and ionic strength in sample matrix were investigated in detail. Under the optimal experimental conditions, the limits of detection were found to be in the range of 0.027–0.12 μg/L. The linear range was 0.10–200 μg/L for 17β-estradiol, 0.25–200 μg/L estriol, ethinylestradiol and estrone, and 0.50–200 μg/L for the other hormones. Satisfactory linearities were achieved for analytes with the correlation coefficients above 0.99. Acceptable method reproducibility was achieved by evaluating the repeatability and intermediate precision with relative standard deviations of both less than 8%. The enrichment factors ranged from 54- to 74-fold. Finally, the proposed method was successfully applied to the analysis of steroid sex hormones in environmental water samples and human urines with spiking recoveries ranged from 75.6 to 116%.

In this study, a new stir cake sorptive extraction using a boron-rich monolith as the adsorbent was prepared by the in situ copolymerization of vinylboronic anhydride pyridine complex and divinylbenzene. The effect of preparation parameters, including the ratio of vinylboronic anhydride pyridine complex and divinylbenzene, monomer mixture, and porogen solvent, on extraction performance was investigated thoroughly. The physicochemical properties of the adsorbent were characterized by infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. Several conditions affecting the extraction efficiency were investigated in detail. Under the optimized conditions, a convenient and sensitive method for the determination of trace fluoroquinolones residues in water and milk samples was established by coupling stir cake sorptive extraction with high-performance liquid chromatography and diode array detection. The limits of detection for the target compounds were 0.10–0.26 and 0.11–0.22 μg/L for water and milk samples, respectively. In addition, the developed method showed good linearity, repeatability, and precision. Finally, the proposed method was successfully applied for the detection of trace fluoroquinolones residues in environmental water and milk samples. Satisfactory recoveries were obtained for the determination of fluoroquinolones in spiking samples that ranged from 68.8 to 120%, with relative standard deviations below 10% in all cases.

Monolithic fibers were synthesized and applied for the solid-phase microextraction and determination of chlorophenols in environmental water samples by coupling with HPLC. The fibers were prepared by copolymerization of vinylimidazole and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The effect of the preparation conditions of monolithic fibers on the extraction efficiencies was investigated in detail. Several characteristic techniques, such as elemental analysis, infrared spectroscopy, mercury-intrusion porosimetry, and SEM were used to characterize the monolithic material. The effect of the extraction parameters, including desorption solvent, extraction and desorption time, pH values, and ionic strength in sample matrix on the extraction performance was investigated thoroughly. Under the improved extraction conditions, the linear ranges of 2-chlorophenol, 2,4-dichlorophenol and pentachlorophenol were 1.0–200 μg/L and 2.0–200 μg/L for 2,4,6-trichlorophenol. The detection limits (S/N = 3) were in the range of 0.16–0.45 μg/L, the RSDs for intraday and interday precisions were <7.0%. Finally, the proposed method was successfully used to detect different environmental water samples. The recoveries of spiked water samples were ranged from 90.0 to 115%. At the same time, satisfactory repeatability was achieved with RSDs < 9.0%.

Nanosized spherical magnetic poly(vinylimidazole-co-divinylbenzene) particles were synthesized and used as a sorbent for the enrichment of trace fluoroquinolones (FQs) from environmental water samples. A suspension polymerization procedure was used to prepare the sorbent. The magnetic sorbent was characterized by SEM, transmission electron microscopy, elemental analysis, and FTIR spectroscopy. Analysis of enrofloxacin, marbofloxacin, fleroxacin, lomefloxacin, and sparfloxacin in environmental water samples by the combination of the magnetic sorbent and HPLC with diode array detection was selected as a paradigm for the practical application of the new adsorbent. Several extraction conditions, including desorption solvent, extraction and desorption time, pH value, and ionic strength in sample matrix, were optimized. Results showed that the new sorbent had high affinity for FQs and could be used to extract them effectively. Under the optimum conditions, low detection (S/N = 3) and quantification (S/N = 10) limits were achieved for the target analytes, within the ranges of 0.20–1.46 and 0.68–4.84 μg/L, respectively. Method repeatability was achieved in terms of intra- and interday precisions, indicated by the RSDs, which were both <10.0%. The method also showed good linearity, simplicity, practicality, and environmental friendliness for the extraction of FQs. Finally, the developed method was successfully applied to the determination of FQs in lake water, surface water, and reservoir water samples. Acceptable recoveries of spiked target compounds in these water samples were in the range of 52.1–104.5%.

In the present study, a convenient and sensitive method for determination of six penicillin antibiotics (amoxicillin, ampicillin, penicillin G, oxacillin, cloxacillin, and dicloxacillin) in milk and honey samples was developed. Milk and honey samples were diluted with water, then directly treated by stir bar sorptive extraction based on poly (vinylimidazole-divinylbenzene) monolithic material as coating. The analytes were analyzed by LC/ESI- MS/MS. Several extraction parameters including extraction and desorption time, pH value, and ionic strength in sample matrix were investigated in detail. Under the optimized extraction conditions, the calculated detection limits for the target compounds were as low as 0.23–2.66 ng/kg in milk and 0.18–1.42 ng/kg in honey, respectively. Good linearity was obtained for analytes with the correlation coefficients (R²) above 0.997. Excellent method reproducibility was achieved in terms of intraday and interday precisions, indicated by the RSDs of <5.0 and <10.0%, respectively. Finally, the proposed method was successfully applied to the determination of penicillin antibiotics residues in different milk and honey samples.

