Standard Calibration Research Articles

A novel sample preparation method based on polarity grouping for comprehensive determination of 315 pesticides and other contaminants in wolfberry by liquid chromatography-tandem mass spectrometry

A novel sample preparation method based on polarity grouping was developed for the comprehensive determination of 315 undesirable low-weight organic pollutants ranging from polar to weakly polar in wolfberry. The method involves the swelling of the sample in ammonium acetate buffer, two-phase extraction, three-phase extraction, and dispersive solid phase extraction (D-SPE) with the assistance of low-temperature centrifugation and analysis by ultrahigh performance liquid chromatography coupled with electrospray ionization tandem mass (UHPLC-ESI-MS-MS) by using the multiple reaction monitoring mode. The recoveries of the analytes with wide range of polarity were satisfactory. The matrix-fortified standard calibration curves were compared for quantification. The results of linearity were satisfactory with linear regression coefficients (R) ranging from 0.9901 to 1.000. The limits of quantification ranged from 1 μg/kg to 10.0 μg/kg, indicating the compliance of products with legal tolerances. The average recoveries for spiked wolfberry were in the range of 69.3 %–145.2 % with RSD values of 0.2 %–28.6 %. The inter-day precision was in the range of 0.2 %–27.0 %. For over 90 % of the analytes, the recoveries were 70 %–120 % with RSD values below 20 %. The application of this method in routine monitoring programs would imply a drastic reduction of both effort and time.

GC–MS determination of 7-dehydrocholesterol and cholesterol in milk to verify eco-friendly conditions in cow housing

Dairy products are consumed worldwide in large quantities and play an important role in a diet. Labelling of these products as “eco”, “bio” or “organic” has become a trend in recent years, and verification of such advertised properties directly from the dairy products themselves, without the possibility of examining the environment where they were produced, is often next to impossible. However, it is crucial for combating potential false advertising. Herein, a simple approach to distinguish between indoor and outdoor rearing based on quantitation of cholesterol and 7-dehydrocholesterol in milk samples by GC–MS was evaluated. Repeated liquid–liquid extraction into n-heptane resulted in 99% extraction yield. Quantitation by internal standard calibration method with epicoprostanol provided limits of quantitation of 0.814 µg/100 g and 5.60 µg/100 g in milk for cholesterol and 7-dehydrocholesterol, respectively. Values of parameter defined as thousandfold 7-dehydrocholesterol to cholesterol ratio ranged from 0.35 to 1.34 for outdoor reared cows in comparison with indoor category (2.14 to 2.85). A statistically significant difference (at 99% confidence level) between indoor and outdoor rearing was observed. The developed method is an efficient tool for verification of livestock living conditions and, hence, for verification of eco-friendly labelling by dairy producers.

Bioavailability Assessment of Heavy Metals and Organic Pollutants in Water and Soil Using DGT: A Review

In recent years, the diffusive gradients in the thin films (DGT) technique has also been increasingly applied to assess the bioavailability of heavy metals and organic pollutants in the soil. The combination of binding and diffusion phases made from different materials allows for the targeted determination of different target substances. This review briefly introduces the compositions and development of the DGT technique and analyzes the composition structure of DGT and the impact of environmental factors, such as pH, ion strength (IS), and dissolved organic matter (DOM), on the bioavailability evaluation of heavy metals and organic pollutants in soil. Finally, the application potential and broad application prospects of the DGT technique were expected. In addition, standardized DGT technique methods and calibration procedures are conducive to the establishment of a more stable and reliable measurement system to enhance the robustness of the DGT technique application in the soil.

Histochemical mapping of the duration of action of photobiomodulation on cytochrome c oxidase in the rat brain.

