Calculated Method Detection Limit Research Articles

Fully Automated QuEChERS Extraction and Clean-up of Organophosphate Pesticides in Orange Juice

A fully automated QuEChERS extraction and extract clean-up method for GC-MS and LC-MS analysis is presented by using an industry standard robotic x,y,z-sampling system. The application describes the analysis of organophosphate pesticides from homogeneous liquid samples, as an example orange juice was used. The automated workflow includes the extraction with acetonitrile, salting out and using a µSPE cartridge for matrix clean-up prior to injection into a GC-MS/MS system. The method validation techniques such as pre-spike and post-spike were fully integrated into the automated workflow as well. Calibration linearities of the applied organophosphate pesticides in orange juice matrix range from 1 to 100 ng/mL with a precision achieved better than 0.995 for all compounds. By spiking 10 ng/mL of pesticides into the orange juice samples, recoveries were obtained in the of range 70% – 115%, while the precision from pre-spike (n=7) and post-spikes (n=6) under the same concentration was less than 10% RSD. The calculated method detection limits (MDLs) of the monitored pesticides were in the range of 1.8 ng/mL to 4.1 ng/mL which are well below the regulated maximum residue limits (MRLs) of 10 ng/g for these pesticides.

N-doped mesoporous carbon as a new sorbent for ultrasonic-assisted dispersive micro-solid-phase extraction of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene, from urine samples

This study aimed to optimize a new sample preparation method using N-doped mesoporous carbon sorbent for simultaneous measurement of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene. The samples were analyzed using high-performance liquid chromatography supplied with ultraviolet detector (HPLC-UV). N-doped mesoporous carbon sorbent was obtained via the hard template procedure. The synthesized nanosorbent was then characterized by transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and elemental analysis (CHN). The effective factors in the extraction of the studied biomarkers were examined by the Box-Behnken (BBD) methodology. Regarding the optimum conditions, the sketched calibration curve for naphthols was linear in the concentration levels of 1–600 µg L-1 for human urine samples. The accuracy and reproducibility of the introduced method were determined using the relative recovery (RR %) and relative standard deviation (RSD %) tests on the fortified urine samples. RR% and RSD% were found to be 97.0–101.2% and 3.1–9.0%, respectively. The calculated method detection limit of the optimized procedure was 0.3 µg L-1 and 0.5 µg L-1 for 1-naphthol and 2-naphthol, respectively.

Optimization of an MMPB Lemieux Oxidation method for the quantitative analysis of microcystins in fish tissue by LC-QTOF MS

Microcystins are toxic heptapeptides produced by cyanobacteria in marine and freshwater environments. In biological samples such as fish, microcystins can be found in the free form or covalently bound to protein phosphatases type I and II. Total microcystins in fish have been quantified in the past using the Lemieux Oxidation approach, where all toxins are oxidated to a common fragment (2-methyl-3-methoxy-4-phenylbutyric acid, MMPB) regardless of their initial amino acid configuration or form (free or protein bound). These studies have been carried out using different experimental conditions and employed different quantification strategies. The present study has further investigated the oxidation step using a systematic approach, to identify the most important factors leading to a higher, more robust MMPB generation yield from fish tissue in order to reduce the method detection limit. Field samples were quantified using an in-situ generated MMPB matrix matched calibration curve by isotope dilution with d3-MMPB via liquid chromatography coupled to time-of-flight mass spectrometry (LC-QTOF MS). This approach improves method's accuracy by taking into account of potential matrix effects that could affect the derivatization, sample prepation and instrumental analysis steps. The validated method showed 16.7% precision (RSD) and +6.7% accuracy (bias), with calculated method detection limits of 7.28 ng g−1 Performance of the method was assessed with the analysis of laboratory exposed Rainbow Trout (Oncorhynchus mykiss) to cyanobacteria as a positive control, where no microcystins were detected in the pre-exposure fish liver and fillet, low levels in the exposed fillet (65.0 ng g−1) and higher levels in the exposed liver (696 ng g−1). Finally, the method was employed for the analysis of 26 fillets (muscle) and livers of Walleye (Sander vitreus) and Yellow Perch (Perca flavescens) from Lake Erie, showing very low concentrations of microcystins in the fillet and higher concentrations in liver, up to 3720 ng g−1.

