Ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction for the determination of phenols in seawater samples

For the first time, an ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction (IL-LLL-SBME) was developed for the analysis of phenols in seawater samples. The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]), was used as the intermediary solvent for LLL-SBME, enhancing the extraction efficiency for polar analytes. In the procedure, the analytes were extracted from the aqueous sample into the ionic liquid intermediary and finally, back-extracted into an aqueous acceptor solution in the lumen of the hollow fiber. The porous polypropylene membrane acted as a filter to prevent potential interfering materials from being extracted, and no additional cleanup was required. After extraction, the acceptor solution could be directly injected into a high-performance liquid chromatographic system for analysis. Six phenols, 2-nitrophenol, 4-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were selected here as model compounds for developing and evaluating the method. The most influential extraction parameters were evaluated, including the ionic liquid, the composition of donor solution and acceptor solution, the extraction time and the extraction temperature, the effect of ionic strength, and the agitation speed. Under the most favorable extraction parameters, the method showed good linearity (from 0.05-50 to 0.5-50 μg/L, depending on the analytes) and repeatability of extractions (RSD below 8.3%, n=5). The proposed method was compared to conventional three-phase LLL-SBME and ionic liquid supported hollow fiber protected three-phase liquid-liquid-liquid microextraction, and showed higher extraction efficiency. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of phenols from environmental water samples.     

An organic solvent-free microwave-assisted extraction of some priority pollutants of phenols in lake sediments.

Alkaline water was used for the microwave-assisted extraction of some priority pollutants of phenols in sediments, i.e. phenol (Ph), 2-chlorophenol (2CP), 2,4-dichlorophenol (2,4DCP), 4-chlorophenol (4CP), 4-dinitrophenol (4NP) and pentachlorophenol (PCP). This organic solvent-free extraction procedure was optimized by studying the parameters such as pH, volume of the alkaline water, extraction pressure and time. Under the optimized conditions, the recoveries of phenols were in the range of 80% to 110%. The extracts were then cleaned-up and concentrated by microcolumn solid phase extraction (SPE) and determined by gas chromatography-flame ionization detection system. The relative standard deviation of the overall-method for most phenol determinations was about 5.0% (n = 6). The proposed method, which needs little volume (1 mL) of ethanol for SPE, has been applied to determine these phenols in sediment samples, and the analytical results are in good agreement with those achieved by Soxhlet extraction.     

Evaluation of a new solid-phase cartridge for the preconcentration of phenolic compounds in water

The aim of this study is to evaluate the efficiency of a new solid-phase extraction cartridge, Spe-ed Advanta, in the extraction and preconcentration of four phenolic compounds (phenol, 2-chlorophenol, 2-nitrophenol, and 2,4-dichlorophenol) from water. The solid phase is a polystyrene-divinylbenzene resin modified with carboxylic groups, these polar groups improve the contact between the matrix and the aqueous solutions in the extraction of polar analytes. We studied several elution solvents in order to find the most efficient one. Sample concentration, sample volume, and sample pH are also investigated as well as the best method for drying the cartridge. Recoveries achieved with the new phase are compared with those obtained with Isolute ENV+, a non-modified polystyrene-divinylbenzene stationary bed. The best experimental conditions were then used for determination of the phenols in spiked environmental waters.     

Column silylation method for determining endocrine disruptors from environmental water samples by solid phase micro-extraction

In solid phase micro-extraction (SPME), the analyte is partitioned between the coating and the sample and then desorption of the concentrated analyte is followed by GC-MS, where the analytes are thermally desorbed and subsequently separated on the column and quantified by the detector. The SPME method preserves all the advantages, such as simplicity, low cost, on site sampling and does not require solvents. Poly(acrylate) coating fibers have been developed for the extraction of phenols (such as 4-tert-butylphenol, 2,4-dichlorophenol, 4-n-pentylphenol, 4-n-hexylphenol, 4-tert-octylphenol, 4-n-heptylphenol, 4-n-nonylphenol, 4-n-octylphenol, pentachlorophenol and bisphenol A) in different water samples. The precision of the HS-SPME method ranges from 3–12% RSDs, depending on the compounds analyzed. More accurate results were obtained by HS-SPME with acidification and salting out, where the fiber is located above the liquid sample. The extraction period was 60 min, followed by desorption for 5 min at 300°C. After the analytes were completely desorbed, 1 μl of bis(trimethylsilyl)trifluoroacetamide (BSTFA) was injected by ordinary GC-MS injection. The trimethylsilylate peaks were improved significantly compared with free phenol peaks. The addition of salt (saturated sodium chloride) and acidification by hydrochloric acid (pH 2.0) were found to be very important for enhancing the partitioning of the polar phenols into the polymer coating and preventing ionization of the analytes. The method is capable of limits of detection of subparts per billion of the total phenols extracted from environmental water samples.     

