Enrichment and quantification of 18 polycyclic aromatic hydrocarbons from intermediates for plastics production by a generic liquid chromatography column switching.

The polycyclic aromatic hydrocarbon concentration in plastic products is regulated in (European Union) No. 1272/2013. However, this only covers the end products and not intermediate substances. Therefore, a generic method was developed to analyze the polycyclic aromatic hydrocarbons listed by the Environmental Protection Agency and the European Union. This method is based on direct large volume injection from solutions of plastic additives followed by liquid chromatography coupled to fluorescence detection. The additives Irganox 1010, ureido methacrylate, and cetyl methacrylate 1618F were used as examples for method development. Two serially coupled columns allowed the matrix to be removed on the first column and the analytes to be separated on the second column. The columns were connected by an intermediate valve. The valve allowed the matrix to be diverted after the first column and water to be dosed upstream of the second column via an additional pump. This allowed samples in aqueous or organic media to be focused at the column head. An injection volume of 100 µl and online aqueous dilution of 1:3 led to a limit of detection below 1 ng/ml for 15 polycyclic aromatic hydrocarbons. Moreover, concentrations between 1.6 and 10.3 ng/ml were found in the three plastic additives.

Comparison of preconcentration methods for nontargeted analysis of natural waters using HPLC-HRMS: Large volume injection versus solid-phase extraction.

Nontargeted analysis of water samples using liquid chromatography combined with high-resolution mass spectrometers is an emerging approach for surface water monitoring and evaluation of water treatment processes. In this study, sample preconcentration via direct, large volume injection with 500 µL and 1000 µL injection volumes was compared to SPE regarding analytical performance parameters in targeted and nontargeted workflows. In targeted analysis, the methods were evaluated in terms of LOD and intrabatch precision of the selected compounds, whereas in nontargeted analysis, the number of detected unknown compounds, the method's intra-batch precision, and the retention time versus molecular mass pattern of the detected unknowns were evaluated. In addition, a novel intensity drift correction method was developed that is not based on quality control samples and makes use of the signals obtained for continuously infused reference compounds, which are conventionally utilized for online mass drift correction. It could be demonstrated that the new correction method significantly reduced the bias introduced by instrumental drift and is important for the reliable intercomparison of different nontargeted methods. Intercomparison of results showed that the 1000 µL large volume injection method revealed the best performance in terms of precision under repeatability conditions of measurement as well as lower LODs for targeted compound analysis. In nontargeted analysis, the SPE method detected a higher number of unknown compounds but exhibited also a higher uncertainty of measurement caused by matrix effects.

A novel chromatographic separation method for rapid enrichment and isolation of novel flavonoid glycosides from Sphaerophysa salsula.

Flavonoid glycosides exist widely in medicine herbs and often used as nutraceuticals because of their excellent bioactivity and low toxicity. For accurate quality control and bioactivity assessment of Sphaerophysa salsula, a rapid and productive method to isolate flavonoid glycosides is needed. Therefore, this work reports the development of a novel comprehensive strategy based on an online middle-pressure chromatography and preparative high-performance liquid chromatography for rapid enrichment and separation of flavonoid glycosides from S. salsula. First, the flavonoid glycosides were enriched using an online middle-pressure chromatographic column containing stationary middle chromatogram isolated phase. During this process, the high-volume injection of the extracting solution was realized by an empty precolumn positioned before the main chromatographic tower. Then, the compounds were separated through preparative high-performance liquid chromatography with Megress C18. As a result, one new flavonol 3-O-glycoside (2) and two known flavonol 3-O-glycosides (1, 3) were targetedly isolated from S. salsula. The content of compounds 1-3 in S. salsula was 0.09, 0.11, and 0.18 wt%, respectively. Comparing to traditional enrichment and separation methods, our technique offers significantly shorter sample pretreatment time as well as high reproducibility. We believe that our separation method has a strong potential to be used for the processing of other medicinal plants.