Droplet method for the determination of sodium and potassium concentrations in highly saline water samples using X-ray fluorescence spectrometry

Wavelength-dispersive X-ray fluorescence spectrometry (WD-XRF) analysis could be a useful tool for the analysis of water samples with high Na and K concentrations. In this paper, we propose the droplet method for XRF analysis with an appropriate filter substrate selected in terms of the dropping area, drying time, and constant shape. In addition, the optimal sample volume has been determined to be 10 μL. Calibration curves were generated over concentration ranges of 1000–20,000 mg/L for Na and 200–1000 mg/L for K with good relative standard deviation values. The calculated method detection limit and the limit of quantification values were 74.1 and 236 mg/L for Na and 12.1 and 38.4 mg/L for K, respectively. The accuracy of the developed droplet method was also examined using two certified standard solutions and was shown to give a reliable relative standard error with −23.3% and 7.12% error for Na and K, respectively. To verify the feasibility of the developed droplet method for WD-XRF analysis, seven water samples, including seawater and groundwater with seawater intrusion, were analyzed. Our findings indicate that WD-XRF technique is suitable for the accurate determination of water samples with high Na and K concentrations without the need for complicated sample preparation methods.

Fast and environmental-friendly methods for the determination of polybrominated diphenyl ethers and their metabolites in fish tissues and feed

Environmental-friendly, cost-effective and fast methods were developed and validated for the analysis of seven PolyBrominated Diphenyl Ethers (PBDEs) and eight methoxylated PBDEs (MeO-PBDEs) in three distinct seafood matrices (muscle, liver and plasma) and feed using a Quick, Easy, Cheap, Efficient, Rugged and Safe (QuEChERS) extraction approach for solid samples and a Dispersive Liquid-Liquid Microextraction method (DLLME) for plasma. Instrumental analyses were performed with gas chromatography coupled to triple quadrupole mass spectrometry using electron impact source (GC-EI-MS/MS) and negative ion chemical ionization (GC-NICI-MS) to assess BDE-209. Statistical validation showed recoveries for all target substances near 100% with average Relative Standard Deviation (RSD) lower than 9% and recovery standards higher than 65% (average RSD below 20%). Average calculated Method Detection Limits (MDLs) were lower than 65 pg·g−1 wet weight (WW) for muscle, 5.35 ng·g−1 WW for liver, 4.50 ng·g−1 WW for feed, and 0.60 ng·mL−1 for plasma samples. Quality assurance and quality control practices were comprehensively described. Methods scored high in an analytical Eco-scale, thus being classified as “an excellent green analysis”. Finally, real seafood samples collected in local markets and local fishermen were analyzed. Positive samples presented both PBDEs and MeO-PBDEs in safe amounts (0.28–125.80 ng·g−1 WW) for human consumption.

QuEChERS extraction for multi-residue analysis of PCBs, PAHs, PBDEs and PCDD/Fs in biological samples

In this study, a fast and rugged method is presented for the analysis of PCBs, PAHs, PBDEs and PCDD/Fs in biological tissues using a simple Quick, Easy, Cheap, Efficient, Rugged and Safe (QuEChERS) extraction and a clean-up by Gel Permeation Chromatography (GPC) and silica Solid Phase Extraction (SPE). Development was performed on blue mussels (Mytilus edulis) and Atlantic salmon (Salmo salar) for evaluation of two ranges of lipid and water content of biological tissues. Statistical validation was performed with Atlantic salmon samples. Forty-five PAHs were analyzed including the priority list of the US EPA and the European Union with 41 PCBs, 24 PBDEs and 17 PCDD/Fs. Instrumental analyses were performed on Gas Chromatography – High Resolution Mass Spectrometry (GC-HRMS). Accuracy was evaluated for PCBs and PCDD/Fs with a certified reference material furnished by the National Research Council Canada (NRCC) and also compared with results obtained by the conventional Soxhlet extraction. Statistical validation showed recoveries for PCBs, PAHs, PBDEs and PCDD/Fs close to 100% with average Relative Standard Deviation (RSD) lower than 10% and internal standard recoveries in the range of 70% with average RSD ranging from 5–15%. Average calculated Method Detection Limits (MDLs) were lower than 0.05μg/Kg for PCBs, 0.2μg/Kg for PAHs and PBDEs and 1ng/Kg for PCDD/Fs. The method is a faster and cheaper alternative to the time-consuming conventional method that has been used in most environmental laboratories.