Trace level determination of phenols as pentafluorobenzyl derivatives by gas chromatography-negative-ion chemical ionization mass spectrometry.

A method for the trace level determination of 11 phenols as pentafluorobenzyl (PFB) derivatives by gas chromatography-mass spectrometry (GC-MS) with negative-ion chemical ionization (NICI) is described. First, the conditions for the PFB derivatisation of phenols were optimized and were found to be reaction temperature 80 degrees C and reaction time 5 h. Second, the detection limits using selected ion monitoring (SIM) were compared between trimethylsilylated (TMS) derivatives in the electron ionization (EI) mode and PFB derivatives in the NICI mode. The responses for the PFB derivatives in the NICI mode were 3.3-61 times higher than those of the TMS derivatives in the EI mode. The instrumental detection limits using NICI-SIM ranged from 2.6 to 290 fg. This method was applied to the analysis of phenols in river water using solid-phase extraction. The recoveries of the phenols from a river water sample spiked with standards at 100 ng l-1 with 2-chlorophenol, 4-chloro-3-methylphenol and pentachlorophenol and at 1000 ng l-1 with phenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 2-nitrophenol, 2,4,6-trichlorophenol and 4-nitrophenol were 81.2-106.3% (RSD 5.1-8.0%), except for 2-methyl-4,6-dinitrophenol and 2,4-dinitrophenol, for which the recoveries were 5.8 and 4.2%, respectively, because water contained in the acetone eluate interfered with the derivatisation of these compounds with two electrophilic nitro groups.     

Complexation of phenols and thiophenol by phosphine oxides and phosphates. Extraction, isothermal titration calorimetry, and ab initio calculations

To develop a new solvent-impregnated resin system for the removal of phenols from water the complex formation of triisobutylphosphine sulfide (TIBPS), tributylphosphate (TBP), and tri-n-octylphosphine oxide (TOPO) with a series of phenols (phenol, thiophenol, 3-chlorophenol, 3,5-dichlorophenol, 4-cyanophenol, and pentachlorophenol) was studied. The investigation of complex formation between the extractants and the phenols in the solvent toluene was carried out using liquid-liquid extraction, isothermal titration calorimetry (ITC), and quantum chemical modeling (B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and MP2/6-311++G(2d,2p)//B3LYP/6-311G(d,p)). The equilibrium constant (binding affinity, Kchem), enthalpy of complex formation (DeltaH), and stoichiometry (N) were directly measured with ITC, and the entropy of complexation (DeltaS) was derived from these results. A first screening of K chem toward phenol revealed a very high binding affinity for TOPO, and very low binding affinities for the other extractants. Modeling results showed that although 1:1 complexes were formed, the TIBPS and TBP do not form strong hydrogen bonds. Therefore, in the remainder of the research only TOPO was considered. Kchem of TOPO for the phenols in toluene increased from 1,000 to 10,000 M(-1) in the order phenol < pentachlorophenol < 3-chlorophenol < 4-cyanophenol approximately 3,5-dichlorophenol (in line with their pKa values, except for pentachlorophenol) in the absence of water, while the stoichiometric ratio remained 1:1. In water-saturated toluene, the binding affinities are lower due to co-complexation of water with the active site of the extractant. The increase in binding affinity for TOPO in the phenol series was confirmed by a detailed ab initio study, in which Delta H was calculated to range from -10.7 kcal/mol for phenol to -13.4 kcal/mol for 4-cyanophenol. Pentachlorophenol was found to behave quite differently, showing a DeltaH value of -10.5 kcal/mol. In addition, these calculations confirm the formation of 1:1 H-bonded complexes.     