Graphitic carbon nitride as sorbent for the emulsification-enhanced disposable pipette extraction of eight organochlorine pesticides prior to GC-MS analysis.

Graphitic carbon nitride (g-C3N4) was explored as a sorbent for the emulsification-enhanced (EE) disposable pipette extraction (DPX) of eight organochlorine pesticides (OCPs) from environmental waters. The OCPs, including α-hexachlorocyclohexane, Aldrin, α-Chlordane, Dieldrin, 4,4'-dichlorodiphenyldichloroethylene, 4,4'-dichlorodiphenyldichloroethane, Heptachlor and Heptachlor epoxide (Isomer A), were analyzed by gas chromatography-mass spectrometry. The sorbent g-C3N4 was characterized by elemental analysis, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared and Raman spectroscopy. As a C-N analogue of graphite, g-C3N4 exhibits good water dispersibility and allows easy analyte recovery - a characteristic not commonly observed in carbon-based materials. When applied to DPX, g-C3N4 rapidly establishes strong interactions with the OCPs. Consequently, g-C3N4 displays superior extraction capability in comparison to six other commercial sorbents. An emulsification step prior to DPX was found to enhance the overall extraction efficiency by pre-concentrating the OCPs into the microdroplets of an organic solvent. The microdroplets were then adsorbed onto g-C3N4. Under the most favorable conditions, wide linear responses spanning over two to four orders of magnitudes are established. The limits of detection range between 2.4 ng·L-1 and 46.2 ng·L-1. The method is reproducible (relative standard deviations ≤ 7.4%) and enrichment factors are between 42 and 57. When applied to the analysis of lake and river water samples, EE-DPX-gas chromatography-mass spectrometry exhibits good resilience against matrix interferences. The relative recoveries range between 77.7% and 106.3%. In comparison to other sorbent-based extraction techniques reported for the analysis of OCPs in aqueous samples, EE-DPX utilizes the minimal amount of sample and solvent, and requires the shortest sample preparation time. Graphical abstractSchematic representation of the emulsification-enhanced disposable pipette extraction (DPX) of organochlorine pesticides (OCPs) using graphitic carbon nitride (g-C3N4) as sorbent. Emulsification and DPX work synergistically, thus allowing rapid dissolution of analytes into microdroplets of organic solvent, before being extracted by g-C3N4.

[Evaluation of an Analytical Method Using GC-MS/MS and a 3-Layer Solid Phase Extraction Mini-Column for Pesticide Residues in Agricultural Products].

We developed a simple rapid analysis of multi-pesticide residues in agricultural products. In this study, we attempted to simplify the purification process, and reduce the amount and type of solvent used. The test solution was prepared by clean-up, a 0.5 mL aliquot of QuEChERS extract solution of agricultural products using a 3-layer solid-phase (C18/SAX/PSA) extraction mini-column, and the test solution was subjected to GC-MS/MS analysis, modified with a large volume injection and a stomach-type glass-lined injector. This method met the acceptability criteria of recovery (70-120%) and standard deviation of repeatability (RSD<25%) in 241-331 pesticides in 8 types of agricultural products.

[Pesticide Analysis in Agricultural Products by GC-MS/MS Using STQ Method].

As a method to detect pesticide residues in agricultural products, we evaluated the pretreatment of agricultural product samples by the solid-phase extracton technique with QuEChERS (STQ) method followed by GC-MS/MS with large-volume injection using a stomach-type glass-lined injector. This method satisfied the target criteria of recovery (70-120%) and the standard deviation of repeatability (RSD<25%) in 238-282 pesticides found in six types of agricultural products.

Vacuum-assisted evaporative concentration combined with LC-HRMS/MS for ultra-trace-level screening of organic micropollutants in environmental water samples.