This is the first study mapping the duration of action of in vivo photobiomodulation (PBM) on cytochrome-c-oxidase (CCO). In cellular bioenergetics, CCO is the terminal rate-limiting enzyme in the mitochondrial electron transport chain, which catalyzes oxygen utilization for aerobic energy production. PBM using transcranial infrared laser stimulation (TILS) is a promising intervention for non-invasively modulating CCO in the brain. TILS of the human prefrontal cortex directly causes CCO photo-oxidation, which is associated with increased cerebral oxygenation and improved cognition. This experiment aimed to map the duration of action of in vivo PBM on CCO activity in discrete neuroanatomic locations within rat brains up to 4 weeks after a single TILS session (50 s, 1064 nm CW, 250 mW/cm2). Control brains from rats treated with a sham session without TILS (laser off) were compared to brains from TILS-treated rats that were collected 1 day, 2 weeks, or 4 weeks post-TILS. Cryostat sections of the 36 collected brains were processed using quantitative enzyme histochemistry and digitally imaged. Densitometric readings of 28 regions of interest were recorded and converted to CCO activity units of oxygen utilization using calibration standards. Data analysis (ANCOVA) compared each laser-treated group to sham with whole-brain average as a covariate. The prefrontal infralimbic cortex showed the earliest significant increase in CCO activity between 1-day post-TILS and sham groups, which continued elevated for 2-4 weeks post-TILS. Significant differences in CCO activity between 2-weeks and sham groups were also found in the lateral septum, accumbens core, CA3 of the hippocampus, and the molecular layer of the hippocampus. The medial amygdala showed a significant decrease in CCO activity between 4-weeks and sham. Further analyses showed significant inter-regional CCO activity correlations among the brain regions as the result of TILS, with the most pronounced changes at 4-weeks post-stimulation. The time course of changes in CCO activity and network connectivity suggested that TILS caused different neuroplasticity types of bioenergetic changes at different time scales, depending on brain region and its depth from the cortex. In conclusion, this controlled CCO histochemical study demonstrated a long-lasting duration of action of PBM in the rat brain.

The Effective Carbon Number of Chlorobenzenes

Detector response of 12 chlorobenzenes was investigated (mono-, di-, tri-, tetra-, penta-, and hexachlorobenzene, CBs) using flame ionization detector in a capillary gas chromatographic system. We determined the signal-reducing effect of the chlorine atom on the aromatic ring relative to the number of the chlorine substituents and expressed with the effective carbon number (ECN). Benzene was applied as a reference substance. Using the signal-modifying pattern of the chlorine atoms on the benzene's response, we developed an alternative calibration measurement method (CBs-ECN method) for the 12 CBs and compared it with classic calibration. The differences in the concentrations calculated by the two quantitative methods were under 4.5% for 11 CBs and 7% for one compound.Taking advantage of the opportunities provided by the CBs-ECN pattern it is not necessary to apply all of the 12 CBs but only one single component, the hexachlorobenzene for the calibration. With this simplification, the preparation of the calibration standards is faster, does not require purchasing all 12 CBs for each subsequent calibration, and the exposure to harm and expenses are reduced.

HPLC Analysis and Risk Assessment of 15 Priority PAHs in Human Blood Serum of COPD Patient from Urban and Rural Areas, Iasi (Romania).

One of the leading risk factors for environmental health problems is air pollution. The World Health Organization (WHO) reports that this risk factor is associated with one of every nine deaths worldwide. Epidemiological studies conducted in this field have shown a solid connection between respiratory pathology and polycyclic aromatic hydrocarbon (PAH) exposure. COPD and asthma are respiratory diseases that were shown to have a strong association with exposure to PAHs. The purpose of the present study was to assess the serum levels of 15 PAHs in 102 COPD patients and to evaluate the results according to the residence environment of the investigated subjects. Analyses were carried out using a high-performance liquid chromatograph Nexera X2-Shimadzu Japan, which was equipped with an LC-30AD pump and an SIL-30AC autosampler. Spiked matrices, procedure blanks, spiked controls, and calibration standards in the acetonitrile were used as quality-assurance samples. Benzo(a)pyrene is the main representative of PAHs and was determined in higher concentrations in subjects with COPD versus the control group from the urban area (0.90/0.47 ng/mL) and rural area (0.73/0.44 ng/mL). The values obtained for the Benzo(a)pyrene-equivalent factor indicate a higher carcinogenic potential for patients diagnosed with COPD in urban areas compared to those in rural areas. These results could be due to traffic and vehicle emissions. This research identifies the need for legislative action to decrease semi-volatile organic compounds, especially PAHs, mainly in urban cities, in order to improve environmental management and health conditions.