Sensitivity enhancement of chlorinated phenols by continuous flow liquid membrane extraction followed by capillary electrophoresis

This paper describes a new analytical system, based on the combination of continuous flow liquid membrane extraction (CFLME) enrichment and capillary electrophoresis (CE) separation, for analysis of chlorinated phenols in water samples. Five chlorinated phenols including 3-chlorophenol (3CP), 4-chlorophenol (4CP) 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) were separated by CE with Tris/sodium dihydrogen phosphate solution containing methanol 1% (v/v) as the run buffer. CFLME related parameters were investigated and optimal enrichment was obtained by using 0.3 mol L(-1) Tris as acceptor and with a sample pH 5.0, a sample flow rate of 4.0 mL min(-1), and an enrichment sample volume of 150 mL. The detection limit (S/N= 3) was 6.9, 1.0, and 1.7 ng mL(-1) for DCP, PCP, and TCP, respectively. The reproducibility (RSD%, n = 6) was 5.7 for DCP, 2.5 for PCP, and 2.8% for TCP (n = 6). The proposed method was applied to the determination of chlorinated phenols in spiked water samples with relatively satisfactory recoveries.     

Use of polymeric sorbents for the off-line preconcentration of priority pollutant phenols from water for high-performance liquid chromatographic analysis

The use of porous polymeric minicolumns for the determination of phenols from the U.S. Environmental Priority Pollutant List was studied. For the off-line preconcentration of priority pollutant phenols from water by solid-phase extraction, minicolumns packed with 1,4-di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and Amberlite XAD-4 were used. In order to compare the sorption properties of these polymeric sorbents, the recoveries and breakthrough volumes of phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 4-chloro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were studied.     

Synthesis and analytical properties of a novel columnar metallomesogenic polymer

A metallomesogenic side-chain polymer with copper carboxylato discotic units in stacks prepared by covalent bonding of 14-pentadecenoic acid, stearic acid and poly(methylhydrosiloxane) is described. The physico-chemical and thermal properties of both monomeric and polymeric metallomesogens were determined by elemental analysis, IR, polarizing optical microscopy, thermal gravimetric analysis and differential scanning calorimetry. The polymeric states showed a discotic lamellar phase at 50-95 degrees C and an ordered discotic hexagonal phase at 95-200 degrees C. By dynamic coating, the metallomesogenic polymer was crosslinked to the capillary wall via benzoyl peroxide. The wall-coated capillary columns (15 m x 0.25 mm I.D.) were used for the separation of phenols. Factors affecting the retention and the sample selectivity were examined. Van 't Hoff plots as a function of temperature indicated that phase transitions were occurring. Thermodynamic properties of the analytes in this system were also studied. For the determination of a mixture of 3-aminophenol, 2-chlorophenol, 2-nitrophenol, 4-nitrophenol, o-methylphenol, m-methylphenol, p-methylphenol, 2,4-dichlorophenol, 2,4-dimethylphenol, 2,4-dinitrophenol, 2,4,6-trichlorophenol, 2,4,6-trimethylphenol, 4-bromophenol, 3-methyl-4-chlorophenol, pentachlorophenol, and unsubstituted phenol, the calibration graphs for most phenols were linear over the range of 10-1000 microg ml(-1) and the mass detection limits were in the ng range based on three times standard deviation of seven measurements of the lowest peak that could be detected.     

Use of lignins as components of background electrolyte in capillary electrophoresis

The electrophoretic behavior of two lignins of different compositions, i.e., spruce dioxane lignin and lignosulfonate, is studied. The lignins are shown to affect the electrophoretic behavior of negatively charged analytes, such as carboxylic acids and phenols; their migration time increases. The addition of lignins improves the analytical parameters of phenol quantification by capillary electrophoresis. By means of a simple non-modified capillary, a mixture of six phenols was separated (simple phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, and perchlorophenol) with the high resolution (up to 20) and efficiency [(1–5) × 10⁵ TPM]. The separation of six phenols takes 10 min, the lower limit of the analytical range makes 1 μg/mL, the relative standard deviation does not exceed 3%. The potency for the determination of simple phenol and m-cresol is shown on an example of the Verrukatsid medication within 7 min.     