Vacuum-assisted evaporative concentration (VEC) was successfully applied and validated for the enrichment of 590 organic substances from river water and wastewater. Different volumes of water samples (6 mL wastewater influent, 15 mL wastewater effluent, and 60 mL river water) were evaporated to 0.3 mL and finally adjusted to 0.4 mL. 0.1 mL of the concentrate were injected into a polar reversed-phase C18 liquid chromatography column coupled with electrospray ionization to high-resolution tandem mass spectrometry. Analyte recoveries were determined for VEC and compared against a mixed-bed multilayer solid-phase extraction (SPE). Both approaches performed equally well (≥ 70% recovery) for a vast number of analytes (n = 327), whereas certain substances were especially amenable to enrichment by either SPE (e.g., 4-chlorobenzophenone, logDow,pH7 4) or VEC (e.g., TRIS, logDow,pH7 - 4.6). Overall, VEC was more suitable for the enrichment of polar analytes, albeit considerable signal suppression (up to 74% in river water) was observed for the VEC-enriched sample matrix. Nevertheless, VEC allowed for accurate and precise quantification down to the sub-nanogram per liter level and required no more than 60 mL of the sample, as demonstrated by its application to several environmental water matrices. By contrast, SPE is typically constrained by high sample volumes ranging from 100 mL (wastewater influent) to 1000 mL (river water). The developed VEC workflow not only requires low labor cost and minimum supervision but is also a rapid, convenient, and environmentally safe alternative to SPE and highly suitable for target and non-target analysis.

A simple, fast method for the analysis of 20 contaminants of emerging concern in river water using large-volume direct injection liquid chromatography-tandem mass spectrometry.

A fast and sensitive method for the determination of a structurally and physico-chemically diverse group of contaminants of emerging concern (CEC) based on large-volume direct injection liquid chromatography-tandem mass spectrometry was developed. The method can be used to determine 20 CECs belonging to different pollutant families (pharmaceuticals, personal care products, and pesticides) in river water at nanogram per liter. A single analytical run is required and the positive and negative ionization modes can be used simultaneously. Because of the large-volume injections of samples and the high sensitivity of the current mass spectrometers, the method has no need of a preconcentration step. The analytes are quantitated with matrix-matched calibration curves. The estimated limits of detection were in the range 0.1-5 ng L-1. The accuracy of the method was in the range 86-114%, and the precision, expressed as a relative standard deviation (RSD %), was below 18% for all the analytes (n = 5, at 5, 10, and 25 ng L-1). The method was applied to water samples taken from different points along the lower course of the Ebro River, Spain. A total of 12 out of the 20 target analytes were detected, and the ones at higher concentrations were caffeine and the pharmaceuticals paracetamol and ibuprofen (184.8 ng L-1, 63.3 ng L-1, and 23.3 ng L-1, respectively).

Simultaneous determination of dechloranes, polybrominated diphenyl ethers and novel brominated flame retardants in food and serum.

A sensitive method for the simultaneous quantification of dechloranes, polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) has been developed for gas chromatography (GC) coupled to tandem mass spectrometry operating in electron capture negative ionization (ECNI) mode. The major advance has been achieved by combining selected ion monitoring (SIM) and multiple reaction monitoring (MRM) modes in well-defined time windows, to determine dechloranes, PBDEs and NBFRs at picogram per gram level in one single analysis in complex matrix biological samples. From the chromatographic point of view, efforts were devoted to study several injection modes using multimode inlet (MMI) in order to obtain low instrumental detection limits, necessary for trace compounds such as Dechlorane Plus (DP) isomers. Method performance was also evaluated: calibration curves were linear from 20 fg µL-1 to 100 pg µL-1 for the studied compounds, with method detection limits at levels of 50 fg g-1 for DPs. Repeatability and reproducibility, expressed as relative standard deviation, were better than 5% even in solvent vent mode for the injection of standards. The application to a wide range of complex samples (including food, human and animal serum samples) indicated a sensitive and reliable way to quantify at the picogram per gram level 4 halogenated norbornenes (HNs), Dechlorane Plus (anti-DP and syn-DP) and 2 of their homologues (Dechlorane-602 and Dechlorane-603), 11 PBDE congeners (no. 28, 47, 49, 66, 85, 99, 100, 153, 154, 183 and 209) and 5 novel BFRs, i.e. decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), hexabromobenzene (HBB), 2,3,4,5-tetrabromo-ethylhexyl-benzoate (TBB) and tetrabromophthalate (TBPH). Graphical Abstract GC-ECNI-MS/MS chromatograms showing the most sensitive transition for DPs when injecting 2 µL of a 16 fg/µL standard solution of s-DP and a-DP at three different source temperatures.