Development and Validation of a Method for the Determination of Pesticide Residues in Beer by Liquid Chromatography–Mass Spectrometry

Research into the fate of pesticides utilized in the commercial production of hops and their subsequent usage in the brewing of beer was conducted. To address the quantitation of pesticides, an analytical method was developed for the multiresidue determination of pesticides in beer. The method utilized acidified acetonitrile extraction with salt-aided liquid–liquid partition, centrifugation, and determination by liquid chromatography with tandem mass spectrometry using positive mode electrospray ionization. Validation of the method occurred at the Pacific Agricultural Laboratory (Portland, OR) and the Trace Analytical Laboratory (University of California, Davis, CA). Method validation recoveries from control beer samples generally ranged from 70 to 120% over three levels of fortification (0.5, 1.0, and 10 ng/mL) with relative standard deviations <20%. The limit of quantitation for beer was 0.5 ng/mL, and the calculated method detection limit ranged from 0.0240 to 0.322 ng/mL.

Development and Validation of a Standardized Method for the Determination of Morpholine Residues in Fruit Commodities by Liquid Chromatography–Mass Spectrometry

An analytical method was developed for the determination of morpholine on apples and citrus. The method utilized acidified methanol extraction, centrifugation, and determination by hydrophilic interaction liquid chromatography with electrospray ionization and tandem mass spectrometry (HILIC-ESI-MS/MS). Validation of the method occurred at the Pacific Agricultural Laboratory (PAL, Portland, OR, USA) and the Trace Analytical Laboratory (TAL, UC Davis, CA, USA). Method validation recoveries from control apple, orange, lemon, and grapefruit samples ranged from 84 to 120% over three levels of fortification (0.01, 0.04, and 0.2 μg/g). The limit of quantitation (LOQ) for all commodities was 0.01 μg/g, and the calculated method detection limit (MDL) ranged from 0.0010 to 0.0040 μg/g.

CLOUD POINT EXTRACTION OF AROMATIC AMINES FROM ENVIRONMENTAL WATER SAMPLES COUPLED WITH HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY

An efficient and environmentally friendly analytical methodology was developed for the extraction and preconcentration of three aromatic amines from environmental water samples coupled with high performance liquid chromatography. It is based on the cloud point extraction of aromatic amines using non-ionic surfactant Triton X-114 as an extraction solvent. Extraction parameters such as the type and amount of surfactant, extraction temperature, extraction time, and concentration of salt were investigated. Under optimal conditions, good linearity was observed between 0.5–100 ng mL−1 for nitroanline, 2.5–500 ng/mL for 2-chloroaniline, and 3.0–800 ng mL−1 for 2-anilinoethanol, respectively, with correlation coefficient above 0.995. The relative standard deviation (RSD) of the method was less than 5.0% (n=5). The calculated method detection limit was 0.03 ng L−1 for nitroanline, 0.05 ng L−1 for 2-chloroaniline, and 0.08 ng L−1 for 2-anilinoethanol. The practical applicability of the technique was demonstrated by analyzing water samples (n=5) collected from Han River and local reservoirs. The average recoveries and relative standard deviations were in the range of 83.6–98.8% and 2.5–4.8%.

Outcompeting GC for the detection of legacy chlorinated pesticides: online-SPE UPLC APCI/MSMS detection of endosulfans at part per trillion levels

