Photometric Detection Research Articles

Fully Integrated, Automated, and Smartphone Enabled Point-of-Source Portable Platform With Microfluidic Device for Nitrite Detection.

Excess limit of Nitrites, which are prevalent within environmental and physiological systems, have severe detrimental effects, thus point-of-source detection becomes an important requirement to take suitable preventive measures. This paper presents the design and development of a standalone, point-of-source, portable, low-cost, automated and integrated microfluidic system for quick detection and quantification of nitrite. Based on multiphysics simulations, a disposable polydimethylsiloxane (PDMS) microfluidic device was employed to carry out the controlled Griess reaction based assay. A low-cost 3D printed syringe pump was developed to inject the sample and reagent. Photometric detection was employed using light emitting diode (LED) and photodiode. A transimpedance amplifier circuit was designed and fabricated to achieve amplified photodiode output with reduced noise. An off-the-shelf microprocessor was used to integrate the whole system and a smartphone application (app) was developed to control the complete system and store the data. Interaction between the application and the microprocessor was achieved using Bluetooth connectivity. Spectrophotometric validation was performed and a calibration equation was obtained which was used to convert the device voltage output to absorption, through specially programmed android app. All the components were integrated in a 3D printed platform whose virtues such as ease of usage and affordability makes, quantification of nitrite, a simple and real time process wherein the limit of detection and limit of quantification values are found to be 0.07103 ppm and 0.21524 ppm respectively with good repeatability.

A flame photometric detector with a silicon photodiode assembly for sulfur detection

A flame photometric detector with a silicon photodiode assembly instead of a photomultiplier tube for sulfur detection was developed and evaluated. The photosensitive area of photodiode, the optical design, and band-pass filters, were optimized. It was found that the optimal photosensitive area of the photodiode was 100 (mm)2, and three focus lenses combined with a broad band-pass filter of 378/52 nm and a QB21 glass yielded the best result. This design fully utilized the wide emission spectrum of S2*, the response characteristics of silicon photodiode, and effective absorption of strong emission spectrums of OH* at wavelength around 310 nm by QB21 glass. The limits of detection for nine kinds of sulfur containing compounds were between 5.8 × 10−12 to 9.5 × 10−12 g s−1. This mode provided a linear response of 3 orders of magnitude for compounds being tested and a selectivity of sulfur over carbon of 105. It is demonstrated for the first time that the overall performance of the flame photometric detector integrated with a silicon photodiode assembly work at room temperature was comparable to a conventional detector coupled with a photomultiplier tube, with advantages of short equilibration time, robust to electromagnetic interference and vibration, and low cost. The new detector can find wide application in gas chromatography and on-line monitoring instruments for sulfur measurement.

Evaluation of the Perceptual Interaction among Sulfur Compounds in Mango by Feller's Additive Model, Odor Activity Value, and Vector Model.

The volatile compounds found in mangoes (Mangifera indica L.) obtained from three cultivars (TN, Tainong no. 1; KT, Keitt; and ZL, Zill; grown in China) were comprehensively analyzed by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS), and GC-flame photometric detection (GC-FPD) analyses. The results showed that 42, 35, and 45 compounds were identified in the TN, KT, and ZL samples, respectively. From these compounds, 19, 14, and 20 compounds were identified as important odorants with odor activity values (OAVs) greater than 1. Of these, 5, 7, and 5 sulfur compounds were respectively identified in the three samples by FPD. Importantly, methanethiol, ethanethiol, 1-propanethiol, methyl propyl disulfide, and 3-mercapto-1-hexanol were detected for the first time in mango. Five sulfur compounds were selected to study interactions using Feller's additive model, OAV, and Vector model. Among these mixtures, six mixtures exhibited a masking effect, three mixtures presented an additive effect, and one mixture showed a synergistic effect.

High Sensitivity Monitoring Device for Onboard Measurement of Dimethyl Sulfide and Dimethylsulfoniopropionate in Seawater and an Oceanic Atmosphere