Measuring the internal concentration of volatile organic compounds in small organisms using micro-QuEChERS coupled to LVI-GC-MS/MS.

There is an increasing demand for analytical tools to measure the internal concentrations of xenobiotic pollutants in small organisms. Such tools are required to determine exposure in ecotoxicological studies yet avoid sophisticated clean-up and enrichment techniques or large-scale experimental design. Thus, this paper presents a modified QuEChERS method coupled to gas chromatography tandem mass spectrometry (GC-MS/MS) for small volume organic samples. Ten zebrafish (Danio rerio) embryos were exposed to a 46-compound mixture at 10 ng/mL. After 72 h of exposure, they were extracted in 200 µL glass inserts using 70 µL of both acetonitrile and water. Volumes of 50 µL of extract were injected into a GC-MS/MS with a multi-mode inlet. Internal concentrations of zebrafish embryos could be reproducibly quantified in the lower nanogram per millilitre range at detection limits of 1-25 ng/mL and with recoveries of 63-133%. Internal concentrations varied over the tested range of compounds between 5.88 ± 0.616 ng/mL for dicofol and 232 ± 18.6 ng/mL for diflufenican. Detectability and recovery were best for compounds with a log D greater than four. As internal concentrations did not seem to exclusively depend on log D, biochemical transport processes could play an important role in the uptake kinetics of early zebrafish life stages. Graphical Abstract This paper presents an extraction and quantification method for 46 volatile organic compounds in zebrafish embryos. After exposure, pools of ten embryos were extracted with 70 µL acetonitrile applying a micro-QuEChERS approach. Internal embryo concentrations were analytically determined and quantified by large volumen injection gas chromatography tandem mass spectrometry (GC-MS/MS).

Determination of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in human serum using programmable-temperature vaporization gas chromatography with high-resolution mass spectrometry.

The determination of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in blood from a non-occupational population is essential for the investigation of adverse health effects from these pollutants. In this study, a sensitive method based on programmable-temperature vaporization with large-volume injection coupled with gas chromatography with high-resolution mass spectrometry was developed to determine these pollutants in 1-2 mL of human serum samples. Various key parameters of programmable-temperature vaporization injector, including vent temperature, vent time, vent flow, transfer temperature and transfer time were optimized by factorial design. The accuracy and precision as well as applicability were assessed by determining polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in calibration standard solutions, standard reference materials and real human serum samples from non-occupational population. The method detection limits of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls were 1.5-9.0 and 0.005-0.02 ng/kg wet weight, respectively. By comparing with typically splitless injection, the application of programmable-temperature vaporization injector could effectively lead to higher detectable rate of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in 1-2 mL of human serum samples.

The applicability of a large-volume injection (LVI) system for quantitative analysis of permanent gases O2 and N2 using a gas chromatograph/barrier discharge ionization detector.