In this study, a new extraction approach for liquid samples – stir cake sorptive extraction using monoliths as extractive medium was developed. The preparation procedure of stir cake is very simple. First, monolithic cake is synthesized according to the in situ polymerization of monolith; then, the cake is inserted in an original unit (holder), which is constructed from a syringe cartridge and allows the magnetic stirring of the cake during the extraction process. The effects of dimension of monolithic cake and unit design on the extraction performance were optimized in detail. To demonstrate the usability of this new extraction approach, poly(vinylimidazole-divinylbenzene) was prepared and acted as the extractive cake. The analysis of steroid hormones in milk samples by the combination of stir cake with high-performance liquid chromatography with diode array detection, was selected as a paradigm for the practical evaluation of stir cake sorptive extraction. Under the optimized extraction conditions, low detection limits (S/N=3) and quantification limits (S/N=10) of the proposed method for the target analytes were achieved within the range between 0.33–0.69 and 1.08–2.28 μg/L, respectively. The method also showed good linearity, repeatability, high feasibility and acceptable recoveries. Because the monolithic cake does not contact with the vessel wall during stirring, there is no friction loss of extractive medium and the stir cake can be used for more than 1000 h.

In the present study, we developed a simple and sensitive method for the simultaneous determination of metronidazole (MTZ), ronidazole (RNZ), dimetridazole (DMZ), and tinidazole (TNZ) in honey. Honey samples were diluted with water, then directly treated by stir bar sorptive extraction (SBSE) based on poly(methacrylic acid-3-sulfopropyl ester potassium salt-co-divinylbenzene) monolithic material. The analytes were analyzed by HPLC equipped with diode array detector. In the optimized process, several parameters, including the composition of desorption solvent, pH value and ionic strength in sample matrix, extraction, and desorption time, were investigated in detail. Under the optimized conditions, the detection limits (S/N=3) and quantification limits (S/N=10) of the proposed method for the target compounds were achieved within the range of 0.47–1.52 and 1.54–5.0 μg/kg from spiked honey sample, respectively. The calibration curves showed the linearity ranging from 2 to 200 μg/kg for dimetridazole and tinidazole, 5–200 μg/kg for metronidazole and ronidazole. Method repeatability presented as intra- and interday precisions were found with the RSDs <4.43 and 4.41%, respectively. Finally, the developed method was successfully applied to the determination of nitroimidazoles in different honey samples and satisfactory recoveries of spiked target compounds were in the range of 71.1–114%.

In this study, a new stir bar sorptive extraction (SBSE) coating based on poly(vinylphthalimide-co-N,N′-methylenebisacrylamide) monolith (SBSE-VPMB) was prepared. The influences of the contents of monomer in polymerization mixture and the percentage of porogen solvent on the extraction performance were investigated thoroughly. Several characteristic techniques, such as elemental analysis, scanning electron microscopy, mercury intrusion porosimetry and infrared spectroscopy, were used to characterize the monolithic material. The analysis of oxfendazole (OFZ) and mebendazole (MBZ) in milk and honey samples by the combination of SBSE with HPLC with diode array detection was selected as paradigms for the practical evaluation of the new coating. Under the optimized extraction conditions, the limits of detection (S/N=3) for OFZ and MBZ were 0.23–0.60 μg/L in milk and 0.24–1.08 μg/L in honey, respectively. The method also showed good linearity, repeatability, high feasibility and acceptable recoveries for real samples. At the same time, the extraction performance and the distribution coefficients (K_VPMB/W) of OFZ and MBZ on SBSE-VPMB were compared with other SBSEs based on porous monoliths and commercial SBSE.

An effective and simple method for polar phenols in water matrix was developed by using stir bar sorptive extraction (SBSE) based on a hydrophilic poly(vinylpyrrolididone-divinylbenzene) (VPDB) monolithic material and HPLC analysis. To achieve optimum extraction performance for phenols, several parameters, including extraction and desorption time, desorption solvent, pH value, and ionic strength of sample matrix, were investigated. Under the optimized experimental conditions, eight phenols were directly enriched from water samples and analyzed by HPLC-DAD. The detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method for the target compounds were achieved within the range of 0.72–1.37 and 2.40–4.27 ng/mL from spiked water, respectively. Recoveries of eight phenolic compounds were found in the range of 55.2–95.9%. The calibration curves showed the linearity ranging from 5 to 150 ng/mL with linear regression coefficient R² values above 0.98. Method repeatability presented as intra- and interday precisions were also found with the RSDs less than 4.10 and 7.61%, respectively. The distribution coefficients between VPDB and water (K_VPDB/W) for phenolic compounds were also calculated and compared with K_O/W. Finally, the proposed method was successfully applied to the determination of the target compounds in tap water, sea water and wastewater samples.