Stability of 10 Beta-Lactam Antibiotics in Human Plasma at Different Storage Conditions.

Recently, several studies have assessed the effects of therapeutic drug monitoring of frequently prescribed beta-lactam antibiotics, for which they were quantified in human plasma samples. Beta-lactams are considered unstable, leading to extra challenges in quantification. Therefore, to ensure sample stability and minimize sample degradation before analysis, stability studies are crucial. This study investigated the stability of 10 frequently used beta-lactam antibiotics in human plasma at relevant storage conditions for clinical use. Amoxicillin, benzylpenicillin, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, flucloxacillin, imipenem, meropenem, and piperacillin were analyzed using ultraperformance convergence chromatography tandem mass spectrometry and liquid chromatography tandem mass spectrometry. Their short-term and long-term stabilities were investigated by measuring quality control samples at low and high concentrations against freshly prepared calibration standards. Measured concentrations at each time point were compared with the concentrations at T = 0. Antibiotics were considered stable if recovery results were between 85% and 115%. Short-term stability results indicated ceftriaxone, cefuroxime, and meropenem to be stable up to 24 hours at room temperature. All evaluated antibiotics, except imipenem, were stable on ice in a cool box for 24 hours. Amoxicillin, benzylpenicillin, and piperacillin were stable for 24 hours at 4-6°C. Cefotaxime, ceftazidime, cefuroxime, and meropenem were stable at 4-6°C up to 72 hours. Ceftriaxone and flucloxacillin were stable for 1 week at 4-6°C. Long-term stability results showed that all antibiotics were stable up to 1 year at -80°C, except imipenem and piperacillin, which were stable for 6 months at -80°C. Plasma samples for amoxicillin, benzylpenicillin, cefotaxime, ceftazidime, flucloxacillin, and piperacillin may be stored for a maximum of 24 hours in a cool box. Refrigeration is suitable for plasma samples of amoxicillin, benzylpenicillin, meropenem, and piperacillin for up to 24 hours and cefotaxime, ceftriaxone, ceftazidime and cefuroxime for 72 hours. Plasma samples for imipenem should be frozen directly at -80°C. For long-term storage, plasma samples can be stored at -80°C for a maximum of 6 months for imipenem and piperacillin and 12 months for all other evaluated antibiotics.

Molecular Detection of Candida auris Using DiaSorin Molecular Simplexa® Detection Kit: A Diagnostic Performance Evaluation.

Candida auris is a globally emerging fungal pathogen that is associated with healthcare-related infections. The accurate and rapid detection of C. auris is crucial for effective infection prevention, control, and patient management. This study aimed to validate the analytical and diagnostic performance of the DiaSorin Molecular C. auris Detection Kit. The analytical specificity, sensitivity, and reproducibility of the assay were evaluated. The limit of detection (LOD) was determined to be 266 CFU/µL using the ZeptoMetrix Candida auris Z485 strain and standard calibration curves. The assay demonstrated high analytical specificity and showed no amplification against a diverse panel of bacteria and fungi. Clinical validation was conducted using deidentified residual axillary/groin surveillance culture specimens from C. auris culture-positive and culture-negative patients. The DiaSorin Molecular Detection Kit exhibited 100% agreement in sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) when compared to cultures coupled with MALDI-TOF identification. Intra- and inter-reproducibility testing demonstrated consistent and reliable diagnostic performance. This validated assay offers rapid and accurate detection of C. auris, facilitating timely implementation of infection control measures and appropriate patient care. The DiaSorin Molecular C. auris Detection Kit has the potential to aid in controlling the outbreaks caused by this emerging fungal pathogen. Providing a reliable diagnostic tool can contribute to the effective management and containment of C. auris infections in healthcare settings and ultimately improve patient outcomes.

