Method Detection Limit Values Research Articles

Development of analytical methods and method validation for the qualitative and quantitative determination of Carboxymethyl Cellulose (CMC) in yogurt and ayran

This study presents the development and validation of analytical methods for the qualitative and quantitative determination of Carboxymethyl Cellulose (CMC) in yogurt and ayran. The methods were evaluated for their detection limit (LOD), quantification limit (LOQ), and method detection limit (MDL) across multiple samples, demonstrating robust sensitivity with MDL and LOD values of 0.03% for both yogurt and ayran. Recovery studies showed high accuracy, with recovery rates between 98% and 100%, and consistent recovery within the acceptable range of 97–103%, reinforcing the methods' reliability. The quantitative analysis exhibited strong repeatability and reproducibility, with low relative standard deviations (RSDr and RSDR), confirming minimal intra-day and inter-day variability. The calibration curves for CMC analysis demonstrated excellent linearity with high coefficients of determination (R2 = 0.9985 for yogurt and 0.9951 for ayran), ensuring accurate quantification over a wide concentration range. Measurement uncertainty analysis further validated the methods' precision and accuracy, showing low relative uncertainties for trueness, repeatability, and reproducibility. Robustness evaluations indicated that the methods maintained consistent recovery rates despite variations in pH, heating time, and sample quantity, highlighting their reliability under different conditions. For qualitative analysis, the visual images method showed exceptional performance with perfect sensitivity and specificity, accurately identifying all positive and negative samples without any false positives or negatives. This high level of accuracy makes the visual images method a valuable tool for ensuring product safety and compliance with quality standards in the dairy industry. Overall, the validated analytical methods for CMC detection in yogurt and ayran demonstrated high precision, accuracy, and reliability, making them essential for quality control and regulatory compliance in dairy production.

An extensive clean-up method for extraction of 17β-estradiol from eel aquaculture waste solids for quantitation via high-performance liquid chromatography tandem-mass spectrometry

The use of 17β-estradiol (E2) in aquaculture feed increases growth and promotes feminization in freshwater eels. E2 and its metabolites (estrone (E1) and estriol (E3)) must be accurately measured in solid and liquid waste streams to ensure proper management. For reliable quantitation of estrogens in complex aquaculture waste solids, a rigorous clean-up method is imperative. The focus of this study was to assess, optimize, and validate a quick, easy, cheap, effective, rugged, and safe (QuEChERS) technique for extraction of estrogens from aquaculture waste solids and quantitation via liquid chromatography tandem-mass spectrometry (LC-MS/MS). Waste solids were collected from a recirculating aquaculture system containing American eels. Waste solids samples (2 g) were spiked to 50 μg kg−1 of E1, E2, and E3 and processed using 800 mg magnesium sulfate (MgSO4) and 400 mg of sodium acetate (NaOAc) as extraction salts. Two dispersive solid phase extraction (dSPE) steps were implemented to achieve optimal E2 recovery efficiency (RE (%)) in preliminary experiments (RE (%) = 102%; RSD = 5%). RE (%) for E1 and E3 were 87% (RSD = 54%) and 60% (RSD = 83%), respectively. Method performance characteristics were further assessed for E2 only and included specificity, linearity, accuracy (RE (%) and process efficiency (PE (%))), precision (intra-day precision, and inter-day precision), matrix effects, method detection limit (MDL), and limit of quantitation (LOQ). MDL and LOQ values for E2 were 0.7 and 2.3 μg kg−1, respectively. PE (%) and RE (%) were excellent (99–101% and 99–100%, respectively) and matrix effects were minimal (99 and 101%). The results of this study indicate that this method can be used for quantitation of E2 in aquaculture waste solids.

