Microwave-assisted Headspace Solid-phase Microextraction Research Articles

Determination and analysis of volatile components from Thymus kotschyanus Boiss with a new solid-phase microextraction fibre and microwave-assisted hydrodistillation by periodic mesoporous organosilica based on alkylimidazolium ionic liquid.

Research on the volatile oil composition of Thymus kotschyanus Boiss was conducted by applying mesoporous organosilica based on alkylimidazolium ionic liquid (PMO-IL) as a fibre coating material via a method referred to as microwave-assisted headspace solid-phase microextraction (MA-HS-SPME). This technique entails microwave irradiation of the sample and collection of the volatile sample components. These components are further introduced into a gas chromatography-mass spectrometry (GC-MS) injection port for further analysis. A simplex method was used for the optimisation of three different parameters affecting the efficiency of the extraction. The MA-HS-SPME method proved to be the most suitable technique in oil determination and extraction from Thymus kotschyanus owing to its advantageous aspects of cost effectiveness, simplicity and solvent independence.

Determination of Polycyclic Aromatic Hydrocarbons in Environmental Water Samples by Microwave-Assisted Headspace Solid-Phase Microextraction

Microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) with a polydimethylsiloxane/divinylbenzene (PDMS/DVB) and PDMS fibers were applied as a single step before determination of polycyclic aromatic hydrocarbon (PAH) concentrations in water using gas chromatography–mass spectrometry (GC-MS). PDMS/DVB was found better in performance and was chosen for the rest of the investigations. Dissolved organic matter (DOM) was found to not effect PAH analysis significantly. This study (MA-HS-SPME) presents the first finding in the literature that total (both freely dissolved and DOM-associated) PAH concentration was determined. To optimize the extraction efficiency of PAHs by MA-HS-SPME, influence of various parameters, including fibers, temperature, duration of thermal desorption, microwave irradiation power and duration, and the temperature of the circulating cooling water system, was studied. Under optimal operating conditions, good linearity of a calibration curve was observed over the studied concentration range for 16 PAHs (0.1–5 μg/L) in aqueous solution. PAH detection limit varied from 26.8 to 128 ng/L. A protocol was then proposed for estimating field binding constant between PAH and DOM through using our proposed MA-HS-SPME method and traditional SPME technique (freely dissolved PAH concentration determined). The proposed method was demonstrated applicable to environmental water samples, especially contaminated aquatic environment samples.

Complexation-flocculation combined with microwave-assisted headspace solid-phase microextraction in determining the binding constants of hydrophobic organic pollutants to dissolved humic substances.

The binding constants, KDOC, of selected polycyclic aromatic hydrocarbons (PAHs)-phenanthrene, anthracene, fluoranthene, and pyrene-to dissolved humic substances (DHS) were determined by complexation-flocculation combined with microwave-assisted headspace solid-phase microextraction (CF-MA-HS-SPME). The results obtained are comparable with KDOC data reported in the literature. No disruption of the PAH to DHS binding equilibrium was observed during the complexation-flocculation process. The present study, which is the first to determine KDOC by CF-MA-HS-SPME, provides an alternative approach to determine the KDOC of PAHs. CF-MA-HS-SPME provides some advantages over other methods, such as no limitation of fluorescent compounds, greater determination speed, and the capability of measuring various compounds simultaneously.

Microwave Assisted Head Space Solid Phase Microextraction for Analysis of Butachlor and Chlorpyrifos Pesticides in Urine

:Microwave assisted head-space solid phase microextraction (MA-HS-SPME) followed by gas chromatography using electron capture detection system (GC-ECD) were developed for determination of chloraacetanilide (butachlor) and chlorpyrifos present in biological samples. The different parameters including microwave irradiation power and microwave irradiation time, which affected on the extraction rate, were optimized. The optimum conditions for extraction of both pesticides were as following: irradiation power of 600 W, microwave irradiation time 10 min, sample volume: 10 ml, sample pH=2 and added salt 10 %. The limit of detection (LOD) for butachlor and chlorpyrifos were 0.0864 and 0.0832 ng/ml, respectively. The optimized methods for both compounds were validated for 6 consequtive days and 6 inter-day using two concentrations of 10 and 100 ng/ml in spiked urine samples that the ranges of obtained recoveries were 91-104 %.