Endosulfan, the last remaining organochlorine pesticide, has been the subject of a number of international regulations and restriction/banning action plans worldwide. Occurrence of endosulfan residues in South Florida environments has been widely described in the literature for more than two decades. This work describes a selective, sensitive, and fast online solid-phase extraction (SPE) method coupled with liquid chromatography separation and tandem mass spectrometry (LC-MS/MS) for the determination of endosulfan isomers and endosulfan sulfate in water samples at low part per trillion levels with very little sample preparation. A negative atmospheric pressure chemical ionization source was carefully optimized to produce reproducible spectra of the target compounds with no adduct ion formation. Selected reaction monitoring transitions were monitored and quantitation was performed against a per-deuterated internal standard β-endosulfan (d4). The automated online SPE clean-up was performed using only 20mL of untreated water sample prior to LC-MS/MS analysis. The method was capable of separating and quantifying endosulfan within a 24-min run using acetonitrile and water as mobile phases and presenting statistically calculated method detection limits of 3, 10, and 7ng/L for endosulfan sulfate, α-endosulfan, and β-endosulfan, respectively. In addition, a QuEChERS method was successfully developed and applied for endosulfan determination in sediments/soils, floating and submerged algal mats, and small fish. Minimal matrix effects were observed in all matrices analyzed and recoveries for all analytes ranged from 50-144%. The developed methodology was applied to monitor the occurrence and to assess the potential transport of endosulfan in the Loveland Slough watershed, an area adjacent to Everglades National Park showing long-term contamination with endosulfans.

Application of ionic-liquid supported cloud point extraction for the determination of microcystin-leucine–arginine in natural waters

A cloud point extraction method has been developed using an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMiM PF 6) for the determination of a widely studied cyanotoxin (microcystin leucine–arginine, MCLR) in natural waters. Extraction parameters such as sample pH, extraction temperature, extraction time, the amount of ionic liquid and the amount of extraction volume were investigated and optimized to achieve the maximum extraction efficiency. The results obtained indicated a good linearity with the correlation coefficient of 0.995 over the range of 0.5–50 μg L −1. The relative standard deviation (RSD) of the method was 7.5% ( n = 6). The calculated method detection limit was 0.03 μg L −1 ( n = 6). The practical applicability of the technique was demonstrated by analyzing water samples ( n = 9) collected from three different sites in local reservoirs.

Determination of urine melamine by validated isotopic ultra‐performance liquid chromatography/tandem mass spectrometry

Little is known about melamine (MEL) analysis in children's urine. In this study, an isotopic ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and systematically validated for the analysis of MEL in urine. The method is easily performed and comprises acidification, solid-phase extraction (SPE) and UPLC/MS/MS analysis. (13)C(3)N(3)((15)NH(2))(3) was used as the internal standard (IS) for calibration. Transition ions m/z 127 > 85 of MEL and m/z 133 > 89 of the IS were used for quantification and m/z 127 > 68 of MEL was used for quantitative confirmation. Recovery and precision were assessed to guarantee the applicability of the method. The limit of quantification (LOQ) was 0.01 microg/mL while the calculated method detection limit was 0.006 microg/mL. The mean recoveries ranged from 96-99%. The method was then applied to analyze urine samples from children who had potentially consumed MEL-tainted dairy products during screening in Taiwan. Ten nephrolithiasis cases and 20 age- and gender-matched controls were selected for this study. Three out of the 10 nephrolithiasis cases had elevated levels of MEL. Comparatively, twenty age- and gender-matched non-nephrolithiasis controls consuming Taiwan brand milk powder all showed MEL levels lower than the detection limit except for two children with background levels of 0.02 microg/mL. The background level in these children urine samples was established by UPLC/MS/MS analysis. Positive results of urine MEL tests might be associated with nephrolithiasis in these candidates. Measurement of urine MEL concentration can be helpful in confirming MEL-related nephrolithiasis, but its clinical application needs further clarification.

Direct determination of melamine in dairy products by gas chromatography/mass spectrometry with coupled column separation

A coupled capillary column system was developed for the qualitative and quantitative determination of melamine with isotope internal standard in dairy products by gas chromatography/mass spectrometry (GC/MS) without derivatization. A 30 m of DB-5ms ((5%-phenyl)-methylpolysiloxane, 0.25 mm i.d., 0.25 μm df) coupled with a 1.5 m of Innowax (polyethylene glycol, 0.32 mm i.d., 0.25 μm df) by a quartz capillary column connector was introduced as separation column. Three advantages were discussed for the coupled system. The sample was fortified with a ring-labeled 13C 3 15N 3-melamine as an isotope internal standard and extracted by 1% of trichloroacetic acid aqueous solution. 2.2% of lead acetate solution was then added to deposit protein in the sample matrix. After purification by cation exchange cartridge, the sample solution was directly injected and detected by GC/MS. A six-point calibration curve ranging from 0.05 to 2 mg kg −1 of melamine in sample was used to establish instrument response. The recovery was 93.9–102% with relative standard deviation from 3.1 to 8.7% when isotope internal standard used. The calculated method detection limit was 0.01 mg kg −1.

