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This work illustrates the introduction of a simple, rugged and flexible column-switching ion chromatography (IC) technique for an automated on-line QuEChERS extracted samples extracts washing followed by sensitive fluorescence (FLD) determination of five acidic pharmaceutical drugs namely; clofibric acid (CLO), ibuprofen (IBU), aspirin (ASP), naproxen (NAP) and flurobrofen (FLU) in three complex samples (spinach, apple and hospital sewage sludge). An old anion exchange column IonPac ® AS11-HC was utilized as a pre-treatment column for on-line washing of inorganic and organic interferences followed by isocratic separation of five acidic drugs with another anion exchange IonPac ® AS12A analytical column by exploiting the column-switching technique. This novel method exhibited good linearity with correlation coefficients (r 2 ) for all drugs were in the range 0.976–0.996. The limit of detection and quantification of all five acidic drugs were in the range 0.024 μg/kg to 8.70 μg/kg and 0.082 μg/kg to 0.029 mg/kg, respectively, and better recoveries in the range 81.17–112.5% with percentage relative standard deviations (RSDs) less than 17.8% were obtained. This on-line sample pre-treatment method showed minimum matrix effect in the range of 0.87–1.25 except for aspirin. This simple rugged and flexible column-switching system required only 28 min for maximum elimination of matrices and interferences in three complex samples extracts, isocratic separation of five acidic drugs and for the continuous regeneration of pre-treatment column prior to every subsequent analysis. Finally, this simple automated IC system was appeared so rugged and flexible, which can eliminate and wash out most of interference, impurities and matrices in complex samples, simply by adjusting the NaOH and acetonitrile concentration in washing mobile phase with maximum recoveries of acidic analytes of interest. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel 2D HILIC–RPLC–MS system was developed with the stop-flow mode. [•] A new stop-flow interface with trap column and make-up flow was designed. [•] The stop-flow 2D LC can avoid sensitivity decrease caused by dilution effect. [•] Peak capacity of the stop-flow 2D LC is similar to comprehensive 2D LC. [•] This system was powerful for qualitative and quantitative analysis of lipids. [ABSTRACT FROM AUTHOR]

Highlights: [•] A systematic approach for the optimization of HILIC×RP-LC analysis was developed. [•] Theoretical findings based on data for HILIC×RP-LC analysis of cocoa procyanidins. [•] A detailed comparison of on-line, off-line and stop-flow modes is presented. [•] Stop-flow operation is shown to be a promising alternative to off-line LC×LC. [ABSTRACT FROM AUTHOR]

Highlights: [•] HILIC×RP-LC analysis of cocoa procyanidins in on-line, off-line and stop-flow modes. [•] Experimental verification of theoretical optimisation studies presented. [•] Off-line and stop-flow provide similar performance for high peak capacities. [•] On-line HILIC×RP-LC suitable for fast screening of procyanidins. [ABSTRACT FROM AUTHOR]

Abstract: A novel on-line gold nanoparticle-catalyzed luminol–H2O2 chemiluminescence (CL) detector for high-performance liquid chromatography (HPLC) was established, in which gold nanoparticles were produced by the on-line reaction of H2O2, NaHCO3–Na2CO3 (buffer solution of luminol), and HAuCl4. Eight phenolic compounds (gallic acid, protocatechuic acid, protocatechuic aldehyde, 2,5-dihydroxybenzoic acid, caffeic acid, 2,3-dihydroxybenzoic acid, (+)-catechin, and (−)-epicatechin) were chosen as the model compounds. Every separated phenolic compound in the column eluent strongly enhanced the CL signal of on-line gold nanoparticle-catalyzed luminol system. The CL and UV–visible absorption spectra and transmission electron microscopy studies were carried out, and the CL enhancement mechanism was ascribed to that the presence of phenolic compound promoted the on-line formation of 38-nm-diameter gold nanoparticles, which better catalyzed the luminol–H2O2 CL reaction. The effects of methanol and phosphoric acid in the proposed HPLC configuration were performed by two gradient elution programs, and the baseline profile revealed that on-line gold nanoparticle-catalyzed luminol–H2O2 CL detector had better compatibility than 38nm gold colloids–luminol–H2O2 CL detector. The proposed CL detector exhibits excellent analytical performance with the low detection limit (S/N=3) of 0.53–0.97ng/mL (10.6–19.4pg) phenolic compounds, and offers a new strategy for developing on-line nanoparticle-catalyzed CL detector for HPLC with sensitive analysis. [Copyright &y& Elsevier]