Development of a novel ultrasound-assisted headspace liquid-phase microextraction and its application to the analysis of chlorophenols in real aqueous samples

A new sample pretreatment technique, ultrasound-assisted headspace liquid-phase microextraction was developed as mentioned in this paper. In the technique, the volatile analytes were headspace extracted into a small drop of solvent, which suspended on the bottom of a cone-shaped PCR tube instead of the needle tip of a microsyringe. More solvent could be suspended in the PCR tube than microsyringe due to the larger interfacial tension, thus the analysis sensitivity was significantly improved with the increase of the extractant volume. Moreover, ultrasound-assisted extraction and independent controlling temperature of the extractant and the sample were performed to enhance the extraction efficiency. Following the extraction, the solvent-loaded sample was analyzed by high-performance liquid chromatography. Chlorophenols (2-chlorophenol, 2,4-dichlorophenol and 2,6-dichlorophenol) were chosen as model analytes to investigate the feasibility of the method. The experimental conditions related to the extraction efficiency were systematically studied. Under the optimum experimental conditions, the detection limit (S/N=3), intra- and inter-day RSD were 6 ng mL(-1), 4.6%, 3.9% for 2-chlorophenol, 12 ng mL(-1), 2.4%, 8.8% for 2,4-dichlorophenol and 23 ng mL(-1), 3.3%, 5.3% for 2,6-dichlorophenol, respectively. The proposed method was successfully applied to determine chlorophenols in real aqueous samples. Good recoveries ranging from 84.6% to 100.7% were obtained. In addition, the extraction efficiency of our method and the conventional headspace liquid-phase microextraction were compared; the extraction efficiency of the former was about 21 times higher than that of the latter. The results demonstrated that the proposed method is a promising sample pretreatment approach, its advantages over the conventional headspace liquid-phase microextraction include simple setup, ease of operation, rapidness, sensitivity, precision and no cross-contamination. The method is very suitable for the analysis of trace volatile and semivolatile pollutants in real aqueous sample.     

Simultaneous derivatization and extraction of chlorophenols in water samples with up-and-down shaker-assisted dispersive liquid–liquid microextraction coupled with gas chromatography/mass spectrometric detection

A new up-and-down shaker-assisted dispersive liquid–liquid microextraction (UDSA-DLLME) for extraction and derivatization of five chlorophenols (4-chlorophenol, 4-chloro-2-methylphenol, 2,4-dichlorophenol, 2,4,6-trichloro-phenol, and pentachlorophenol) has been developed. The method requires minimal solvent usage. The relatively polar, water-soluble, and low-toxicity solvent 1-heptanol (12 μL) was selected as the extraction solvent and acetic anhydride (50 μL) as the derivatization reagent. With the use of an up-and-down shaker, the emulsification of aqueous samples was formed homogeneously and quickly. The derivatization and extraction of chlorophenols were completed simultaneously in 1 min. The common requirement of disperser solvent in DLLME could be avoided. After optimization, the linear range covered over two orders of magnitude, and the coefficient of determination (r ²) was greater than 0.9981. The detection limit was from 0.05 to 0.2 μg L^?1, and the relative standard deviation was from 4.6 to 10.8 %. Real samples of river water and lake water had relative recoveries from 90.3 to 117.3 %. Other emulsification methods such as vortex-assisted, ultrasound-assisted, and manual shaking-enhanced ultrasound-assisted methods were also compared with the proposed UDSA-DLLME. The results revealed that UDSA-DLLME performed with higher extraction efficiency and precision compared with the other methods.     

Quantitative determination of chlorophenols in leather by pressurized liquid extraction and liquid chromatography with diode-array detection

Pressurized liquid extraction (PLE) with acetonitrile was used for the recovery of chlorophenols (4-chloro-3-methylphenol, 4-chloro-2-methylphenol, 2,4-dichlorophenol, 2-phenylphenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) present as biocides in leather. After a single cycle PLE treatment, solutions underwent pre-concentration by evaporation of the solvent under vacuum and clean-up treatment with solid-phase extraction cartridges. Quantitative analysis of the target compounds was carried out by liquid chromatography with gradient elution and UV spectrophotometric detection at variable wavelength for the various analytes in the range 190-240 nm. Instrumental detection limits and operative detection limits in the real matrices were determined according to the Hubaux-Vos approach and to the US Environmental Protection Agency procedures. The detection limits for the seven analytes ranged from 10 to 70 microg kg(-1). Linearity was very good in the explored range (10(-7)-10(-5)M) giving R(2) values from 0.995 to 1.000 for pentachlorophenol and 2,4-dichlorophenol, respectively. Repeatability was satisfactory, 2-5% for a 1 x 10(-6)M level of concentration, on five repeated measurements on the sample. Recovery yield values with the proposed procedure were determined using spiked samples. Overall recovery ranged from 88 to 97%. The method was used for routine analysis of real leather samples.     