Simultaneous determination of non-steroidal anti-inflammatory drugs and natural estrogens in the mussels Mytilus edulis trossulus

In this study, an ASE (Accelerated Solvent extraction)-SPE (Solid Phase Extraction)-GC/MS(SIM) method for the simultaneous determination of five non-steroidal anti-inflammatory drugs (NSAIDs: ibuprofen (IBU), paracetamol (PAR), diclofenac (DIC), naproxen (NAP) and ketoprofen (KET)) and three natural estrogens (estrone (E1), 17β-estradiol (E2), estriol (E3)) in mussels was proposed, which is simple, cheap and easy for use in environmental laboratories. For the first time, the sorbents: PSA (Primary Secondary Amine) and FLORISIL®, placed directly inside the extraction cells, were used for the improvement of the ASE procedure for the isolation of these pollutants from mussel samples. The application of FLORISIL® especially allowed the purification of the extract to increase recovery, without the loss of analytes, or prolongation of the extraction time. The proposed ASE-SPE-GC/MS(SIM) method was validated (the method detection limit values were in the range of 1 ng/g dry weight (d.w.) for IBU to 7 ng/g d.w. for E1; the measurement intermediate precision was between 0.24% and 7.85%; the mean recovery was in the range of 80–118%) and used for the determination of NSAIDs and estrogenic hormones in whole tissue of the mussels Mytilus edulis trossulus collected from the Gulf of Gdansk (southern Baltic Sea). IBU, NAP, DIC and E1 were determined in these samples; however, the pharmaceuticals were found only in smaller (with a length of 2–3 cm) individuals. The observed differences in the concentrations of CEC in smaller and older mussel organisms were fully discussed. Summarizing, this method could be used for monitoring these CEC in such organisms in order to expand our knowledge of their influence on the water ecosystem, however, in such investigations smaller mussel organisms should be used.

Evaluation of multiple alternative instrument platforms for targeted and non-targeted dioxin and furan analysis.

The use of gas chromatography coupled to high-resolution magnetic sector mass spectrometers (GC-HRMS) is well established for dioxin and furan analysis. However, the use of gas chromatography coupled to triple quadrupole (MS/MS) and time of flight (TOF) mass spectrometers with atmospheric pressure ionization (API) and traditional electron ionization (EI) for dioxin and furan analysis is emerging as a viable alternative to GC-HRMS screening. These instruments offer greater versatility in the lab for a wider range of compound identification and quantification as well as improved ease of operation. The instruments utilized in this study included 2 API-MS/MS, 1 traditional EI-MS/MS, an API-quadrupole time of flight mass spectrometer (API-QTOF), and a EI-high-resolution TOF (EI-HRTOF). This study compared these 5 instruments to a GC-HRMS using method detection limit (MDLs) samples for dioxin and furan analysis. Each instrument demonstrated acceptable MDL values for the 17 chlorinated dioxin and furans studied. The API-MS/MS instruments provide the greatest overall improvement in MDL value over the GC-HRMS with a 1.5 to 2-fold improvement. The API-QTOF and EI-TOF demonstrate slight increases in MDL value as compared with the GC-HRMS with a 1.5-fold increase. The 5 instruments studied all demonstrate acceptable MDL values with no MDL for a single congener greater than 5 times that for the GC-HRMS. All 5 instruments offer a viable alternative to GC-HRMS for the analysis of dioxins and furans and should be considered when developing new validated methodologies.

Assessment of the trace element distribution in soils in the parks of the city of Zagreb (Croatia).

This paper presents the results of the preliminary testing of the selected trace elements in the soils of several parks in the city of Zagreb, Republic of Croatia. In each park, the samples were taken from several points-at various distances from the roads. The samples were taken at two different depths: 0-5 and 30-45cm. Composite samples were done for each sampling point. Microwave-assisted wet digestion of the soil samples was performed and the determination by ICP-AES technique was done. Results obtained for Al, As, Ba, Mn, Ti, V, and K are in a good agreement with the results published in the scientific literature so far. The mass fraction values of Cd, Cr, Cu, Ni, Pb, and Zn are somewhat higher than the maximum values given in the Croatian Directive on agricultural land protection against pollution. Be, Mo, Sb, Se, and Tl in the samples were present in the concentrations that are lower than their method detection limit values.