Analysis of essential oil compositions ofLavandula angustifoliaby HS-SPME and MAHS-SPME followed by GC and GC-MS

Summary Head space solid phase microextraction (HS-SPME) and microwave-assisted HS-SPME (with polydimetyhylsiloxane [PDMS] fiber) were used for isolation of the volatile contents of Lavandula angustifolia. HS-SPME was done at 70°C for 5 min and microwave-assisted HS-SPME (MA-HS-SPME) was performed in 500 W of microwave power for 5 min. The results of the GC and GC-MS analysis showed that low levels of volatile compounds, which were not found by hydrodistillation, were obtained by SPME methods. The major extracted compounds were the same as hydrodistillation, including 1,8-cineole (41.37% and 54.84%), camphor (15.83% and 23.25%), and borneol (12.32% and 5%) extracted by HS-SPME and MA-HS-SPME, respectively.

GC–MS study of compounds isolated from Coffea arabica flowers by different extraction techniques

Headspace (HS), extractive, and distillative methods were employed to isolate volatile and semivolatile compounds from fresh Coffea arabica flowers. Static HS solid-phase microextraction (HS-SPME), microwave-assisted HS-SPME (MW-HS-SPME) with simultaneous hydrodistillation, and extraction with hexane or supercritical CO2 -isolated mixtures in which around 150 different chemical substances were identified or tentatively identified by GC-MS analysis. n-Pentadecane (20-37% relative peak area, RPA) was the most abundant compound in the HS fractions from fresh flowers, followed by 8-heptadecene (8-20% RPA) and geraniol (6-14% RPA). Hydrocarbons (mostly C13 -C30 paraffins) were the predominant compound class in all the sorptive extractions (HS-SPME, MW-HS-SPME, distillate), followed by terpenoids or oxygenated compounds (which varied with the isolation technique). Caffeine, a distinctive component of coffee fruits and beans, was also found in relatively high amounts in the supercritical CO2 extract of C. arabica flowers.

A Microwave‐assisted Headspace Solid‐phase Microextraction for Rapid Determination of Synthetic Polycyclic and Nitro‐aromatic Musks in Fish Samples

AbstractRapid solvent‐free microwave‐assisted headspace solid‐phase microextraction (MA‐HS‐SPME) coupled with gas chromatography‐mass spectrometry (GC‐MS) was developed to determine synthetic polycyclic and nitro‐aromatic musks in fish samples. Four commonly used synthetic musks, galaxolide (HHCB), tonalide (AHTN), musk xylene (MX) and musk ketone (MK) were employed in the method development and validation. The parameters (microwave irradiation time, irradiation power, amount of water addition, pH value and addition of NaCl) affecting the extraction efficiency of analytes from fish slurry were systematically investigated and optimized. The best extraction conditions were achieved when the fish sample 2‐g mixed with 4‐mL methanol and 15‐mL deionized water (containing 4 g of NaCl, pH 2.0 in a 40‐mL sample‐vial) was microwave irradiated at 80 watt for 5 min. The limits of quantification (LOQ) were 0.4 to 1.2 ng/g in 2‐g of wet tissue. The precision for these analytes, as indicated by relative standard deviations, were less than 9% for both intra‐ and inter‐day analysis. Accuracy, expressed as the mean extraction recovery, was between 80 to 92%. A standard addition method was used to quantitate these four synthetic musks, and the total concentrations ranged from 2.1 to 23.1 ng/g in various fish samples.