Headspace single drop and hollow fiber liquid phase microextractions for HPLC determination of phenols

Two methods based on headspace single drop microextraction (HS-SDME) and headspace hollow fiber liquid phase microextraction (HS-HF-LPME) were developed and critically compared with HPLC-UV determination of phenols (including phenol (Ph), 2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP)) in this paper. The significant parameters affecting the extraction efficiency of the target analytes in both extraction modes were studied and the optimal extraction conditions were established. Under the optimal conditions, the detection limits (S/N = 3) for Ph, CP, DCP and TCP obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 2.1, 0.2, 0.8,1.1 ng/mL and 4.2, 0.4, 0.4, 0.4 ng/mL with enrichment factors of 15.8, 198.9, 159.7, 194.8 and 9.2, 149.9, 301.9, 411.1, respectively. The RSDs obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 3.7, 4.0, 9.8, 6.7% and 6.3, 3.6, 3.1, 4.8% for Ph, CP, DCP and TCP, respectively. Both extraction modes have a comparable analytical performance, but HS-HF-LPME was more robust than HS-SDME, while HS-SDME was simpler than HS-HF-LPME. The two headspace microextraction modes were applied for HPLC-UV determination of target phenols in water, honey and toner samples, and the determined values obtained by both techniques were in good agreement with each other.     

Preparation of Fe3O4@C@PANI magnetic microspheres for the extraction and analysis of phenolic compounds in water samples by gas chromatography-mass spectrometry

In this work, core-shell structure Fe(3)O(4)@C@polyaniline magnetic microspheres were synthesized using simple hydrothermal reactions. The carbon-coated magnetic microspheres (Fe(3)O(4)@C) were first synthesized by a hydrothermal reaction, and then aniline was polymerized on the magnetic core via another hydrothermal reaction. Then, the obtained Fe(3)O(4)@C@polyaniline magnetic microspheres were applied as magnetic adsorbents for the extraction of aromatic molecules due to π-π interactions between polyaniline shell and aromatic compounds. In our study, five kinds of phenols including phenol, 2,4-dichlorophenol (DCP), 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) and bisphenol A (BPA) were selected as the model analytes to verify the extraction ability of Fe(3)O(4)@C@PANI microspheres. After derivatization, the phenols were detected using gas chromatography-mass spectrometry (GC-MS). The dominant parameters affecting enrichment efficiency were investigated and optimized. Under the optimal conditions, the proposed method was evaluated, and applied to the analysis of phenols in real water samples. The results demonstrated that our proposed method based on Fe(3)O(4)@C@polyaniline magnetic microspheres had good linearity (r(2)>0.991), and limits of quantification (2.52-29.7 ng/mL), high repeatability (RSD<13.1%) and good recovery (85.3-110.6%).     

固相萃取-高效液相色谱串联质谱法同时检测地表水中的2,4-二氯酚、2,4,6-三氯酚和五氯酚

建立了简便、快速、同时测定地表水中2,4-二氯酚、2,4,6-三氯酚和五氯酚的固相萃取-高效液相串联质谱方法。HLB固相萃取小柱富集水样中待测物质,经二氯甲烷-丙酮(1∶1,V/V)混合溶液洗脱后,氮吹浓缩,溶剂转换为甲醇,采用高效液相色谱串联质谱检测,选择反应监测模式(SRM),进行特征母离子-子离子采集信号。本方法对2,4-二氯酚、2,4,6-三氯酚和五氯酚检测的线性方程分别为Y=2524 X-6029、Y=1809 X-11341、Y=2296 X-2894,相关系数分别为0.9993、0.9996和0.998;检出限(LOD)分别为2.0,3.0和0.1ng/L;定量限(LOQ)分别为6.7,10.1和0.3ng/L;7次加标回收相对标准偏差在2.2%～14.7%之间;回收率为70.5%～102.3%,能很好地满足水源地监测的需求。     

