Liquid chromatography-atmospheric pressure ionization mass spectrometry for the determination of chloro- and nitrophenolic compounds in tap water and sea water

Assessment of priority phenolic compounds in sediments from an extremely polluted coastal wetland (Lake Maryut, Egypt)

Although high concentrations of trace organic pollutants were recorded along the Egyptian Mediterranean Coast and its corresponding coastal wetlands, no published data are available for the levels of phenolic compounds. Thus, this work aimed to investigate the levels of phenolic compounds in sediments of a heavily polluted coastal wetland (Lake Maryut, Egypt). For that purpose, a method was optimized for the extraction and detection of chlorophenols, methylphenols, and nitrophenols in sediments using GC-MS. Sediments were extracted with 0.1 M NaOH/methanol by sonication. Cleanup of sediment extracts using liquid-liquid extraction and SPE was found important to remove most of the interfering co-extracts. The proposed analytical methodology was validated by analysis of matrix spikes. Detection limits were 0.063-0.694 μg/kg dw for sediments. Good recoveries (70-110%) and precision values (RSD < 20%) were obtained from the fortification experiments at the parts per billion level in sediments. The method was applied to investigate the level of contamination with phenols in 19 sediment samples from Lake Maryut. Results revealed that higher concentrations were observed in the main basin (MB) of Lake Maryut affected by the discharge of effluents from a primary wastewater treatment plant, direct discharge of industrial effluents, domestic wastes, and agricultural effluents from Qalaa Drain (QD). Chlorophenols (CPs) were the major group detected in the lake sediments followed by methylphenols (MPs) and nitrophenols (NPs). CPs were dominated by 2-, 4-, and 3-chlorophenols. Concentrations of CPs were higher at the north and northwestern parts of the MB indicating the influence of industrial effluents discharged into the lake. On the other hand, higher concentrations of NPs were observed at the south and southwestern parts of the MB, which is subjected to the discharge of agricultural and domestic effluents via QD. Results of the risk assessment revealed that phenol, cresols, 2,4-dinitrophenol, 4-NP, 2-CP, 2,3,4,6-tetrachlorophenol and 2,4-dimethylphenol are contaminants of concern and that adverse ecological effects could possibly occur to benthic species from the exposure to these pollutants in Lake Maryut and thus phenols should be included in monitoring and pollution prevention programs in the Egyptian aquatic environment affected by anthropogenic activities.

Conductometric tyrosinase biosensor for the detection of diuron, atrazine and its main metabolites

The determination of diuron, atrazine, desisopropylatrazine (DIA) and desethylatrazine (DEA) were investigated using conductometric tyrosinase biosensor. Tyrosinase was immobilised on the biosensor sensitive part by allowing it to mix with bovine serum albumin (BSA) and then cross-linking in saturated glutaraldehyde (GA) vapour for 30min. The determination of pollutants in a solution was performed by comparison of the output signal (i.e percentage of the enzymatic activity) of the biosensor before and after contact with pollutants. The measurement of the enzymatic activity was performed using 4-chlorophenol, phenol and catechol substrates and response times ranging from 1 to 5min were observed. A 4-chlorophenol substrate was used to detect pesticides. A 30min contact time of the biosensor in the pollutant solution was used. Under the experimental conditions employed, detection limits for diuron and atrazine were about 1ppb and dynamic range of 2.3-2330 and 2.15-2150ppb were obtained for diuron and atrazine, respectively. A relative standard deviation (n=3) of the output signal was estimated to be 5% and a slight drift of 1.5muSh(-1) was observed. The 90% of the enzyme activity was still maintained after 23 days of storage in a buffer solution at 4 degrees C.