An automated device has been developed to measure aqueous dimethyl sulfide (DMSaq), its precursor dimethylsulfoniopropionate (DMSP), and atmospheric gaseous dimethyl sulfide (DMSg). In addition to having a role in the oceanic atmosphere, DMS and DMSP have recently gained substantial interest within the biosciences and are suspected as chemoattractants for predators searching for prey. To provide the spatial resolution relevant for biogeochemical functions, fast and on-site analysis of these compounds is an important technique. The system described measures the dimethyl sulfur compounds by sequential vaporization of DMSaq and DMSP to their gas phase, which is then analyzed by chemiluminescence detection (SVG-CL). The device has five analysis modes (full, DMS, water, gas, and DMSP mode) that can be selected by the user depending on the required analyte or desired sampling rate. Seawater analyses were performed by the developed SVG-CL system and, simultaneously, by an ion molecule reaction-mass spectrometer and a gas chromatograph-flame photometric detector to verify quantitative analysis results. Results obtained by the new method/device agreed well with those by the other methods. Detection limits of the SVG-CL system are 0.02 ppbv and 0.04 nM for DMSg and DMSaq/DMSP, respectively, which are much better than those of the mass spectrometer. The SVG-CL system can be easily installed and operated on a boat. Spatial variability in DMS and DMSP off the coast of Japan were obtained, showing significant changes in the concentrations of the components at the brackish/saline water interface and at the channel between the closed and open seas.

Identification of the source of volatile sulfur compounds produced in milk during thermal processing

Volatile sulfur compounds in ultra-pasteurized (UP) milk are the major contributors to sulfur/burnt and eggy flavors, and these flavors are disliked by consumers. Previous research has established distinct differences in flavor profiles of fluid milk processed by high temperature, short time pasteurization (HTST) and UP by direct steam injection (DSI-UP) or indirect heat (IND-UP). An understanding of the contribution of the individual milk proteins to sulfur off-flavors would clarify the source of sulfur flavors in UP milks. The objective of this study was to determine the source of volatile sulfur compounds in fluid milk with a specific focus on the comparison of heat treatment effects on milks by HTST and UP. Formulated skim milks (FSM) were manufactured by blending micellar casein concentrate and serum protein isolate (SPI). Three different caseins as a percentage of true protein (FSM95, FSM80, and FSM60) were formulated to determine the source of sulfur/burnt and eggy flavors. Freshly processed micellar casein concentrate or SPI were blended to achieve a true protein content of about 3.2%. Raw skim milk served as a control. Skim milk and FSM were pasteurized at 78°C for 15 s (HTST) or 140°C for 2.3 s by IND-UP or DSI-UP. The experiment was replicated twice. Sensory properties of milks and FSM were documented by descriptive sensory analysis. Volatile sulfur compounds in milks and FSM were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry combined with a sulfur selective flame photometric detector. The FSM with higher SPI as a percent of true protein had higher sensory sulfur/burnt and eggy flavors along with elevated concentrations of hydrogen sulfide and carbon disulfide compared with skim milk or FSM with lower proportions of SPI. Sulfur compounds including dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, dimethyl sulfoxide, and methional were not associated with sulfur/burnt and eggy flavors, which suggests that these compounds may not specifically contribute to the sulfur/burnt and eggy off-flavors of UP milks. Sensory panelists found higher overall aroma impact, and cooked, sulfur/burnt, and eggy flavors for DSI-UP, followed by IND-UP and HTST. The combination of sensory and instrumental methods used in the current study effectively identified that milk serum proteins are the source of sulfur compounds in milk, and further confirmed the contribution of hydrogen sulfide and carbon disulfide to eggy and sulfur/burnt flavors, respectively.

Quantitative determination of 0.05 % chlorhexidine solution by capillary electrophoresis

The aim of the work was to estimate the quantitative content of 0.05 % chlorhexidine solution by capillary electrophoresis.Materials and methods. The object of the study was the drug 0.05 % solution of chlorhexidine for local and external use of pharmacopoeia quality. The study was carried out on a Kapel-104T device, equipped with an ultraviolet photometric detector and personal computer with the Multichrom software.Electrophoretic determination of the quantitative content of chlorhexidine was carried out in the UV region of the spectrum at a wavelength of 254 nm with a positive voltage on a capillary of 16 kV and a recommended capillary thermostating from 20 °C to 30 °C. The sample was introduced in pneumatical mode in the 30 mbar for 5 seconds. The analysis time was 5 minutes. As the leading electrolyte an aqueous solution consisting of 0.6 % solution of imidazole, 0.6 % solution of sodium tetraborate and 0.5 % solution of tartaric acid were used. The determination of chlorhexidine in the test solution was carried out in the UV spectral region at a wavelength of 254 nm, since at this wavelength one of the absorption maxima of the indicated drug was observed.Results. The validation analysis showed that the technique is characterized by specificity, linearity in the concentration range from 100 μg/ml to 700 μg/ml (y = 0.3438х - 12.4789; r = 0.9913), accuracy for chlorhexidine levels of 80–120 % (R = 98.82–100.44 %), precision (Sr = 0.44–0.61 %). The relative error of the result of separate determination of chlorhexidine in 0.05 % solution using capillary electrophoresis was 1.28 %.Conclusions. Quantitative determination of 0.05 % chlorhexidine solution by capillary electrophoresis was carried out and the parameters of the validation of the electrophoretic technique were established. The proposed electrophoretic conditions can serve as the basis for the development of methods for the quantitative determination of chlorhexidine bigluconate as part of this drug.