Development of microwave-assisted headspace solid-phase microextraction followed by gas chromatography-mass spectrometry for the analysis of phenol in a cigarette pad

Phenol is a mainstream cigarette smoke constituent and has been classified as a main toxic component directly related to environmental and health issues. Analysis of phenol in mainstream cigarette smoke is of great importance. In this work, microwave-assisted headspace solid-phase microextraction (HS-SPME) was developed for the fast analysis of phenol in a cigarette pad. Analyte in a Cambridge cigarette pad, activated by a short period of microwave irradiation, was headspace extracted by SPME and analyzed by GC-MS. Extraction conditions such as microwave irradiation time, SPME fiber coating, adsorption time and desorption time were investigated and optimized to achieve the best effect. The method was validated through the investigation of linearity, detection limit, recovery and precision. The linearity was in a wide range of 0.005–1 μg mL−1 with a correlation coefficient R2 = 0.999. The limit of detection was as low as 0.5 ng mL−1, and acceptable recovery and RSD values of 86.5% and 11.5% were achieved. The proposed method was successfully applied to the analysis of phenol in cigarette pad samples. The experimental results have demonstrated that microwave-assisted HS-SPME followed by GC-MS was a rapid, efficient and convenient method for the determination of phenol in tobacco products.

Rapid determination of alkylphenols in aqueous samples by in situ acetylation and microwave‐assisted headspace solid‐phase microextraction coupled with gas chromatography–mass spectrometry

A rapid and solvent-free procedure for the determination of 4-tert-octylphenol and 4-nonylphenol isomers in aqueous samples is described. The method involves in-situ acetylation and microwave-assisted headspace solid-phase microextraction prior to their determination using gas chromatography-ion trap mass spectrometry operated in the selected ion storage mode. The dual experimental protocols to evaluate the effects of various derivatization and extraction parameters were investigated and the conditions optimized. Under optimized conditions, 300 μL of acetic anhydride mixed with 1 g of potassium hydrogencarbonate and 2 g of sodium chloride in a 20 mL aqueous sample were efficiently extracted by a 65 μm polydimethylsiloxane-divinylbenzene fiber that was located in the headspace when the system was microwave irradiated at 80 W for 5 min. The limits of quantitation were 5 and 50 ng/L for 4-tert-octylphenol and 4-nonylphenol isomers, respectively. The precision for these analytes, as indicated by relative standard deviations, were less than 8% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 to 88%. A standard addition method was used to quantitate 4-tert-octylphenol and 4-nonylphenol isomers, and the concentrations ranged from 120 to 930 ng/L in various environmental water samples.

Rapid Analysis of Volatile Components from Teucrium polium L. by Nanoporous Silica‐polyaniline Solid Phase Microextraction Fibre

The development of simple, rapid and solvent-free methods for the analysis of essential oils is highly desirable. Microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) is a new sampling and concentration technique for the extraction of volatile components in medicinal plants. The main advantages of this method are the reduction of extraction time and of organic solvent. A highly porous Santa Barbara amorphous (SBA-15)/polyaniline material was prepared in order to produce a SPME fibre. The proposed fibre was evaluated for the extraction of the volatile component of Teucrium polium L. A homemade MA-HS-SPME apparatus was used for the extraction of volatile components. Highly porous SBA-15/polyaniline materials were prepared for SPME. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fibre. The SBA-15/polyaniline nanonporous fibre could adsorb volatile components of T. polium efficiently. In comparison with a HD method, the proposed technique could equally monitor almost all the components of the sample, but in an easier way that was rapid and required a much lower amount of sample. The experimental results showed that the nanoporous fibre was suitable for the semi-quantitative study of the composition of essential oils in plant materials and monitoring the variations in the volatile components of the plants.

Microwave-assisted headspace solid-phase microextraction to quantify polycyclic aromatic hydrocarbons in pine trees