Solid-phase extraction combined with dispersive liquid–liquid microextraction-ultra preconcentration of chlorophenols in aqueous samples

The solid-phase extraction (SPE) joined with the dispersive liquid-liquid microextraction (DLLME) has been developed as an ultra preconcentration technique for the determination of chlorophenols in water samples. Chlorophenols (CPs) were employed as model compounds to assess the extraction procedure and were determined by gas chromatography-electron-capture detection (GC-ECD). In solid-phase extraction-dispersive liquid-liquid microextraction (SPE-DLLME), CPs were adsorbed from a large volume of aqueous samples (100 mL) into 100 mg functionalized styrene-divinylbenzene polymer (PPL) sorbent. After the elution of the desired compounds from the sorbent by using acetone, DLLME technique was performed on the obtained solution. Some important extraction parameters, such as sample solution flow rate, breakthrough volume, sample pH, type and volume of the elution solvent as well as the salt addition, were studied and optimized. The new method (SPE-DLLME) provided an ultra enrichment factor (4390-17,870) for 19 CPs. The calibration graphs were linear in the range of 0.001-20 microg L(-1) and the limits of detection (LODs) ranged from 0.0005 to 0.1 microg L(-1). The relative standard deviations (RSDs, for 10.0 microg L(-1) of MCPs, 5.00 microg L(-1) of DCPs, 0.200 microg L(-1) of TCPs, 0.100 microg L(-1) of TeCPs and PCP) with and without the internal standard varied from 1.1 to 6.4% (n=7) and 2.5-9.7% (n=7), respectively. The relative recoveries of the well, tap and river water samples, spiked with different levels of CPs, were 71-110%, 73-115% and 88-121%, respectively.

Determination of chlorophenols in water samples using simultaneous dispersive liquid–liquid microextraction and derivatization followed by gas chromatography-electron-capture detection

Simultaneous dispersive liquid-liquid microextraction (DLLME) and derivatization combined with gas chromatography-electron-capture detection (GC-ECD) was used to determine chlorophenols (CPs) in water sample. In this derivatization/extraction method, 500 microL acetone (disperser solvent) containing 10.0 microL chlorobenzene (extraction solvent) and 50 microL acetic anhydride (derivatization reagent) was rapidly injected by syringe in 5.00 mL aqueous sample containing CPs (analytes) and K(2)CO(3) (0.5%, w/v). Within a few seconds the analytes derivatized and extracted at the same time. After centrifugation, 0.50 microL of sedimented phase containing enriched analytes was determined by GC-ECD. Some effective parameters on derivatization and extraction, such as extraction and disperser solvent type and their volume, amount of derivatization reagent, derivatization and extraction time, salt addition and amount of K(2)CO(3) were studied and optimized. Under the optimum conditions, enrichment factors and recoveries are in the range of 287-906 and 28.7-90.6%, respectively. The calibration graphs are linear in the range of 0.02-400 microg L(-1) and limit of detections (LODs) are in the range of 0.010-2.0 microg L(-1). The relative standard deviations (RSDs, for 200 microg L(-1) of MCPs, 100 microg L(-1) of DCPs, 4.00 microg L(-1) of TCPs, 2.00 microg L(-1) of TeCPs and PCP in water) with and without using internal standard are in the range of 0.6-4.7% (n=7) and 1.7-7.1% (n=7), respectively. The relative recoveries of well, tap and river water samples which have been spiked with different levels of CPs are 91.6-104.7, 80.8-117.9 and 83.3-101.3%, respectively. The obtained results show that simultaneous DLLME and derivatization combined with GC-ECD is a fast simple method for the determination of CPs in water samples.

Ion chromatography-atmospheric pressure chemical ionization mass spectrometry for the determination of trace chlorophenols in clam tissues

A novel analytical method has been developed for the determination of 14 trace chlorophenols in clam tissues by ion chromatography (IC) coupled with atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in the negative mode. The method comprised a fast ultrasound-assisted extraction using a mixture of methanol/water (4:1v/v) containing 5% triethylamine (TEA) as extraction solvent, solid-phase extraction with an Oasis HLB cartridge and gradient separation using KOH/acetonitrile at a flow rate of 1.0 mL/min on an IonPac AG11 guard column (50 mm x 4.0 mm I.D.) and an IonPac AS11 analytical column (250 mm x 4.0 mm I.D.). The molecular ions m/z [M-H](-) 127, 129; 161, 163; 195, 197 and 263, 265, 267 were selected for quantification in the selected ion monitoring (SIM) mode for monochlorophenols (MCPs), dichlorophenols (DCPs), trichlorophenols (TCPs) and pentachlorophenol (PCP), respectively. The average recoveries of the objective compounds spiked in clam tissues were between 80.2% and 98.2%. Within-day and day-to-day relative standard deviations were less than 12.6% and 13.2%, respectively. The optimum IC-APCI-MS conditions were successfully applied to the analyses of 14 trace chlorophenols in clam tissues.