Analysis of formaldehyde formation in wastewater using on-fiber derivatization–solid-phase microextraction–gas chromatography–mass spectrometry

A method has been developed for the quantification of the formation of formaldehyde during the advanced oxidation treatment (AOT) of wastewater destined for reuse. This method uses solid-phase microextraction (SPME) with on-fiber derivatization followed by gas chromatography–mass spectrometry (GC–MS) analysis. Based on calculated method detection limits (MDL) and ambient background levels, the method reporting (MRL) limit for formaldehyde was set at 10 μg/L. Precision for formaldehyde using this technique resulted in 23% relative standard deviation (RSD), while the internal standard, acetone-d 6, was only 6%. This method was used to evaluate the formation of formaldehyde in bench scale UV–AOT experiments using natural organic matter (NOM) fortified reagent water and tertiary treated wastewater effluent. Results suggest that the formation of formaldehyde increases in both the reagent water and wastewater matrices with increasing UV exposure and hydrogen peroxide concentrations, with overall higher concentrations of formaldehyde in the wastewater samples. No appreciable amount of formaldehyde formation was observed when UV was applied in the absence of hydrogen peroxide in both matrices tested.

The determination of melamine in muscle tissue by liquid chromatography/tandem mass spectrometry

In early 2007 it was determined that the compound melamine, suspected of having been involved in the deaths of numerous pets, had been fed to hogs intended for human consumption. This report describes a method for the analysis of melamine in porcine muscle tissue using solid-phase extraction (SPE) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Melamine was extracted in 50% acetonitrile in water. Homogenates were centrifuged and supernatants were acidified and washed with methylene chloride. The aqueous extracts were cleaned up using mixed-mode C8/strong cation exchange SPE and then concentrated, fortified with a stable isotope-labeled analog of melamine, and analyzed by HPLC/MS/MS. Gradient HPLC separation was performed using an ether-linked phenyl column with ammonium acetate/acetic acid and acetonitrile as the mobile phase. Multiple reaction monitoring (MRM) mode of two precursor-product ion transitions for melamine and one for the internal standard was used. A five point calibration curve ranging from 50 to 2000 ng/mL of melamine in solvent was used to establish instrument response. The method was validated by analysis of seven replicate porcine muscle tissue samples fortified with 10 ng/g of melamine. The mean recovery for the seven replicates was 83% with 6.5% relative standard deviation and the calculated method detection limit was 1.7 ng/g.

Determination of α-Amanitin in Serum and Liver by Multistage Linear Ion Trap Mass Spectrometry

This paper describes a rapid LC-MS/MS/MS method for the analysis of alpha-amanitin in serum and liver. Serum was initially prepared by precipitation of proteins with acetonitrile and subsequent removal of acetonitrile with methylene chloride. Liver was prepared by homogenization with aqueous acetonitrile and subsequent removal of acetonitrile using methylene chloride. For both matrices, the aqueous phase was then extracted using mixed-mode C18/cation exchange SPE cartridges and analyzed on a linear ion trap LC-MS system. Standards were prepared in extracts of control matrix. Seven replicate fortifications of serum at 0.001 mug/g (1 ng/g) of alpha-amanitin gave a mean recovery of 95% with 8.8% CV (relative standard deviation) and a calculated method detection limit of 0.26 ng/g. Seven replicates of control liver fortified at 1 ng/g gave a mean recovery of 98% with 17% CV and a calculated method detection limit of 0.50 ng/g. This is the first report of a positive mass spectrometric identification and quantitation of alpha-amanitin in serum and liver from suspect human and animal intoxications.