A methodology for the extraction and quantification of 16 polycyclic aromatic hydrocarbons (PAHs) based on microwave-assisted extraction coupled with headspace solid-phase microextraction followed by gas chromatography/mass spectroscopy was validated for needles and bark of two pine species (Pinus pinaster Ait. and Pinus pinea L.). The limits of detection were below 0.92 ng g(-1) (dry weight) for needles and below 0.43 ng g(-1) (dw) for bark. Recovery assays were performed with two sample masses spiked at three levels and the overall mean values were between 70 and 110 % for P. pinaster and 75 and 129 % for P. pinea. In the first species, the increase in sample mass lowered the recoveries slightly for most PAHs, whereas for the second, the recoveries were higher for the needles. Naturally contaminated samples from 4 sites were analysed, with higher levels for urban sites (1,320 and 942 ng g(-1) (dw) vs. 272 and 111 ng g(-1) (dw) for needles and 696 and 488 ng g(-1) (dw) vs. 270 and 103 ng g(-1) (dw) for bark) than for rural ones and also for P. pinaster samples over P. pinea. It is also shown that gas-phase PAHs are predominant in the needles (over 65 % of the total PAHs) and that the incidence for particulate material in bark, reaching 40 % as opposed to a maximum below 20 % for the needles. The method has proved to be fit and improved some of the existing approaches, on the assessment of particulate PAHs and bark levels.

Antibacterial Activity and Comparison of the Volatile Constituents Obtained by Several Extraction Methods from the Flowers, Stems and Leaves of Astrodaucus orientalis

The oils of the flowers, stems and leaves of Astrodaucus orientalis L. were separately extracted using hydrodistillation (HD), head-space solid-phase microextraction (HS-SPME) and microwave assisted head-space solid-phase microextraction (MA-HS-SPME). The volatile constituents were analyzed by GC and GC/MS. Temperature and time of extraction, microwave power and exposure time of extraction were optimized. Polydimethylsiloxane (PDMS) fiber was used as the solid phase for SPME methods. The main constituents of the flower, stem and leaf oils isolated by HD, HS-SPME and MA-HS-SPME are as follows, respectively: beta-pinene (20.5%, 13.9% and 30.4%), alpha-thujene (8.7%, 16.2% and 10.9%) and alpha-pinene (7.6%, 14.3% and 10.9%) for the flowers, sabinene (11.8%, 32.3% and 11.8%), alpha-pinene (8.7%, 28.8% and 6.1%) and p-mycrene (2.5%, 12% and 8.5%) for the stem, and alpha-pinene (9.4%, 37.1% and 22.5%), sabinene (13.5%, 26.3% and 23.5%), beta-pinene (6.3%, 9.8% and 10%) and p-mycrene (3.2%, 2.5% and 15.6%) for the leaf. The minimum inhibitory concentrations (MIC) were determined for all essential oils obtained by HD against both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria using the agar dilution method. These oils showed the good activities against the both bacteria (0.5 - 1.5 mg/mL).

One-step microwave-assisted headspace solid-phase microextraction for the rapid determination of synthetic polycyclic musks in oyster by gas chromatography–mass spectrometry

A rapid, simple and solvent-free procedure was developed for the determination of synthetic polycyclic musks in oyster samples by using one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) and gas chromatography–mass spectrometry (GC–MS). Two commonly used synthetic polycyclic musks, galaxolide (HHCB) and tonalide (AHTN), were selected in the method development and validation. The parameters (microwave irradiation power, extraction time, amount of water added, pH value and addition of NaCl) affecting the extraction efficiency of analytes from oyster slurry were systematically investigated and optimised. The best extraction conditions were achieved when the oyster tissue mixed with 10-mL deionised water (containing 3g of NaCl in a 40-mL sample-vial) was microwave irradiated at 80W for 5min. The limit of quantification (LOQ) was 0.1ng/g in 5-g of wet tissue. The good precision and accuracy of one-step MA-HS-SPME coupled with GC–MS for the determination of trace level of AHTN in oyster samples was also demonstrated.