Determination of the flame retardant tetrabromobisphenol A in air samples by liquid chromatography-mass spectrometry

An original method based on LC-MS for determination of the flame retardant tetrabromobisphenol A (TBBPA) in air is presented, as an alternative to the traditionally used GC-MS. The soft ionization in LC-MS makes it possible to monitor the intact molecule and to use 13C-labelled TBBPA as an internal surrogate standard, two features that improve both accuracy and precision of the analyses. Comparison of different acquisition modes in electrospray ionization showed that the lowest detections limit, 3.1 pg TBBPA injected, was obtained in SIM monitoring the molecular ions 542.7/544.7. A fragmentation pathway of TBBPA in LC-ESI-MS is suggested. The only sample clean-up steps required are solvent reduction and filtration of the sample extract. Recoveries were 93% at a 30 ng level and 75% at 3 ng. The new method was tested by analyses of air samples collected at a recycling plant for electronic equipment. The amount of TBBPA found was 13.8 ng/m3 with an RSD of 5.9%. Furthermore, it was found that TBBPA in a standard solution could be partially debrominated, if not carefully protected from light during storage.

Development of a solid-phase microextraction method for direct determination of pentachlorophenol in paper and board samples: Comparison with conventional extraction method

A solid-phase microextraction (SPME) method has been developed for the determination of pentachlorophenol (PCP) in paper and board samples. The analytical procedure involves direct extraction of PCP from paper and board samples and determination by gas chromatography with electron capture detection (GC-ECD). Two kinds of commercially available fibres; 100 microm polydimethylsiloxane (PDMS), apolar, and 85 microm polyacrylate (PA), quite polar, were evaluated to determine the extraction efficiency of pentachlorophenol. Parameters affecting the extraction process, such as temperature and time, were studied. Moreover, time of desorption and the effect of addition of salt were also investigated. The optimized procedure was applied to the analysis of pentachlorophenol (PCP) in five samples of virgin and recycled paper and board. The PCP content was determined by GC-ECD. To evaluate the effectiveness of the proposed method, it was compared with conventional extraction method with liquid-liquid extraction and derivatization. Detection limit of 0.015 microg/g for PCP in paper was achieved with a RSD of 14%.

Determination of weakly acidic endocrine-disrupting compounds by liquid chromatography–mass spectrometry with post-column base addition

A sensitive analytical method based on liquid chromatography-electrospray ionisation mass spectrometry (LC-ESI-MS) has been developed for the determination of seven endocrine-disrupting compounds: 4-n-nonylphenol (NP), 4-tert-butylphenol (t-BP), bisphenol A (BPA), 2,4-dichlorophenol (DCP), 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) and 4-tert-butylbenzoic acid (BBA) in water samples. To achieve a good LC separation, acidification of the LC mobile phase was necessary, but this led to MS signal suppression for the less acidic compounds. In order to enhance the sensitivity for these analytes, post-column addition of different bases such as ammonia, trimethylamine, and 1,8-diazabicyclo-(5,4,0)undec-7-en (DBU) was evaluated. The post-column addition of base is proposed here to raise effluent pH, helping in the ionisation process of the compounds with higher pKa values (t-BP, BPA, DCP and NP). The use of DBU, diluted in MeOH, proved to be the most efficient post-column reagent for enhancing the MS signal. The signal-to-noise ratios for t-BP and NP increased by more than 200-fold and 35-fold, respectively, whereas for DCP and BPA an increase of about 10-fold was achieved. This strategy permitted direct determination of the seven compounds at low ppb levels. For application to real water samples, an extraction and preconcentration step using the solid-phase extraction (SPE) technique was carried out. The applicability of three solid-phase materials--Bond Elut C18, and two polymeric sorbents: LiChrolut EN and Oasis HLB--and the optimization of other SPE parameters such as the elution solvent and sample volume used, were studied in order to maximize extraction efficiency. Oasis HLB provided the best results, obtaining--with the proposed SPE procedure--satisfactory percentage recoveries for all compounds (70-110%) with the exception of NP, for which a recovery of 54% was achieved. Application of the whole method, SPE-LC-(ESI)-MS, to natural waters permitted low nanogram-per-liter determination of all seven compounds.