Determination of phenols in waters by stir membrane liquid-liquid-liquid microextraction coupled to liquid chromatography with ultraviolet detection

A simple and rapid method for the determination of eleven phenols in water samples is presented. The target analytes are isolated by stir membrane liquid-liquid microextraction working under the three-phase mode. An alkaline aqueous solution is used as extractant phase while octanol is selected as supported liquid membrane solvent. The target analytes are separated and determined by liquid chromatography (LC) with ultraviolet detection (UV). All the variables involved in the extraction process have been studied in depth. Low detection limits (in the range from 82.1 ng/L for phenol to 452 ng/L for 2,4,5-trichlorophenol) were obtained. The repeatability, expressed as relative standard deviation (RSD), varied between 1.3% (for 4-nitrophenol) and 8.0% (for 4-chlorophenol). The enrichment factors were in the range from 168 (for 2,4,5-trichlorophenol) to 395 (for 3-chlorophenol). The proposed procedure was applied for the direct determination of the eleven phenols in some real water samples including river, well and tap waters. The accuracy was evaluated by means of a recovery study, the results being in the range of 87-120%.     

A direct Capillary Liquid Chromatography with electrochemical detection method for determination of phenols in water samples

A fast and direct method based on the use of Capillary Liquid Chromatography (LC) with electrochemical (EC) detection has been described for phenols pollutants in water samples. Concretely, phenol, o-cresol, 2-chlorophenol and bisphenol A have been selected as target analytes. The combination of Capillary LC with EC detection avoided the necessity of preconcentration steps typically used in environmental analysis. The sample injected volume was 2μL. The achieved detection limits were between 1 and 2μg/L and the linear dynamic range was up to 50μg/L for all studied phenols. The precision and uncertainty were satisfactory. The analysis time per sample was 10min. The proposed procedure has been proved useful for treated waters.     

Development,validation and application of an HPLC method for phenol electrooxidation products in the presence of chloride

A high-performance liquid chromatography (HPLC) method was developed and validated to determine phenol and potential intermediates from hydroxylation (hydroquinone, benzoquinone, catechol) and hypochlorination (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,3,6-trichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) pathways during electrooxidation in the presence of chloride. A Hypersil ODS column (150 mm L × 4.6 mm I.D.) was used for the separation. The best separation was achieved when using a time variant gradient between a water mobile phase (with 0.1% formic acid adjusted to pH 3.0 with 0.1 mM sulfuric acid) and an organic phase (90:5:5 by volume mixture of acetonitrile:methanol:acetic acid). The flow rate was 0.8 mL min^?1 and UV absorbance was monitored at 270, 280, 290 and 300 nm, choosing the wavelength of strongest response for each compound. The intra- and inter-day accuracy and precision were tested using five replicates each day on three consecutive days.     

Determination of Carotenoids in the Chinese Medical Herb Jiao-Gu-Lan (Gynostemma Pentaphyllum MAKINO) by Liquid Chromatography

A QSTAR Pulsar quadrupole time-of-flight mass spectrometer was used for the determination of chlorophenols in surface water samples. The investigated compounds were: 2-chlorophenol; 4-chloro-3-methylphenol; 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol. Each analyte is listed by the US-EPA as a priority pollutant. Sample enrichment of water samples was achieved by a solid-phase extraction procedure, using a Waters Oasis HLB cartridges followed by LC-Tandem-MS. A narrow-bore 2.1-mm-i.d. reversed phase LC C-18 column operating with a mobile phase flow rate of 0.2 mL min^–1. was used to separate the analytes. The whole column effluent was diverted to the ion spray interface source. For the determination of the analytes the hybrid quadrupole time-of-flight spectrometer operated in product ion scan acquisition mode. Average recoveries from 2 L samples varied from 91 to 110% and relative standard deviations (RSD) were less than 10% for all samples. The limit of detection (signal-to-noise ratio=3) of the method for the phenols in drinking water samples is less than 10 ng L^–1. In real environmental samples, levels of the selected analytes varied from non-detected up to 0.5 g L^–1 for pentachlorophenol.