Microwave-assisted headspace solid-phase microextraction for the rapid determination of organophosphate esters in aqueous samples by gas chromatography-mass spectrometry

The rapid and solvent-free determination of organophosphate esters (OPEs) in aqueous samples via one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS) analysis is described. Tri-n-butyl phosphate (TnBP) and tris-(2-ethylhexyl) phosphate (TEHP) were selected as model compounds for the method of development and validation. The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes, in a 20mL water sample (in a 40mL sample bottle containing 2g of NaCl, pH 3.0), were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 140W for 5min. The limits of quantification (LOQs) for TnBP and TEHP were 0.5 and 4ng/L, respectively. Using the standard addition method, MA-HS-SPME coupled with GC–MS was utilized to determine selected OPEs in surface water and wastewater treatment plants (WWTP) influent/effluent samples. Preliminary results show that TnBP was commonly detected OPEs in these aqueous samples, the correlation coefficients (r2) of the standard addition curves were greater than 0.9822, indicating that the developed method appears to be a good alternative technique for analyzing OPEs in aqueous samples.

The Investigation of Essential Oil of Vitex pseudo-negund With Different Analytical Methods: Hydrodistillation, SFME, HS-SPME and MA-HS-SPME

Various analytical methods were used for extraction of essential oil of Vitex pseudo-negund and then analyzed by GC and GC-MS. The investigations testified that these analytical methods were able to extract different types of essential oil compounds. The microwave assisted methods: solvent-free microwave extraction (SFME) and microwave assisted head-space solid phase microextraction (MA-HS-SPME) were more adequate for extraction oxygenated compounds and the head-space solid phase microextraction (HS-SPME) methods with polydimethylsiloxane (PDMS) fiber were more proper to isolate the non-polar (mono and sesquiterpenes) than hydrodistillation as a traditional method.

Fast determination of synthetic polycyclic musks in sewage sludge and sediments by microwave-assisted headspace solid-phase microextraction and gas chromatography–mass spectrometry

One-step in situ microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS) analysis is presented as a fast and solvent-free technique to determine synthetic polycyclic musks in sewage sludge and sediment samples. Six synthetic polycyclic musks (galaxolide (HHCB), tonalide (AHTN), celestolide (ADBI), traseolide (ATII), cashmeran (DPMI) and phantolide (AHMI)) were selected in the method development and validation. The effects of extraction parameters for the quantitative extraction of these analytes by one-step MA-HS-SPME were systematically investigated. The dewatered solid sample mixed with 20-mL deionized water (containing 3 g of NaCl in a 40-mL sample-vial) was efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the extraction slurry was microwave irradiated at 80 W for 5 min. The limits of detection (LODs) ranged from 0.04 to 0.1 ng/g, and the limits of quantification (LOQs) ranged from 0.1 to 0.3 ng/g (fresh weight). A preliminary analysis of sludge and sediment samples revealed that HHCB and AHTN were the two most commonly detected synthetic polycyclic musks; using a standard addition method, their total concentrations were determined to range from 0.3 to 10.9 ng/g (fresh weight) with relative standard deviation (RSD) ranging from 4% to 10%.

Determination of synthetic polycyclic musks in water by microwave-assisted headspace solid-phase microextraction and gas chromatography-mass spectrometry

This paper describes a rapid and solvent-free method, microwave-assisted headspace solid-phase microextraction (MA-HS-SPME), for the extraction of six commonly used synthetic polycyclic musks: galaxolide (HHCB), tonalide (AHTN), celestolide (ADBI), traseolide (ATII), cashmeran (DPMI) and phantolide (AHMI) from water samples prior to their determination using gas chromatography-mass spectrometry (GC-MS). The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes in a 20-mL water sample (in a 40-mL sample-vial containing 4 g of NaCl) were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 180 W for less than 4 min. The limits of detection (LODs) ranged from 0.05 to 0.1 ng/L, and the limits of quantification (LOQs) were less than 0.2 ng/L. A preliminary analysis of wastewater samples revealed that HHCB and AHTN were the two most commonly detected synthetic polycyclic musks; using a standard addition method, their concentration were determined to range from 1.2 to 37.3 ng/L with relative standard deviation (RSD) ranging from 2 to 6%. The results obtained using this approach are better than those from the conventional oil-bath HS-SPME.