Rapid determination of mono and dinitrophenols by DPP, in the presence of lead and cadmium and using concentrated CaCl2 electrolyte

The contamination of drinking water and industrial wastewaters is a critical environmental problem. The nitrophenol, dinitrophenol, cadmium, and lead contaminants are classified as hazardous compounds. Their rapid determination may be obtained using differential pulse polarography with concentrated electrolyte. CaCl2, which is very soluble to levels exceeding 5 mol l(-1), allows separation of coalescent peaks at 0.1 mol l(-1). A systematic study undertaken from 0.1 to 5 mol l(-1) shows good separation of lead and cadmium from the organic compounds, and optimization of the electrolyte concentration according to the objective is described. Preconcentration of real samples is necessary because pollution levels are usually very low.

Determination of nitrated phenolic compounds in rain by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A sensitive, specific, and rapid analytical method based on liquid-liquid extraction and liquid chromatography/atmospheric pressure chemical ionization mass spectrometry has been developed for trace analysis of nitrated phenolic compounds in rain samples. Selective detection in the low nanogram-per-milliliter range was achieved on the basis of selected ion monitoring of the respective phenolate anions [M - H]-. The presence of alkylated (C1-C3) and nonalkylated nitrophenols (C0) was confirmed by their characteristic neutral loss of nitrogen dioxide upon collision-induced dissociation in tandem mass spectrometry mode. In individual rain samples, 27 C0-C3-nitrophenol isomers as well as 16 C0-C3-dinitrophenol isomers were detected. Total levels of nitro- and dinitrophenol isomers were estimated on the basis of 2-nitrophenol and 2,6-dinitrophenol. Concentrations between 0.66 and 2.0, 12-29, 12-36, and 5.5-12 microg/L were obtained for the C0-, C1-, C2-, and C3-nitrophenols, respectively. Lower levels of 0.19-1.4, 0.39-2.1, 0.053-0.55, and 0.081-0.10 microg/L were estimated for the corresponding C0-, C1-, C2-, and C3-dinitrophenols. The highest number of individual isomers was found in winter rain samples, and distinctive isomeric patterns were observed for individual samples. Mono- and dialkylated nitrophenols and non- and monoalkylated dinitrophenols represent the major part of nitro- and dinitrophenol species. Comparing the pattern of Co-, C1-, and C2-nitrophenols in rain with the corresponding Co-, C1-, and C2-benzene pattern in ambient air suggests that atmospheric oxidation and nitration processes of alkylbenzenes are favored, as compared to those of benzene.

Liquid chromatography-mass spectrometry and strategies for trace-level analysis of polar organic pollutants

Liquid chromatography-mass spectrometry using atmospheric pressure ionization (LC-API-MS) has drastically changed the analytical methods used to detect polar pollutants in water. The present status of application of this technique to organic water constituents is reviewed. The selection of the appropriate LC conditions, whether reversed-phase liquid chromatography, ion-pair chromatography, capillary electrophoresis or ion chromatography, and of the most sensitive ionization mode, electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), depends upon the polarity and acidity of the analytes. Strongly acidic compounds such as aromatic sulfonates, sulfonated dyes, haloacetic acids, linear alkylbenzene sulfonates, aliphatic sulfonates and sulfates and complexing agents, weakly acidic compounds such as carboxylates and phenols, neutral compound classes, namely alkylphenol ethoxylates, alcohol ethoxylates and polycyclic aromatic hydrocarbons and the basic toxins, quaternary ammonium compounds and organometallic compounds are considered. The selection of the mass spectrometer depends upon the analytical task: triple-quadrupole mass spectrometers are highly suited for sensitive quantitation and for qualitative analyses, ion traps are especially suited for structure elucidation, whereas time-of-flight mass spectrometers and quadrupole time-of-flight mass spectrometers with their higher mass resolution are ideal for the determination of molecular formulas of unknown compounds and for screening purposes. While large steps have already been made, future efforts with respect to water analysis may be directed at fine-tuning the methodical arsenal for increased sensitivity and selectivity and to extend LC-MS application to transformation products.