The degradation behaviour, residue distribution, and dietary risk assessment of malathion on vegetables and fruits in China by GC-FPD

The gas chromatography-flame photometric detector (GC-FPD) was used to detect malathion residues content in vegetables (cherry tomatoes and broccoli) and fruits (mulberries, cranberries, and figs). The recoveries of samples were 76.2 ± 3.5%–103.9 ± 3.6% at a spike level of 0.01–10 mg/kg, the relative standard deviation (RSDs) were 2.1%–7.3%, and the limit of quantification (LOQs) were 0.01–0.02 mg/kg. On the basis of the normative field trials, the degradation half-life of malathion were 1.10–2.15 days, which indicated that malathion degrades quickly. The final distribution of malathion residues in various vegetables and fruits varied from <0.01 to 0.58 mg/kg. The long-term dietary risk assessment results showed that the national estimated daily intake (NEDI) of malathion in various populations of China ranged from 0.000021 to 0.000549 mg/kg bw, and the risk quotient (RQ) ranged from 0.007% to 0.183% and were less than 100%, which indicated that malathion has a low risk for long-term dietary intake these crops. The maximum residual limits (MRLs) of malathion can be set as 1 mg/kg for cherry tomatoes, broccoli, mulberries, cranberries, and 0.2 mg/kg for figs, respectively. These results would be considered as important references for monitoring and assessing the quality safety of agricultural products and protecting consumer health.

Determination of Volatile Low-Molecular-Weight Amines in Water by Capillary Electrophoresis after Headspace Microextraction

A method for the simultaneous determination of ammonium and seven volatile alkylamines (methylamine, dimethylamine, trimethylamine, ethylamine, n-propylamine, isopropylamine, and diethylamine) in aqueous media by capillary electrophoresis after headspace microextraction into a 5-μL drop of a 0.01 M solution of H3PO4 was developed. A solution containing 2 mM acridine, 20 mM acetic acid, and 0.05% Tween 20 was chosen as a background electrolyte for indirect photometric detection. Hydrodynamic sample injection was used. The method was tested using the samples of drinking water with the addition of ammonium and alkylamines. The accuracy of the results was confirmed by a standard addition method. The method developed provides an analytical range from 0.003 to 20 mg/L.

SPECTROPHOTOMETRIC DETERMINATION OF HEAVY METALS IN SOILS

Simple, selective and highly sensitive extraction-photometric methods for determination of Cu, Hg, У Mn, Fe, Co, and Ni are developed using dimercaptophenols (DF) and hydrophobic amines (Am) (2,6-dimercaptophenol(DMP), 2,6-dimercapto-4-methylphenol(DMMP), 2,6-dimercapto-4-ethylphenol(DMEP), 2,6-dimercapto-4-propylphenol(DMPP), and 2,6-dimercapto-4-tertbutylphenol(DMBP)) as complexing reagents. Optimal conditions for formation and extraction of heteroligand compounds (HLC) are specified and the ratios of the components in the complexes are determined. The optimum pH value providing maximum and constant optical density ranges within 3.0-8.1, chloroform (extraction ratio: 98.4-99.6%) being used as an extractant. Optimal concentrations of DP and Am are (0.6 - 0.8) x 10-3and (0.8 - 1.2) x 10-3mol/liter, respectively. HLC are stable and do not decompose for three days in aqueous and organic solvents, and after extraction for more than a month. The maximum analytical signal for M(II) complexing with DP and Am is observed at 464 - 630 nm (εk= 1.82 - 4.40 x 104). The structure of the HLC was studied using thermogravimetry and IR-spectroscopy Comparison of the analytical capabilities of the studied reagents showed that the contrast and sensitivity of the reaction decreases in the series DMBP — DMPP — DMEP — DMMP — DME The interfering impact of ions can be eliminated through changing pH of the medium, masking substances and extraction. The limits of photometric detection and quantitative determination of M (II) in the form of HLC were calculated using calibration graphs. The developed procedures have been successfully used in determination of the trace amounts of Cu, Hg, У Mn, Fe, Co, Ni in different soils: sod-podzolic sandy and sandy-loamy sod-podzolic loamy and clayey, gray forest, black soils, chestnut and river (soil of river floodplains) soils. The determination limits range within 27 - 43 ng/cm3.