In vitro Antioxidant, Antibiotic Complementing or Supplementing Potential and Urobactericidal Activity of Leaf Extract of Marsilea quadrifolia L.: The Water Fern

From generations, most of the communities of India are dependent on locally available ethnomedicines for tackling urogenital related issues. The efficacies of these herbal supplements for prophylactic and curative purposes need immediate scientific validation. For this, the accurate antibacterial potential of methanolic extracts of leaves of Marsilea quadrifolia L. (MMq) are investigated via each possible method of estimation including the supplementary and complementary antibacterial effects on pathogenic strains. The phytochemical constituents like carbohydrates, flavonoids, glycosides, phenolics, steroids and terpenoids are tested positive in the MMq. The total phenolic content (TPC) and total flavonoid content (TFC) are calculated to be 16.48 ± 0.4 mg/g of gallic acid equivalent and 96.33±4.4 mg/g of rutin equivalent respectively from the standard calibration curves. The IC50 value of MMq is found to be 258.55μg/ml in 1, 1 diphenyl-2-picrylhydrazyl radical (DPPH) assay by taking ascorbic acid as the standard. The extract gives significant complementary or supplementary inhibitory effects when added to certain antibiotic discs specifically against Enterococcus faecalis and Escherichia coli. The efficacy of MMq is verified and confirmed through different antibacterial assays against all the test uropathogenic bacteria. A reduction of 52%, 20.9%, 39.7% and 86.6% in number of colonies is noted in cfu/ml on treating the bacterial stains of E. coli, Staphylococcus aureus, E. faecalis and Proteus vulgaris respectively with a higher dose of MMq (1200μg) as compared to a lower dose of (200μg) in spread plate method. Present study recorded a minimum inhibitory concentration (MIC) of 2.5mg/ml of MMq each against E. faecalis, E. coli, Pseudomonas aeruginosa and 1.25mg/ml against S. aureus and P. vulgaris respectively. The preliminary reports of this study on MMq affirm an in-depth analysis of the usefulness of this plant as a miracle drug against certain uropathogens and urinary tract infections.

Hydrophilic interaction liquid chromatography (HILIC) with DAD detection for the determination of relatively non polar fungicides in orange samples

A new, sensitive, rapid, economic and validated high performance liquid chromatography/ diode array detector (HPLC/DAD) method has been developed for the determination of five fungicides namely; Carbendazim (MBC), Thiabendazole (TBZ), Metalaxyl (MET), Imazalil (IMA) and Propiconazole (PCZ). The analytical method was carried on hydrophilic interaction liquid chromatography (HILIC) column using isocratic elution of acetonitrile and water. Prior extraction of orange samples was done using a mixture of diethyl ether and ethyl acetate as an extraction solvent in liquid liquid extraction. The total run time was 15 min which makes it suitable for routine analysis of MBC, TBZ and IMA in oranges. Procedural standard calibration was applied to compensate the matrix effect. In order to measure the lowest concentration of the investigated fungicides below maximum residue limits (MRL), HPLC parameters were optimized. Mean recoveries were obtained ranging from 99.32% to 101.08% with average %RSD < 5.27%. The selected fungicides' residual quantities were successfully measured using the suggested method in various markets and organic orange samples. The investigation of carbendazim's kinetics of degradation, as well as its half-life and predicted preharvest interval (PHI), in real orange samples obtained from orange trees after being treated with the investigated fungicides, is the first to separate relative nonpolar components using HILIC.