Evaluation of thermal desorption analysis on a portable GC–MS system

ABSTRACTThe HAPSITE-ER-TD (Hazardous Air Pollutants on Site Extended Range HAPSITE-ER) portable gas chromatograph–mass spectrometer (GC–MS) combines the sensitivity of a thermal desorption (TD) GC–MS with the advantages of field-portable instrumentation. Though previous iterations of the HAPSITE have been extensively evaluated in the literature, performance assessment of the TD-equipped instrument is lacking. In this manuscript, the variability in the HAPSITE-ER-TD response was established for both internal standards and test compounds across three instruments over a 5-week time course. These data show poor normalised internal standard reproducibility with %RSD values from 17.84% to 49.97% on the HAPSITE-ER-TD when compared to a bench-top instrument (%RSD < 11.6%), suggesting that use of TD tubes preloaded with an internal standard may be valuable for normalisation purposes. Though our determined method detection limit (MDL) values reveal that substantial variabilities exist between separate HAPSITE-ER-TD systems, MDL values comparable to the standard bench-top equipment can be achieved. Additionally, data generated with the TO-15/TO-17 65 component target compound mix and JP-8 jet fuel show statistically significant (p value = 0.0014) compound-dependent system carryover on the HAPSITE-ER-TD, indicating that procedural modifications to eliminate instrumental carryover may be necessary. This study establishes several limitations associated with the use of the HAPSITE-ER TD accessory with suggestions for addressing the shortcomings to allow for reliable field use.

Simple and fast determination of perfluorinated compounds in Taihu Lake by SPE-UHPLC-MS/MS.

A simple and fast analytical method for determination of eleven Polyfluorinated Compounds (PFCs) in source water was developed in the present work. The water sample was prepared without filtered through microfiltration membrane and 500mL of source water was enriched by the solid phase extraction (SPE). The targent compounds were analyzed by ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The optimized analytical method was validated in terms of recovery, precision and method detection limits (MDLs). The recovery values after correction with the corresponding labeled standard were between 97.3 and 113.0% for samples spiked at 5ng/L, 10ng/L and 20ng/L. All PFCs showed good linearity and the linear correlation coefficient was over 0.99. The precisions were 1.0-9.0% (n=6). As the result of the enrichment, the MDL values ranged from 0.03 to 1.9ng/L and were enough for analysis of the trace levels of PFCs in the Taihu Lake. The method was further validated in determining the source water and the results showed that PFHxS, PFHxA, PFOA and PFOS were the primary PFCs in Taihu Lake which might be different from the other researches. The method can be used for determination of PFCs in water with a stable recovery, good reproducibility, low detection limit, less solvent consumption, time saving and labor saving. To our knowledge, this is the first method that describes the effect of the filter membrane on the determination of PFCs in water which might acquire more accurate concentration of PFCs in Taihu Lake.

Fast and simple determination of perfluorinated compounds and their potential precursors in different packaging materials

A simple and fast analytical method for the determination of fourteen perfluorinated compounds (PFCs), including three perfluoroalkylsulfonates (PFSAs), seven perfluorocarboxylic acids (PFCAs), three perfluorophosphonic acids (PFPAs) and perfluorooctanesulfonamide (PFOSA) and ten potential precursors, including four polyfluoroalkyl phosphates (PAPs), four fluorotelomer saturated acids (FTCAs) and two fluorotelomer unsaturated acids (FTUCAs) in different packaging materials was developed in the present work. In order to achieve this objective the optimization of an ultrasonic probe-assisted extraction (UPAE) method was carried out before the analysis of the target compounds by liquid-chromatography-triple quadrupole-tandem mass spectrometry (LC-QqQ-MS/MS). 7mL of 1 % acetic acid in methanol and a 2.5-min single extraction cycle were sufficient for the extraction of all the target analytes. The optimized analytical method was validated in terms of recovery, precision and method detection limits (MDLs). Apparent recovery values after correction with the corresponding labeled standard were in the 69–103 % and 62–98 % range for samples fortified at 25ng/g and 50ng/g concentration levels, respectively and MDL values in the 0.6–2.2ng/g range were obtained. The developed method was applied to the analysis of plastic (milk bottle, muffin cup, pre-cooked food wrapper and cup of coffee) and cardboard materials (microwave popcorn bag, greaseproof paper for French fries, cardboard box for pizza and cinema cardboard box for popcorn). To the best of our knowledge, this is the first method that describes the determination of fourteen PFCs and ten potential precursors in packaging materials. Moreover, 6:2 FTCA, 6:2 FTUCA and 5:3 FTCA analytes were detected for the first time in microwave popcorn bags.