Analysis of Chemical Composition of Extractives by Acetone and the Chromatic Aberration of Teak (Tectona Grandis L.F.) from China.

In order to clarify the chemical color change of teak (Tectona grandis L.F.), the difference of chemical composition between the heartwood and sapwood of teak was investigated by gas chromatography–mass spectrometry (GC-MS) based on the acetone extractive compounds. The results showed that the difference in content of the main components between heartwood and sapwood was not obvious. However, the amount of extractives in heartwood was higher than that in sapwood, especially for phenols, quinones, and ketones. The most obvious different substances in the acetone extractive between heartwood and sapwood were 4-tert-butyl-2-phenyl-phenol,2-methyl-anthraquinone, and 2,3-dimethyl-1,4,4a,9a-tetrahydro-9,10-anthracenedione, which might be the main composition for the chromatic aberration of teak. This paper focuses on a preliminary study and further work such as high-performance liquid chromatography (HPLC) with ultraviolet photometric detector (UV)/mass spectrometry (MS) will be carried out.

Photocatalytic degradation of hydrocarbons present in water, using Fe (III) modified TiO2

ABSTRACT&#x0D; This research work focused on the degradation of total hydrocarbons in synthetic water mixtures and in samples obtained from the inflow of a skimmer (production water) by means of heterogeneous photocatalysis. Titanium dioxide (TiO2) was used, modified with iron oxide (III) as photocatalyst, supported on polymethyl methacrylate plates, arranged in two reactors with volumetric capacities of 15.0 mL and 1.0 L. The degradation process was studied using two analysis methods: Photometric detection and gravimetric partition. Degradation percentages of 91.2% and 98% were obtained in field samples and synthetic mixtures respectively, with 4 h times; this allows for assessment of this technique's impact on the treatment of produced water in the oil industry, seeking for an alternative to the methods for treating water contaminated with hydrocarbons.

Levels of tin and organotin compounds in human urine samples from Iowa, United States

Exposure to tin in the general US population is near ubiquitous, as determined using urinary tin levels measured by inductively coupled plasma mass spectrometry (ICP-MS). Urinary tin levels are associated with chronic health outcomes, such as diabetes; however, it is unclear if these associations are due to the presence of inorganic and organic forms of tin in urine. To address this knowledge gap, levels of total tin and several organotin compounds (OTCs) were measured in convenience urine samples from pregnant women and adults from Iowa, United States. Total tin and OTC levels in urine samples were quantified using ICP-MS and gas chromatography with pulsed flame photometric detection (GC-PFPD), respectively. ICP-MS detected tin in almost all urine samples from both study populations. Low levels of dibutyltin were detected in two out of fifty human urine samples. Importantly, storage of urine samples in plastic containers, but not HNO3-pretreated glass vials drastically reduced the recoveries of OTCs, in particular, tributyltin. Although their detection frequency is low, exposures to OTC should be considered when studying associations between human exposures to tin compounds and adverse health outcomes; however, urinary OTC levels measured in banked urine samples may not be suitable as biomarkers of OTC exposure.

Nanolitre-scale cell based on L-shaped silica capillary and optical fibre for absorption photometric detection in capillary liquid chromatography

Miniaturised photometric detection cell based on the 150 μm I. D. L-shaped fused silica capillary (L-cell) and silica optical fibre is discussed in this paper. Light enters the cell via right angle bend and transmitted light is collected by silica optical fibre inserted into the capillary outlet. Ray trace analysis reveals that L-cell geometry works as a waveguide and effectively eliminates parasitic light, which is guided by the wall of any fused silica capillary cell. Low total level of stray light is further documented by measurement of absorbance of acetone-water mixture at 266 nm with the observed upper limit of dynamic range 2.2 AU. 3-mm L-cell has a volume of 53 nL and exhibits effective optical path 2.7 mm. Cell variance determined in the flow rate range 1–10 μL min−1 indicates, that 3-mm L-cell is optimal for use with 200–300 μm I. D. capillary columns. Furthermore, isocratic separation of alkylbenzenes mixture at 0.5 μL min−1 demonstrates effective use of 0.5-mm L-cell (8.8 nL) and possible performance of longer L-cells with high efficiency 100 μm I. D. capillary column.