Solid-phase microextraction liquid chromatography/tandem mass spectrometry for the analysis of chlorophenols in environmental samples

Liquid chromatography with atmospheric pressure chemical ionisation mass spectrometry (LC/APCI-MS), using negative ion detection in a triple quadrupole instrument, was used for the determination of chlorophenols (CPs) in environmental samples. In-source collision-induced dissociation (CID) was compared with MS/MS fragmentation. In general, less fragmentation was observed in MS/MS as compared with in-source CID, with the latter providing more intense fragment ions due to chemical ionisation. Under MS/MS conditions [M - H - HCl](-) was the main fragment ion observed for all compounds except for pentachlorophenol, which showed no fragmentation. For multiple reaction monitoring (MRM) acquisition mode, the transition from [M - H](-) to [M - H - HCl](-) was selected, leading to detection limits down to 0.3 ng injected. Direct and headspace-solid-phase microextraction (HS-SPME) were used as preconcentration procedures for the analysis of CPs in wood and in industrially contaminated soils. CPs were quantified by standard addition, which led to good reproducibility (RSD between 4 and 11%) in both SIM and MRM modes, and detection limits down to ng/g. The combination of MS/MS and in-source CID allowed confirmation of the presence of CPs in environmental samples.

Universal screening method for the determination of US Environmental Protection Agency phenols at the lower ng l(-1) level in water samples by on-line solid-phase extraction-high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry within a single run

The applicability of a previously optimized method for the analysis of the US Environmental Protection Agency (EPA) regulations phenols, based on on-line solid-phase extraction coupled to liquid chromatography with mass spectrometric (MS) detection in different matrix loaded water samples is demonstrated. The comprehensive optimization of the mobile phase conditions and their influence on the ionization process in atmospheric pressure ionization is described in detail. In particular, MS detection of the weakly acidic phenols such as phenol, monochlorinated phenols and methylated phenols requires the absence of acidic mobile phase modifiers and buffers. Thus lower retention times and slight peak broadening of the more acidic dinitrophenols are obtained if the entire range of EPA phenols is analyzed within a single chromatographic run. The figures of merit for the method were determined and the applicability to real water samples was investigated. Limits of detection for phenols ranging from 40 to 280 ng l(-1) and relative standard deviations below 8% in SCAN mode are obtained for all phenols if only 10-ml river water samples with low dissolved organic carbon (DOC 5 mg C l(-1) concentrations are preconcentrated. The method was used to detect 2-nitrophenol and 4-nitrophenol in river water samples in the lower ng l(-1) range. The analysis of highly matrix-loaded samples (DOC 210 mg C l(-1)) requires a reduced enrichment volume resulting in decreased sensitivity. Still the method is capable of reaching excellent detection limits which demonstrates its excellent suitability for screening analysis.

Determination of chlorophenols by solid-phase microextraction and liquid chromatography with electrochemical detection

A solid-phase microextraction method has been developed for the determination of 19 chlorophenols (CPs) in environmental samples. The analytical procedure involves direct sampling of CPs from water using solid-phase microextraction (SPME) and determination by liquid chromatography with electrochemical detection (LC-ED). Three kinds of fibre [50 microm carbowax-templated resin (CW-TPR), 60 microm polydimethylsiloxane-divinylbenzene (PDMS-DVB) and 85 microm polyacrylate (PA)] were evaluated for the analysis of CPs. Of these fibres, CW-TPR is the most suitable for the determination of CPs in water. Optimal conditions for both desorption and absorption SPME processes, such as composition of the desorption solvent (water-acetonitrile-methanol, 20:30:50) and desorption time (5 min), extraction time (50 min) and temperature (40 degrees C) as well as pH (3.5) and ionic strength (6 g NaCl) were established. The precision of the SPME-LC-ED method gave relative standard deviations (RSDs) of between 4 and 11%. The method was linear over three to four orders of magnitude and the detection limits, from 3 to 8 ng l(-1), were lower than the European Community legislation limits for drinking water. The method was applied to the analysis of CPs in drinking water and wood samples.