Determination of Trace Level Perchlorate in Sludge Samples by Ion Chromatography-Electrospray Tandem Mass Spectrometry

A rapid and highly sensitive method for the determination of trace level perchlorate was set up using ion chromatography-electrospray tandem mass spectrometry (IC/ESI-MS/MS) in the negative electrospray interface (ESI) and the multiple reaction-monitoring (MRM) mode. Using high capacity and hydroxide selective column IonPac AS20, perchlorate was separated by KOH eluent generated from Eluent Generator Cartridge (EGC). The transition of 100.8/84.9, 98.8/66.9 and 100.8/68.9 were monitored for confirmation of the target analyte and 98.8/82.9 for quantifying. The calculated method detection limit of quantitation ( S/N = 3) was as good as that of 0.01 μg l −1 for perchlorate. A linear calibration was obtained over the range of 0.05–100 μg l −1 with a correlation coefficient of 0.9988. The relative standard deviation for nine successive injections of 0.2 μg l −1 perchlorate was 2.3%. This method was applied for the detection of trace level perchlorate in sludge samples, which were obtained from different areas in China. The recoveries of spiked standard were 88.5%–102.2%.

Development of an extraction method for perchlorate in soils

Perchlorate originates as a contaminant in the environment from its use in solid rocket fuels and munitions. The current US EPA methods for perchlorate determination via ion chromatography using conductivity detection do not include recommendations for the extraction of perchlorate from soil. This study evaluated and identified appropriate conditions for the extraction of perchlorate from clay loam, loamy sand, and sandy soils. Based on the results of this evaluation, soils should be extracted in a dry, ground (mortar and pestle) state with Milli-Q water in a 1 ratio 1 soil ratio water ratio and diluted no more than 5-fold before analysis. When sandy soils were extracted in this manner, the calculated method detection limit was 3.5 microg kg(-1). The findings of this study have aided in the establishment of a standardized extraction method for perchlorate in soil.

Analysis of Perchlorate in Water by Reversed-Phase LC/ESI-MS/MS Using an Internal Standard Technique

A new method was developed for the analysis of perchlorate in water by using reversed-phase liquid chromatograhy/electrospray ionization-mass spectrometry/mass spectrometry (LC/ESI-MS/MS) in the negative ESI mode. Selective and sensitive perchlorate detection was obtained by monitoring the 35ClO4- --> 35ClO3- and 37ClO4- --> 37ClO3- mass transitions. The 35ClO4- --> 35ClO3- transition was quantitated against the internal standard oxygen-labeled sodium perchlorate (NaCl18O4). Sample pretreatment for the removal of major common anions and dissolved metal ions along with internal standard quantitation sufficiently compensated for ion suppression caused by the matrix. The 37ClO4- --> 37ClO3- transition was examined to provide additional specificity. The method sensitivity, accuracy, and precision were investigated by analyzing fortified blank samples, field samples, and performance evaluation samples. The results (1.01-13.5 microg/L) for the proficiency evaluation samples differed from the certified values (1.04-14.1 microg/L) by 3-18%. The developed reversed-phase LC/ESI-MS/MS method was rapid, accurate, and reproducible. The calculated method detection limits were 0.007 microg/L for deionized reagent water and 0.009 microg/L for synthesized reagent water, respectively. The minimum reporting limit was conservatively set to 0.05 microg/L.

Improved application of ion chromatographic determination of carboxylic acids in ozonated drinking water

A direct ion chromatographic method of measuring carboxylic acids was modified and expanded to include measurement of eight components at parts-per-billion levels. These components, listed by eluting order, were acetate, propionate, formate, pyruvate, glyoxalate, dichloroacetate, oxalate and ketomalonate. The calculated method detection limits were 2–6 μg/l. Preliminary data were obtained by using California state project water from the filter influent of the Oxidation Demonstration Plant of the Metropolitan Water District of Southern California. Oxalate was measured at levels above 200 μg/l, formate above 100 μg/l, acetate above 50 μg/l, pyruvate and glyoxalate at approximately 30 μg/l and propionate and ketomalonate at trace levels near the detection limits. This method utilizes a new preservative, benzalkonium chloride, as a substitute for the environmentally unsafe mercuric chloride that had previously been used. Preservation studies indicate that all eight compounds are stable for a testing period of 30 days when benzalkonium chloride is maintained at or above 30 mg/l in the water sample.