To develop accurate quantitation methods for two major permanent gases, N2 and O2, a series of calibration experiments were carried out using a gas chromatograph (GC)/barrier discharge ionization detector (BID) equipped with a large-volume injection (LVI) system. To this end, gaseous working standards (WSs) diluted with helium gas were prepared at ten different concentration levels representing three different concentration ranges (in ppm) in 1-L polyester aluminum (PEA) bags ((1) low, 209~2090 (O2) and 791~7910 (N2); (2) moderate, 2090 ~ 20,900 (O2) and 7910~79,100 (N2); and (3) high, 20,900~209,000 (O2) and 79,100~791,000 (N2)). Cross-calibration experiments for each individual WS were carried out using the loop injection system with four different capacities (0.01, 0.5, 1, and 10 mL). The calibration results were then evaluated with respect to key variables including loop capacity, concentration, and mass quantity. Accordingly, we observed the optimal performance of the BID in terms of sensitivity and linearity (R 2 > 0.98) when the WS of the moderate concentration range was analyzed with the small loop (0.01 and 0.5 mL). The method detection limit (MDL) values of the four loop sizes (between 0.01 and 10 mL) were 7~500 ng for O2 (38.4~557 ppm) and 24~2230 ng for N2 (195~2105 ppm).

Micro-liquid chromatography mass spectrometry for the analysis of antineoplastic drugs from wipe samples.

A fast quantification method for the determination of 11 antineoplastic drugs from wipe samples was developed using micro-scale liquid chromatography in combination with tandem mass spectrometry. The extraction efficiency from the wipes has been investigated using different extraction solvents. The results indicate that a mixture of 70/30 water/isopropanol (v/v) acidified with 0.1 % formic acid is suitable to desorb the antineoplastic drugs with sufficient recovery between 80 and 120 %. Compared to conventional liquid chromatography, the total analysis time can be reduced to 2.25 min using a 50 × 0.3 mm column at a flow rate of 25 µL min-1. Ion source parameters as well as the injection volume were optimized to ensure the highest sensitivity. The results of method validation showed an instrumental limit of quantification between 0.0068 and 0.0488 ng mL-1 using an injection volume of 4.25 µL estimated by the signal to noise ratio. Moreover, the retention time repeatability was determined with a maximum relative standard deviation of 0.4 %. Graphical abstract Micro-LC-MS/MS separation of 11 antineoplastic drugs from wipe samples.

Cyclic volatile methylsiloxanes in human blood as markers for ruptured silicone gel-filled breast implants.

The replacement of medical-grade silicone with industrial-grade silicone material in some silicone gel-filled breast implants (SBI) manufactured by Poly Implant Prothèse and Rofil Medical Nederland B.V., reported in 2010, which resulted in a higher rupture tendency of these SBI, demonstrates the need for non-invasive, sensitive monitoring and screening methods. Therefore a sensitive method based on large volume injection-gas chromatography coupled to mass spectrometry (LVI-GC/MS) was developed to determine octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclo-hexasiloxane (D6) in blood samples from women with intact (n = 13) and ruptured SBI (n = 11). With dichloromethane extraction, sample cooling during preparation, and analysis extraction efficiencies up to 100 % and limits of detection of 0.03-0.05 ng D4-D6/g blood were achieved. Blood samples from women with SBI were investigated. In contrast to women with intact SBI, in blood from women with ruptured SBI higher D4 and D6 concentrations up to 0.57 ng D4/g blood and 0.16 ng D6/g blood were detected. With concentrations above 0.18 D4 ng/blood and 0.10 ng D6/g blood as significant criteria for ruptured SBI, this developed analytical preoperative diagnostic method shows a significant increase of the recognition rate. Finally a higher precision (error rate 17%) than the commonly used clinical diagnostic method, mamma sonography (error rate 46%), was achieved.

Direct determination of acrylamide in food by gas chromatography with nitrogen chemiluminescence detection.

A method of gas chromatography with nitrogen chemiluminescence detection and using standard addition is described for the determination of acrylamide in heat-processed foods. Using a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation method removes the acrylamide precursors completely, and the risk of overestimating acrylamide concentration due to additional analyte formation in the hot gas chromatograph inlet is also avoided. Sample preparation is rapid and inexpensive. A Deans switch device is utilized to heart-cut acrylamide and to prevent interferences from the solvent and matrix from reaching the detector. The pre-column is backflushed at high temperature to maintain a clean baseline and shorten the cycle time compared to baking out the column. Quantitation using standard addition is employed for compensation of potential variability in the acrylamide extraction efficiency in acetonitrile. The limit of detection and the limit of the quantification obtained for this method are 27 and 81 µg/kg, respectively, in food samples (equivalent to 3.5 and 10.6 µg/L in acetonitrile, respectively), and the linear range is 76-9697 µg/kg in food samples (equivalent to 10-1280 µg/L in acetonitrile) with an R(2) value of 0.9999.