A multi-residue method for trace analysis of pesticides in soils with special emphasis on rigorous quality control

A multi-residue trace analytical method is presented to accurately quantify 146 currently used pesticides in (agricultural) soils with varying soil properties. Pesticides were extracted using an optimized quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach and chemical analysis was carried out by liquid chromatography coupled to tandem mass spectrometry (triple quadrupole). Quantification was based on matrix-matched internal standards calibration, using 95 isotopically labeled analyte analogues. In contrast to the common approach of method validation using soils freshly spiked with analytes shortly before the extraction, our method is additionally validated via an in-house prepared partly aged soil, which contains all target pesticides and via agricultural field soils with native pesticide residues. The developed method is highly sensitive (median method limit of quantification: 0.2 ng/g), precise (e.g., median intra-day and inter-day method precision both ~ 4% based on field soils), and true ((i) quantified pesticide concentrations of the partly aged soil remained stable during 6 months, were close to the initially spiked nominal concentration of 10 ng/g, and thus can be used to review trueness in the future; (ii) median freshly spiked relative recovery: 103%; and (iii) participation in a ring trial: median z-scores close to one (good to satisfactory result)). Its application to selected Swiss (agricultural) soils revealed the presence of in total 77 different pesticides with sum concentrations up to 500 ng/g. The method is now in use for routine soil monitoring as part of the Swiss Action Plan for Risk Reduction and Sustainable Use of Plant Protection Products.Graphical abstract

The calibration of transfer standards for the measurement of 222Rn at NIM

A high-purity germanium (HPGe) gamma-ray spectrometer and an Alpha-GUARD radon monitor are the activity and activity concentration transfer standards of 222Rn, respectively. The gaseous 222Rn standard source traceable to the NIM's absolute standardization apparatus of 222Rn was developed for calibrating these transfer standards. The calibration results of HPGe detector at three different distances show that the uncertainties of experimental efficiency are less than 0.77% (k = 1). Meanwhile, the Monte Carlo (MC) simulation was carried out at wider distances range for the HPGe calibration as well, and the deviation at same three distances between experiments and simulations results is within ±3.0%. The advantage of calibration using MC simulation and the possible reasons for the deviation were discussed in detail in this article. In addition, a reference activity concentration environment based on the gaseous 222Rn standard source was also developed to calibrate the radon monitor, and the typical uncertainty for calibration factor of Alpha-GUARD radon monitor could be reduced to 1.9% (k = 1).

Calibration of Heat Distortion and Vicat Softening Temperature Apparatus

Heat distortion and Vicat softening temperature apparatus are mainly used for measuring the thermal deformation temperature and Vicat softening point temperature of non-metallic materials. Parameters such as temperature indication error, heating rate error, deformation indication error, and mass indication error of loaded weights can directly decide the quality of heat distortion and Vicat softening temperature apparatus. There is no relevant calibration specification or method for heat distortion and Vicat softening temperature apparatus in China. This article presents a novel calibration method by determining corresponding environmental conditions, calibration standards, and calculation equations. The calibration results show that the method is scientific and practical for metrological performance evaluation of heat distortion and Vicat softening temperature apparatus.

Joint Collaboration on Comparing NOAA’s Ground-Based Weather Radar and NASA–JAXA’s Spaceborne Radar

Abstract The National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration (NOAA) have a long and successful history of weather radar research. The NOAA ground-based radars—WSR-88D network—provide nationwide precipitation observations and estimates with advanced polarimetric capability. As a counterpart, the NASA–JAXA spaceborne radar—the Global Precipitation Measurement Dual-Frequency Precipitation Radar (GPM DPR)—has global coverage and higher vertical resolution than ground-based radars. While significant advances from both NOAA’s WSR-88D network and NASA–JAXA’s spaceborne radar DPR have been made, no systematic comparisons between the WSR-88D network and the DPR have been done. This study for the first time generates nationwide comprehensive comparisons at 136 WSR-88D radar sites from 2014 to 2020. Systematic differences in reflectivity are found, with ground radar reflectivity on average 2.4 dB smaller than that of the DPR (DPR version 6). This research found the discrepancies between WSR-88D and DPR arise from different calibration standards, signal attenuation correction, and differences in the ground and spaceborne scattering volumes. The recently updated DPR version 7 product improves rain detection and attenuation corrections, effectively reducing the overall average WSR-88D and DPR reflectivity differences to 1.0 dB. The goal of this study is to examine the systematic differences of radar reflectivity between the NOAA WSR-88D network and the NASA–JAXA DPR and to draw attention to radar-application users in recognizing their differences. Further investigation into understanding and alleviating the systematic bias between the two platforms is needed.