Analysis of aqueous pyrethroid residuals by one-step microwave-assisted headspace solid-phase microextraction and gas chromatography with electron capture detection

A one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) has been applied to be a pretreatment step in the analysis of aqueous pyrethroid residuals by gas chromatography (GC) with electron capture detection (ECD). Microwave heating was applied to accelerate the vaporization of pyrethroids (bioallenthrin, bifenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, cypermethrin, fluvalinate, fenvalerate and deltamethrin) into the headspace, and then being absorbed directly on a SPME fiber under the controlled conditions. Optimal conditions for the SPME sampling, such as the selection of sampling fiber, sample pH, sampling temperature and time, microwave irradiation power, desorption temperature and time were investigated and then applied to real sample analysis. Experimental results indicated that the extraction of pyrethroids from a 20-mL aquatic sample (pH 4.0) was achieved with the best efficiency through the use of a 100-μm PDMS fiber, microwave irradiation of 157 W and sampling at 30 °C for 10 min. Under optimum conditions, the detections were linear in the range of 0.05–0.5 μg/L with the square of correlation coefficients ( R 2) of >0.9913 for pyrethroids except bifenthrin being 0.9812. Method detection limits (MDL) were found to be varied from 0.2 to 2.6 ng/L for different pyrethroids based on S/N (signal to noise) = 3. The coefficients of variation (CVs) for repeatability were 7–21%. A field underground water sample was analyzed with recovery between 88.5% to 115.5%. This method was proven to be a very simple, rapid, and solvent-free process to achieve the sample pretreatment before the analysis of trace pyrethroids in aqueous samples by gas chromatography.

Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

The novel pretreatment technique, microwave-assisted heating coupled to headspace solid-phase microextraction (MA-HS-SPME) has been studied for one-step in situ sample preparation for polycyclic aromatic hydrocarbons (PAHs) in aqueous samples before gas chromatography/flame ionization detection (GC/FID). The PAHs evaporated into headspace with the water by microwave irradiation, and absorbed directly on a SPME fiber in the headspace. After being desorbed from the SPME fiber in the GC injection port, PAHs were analyzed by GC/FID. Parameters affecting extraction efficiency, such as SPME fiber coating, adsorption temperature, microwave power and irradiation time, and desorption conditions were investigated. Experimental results indicated that extraction of 20 mL aqueous sample containing PAHs at optional pH, by microwave irradiation with effective power 145 W for 30 min (the same as the extraction time), and collection with a 65 μm PDMS/DVB fiber at 20 °C circular cooling water to control sampling temperature, resulted in the best extraction efficiency. Optimum desorption of PAHs from the SPME fiber in the GC hot injection port was achieved at 290 °C for 5 min. The method was developed using spiked water sample such as field water with a range of 0.1–200 μg/L PAHs. Detection limits varied from 0.03 to 1.0 μg/L for different PAHs based on S/N = 3 and the relative standard deviations for repeatability were <13%. A real sample was collected from the scrubber water of an incineration system. PAHs of two to three rings were measured with concentrations varied from 0.35 to 7.53 μg/L. Recovery was more than 88% and R.S.D. was less than 17%. The proposed method is a simple, rapid, and organic solvent-free procedure for determination of PAHs in wastewater.

Analysis of semi-volatile organic compounds in aqueous samples by microwave-assisted headspace solid-phase microextraction coupled with gas chromatography–electron capture detection

The pretreatment technique of microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) has been developed and studied for the extraction of semi-volatile organic compounds (SVOCs) in aqueous samples prior to chromatographic analysis. The optimum conditions for obtaining extraction efficiency, such as the extraction time, extraction temperature, addition of salts, and the ratio of sample to headspace volume parameters were investigated. Experimental results indicated that the proposed MA-HS-SPME technique attained the best extraction efficiency under the optimized conditions, i.e., irradiation of extraction solution (20 mL aqueous sample in 40 mL headspace vial with no addition of salt) under 30 W microwave power for 30 min at 70 °C. The detection was linear at 1–250 ng/L with correlation coefficient exceeding 0.997. The detection limits obtained were between 0.2–10.7 ng/L, repeatability range from 2 to 15%. Real water samples collected from known sites in southern Taiwan were analyzed using the optimized conditions.