Determination of rifampicin in rat plasma by modified large-volume direct injection RAM-HPLC and its application to a pharmcokinetic study.

A direct large volume injection high-performance liquid chromatography (HPLC) method with homemade restricted-access media (RAM) pre-column and combined with a column-switching valve was established and developed for determination rifampicin (RIP) in rat plasma. The rat plasma samples (100 µL) were injected directly onto pre-column, where RIP was retained and pre-concentrated, while proteins were washed to waste using a methanol-water (5:95) as the mobile phase at a flow rate of 1 mL/min. Then, by rotation of the switching valve at 5 min, the RIP were eluted from the pre-column and transferred to an Luna C18 analytical column by the chromatographic mobile phase consisting of methanol-acetonitrile-10 mm ammonium format (60:5:35) at a flow rate of 1 mL/min. The total analytical run time was 15 min with UV detection wavelength at 254 nm. Carbamazepine was used as the internal standard. Excellent linear correlation (r = 0.9993) was obtained in the range of 0.25-8 µg/mL for rat plasma. The intra-day and inter-day precisions of RIP were all <5.0%. The recoveries were in the range of from 99.98-113.66% for plasma. This on-line RAM-HPLC method was successfully applied to the pharmacokinetic study of RIP in rat plasma.

Determination of organophosphorus pesticides by gas chromatography with mass spectrometry using a large-volume injection technique after magnetic extraction.

A fast and efficient method was developed for the extraction and determination of organophosphorus pesticides in water samples. Organophosphorus pesticides were extracted by solid-phase extraction using magnetic multi-walled carbon nanotubes and determined by gas chromatography with ion-trap mass spectrometry. Parameters affecting the extraction were investigated. Under optimum conditions of the method, 10 mg magnetic multi-walled carbon nanotubes were added into 10 mL sample. After 2 min, adsorbent particles settled at the bottom of test tube with a magnet. After removing aqueous supernatant, the analytes were desorbed with acetonitrile. Then, 70 µL of acetonitrile phase was injected into the gas chromatography and mass spectrometry system that had an ion-trap analyzer. To achieve high sensitivity, the large-volume-injection technique was used with a programmed temperature vaporization inlet, and the ion-trap mass spectrometer was operated in single ion storage mode. Under the best conditions, the enrichment factors and extraction recoveries were in the range of 113-124 and 74-103%, respectively. The limits of detection were between 3 and 15 ng/L, and the relative standard deviations were < 10%. This method was successfully used for the determination of organophosphorus pesticides in dam water, lagoon water, and river water samples with good reproducibility and recovery.

Rapid and simultaneous determination of ultrashort-, short- and long- chain perfluoroalkyl substances by a novel liquid chromatography mass spectrometry method.

Per- and Polyfluoroalkyl Substances (PFAS) are a group of persistent organic pollutants that have received considerable attention from public and regulatory groups. Due to regulations of long-chain PFAS, the use of short-chain and ultrashort-chain PFAS is rapidly growing. Thus, there is an urgent need to develop quantitative methods for determining PFAS with different chain lengths in various environmental matrices. This study introduces an innovative liquid chromatography-mass spectrometry (LC-MS) system combining large volume injection (LVI) and online solid phase extraction (SPE). This system incorporates three columns: a reverse-phase (RP) column, a weak anion exchange (WAX) trap column, and a hybrid HILIC/ion-exchange (HILIC/IE) column, controlled by two valves. With valve switching, ultrashort-chain PFAS that are not retained by the RP column are enriched by the trap column, while other PFAS are separated by the RP column. The trapped ultrashort PFAS are then transferred to the HILIC/IE column for further separation. The LVI significantly enhances the method's sensitivity, allowing for rapid and simultaneous determination of ultrashort-, short- and long- chain PFAS in aqueous samples. The matrix effects from various environmental samples were evaluated, and the results indicate that this unique LC-MS method is suitable for analyzing all chain-length PFAS in various matrices, including surface water, sewage effluent, and seawater. Finally, this novel LC-MS method was applied to quantify PFAS in various water samples.