Abstract: A novel sample preparation technique termed dynamic liquid–liquid–solid microextraction (DLLSME) was developed and on-line coupled to high performance liquid chromatography (HPLC) for direct extraction, desorption, and analysis of trace estrogens in complex samples. The DLLSME consists of the aqueous donor phase, the organic medium phase and the molecularly imprinted polymer filaments (MIPFs) as solid acceptor phase. The organic solvent with lesser density was directly added on top of the aqueous sample, and the dynamic extraction was performed by circulating the organic solvent through the MIPFs inserted into a PEEK tube which served as an extraction and desorption chamber. Afterwards, the extracted analytes on the MIPFs were on-line desorbed and then introduced into the HPLC for analysis. To evaluate the feasibility of the on-line system, a new DLLSME-HPLC method was developed for the analysis of five estrogens in aqueous samples by using 17β-estradiol MIPFs as the solid phase. Under the optimized conditions, the enrichment factors of 51–70, limits of detection of 0.08–0.25μg/L and precision within 4.5–6.9% were achieved. Furthermore, the proposed method was applied to the analysis of real samples including urine, milk and skin toner, satisfactory recovery (81.9–99.8%) and reproducibility (4.1–7.9%) were obtained. Especially, 0.59μg/L of 17β-estradiol was determined in female urine sample. The DLLSME offers an attractive alternative for direct analysis of trace analytes in aqueous samples and could potentially be extended to other adsorptive materials. [Copyright &y& Elsevier]

Abstract: A novel method of on-line single drop microextraction (SDME) coupled with sweeping micellar electrokinetic chromatography (MEKC) for the selective extraction and dual preconcentration of alkaloids was developed. In this technique, analytes of three alkaloids were firstly extracted from 4.0mL basic aqueous sample solution (donor phase, 500mM NaOH) into a layer of n-octanol at temperature 30°C with the stirring rate of 1150rpm, then back-extracted into the acidified aqueous acceptor (acceptor phase, 50mM H3PO4) suspended at the tip of a capillary at 650rpm. Then, the aqueous acceptor was introduced into capillary by hydrodynamic injection with a height difference of 15cm between the inlet and outlet of capillary for 300s, and analyzed directly by on-line sweeping MEKC. With the selective SDME, we were able to extract three alkaloids without any interfering components in human urine samples. Under the optimum conditions, the proposed method achieved limits of detections (LOD) of between 0.2ngmL−1 and 1.5ngmL−1 with 1583–3556-fold increases in detection sensitivity for three analytes, which indicated that it was a promising method for analysis of alkaloids in human urine. [Copyright &y& Elsevier]

Abstract: A fast and efficient on-line coupled dynamic sonication-assisted extraction–liquid chromatography (DSAE–LC) method was developed for the determination of phenolic acids in basil, oregano, rosemary, sage, spearmint and thyme. The extraction and chromatography were coupled via a solid-phase trap filled with strong anion exchange material. The relative standard deviations (RSDs) for the retention times were less than 0.4% and those for the peak heights less than 3% except for gallic acid (RSD 1.2% for the retention times and 11% for the peak heights). Limits of detection were below ∼3ng. [Copyright &y& Elsevier]

Abstract: An on-line configuration of microdialysis (MD), Au/TiO2 nanoparticle preconcentration, and high-performance liquid chromatography-ultraviolet (HPLC-UV) detection method was developed for the simultaneous measurement of cobalt (Co) and nickel (Ni) concentrations in water. The sample matrix was first cleaned with an MD system using a MD probe. A continuously flowing dialysate stream was introduced into tubing coated with Au/TiO2 nanoparticles to adsorb metals, followed by elution by an acidic eluent. The enriched samples were derivatized on-line using 8-hydroxyquinoline. The separation of Co and Ni were achieved by using a LC-C18 column. The three aforementioned system components were connected on-line using a valve control. The UV detection was performed at 319nm. Validation experiments demonstrate good linearity, precision, accuracy, and recovery. The proposed method offers a simple and reliable procedure to determine the levels of Co and Ni in environmental water samples. Moreover, the methodology described in this study adheres to the concept of green chemistry, including the absence of organic solvents in the MD sampling and extraction processes. To the best of our knowledge, the proposed method is the first reported on-line connection of MD, Au/TiO2 nanoparticle tubing, and HPLC devices for the measurement of Co and Ni concentrations in water. [Copyright &y& Elsevier]