Determination of phenoxyacid herbicides and their phenolic metabolites in surface and drinking water

An evaluation was made of the feasibility of using reversed-phase liquid chromatography/tandem mass spectrometry with an electrospray interface (LC/ESI-MS/MS) to measure traces of phenoxyacid herbicides and their metabolites in surface and drinking water samples. The procedure involved passing 0.5 L of river and drinking water samples through a 0.5 g graphitized carbon black (GCB) extraction cartridge. Recovery was higher than 85% irrespective of the aqueous matrix in which the analytes were dissolved. A conventional 4.6-mm i.d. reversed-phase LC C-18 column operating with a mobile phase flow rate of 1 mL/min was used to chromatograph the analytes. A flow of 200 microL/min of the column effluent was diverted to the ESI source. The limits of detection (signal-to-noise ratio = 3) of the method for the pesticides considered in drinking and surface water samples are less than 0.1 ng/L for phenoxyacid herbicides, and about 5-10 ng/L for their metabolites (2,4-dichlorophenol and 4-chloro-2-methylphenol).

Determination of phenols in water using liquid phase microextraction with back extraction combined with high-performance liquid chromatography

Liquid phase microextraction with back extraction (LPME/BE) combined with high-performance liquid chromatography (HPLC) was studied for the determination of a variety of phenols in water samples. The target compounds were extracted from 2-ml aqueous sample adjusted to pH 1 (donor solution) through a microliter-size organic solvent phase (400-microl n-hexane), confined inside a small PTFE ring, and finally into a 1-microl basic aqueous acceptor microdrop suspended inthe aforementioned solvent phase from the tip of a microsyringe needle. After extracting for a prescribed time, the microdrop was taken back into the syringe and directly injected into an HPLC for detection. Factors relevant to the extraction procedure were studied. At the optimized extraction conditions, a large enrichment factor (more than 100-fold) can be achieved for most of the phenols within 35 min. The detection limit range was 0.5-2.5 microg/l for different analytes in aqueous samples. The results demonstrate the suitability of the LPME/BE approach to the analysis of polar compounds in aqueous samples.

Phenyl-modified reversed-phase liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry: a universal method for the analysis of partially oxidized aromatic hydrocarbons

A new liquid chromatographic method for the efficient separation of aromatic compounds having a wide range of sizes, molecular structures, and polarities has been developed. Based on a phenyl-modified silica reversed stationary phase and a methanol-water solvent gradient, it allows the separation of mono- and polycyclic aromatic hydrocarbons (PAHs) having up to five condensed aromatic rings and partially oxidized derivatives within a single chromatographic run of 40-min duration. The applicability of the method is demonstrated using 81 reference substances (PAHs, phenols, quinones, acids, lactones, esters, etc.) and real samples of environmental, medical, and technical relevance (ozonized PAHs, lake water, human urine, diesel exhaust condensates). The retention times of the investigated aromatics exhibit a regular increase with molecular mass and a systematic decrease with increasing number and polarity of functional groups. In case of intramolecular hydrogen bonding, a positive shift of retention time provides additional structural information. The combination of chromatographic retention time with the molecular mass and structural information from mass spectrometric detection allows the tentative identification of unknown aromatic analytes at trace levels, even without specific reference substances. With atmospheric pressure chemical ionization (APCI), low detection limits and highly informative fragmentation patterns can be obtained by in-source collision-induced fragmentation in a single-quadrupole LC-APCI-MS system as applied in this study, and multidimensional MS experiments are expected to further enhance the potential of the presented method.

Comparison of different sorbent materials for on-line solid-phase extraction with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry of phenols

On-line solid-phase extraction (SPE) was interfaced to liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) for the determination of US Environmental Protection Agency (EPA) phenols. The system, allowing fully automated operation, was used to evaluate different SPE cartridge materials and dimensions. Six different SPE materials (C18 HD, Polymer Labs PLRP-s, Hamilton PRP-1, Hysphere GP, Hysphere SH and Waters Oasis) were tested. Criteria for their comparison were first the recovery for the different phenols and its reproducibility, but also chromatographically relevant items like peakshape in the on-line elution mode. High recoveries and good relative standard deviations were obtained particularly for the newer, strongly retaining SPE materials that have become commercially available recently (the Hysphere materials and Waters Oasis) compared to the well known silica-based and weaker polymeric adsorbents like PLRP-s and PRP-1. These advantages are, however, traded in for good chromatographic peakshape, since the stronger adsorbents give rise to notable peak broadening in on-line elution. This is particularly true when using APCI-MS detection which on the one hand offers excellent selectivity and sensitivity, but imposes additional restrictions on the mobile phase composition in order not to suppress the response significantly. The influence of these parameters on the on-line-SPE-HPLC-MS determination of EPA phenols is discussed and present limitations are pointed out.