Study on Calibration of Oxygen Transmission Rate Measurement Apparatus for Plastic Film and Sheeting

The oxygen transmission rate measurement apparatus for plastic film and sheeting is mainly used to measure the oxygen transmission rate and oxygen transmission coefficient of plastic film and sheeting. Oxygen transmission tests can analyze and solve the problems caused by oxygen, such as oxidation deterioration. At present, there is no relevant calibration specification or method for oxygen transmission rate measurement apparatus for plastic film and sheeting in China. This article presents a novel calibration method to evaluate the measurement accuracy and temperature control performance of the apparatus by determining corresponding environmental conditions, calibration standards, and calculation equations. The calibration results show that the calibration method is scientific and practical for the metrological performance evaluation of oxygen transmission rate measurement apparatus for plastic film and sheeting.

Characterisation of hydrophone sensitivity with temperature using a broadband laser-generated ultrasound source

In this work, we present a novel method for characterising the relative variation in hydrophone sensitivity with temperature, addressing a key aspect of measurements in the field of ultrasound metrology. Our study focused on a selection of miniature ultrasonic hydrophones commonly used in medical applications. The method is based on using water as a temperature-sensitive laser-generated ultrasound (LGUS) source for calibration, allowing for flexible characterisation across a wide temperature range. The measurements were performed using both the LGUS method and the established self-reciprocity method. Our results demonstrate good agreement within 5% between the two methods, validating the effectiveness of the LGUS approach. We found that the sensitivity of the tested hydrophones exhibited low temperature dependence less than −0.2% per ∘C within the studied temperature range from 17 ∘C up to 50 ∘C. The presented LGUS method offers greater flexibility than current approaches as it allows for characterisation of membrane hydrophones with small element sizes and non-electrical transducers. By combining the relative sensitivity variation obtained through the LGUS method with the standard calibration at room temperature, absolute values of hydrophone sensitivity can be determined. The expanded uncertainty of our measurements, which was evaluated at temperature intervals of 8 ∘C, was determined to be on average 10%. Our work provides valuable insights into the temperature dependence of hydrophone sensitivity and lays the foundation for further investigations in this area. The LGUS method holds promise for future enhancements, such as increased bandwidth of the LGUS source and frequency domain analysis, to explore the frequency dependency of sensitivity variation with temperature.

Determination of eight herbicide residues in foodstuffs of plant origin by gas chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry

This study uses gas chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry (GC–APCI–MS/MS) to detect and identify 8 herbicide residues in foodstuffs of plant origin. In contrast to the extensive fragmentation caused by traditional electron impact ionization (EI) with high energy, APCI is a soft ionization technique. Therefore, more molecular ions and/or protonated molecules are present, improving the sensitivity and selectivity of analytical methods. The standard calibration curves ranged from 0.5 to 50 ng/mL; recoveries were in the range of 76.3–108.5%. The limit of quantification was 1.0 µg/kg for all samples. The results demonstrate the potential of GC–APCI–MS/MS to routinely detect and identify 8 herbicide residues in foodstuffs of plant origin.

ATR-FTIR spectroscopy combined with chemometrics for quantification of total nicotine in Algerian smokeless tobacco products

Chemma, an oral moist snuff widespread used in Algeria, is prepared from grounded tobacco and inorganic salts or other plant materials. In addition to its adverse health issues, Chemma contains unknown amounts of nicotine and other harmful constituents. Twenty seven samples of commercial products and tobacco leaves varieties were characterized in the aim to quantitatively determine total nicotine by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy coupled with two regression methods (univariate and multivariate). For this purpose, a highly specific-to-analyte extraction method was applied on calibration and test sets of standards for a wide concentration range. The optimal analytical models were evaluated by selecting the appropriate spectral measurement, spectral pre-processing strategies and critical figures of merit estimated according to the latest approaches. Then, the predictive ability of the method was demonstrated with the elliptical joint confidence region test and with comparing to results in literature.The linear baseline correction and the extended multiplicative scatter correction pre-processing of the combined reduced spectral regions 1333–1299 and 740–690 cm−1 followed by partial least squares regression (PLSR) offered the best analytical outcomes. Using this latter, total nicotine content in the manufactured smokeless tobacco (ST) products have been found ranging from 3.9 to 12.6 mg/g of dry weight; while in the ST leaves, it was between 5.9 and 45.0 mg/g, dry weight basis. The developed method, besides to the high predictive performance, provides advanced statistical tests that can qualitatively assess the target analyte in real sample spectra, allowing more reliable result.With the increasing number of new products containing complex agents and adulterants, the aforementioned method can be successfully adapted to routine analyses for rapid quality control of nicotine in ST and cigarettes.