Abstract: A unique automated on-line high-performance liquid chromatography–mass spectrometry (LC–MS) method was developed allowing injection of a large volume of urine for the improvement of sensitivity using estrogens as analytes. The urine sample was precipitated by acetonitrile (sample:acetonitrile, 1:2, v/v) to remove most proteins. Then the supernatant was directly delivered at 0.3mL/min by a pump, which broke through the limit of autosampler with fixed loop. Then the sample was loaded onto a restricted access media (RAM) pre-column after on-line dilution with NH4Ac solution which was delivered by another pump under high flow-rate. After the addition of on-line dilution line, the content of organic solvent in the sample aliquot was sharply decreased so that the analytes were effectively trapped by pre-column. In addition, another 6-port valve was added to selectively deliver the effluent containing analytes into MS, which minimized the pollution of the MS and matrix effect. After optimization of the condition of extraction method, 3mL sample (containing 1mL urine) could be successfully enriched. The injection volume increased 10 times compared with conventional on-line LC–MS methods for biofluid analysis, significantly improving sensitivity. Moreover, no obvious increase of column pressure was observed after 300 injections. The method was validated by spiking urine. Linearity was determined by sample which was in the range of 1–500ng/mL. The process efficiency ranged from 70.2 to 106% with RSDs less than 15% with the exception of a few analytes. The limit of detection (LOD) and quantification (LOQ) ranged from 0.3 to 2ng/mL and 1 to 8ng/mL, respectively, corresponding a decrease of 1–2 orders of magnitude compared with those of off-line and on-line methods. [Copyright &y& Elsevier]

Abstract: A high through-put miniaturised separation-quantification method for the heterocyclic aromatic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in urine was developed. The limit of detection was of 0.65fmol (0.14pg) injected or 65pM. Heterocyclic aromatic amines are mutagenic and carcinogenic compounds formed at low levels in protein-rich food during cooking. Due to the low concentrations and the high complexity of the matrix in which they exist (food, blood, and urine), and the often small sample volumes (capillary blood; urine, blood and milk from small animals), very sensitive and selective analytical methods are required for their detection. Miniaturisation was accomplished by micro solid-phase extraction in capillaries with blue chitin as solid-phase, coupled on-line (in-capillary) to capillary electrophoresis with nanospray tandem mass spectrometric detection. This new technique provided a total analysis time of only 15min, including extraction and separation, together with low sample and solvent consumption. Blue chitin showed high tolerance towards the urine matrix. Urine collected 12h after consumption of fried chicken contained 1.8nmolL−1 (0.40pgμL−1) of PhIP. [Copyright &y& Elsevier]

Abstract: An on-line immunoaffinity column with liquid chromatography/tandem mass spectrometry (IAC-LC–MS/MS) method for the determination of diuron in water matrices was described. This method used a sol–gel immunoaffinity column (20mm×4mm I.D.) for on-line sample cleanup and enrichment, a monolithic analytical column (100mm×4.6mm I.D.) for separation, and a triple quadrupole mass spectrometer for quantitation. The major challenges for the on-line set-up were discussed. The optimized on-line protocol was emphasized by the fact that low limit of quantitation (LOQ) of 1.0ng/L was achieved with only 2.5-mL sample. In addition, a satisfactory accuracy (∼90% of recovery) and precision (<6% of relative standard deviation) at 50ng/L concentration were also obtained. Due to the ability of the sol–gel immunoaffinity column to eliminate matrix effect, the on-line IAC-LC–MS/MS analysis method can reliably determine diuron in wastewater treatment plant effluent sample. [Copyright &y& Elsevier]

Abstract: A method for direct determination of dl-tetrahydropalmatine (dl-THP) in Corydalis yanhusuo, a traditional Chinese herb, by l-THP imprinted monolithic precolumn on-line/off-line coupling with reversed-phase high performance liquid chromatography (RP-HPLC) was developed. The l-THP imprinted monolithic column has been prepared by in situ polymerization using methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. With the optimization of chromatographic conditions, such as mobile phase composition, flow rate, column temperature and sample loading, for the separation of enantiomer, dl-THP was base-line separated on the MIP. The imprinted monolithic column was used as a precolumn for fractionation of the C. yanhusuo extract. Both the non-retained and retained fractions were separated by RP-HPLC. Meanwhile, the d-THP and l-THP can be detected in the non-retained and retained fractions, respectively. Additionally, direct determination of l-THP using molecularly imprinted monolith on-line coupling with a reversed-phase column was acquired. [Copyright &y& Elsevier]