A fully-automated analyzer for determining haloacetic acid concentrations in drinking water

A fully-automated, on-line, real-time analyzer has been developed for preconcentration and analysis of haloacetic acids (HAAs). Preconcentration of HAAs is achieved by sample acidification and solid phase extraction onto a hydrophobic polymeric resin using sequential injection analysis (SIA). The HAAs preconcentrate is then analyzed using post-column reaction-ion chromatography (PCR-IC), which is selective for HAAs. Systematic optimization of SIA preconcentration parameters are described followed by detailed method detection limit (MDL), accuracy, precision, and linearity studies. MDL values for the individual HAA9 species range from 0.4 to 0.9μgL−1. Side-by-side comparison studies of HAAs analysis in 14 real-world drinking water samples from Alabama, Arkansas, Kentucky, Minnesota, Missouri, Mississippi, New York, Pennsylvania and Tennessee are presented that compare the optimized SIA-PCR-IC to USEPA Method 552.3. Trace levels of HAAs detected in select samples are reported, and the bias values calculated between the two methods are typically less than 5μgL−1 for eight of the nine individual HAAs.

Focused ultrasound assisted extraction for the determination of PBDEs in vegetables and amended soil

Focused-ultrasound solid-liquid extraction was developed for the extraction of polybrominated diphenyl ethers in vegetables and amended soil. Firstly, solid-phase extraction clean-up using 2g and 5 g of Florisil and 2-g silica cartridges were evaluated and elution profile was also optimised. Similar recoveries were obtained for most compounds while better recoveries were obtained for 5-g Florisil in the case of the heavier PBDEs. FUSLE extraction time (2 min) guaranteed quantitative extraction of the target analytes in the four studied matrices (69-130%). Method detection limit values were in the range of 1-5 ng g(-1) for splitless injection in a gas chromatograph coupled to a mass spectrometer and no significant improvement was obtained for large volume injection. Relative standard deviation values were between 1% and 30%. Recoveries obtained using FUSLE were compared with those obtained with microwave assisted extraction and the developed method was also applied to a certify reference material of polybrominated diphenyl ethers and polychlorinared biphenyls in sediment. Similar values were obtained in the case of carrot and pepper matrices (77-130% for FUSLE and 77-112% for MAE). However, MAE provided extraction recoveries higher than 100% for most of the BDE congeners in lettuce and amended soil.

Limit of detection and limit of quantification development procedures for organochlorine pesticides analysis in water and sediment matrices

BackgroundReliable values for method validity of organochlorine pesticides determination were investigated, in water by solid phase extraction and in sediment by Soxhlet extraction, followed by gas chromatography equipped with an electron capture detector. Organochlorine pesticides are categorized as Persistent Organic Pollutants. Hence, critical decisions to control exposure to these chemicals in the environment are based on their levels in different media; it is important to find valid qualitative and quantitative results for these components. In analytical chemistry, internal quality procedures are applied to produce valid logical results.ResultIn this study, 18 organochlorine pesticides were targeted for analysis and determination in water and river sediment. Experiments based on signal-to-noise ratio, calibration curve slope and laboratory fortified blank methods were conducted to determine the limits of qualification and quantification. The data were compared with each other. The limitation values, following Laboratory Fortified Blank, showed significant differences in the signal-to-noise ratio and calibration curve slope methods, which are assumed in the results for the sample concentration factor to be 1,000 times in water and 10 times in sediment matrices. The method detection limit values were found to be between 0.001 and 0.005 μg/L (mean of 0.002 ± 0.001) and 0.001 and 0.005 μg/g (mean of 0.001 ± 0.001). The quantification limits were found to be between 0.002 and 0.016 μg/L (mean of 0.006 ± 0.004) and 0.003 and 0.017 μg/g (mean of 0.005 ± 0.003 μg/L) for water and sediment, respectively, based on the laboratory fortified blank method. Because of different slopes in the calibration methods, it was also found that the limitation values for some components from the internal standard were higher than from external standard calibration, because in the latter a factor for injection efficiency is applied for calibration.ConclusionTechnically, there are differentiations between detection limits for quality and quantity from component to component, resulting from noise, response factors of instruments and matrix interference. However, the calculation method is the cause of differentiation for each component of the different methods. The results show that for no matter what component, the relationship between these levels in different methods is approximately: Signal to Noise : Calibration Slope = 1:10. Therefore, due to different methods to determine LOD and LOQ, the values will be different. In the current study, laboratory fortified blank is the best method, with lower limitation values for Soxhlet and solid phase extraction of OCPs from sediment and water, respectively.