Sensitivity and quantitativeness of large-volume injection combined with liquid chromatography/high-resolution mass spectrometry for target screening analysis of emerging contaminants.

Solid phase extraction (SPE) has been widely used for pretreatment in target screening (TS) analysis. However, some compounds are difficult to recover by SPE or their recovery is unstable for environmental samples. In this study, we tested large-volume injection (LVI) without SPE for TS analysis of 103 compounds listed by the Ministry of the Environment (Japan)-so-called 'items to be surveyed'-using liquid chromatography high-resolution mass spectrometry. We evaluated the limit of quantification (LOQ) by LVI and compared this LOQ with the LOQ by SPE pretreatment using a hydrophilic-lipophilic balance (HLB) combined with activated carbon, which was found previously to afford the best SPE cartridges for target compounds recovery. The LOQ generally decreased as the injection volume increased, and the LOQ was at least 250 times lower for a 500-µL injection than for a 2-µL injection for half of the compounds. LVI provided LOQs lower than the predicted no effect concentration for more compounds than the SPE method. The average matrix effect (ME) by LVI was in the range 70%-130% for 69 out of 97 compounds. The ME was higher or lower for some of the remaining compounds, but the ME was in the range 10%-1000% for all 18 water samples for 84 of the 97 compounds. Comparing the ME by LVI and the recovery ratio by the SPE method showed that LVI achieved more accurate quantitation than the SPE method for a larger number of compounds. Therefore, LVI provides better sensitivity and quantitativeness than the SPE method using HLB and activated carbon for TS analysis of as many 'items to be surveyed' as possible.

Development of a column switching for direct online enrichment and separation of polar and nonpolar analytes from aqueous matrices.

Trace substances in surface waters may threaten health and pose a risk for the aquatic environment. Moreover, separation and detection by instrumental analysis is challenging due to the low concentration and the wide range of polarities. Separation of polar and nonpolar analytes can be achieved by using stationary phases with different selectivity. Lower limits of detection of trace substances can be obtained by offline enrichment on solid phase materials. However, these practices require substantial effort and are time consuming and costly. Therefore, in this study, a column switching was developed to enrich and separate both polar and nonpolar analytes by an on-column large volume injection of aqueous samples. The column switching can significantly reduce the effort and time for analyzing trace substances without compromising on separation and detection. A reversed phase (RP) column is used to trap the nonpolar analytes. The polar analytes are enriched on a porous graphitized carbon column (PGC) coupled serially behind the RP column. A novel valve switching system is implemented to enable elution of the nonpolar analytes from the RP column and, subsequently, elution of polar analytes from the PGC column and separation on a hydrophilic interaction liquid chromatography (HILIC) column. To enable separation of polar analytes dissolved in an aqueous matrix by HILIC, the water plug that is flushed from the PGC column is diluted by dosing organic solvent directly upstream of the HILIC column. The developed method was tested by applying target analysis and non-target screening, highlighting the advantage to effectively separate and detect both polar and nonpolar compounds in a single chromatographic run. In the target analysis, the analytes, with a logD at pH 3 ranging from -2.8 to + 4.5, could be enriched and separated. Besides the 965 features in the RP phase, 572 features from real wastewater were observed in the HILIC phase which would otherwise elute in the void time in conventional one-dimensional RP methods.