Improvements on the analysis methods of asphalt fumes generated in asphalt production and construction

Asphalt fumes are generated when producing and processing asphalt materials, and polycyclic aromatic hydrocarbons (PAHs) are commonly used as indicators to evaluate the hazardous potentials of asphalt fumes. However, the quantitative analysis of PAHs in asphalt fumes remains a challenge. Particularly, the influences of matrix compounds in asphalt fumes on PAH quantification have not been evaluated, even though matrix effect may lead to biased results. To address such a research gap, this study (1) examined the matrix effect in analyzing PAHs in asphalt fumes, (2) evaluated the effectiveness of clean-up methods, and (3) assessed the effectiveness of different methods for matrix effect compensation. Asphalt fumes from seven asphalt materials or conditions were collected and analyzed. Four clean-up methods were evaluated for their influences on PAH identification and matrix effect mitigation. Two approaches were experimented for matrix effect compensation. This study found an obvious matrix effect in the quantitative analysis of PAHs in asphalt fumes. None of the clean-up methods can effectively remove the matrix effect, but both the standard addition calibration (SAC) method and the internal standard calibration (ISC) method can compensate such effect. The findings are expected to assist in accurate quantification and evaluation of PAHs in asphalt fumes.

Method for quantitative analysis of the marker substrate ABCB1-protein fexofenadine in Caco-2 cell lysate

One way to analyze the activity of the ABCB1 protein is to assess the accumulation of its substrate fexofenadine (F.) inside the test cells. The goal is to develop and validate a method for the quantitative analysis of F. in Caco-2 cell lysate using HPLC-MS/MS. Materials and methods. Caco-2 cell lysate was used as a matrix. The analysis was performed on an "Ultimate 3000" chromatograph with a TSQ Fortis triple quadrupole mass detector, a UCT Selectra C18 4.6 mm*100 mm 5 µm column in a gradient elution mode. The mobile phase rate was 0.3 ml/min, the sample volume was 20 µl, the ionization mode was positive, and the internal standard was amantadine (ng/ml). Sample preparation — precipitation of cell lysate protein with acetonitrile. The method was validated for the following parameters: selectivity, linearity, lower limit of quantitation (LLOQ), correctness, precision, sample transfer and sample stability. Results. Chromatograms of the blank lysate of Caco-2 cells showed no peaks with retention times characteristic of F. (5.70 min) and amantadine (3.58 min). NPKO F. was 0.5 ng/ml. F.'s transfer did not exceed 20% of NPKO, and amantadine — 5%. Based on the results of the analysis of three series of calibration standards (0.5; 1; 1.5; 5; 10; 25; 40; 50 ng/ml), linear regression equations were obtained, the correlation coefficients exceeded 0.99. Accuracy and precision were assessed within and between cycles by analyzing F. solutions in the matrix (0.5; 1.5; 25 and 40 ng/ml) within three cycles. The parameters did not exceed 20% for LLPO and 15% for other points. The stability of F. solutions (1.5 and 40 ng/ml) in the lysate was analyzed during storage at room temperature, after 3-fold freezing-thawing, storage at -80 °C for 60 days, after sample preparation and being in the autosampler for 24 hours. The accuracy was within 15% of the nominal values. Conclusions. A method for the quantitative determination of F. in Caco-2 cell lysate using HPLC-MS/MS has been developed and validated.