Determination of polycyclic and nitro musks in environmental water samples by means of microextraction by packed sorbents coupled to large volume injection-gas chromatography–mass spectrometry analysis

In this work the development and validation of a new procedure for the simultaneous determination of 9 nitro and polycyclic musk compounds: musk ambrette (MA), musk ketone (MK), musk mosken (MM), celestolide (ADBI), phantolide (AHMI), tonalide (AHTN), traseolide (ATII), cashmeran (DPMI) and galaxolide (HHCB) in environmental water samples (estuarine and wastewater) using microextraction by packed sorbent (MEPS) followed by large volume injection-gas chromatography–mass spectrometry (LVI-GC–MS) was carried out. Apart from the optimization of the different variables affecting MEPS (i.e., nature of the sorbent, nature of the solvent elution, sample load, and elution/injection volume) extraction recovery was also evaluated, not only for water samples but also for environmental water matrices such as estuarine and waste water. The use of two deuterated analogs ([2H3]-AHTN and [2H15]-MX) was successfully evaluated in order to correct matrix effect in complex environmental matrices such as influent samples from wastewater treatment plants. Method detection limits (MDLs) ranged from 5 to 25ngL−1, 7 to 39ngL−1 and 8 to 84ngL−1 for influent, effluent and estuarine samples, respectively. Apparent recoveries were higher than 75% for all target compounds in all the matrices studied (estuarine water and wastewater) and the precision of the method, calculated as relative standard deviation (RSD), was below 13.2% at 200ngL−1 concentration level and below 14.9% at low level (20ngL−1 for all the target analytes, except for AHTN which was set at 40ngL−1 and HHCB at 90ngL−1, due to the higher MDL values presented by those target compounds). Finally, this MEPS procedure was applied to the determination of the target analytes in water samples, including estuarine and wastewater, from two estuaries, Urdaibai (Spain) and Adour (France) and an established stir-bar sorptive extraction-liquid desorption/large volume injection-gas chromatography–mass spectrometry (SBSE-LD/LVI-GC–MS) method was performed in parallel for comparison. Results were in good agreement for all the analytes determined, except for DPMI.

Determination of β-sitosterol and cholesterol in oils after reverse micelles with Triton X-100 coupled with ultrasound-assisted back-extraction by a water/chloroform binary system prior to gas chromatography with flame ionization detection

Ultrasonic back-extraction of Triton X-100 reverse micelles by a water/chloroform binary system and gas chromatography with flame ionization detection (GC-FID) was developed for extraction and determination of β-sitosterol and cholesterol in soybean and sunflower oil samples. After the homogenization of the oil samples with Triton X-100, an aliquot of 200 μL of methanol was added to the samples to form two phases. The clear Triton X-100 extract obtained by centrifugation was treated with a mixture of water (1000 μL) and chloroform (300 μL) for back-extraction of the analytes into the chloroform phase by ultrasonication. After centrifugation, the sedimented chloroform layer was withdrawn easily by a microsyringe and directly injected into the GC-FID system. The influence of several important parameters on the extraction efficiencies of the analytes was evaluated. Under optimized experimental conditions, the calibration graphs were linear in the range of 1.0–30.0 mg L −1 with coefficient of determination more than 0.994 for both analytes. The method detection limit values were in the range of 0.2–0.7 mg L −1. The lower limit of quantification values were in the range of 0.7–2.4 mg L −1. Intra-day relative standard deviations were in the range of 1.0–2.7%. This procedure was successfully applied with satisfactory results to the determination of β-sitosterol and cholesterol in spiked oil samples. The relative mean recoveries of oil samples ranged from 93.6% to 105.0%.

Analysis of haloacetic acids in drinking water using post-column reaction-ion chromatography with on-line internal standardization

A post-column reaction-ion chromatography analyzer (PCR-IC) with automated internal standardization (IS) has been optimized to determine nine haloacetic acid (HAAs) species in drinking water while operating in near real-time with a one hour analysis time. The IS-PCR-IC method requires minimal sample preparation that consists of passing water samples through cartridges to remove anions and introducing the pretreated samples into the on-line channel of the automated instrumentation. Two sets of water samples have been analyzed and method detection limit (MDL), accuracy and precision measurements have been conducted prior to the water sample analysis. The experimental MDL values for the HAA species ranged from 1.4 to 7.8 μg L−1; the accuracy ranged from 75.9 to 112%; and the precision ranged from 6.2 to 34.6%. The concentration of each HAA and the Total HAAs found in these water samples were determined using internal standardization and the results were compared to USEPA Method 552.3. The bias estimates between these two methods for Total HAA9 range from −8.3 to 12.5 μg L−1.