Capillary electrophoresis-electrospray ion-trap mass spectrometry for the separation of chlorophenols

Eighteen positional isomers of chlorophenols were separated by capillary electrophoresis (CE) and detected on-line by electrospray ionization ion-trap mass spectrometry (MS). Conditions for the coupling of CE to MS, e.g., the concentration of carrier electrolyte, the sheath liquid composition and the sheath gas flow-rate were optimized. Diethylmalonic acid (5 mM) at pH 7.25 and isopropanol-250 mM dimethylamine (80:20) as sheath liquid were used. The activation parameters for ion-trap mass spectrometric analysis of chlorophenols were optimized. The mass spectra, obtained for all the analytes, revealed that the [M-H]- ion was the base peak for all chlorophenols. Moreover, conditions for CE-MS-MS detection were established and [M-H-HCl]- ions were detected.

Application of spectral libraries for high-performance liquid chromatography-atmospheric pressure ionisation mass spectrometry to the analysis of pesticide and explosive residues in environmental samples

The coupling of high-performance liquid chromatography (HPLC) and atmospheric pressure ionisation mass spectrometry (API-MS) seems to be the method of choice if good separation and selective detection of semi-volatile, thermolabile, and polar substances is required. Libraries of mass spectra will make the identification of unknown substances in complex environmental samples easier and more user-friendly. Unfortunately, existing GC-MS libraries are not applicable to HPLC-API-MS analysis. Thus, new and extensive mass spectral libraries were constructed. Several investigations of chromatographic (composition and salt concentration of the eluent) as well as mass spectrometric (orifice voltage) parameters and a few applications of real environmental samples are used to discuss the possibilities and limits of these libraries.

New carrier electrolytes for the separation of chlorophenols by capillary electrophoresis

Optimum conditions for the separation of positional isomers of chlorophenols by capillary zone electrophoresis (CZE) were established. The behavior of five volatile electrolytes (L-cysteic acid, 3-amino-1-propanesulfonic acid, aminomethanesulfonic acid, diethylmalonic acid, and ammonium acetate) was compared. The best performance based on low electrophoretic current and high separation efficiency was obtained for diethylmalonic acid as working electrolyte. The influence of pH on the separation, using both uncoated fused-silica capillaries and modified capillaries (NaAMPS from EKT) with anionic coating, was discussed. Moreover, the effect of electrolyte concentration and applied voltage using fused-silica capillaries was studied. The optimum CZE conditions that allowed the separation of 16 chlorophenols were 20 kV, 30 mM diethylmaIonic acid, pH 7.25, and uncoated fused-silica capillary. Figures of merit such as run-to-run and day-to-day precision, linearity, and limits of detection were calculated.

Rapid determination of chlorogenic acid and related compounds in sunflower seeds by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

High-performance liquid chromatography (HPLC) in combination with atmospheric pressure chemical ionization mass spectrometry (APcI-MS) was applied to the determination of the phenolic fraction found in methanolic extracts of sunflower seeds (mainly chlorogenic acid and derived compounds). These extracts were directly separated by HPLC and detected by both negative and positive APcI-MS. Abundant structural information about these compounds can be obtained even at low extraction cone voltages. This method has been shown to be a rapid and effective method for the analysis of crude extracts from sunflower seeds.

Effect of sucrose on the perceived flavor intensity of chewing gum

The release of sucrose and menthone from chewing gum was measured in-mouth and in-nose, respectively, during eating. Swabs of saliva were taken from the tongue and analyzed using a rapid, direct liquid-mass spectrometry procedure. Menthone concentration in-nose was monitored on a breath-by-breath basis using direct gas phase atmospheric pressure chemical ionization-mass spectrometry. Simultaneously with the volatile release, trained panelists followed the change in mint flavor by time-intensity (TI) analysis. Two types of commercial chewing gum were analyzed. Both showed that the panelists perception of mint flavor followed sucrose release rather than menthone release. The temporal analysis of the chemical stimuli, with simultaneous TI analysis, provided unequivocal evidence of the perceptual interaction between nonvolatile and volatile flavor compounds from chewing gum.