Accuracy, precision, and method detection limits of quantitative PCR for airborne bacteria and fungi.

Real-time quantitative PCR (qPCR) for rapid and specific enumeration of microbial agents is finding increased use in aerosol science. The goal of this study was to determine qPCR accuracy, precision, and method detection limits (MDLs) within the context of indoor and ambient aerosol samples. Escherichia coli and Bacillus atrophaeus vegetative bacterial cells and Aspergillus fumigatus fungal spores loaded onto aerosol filters were considered. Efficiencies associated with recovery of DNA from aerosol filters were low, and excluding these efficiencies in quantitative analysis led to underestimating the true aerosol concentration by 10 to 24 times. Precision near detection limits ranged from a 28% to 79% coefficient of variation (COV) for the three test organisms, and the majority of this variation was due to instrument repeatability. Depending on the organism and sampling filter material, precision results suggest that qPCR is useful for determining dissimilarity between two samples only if the true differences are greater than 1.3 to 3.2 times (95% confidence level at n = 7 replicates). For MDLs, qPCR was able to produce a positive response with 99% confidence from the DNA of five B. atrophaeus cells and less than one A. fumigatus spore. Overall MDL values that included sample processing efficiencies ranged from 2,000 to 3,000 B. atrophaeus cells per filter and 10 to 25 A. fumigatus spores per filter. Applying the concepts of accuracy, precision, and MDL to qPCR aerosol measurements demonstrates that sample processing efficiencies must be accounted for in order to accurately estimate bioaerosol exposure, provides guidance on the necessary statistical rigor required to understand significant differences among separate aerosol samples, and prevents undetected (i.e., nonquantifiable) values for true aerosol concentrations that may be significant.

Determination of nicotine, anabasine, and cotinine in urine and saliva samples using single-drop microextraction

A simple, sensitive, and inexpensive singe-drop microextraction (SDME) followed by gas chromatography and flame-ionization detection (GC-FID) was developed for determination of nicotine, anabasine, and cotinine in human urine and saliva samples. The target compounds were extracted from alkaline aqueous sample solution into an organic acceptor drop suspended on the tip of a 25-μL GC microsyringe in the aqueous sample solution. This microsyringe was also used for direct injection after extraction. Under optimized experimental conditions, calibration plots were found to be linear in the range of 0.5–25.0, 0.5–65.0, and 0.5–45.0 mg L −1 for nicotine, anabasines and cotinine, respectively. The method detection limit values were in the range of 0.33–0.45 mg L −1. Intra-day and inter-day precisions for peak area ratios were in the range of 1.3–9.2% and 2.0–7.0%, respectively. The proposed procedure was successfully applied to the determination of analytes in spiked urine and saliva samples with satisfactory results. The mean relative recoveries of spiked water samples ranged over 71.2–111.0%, with relative standard deviations varying from 2.3% to 10.0%.

Comparison of various detection limit estimates for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection

This paper addresses the variations that presently exist regarding the definition, determination, and reporting of detection limits for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection (GC-PFPD). Gas standards containing hydrogen sulphide (H 2S), carbonyl sulphide (COS), sulphur dioxide (SO 2), methyl mercaptan (CH 3SH), dimethyl sulphide (DMS), carbon disulphide (CS 2), and dimethyl disulphide (DMDS) in concentrations varying from 0.36 ppb (v/v) up to 1.5 ppm (v/v) in nitrogen were prepared with permeation tubes and introduced in the gas chromatograph using a 0.25-ml gas sampling loop. After measuring the PFPD response versus concentration, the method detection limit (MDL), the Hubaux–Vos detection limit ( x D), the absolute instrument sensitivity (AIS), and the sulphur detectivity ( D s) were determined for each sulphur compound. The results show that the MDL determined by the US Environmental Protection Agency procedure consistently underestimates the minimum concentrations of volatile sulphur compounds that can be practically distinguished from the background noise with the PFPD. The Hubaux–Vos detection limits and the AIS values are several times higher than the MDL, and provide more conservative estimates of the lowest concentrations that can be reliably detected. Sulphur detectivities are well correlated with AIS values but only poorly correlated with MDL values. The AIS is recommended as a reliable and cost-effective measure of detection limit for volatile sulphur compounds by GC-PFPD, since the AIS is easier and faster to determine than the MDL and the Hubaux–Vos detection limit. In addition, this study confirmed that the PFPD response is nearly quadratic with respect to concentration for all volatile sulphur compounds.

Determination of the method detection limits for acid extractable metals in environmental solids: a comparative approach

The accurate determination of method detection limits (MDLs) for acid extractable metals in environmental solid samples (soils, sediments and solid wastes) has been shown to be difficult because not only is it difficult to obtain a representative reference soil sample but also sample spiking is difficult. The use of reagent water as the reference matrix for the determination of MDL in soils does not reflect the matrix effect of real world samples. This paper proposes a comparative approach for determining MDLs for acid extractable metals in soils by first comparing the MDL derived from environmental surface waters with the MDL estimated from the replicate analyses of real soil samples, before assigning a rational MDL values for use in soils. This comparative approach does not require spiking soil and provides more realistic MDL values than the reagent water-based MDLs because they reflect the matrix effect of soils. This paper also provides a method for quantitative description of the matrix effect, which has been a qualitative description in the literature to date. The assigned MDL is verified using the relative standard deviation (RSD) obtained from the analysis of soils of different textures.

Estimation of Organic Carbon Blank Values and Error Structures of the Speciation Trends Network Data for Source Apportionment

Because the particulate organic carbon (OC) concentrations reported in U.S. Environment Protection Agency Speciation Trends Network (STN) data were not blank corrected, the OC blank concentrations were estimated using the intercept in particulate matter ≤2.5 µm in aerodynamic diameter (PM2.5) regression against OC concentrations. The estimated OC blank concentrations ranged from 1 to 2.4 μg/m3 showing higher values in urban areas for the 13 monitoring sites in the northeastern United States. In the STN data, several different samplers and analyzers are used, and various instruments show different method detection limit (MDL) values, as well as errors. A comprehensive set of error structures that would be used for numerous source apportionment studies of STN data was estimated by comparing a limited set of measured concentrations and their associated uncertainties. To examine the estimated error structures and investigate the appropriate MDL values, PM2.5 samples collected at a STN site in Burlington, VT, were analyzed through the application of the positive matrix factorization. A total of 323 samples that were collected between December 2000 and December 2003 and 49 species based on several variable selection criteria were used, and eight sources were successfully identified in this study with the estimated error structures and min values among different MDL values from the five instruments: secondary sulfate aerosol (41%), secondary nitrate aerosol (20%), airborne soil (15%), gasoline vehicle emissions (7%), diesel emissions (7%), aged sea salt (4%), copper smelting (3%), and ferrous smelting (2%). Time series plots of contributions from airborne soil indicate that the highly elevated impacts from this source were likely caused primarily by dust storms.

Determination of Eight Organochlorine Pesticides at Low Nanogram/Liter Concentrations in Groundwater Using Filter Disk Extraction and Gas Chromatography

Abstract Eight organochlorine pesticides may be quantitated routinely at levels below 10 parts per trillion (ng/L) in natural groundwaters. Analytes are extracted rapidly from 1 L groundwater samples by using conditioned Teflon filter disks impregnated with silica containing bonded octadecyl phase. Filter is dried briefly under vacuum, and pesticides are eluted with 10 mL ethyl acetate. The extract is dried with about 1 g anhydrous sodium sulfate and then concentrated to exactly 1 mL. Pesticides are separated in a gas chromatograph equipped with a capillary column, detected by a high-sensitivity electron capture detector, and quantitated by the method of external standards. Certified reporting limit (CRL) values for the 8 pesticides ranged between 2 and 7 ng/L. Preliminary data demonstrated that the organochlorine pesticides could be collected on the filter disks and stored up to 4 weeks in the dark at either refrigerated or ambient temperature without obvious degradation of the sample. Calculated CRL values are comparable (within a factor of 2) to method detection limit values defined by the U.S. Environmental Protection Agency.