Micro-Flame Photometric Detection in Miniature Gas Chromatography on a Titanium Tile

A novel miniaturized gas chromatography–flame photometric detection device built within a titanium platform (Ti µGC–FPD) is presented. The 7.5 cm × 15 cm monolithic Ti device contains both an OV-101 coated separation column (5 m × 100 µm i.d.) and a shielded cavity to house the hydrogen-rich detector flame. The FPD employs a micro counter-current flame (about 250 µm in diameter) that is stabilized by opposing relatively low flows of oxygen and hydrogen (7–10 mL/min O2 and 40 mL/min H2). Under optimal conditions, the minimum detectable limits are about 70 pg S/s for sulfur and 8 pg P/s for phosphorous. The natural (i.e., unfiltered) selectivity for these responses over carbon is near 104.3 for S/C and 105 for P/C. Even greater selectivity over hydrocarbons can further still be obtained by employing conventional interference filters. Overall, good separations with stable and sensitive detector performance are obtained with the device, and its sturdy Ti structure supports robust operation. Results indicate that this Ti µGC–FPD device may be a useful alternative approach for incorporating selective FPD sensing in µGC analyses.

A multi-pumping flow analysis system for β-galactosidase activity assays

A fully mechanized Arduino-controlled multi-pumping flow analysis system and procedure for the determination of β-galactosidase activity are proposed. The applied bioanalytical method is based on the determination of p-nitrophenol formed in the course of enzyme-catalyzed hydrolysis of p-nitrophenyl-galactopyranosides. The photometric detection is performed using dedicated flow-through optoelectronic detector made of paired light emitting diodes. The developed bioanalytical system was applied for evaluation of optimal enzyme detection conditions (pH, temperature and reaction time), selection of appropriate substrate for the assays, comparison of enzymes of different origins (isoenzymes), detection of β-galactosidase inhibitor and finally to the determination of enzyme activity in some dietary supplements dedicated for people suffering from lactose intolerance. Depending on measurements conditions the developed bioanalytical system allows determination of β-galactosidase in the wide range of activity (up to 15 U/mL at detection limit ca 0.01 U/mL) with high sample flowthroughput (up to 30 detections per hour). Additionally, the potential utility of the developed analytical system for amyloglucosidase activity assays has been demonstrated.

Re-evaluating Small Long-period Confirmed Planets from Kepler

Abstract We re-examine the statistical confirmation of small long-period Kepler planet candidates in light of recent improvements in our understanding of the occurrence of systematic false alarms in this regime. Using the final Data Release 25 (DR25) Kepler planet candidate catalog statistics, we find that the previously confirmed single-planet system Kepler-452b no longer achieves a 99% confidence in the planetary hypothesis and is not considered statistically validated in agreement with the finding of Mullally et al. For multiple planet systems, we find that the planet prior enhancement for belonging to a multiple-planet system is suppressed relative to previous Kepler catalogs, and we also find that the multiple-planet system member, Kepler-186f, no longer achieves a 99% confidence level in the planetary hypothesis. Because of the numerous confounding factors in the data analysis process that leads to the detection and characterization of a signal, it is difficult to determine whether any one planetary candidate achieves a strict criterion for confirmation relative to systematic false alarms. For instance, when taking into account a simplified model of processing variations, the additional single-planet systems Kepler-443b, Kepler-441b, Kepler-1633b, Kepler-1178b, and Kepler-1653b have a non-negligible probability of falling below 99% confidence in the planetary hypothesis. The systematic false alarm hypothesis must be taken into account when employing statistical validation techniques in order to confirm planet candidates that approach the detection threshold of a survey. We encourage those performing transit searches of K2, TESS, and other similar data sets to quantify their systematic false alarm rates. Alternatively, independent photometric detection of the transit signal or radial velocity measurements can eliminate the false alarm hypothesis.

Performance Evaluation of Cardiac Troponin I Assay: A Comparison Between the Point-of-care Testing Radiometer AQT90 FLEX and the Central Laboratory Siemens Advia Centaur Analyzer.

BackgroundTo validate the point of care testing (POCT) Trop-I analyzer and compare it with a central laboratory-based chemiluminescence immunoassay, in order to evaluate its performance for use in critical care areas. Moreover, for clinical decision-making, it is imperative to know the extent to which patient stratification will differ based on the analytic method being used. In particular, the aim of this study was to evaluate the analytical performance of the point-of-care analyzer and demonstrate the agreement with the central laboratory measurements in patients presenting to the emergency department (ED) with chest pain and suspected acute coronary syndrome (ACS).MethodsThis cross-sectional study was performed at the section of chemical pathology, department of pathology and laboratory medicine, the Aga Khan University (AKU), Karachi, from October to November 2017. Samples from patients and the quality control material of Trop-I were analyzed for imprecision, linearity, and method comparison on Advia Centaur (Siemens Diagnostics, CA, USA), and the AQT90 FLEX analyzer (Radiometer Medical ApS, Brønshøj, Denmark) with photometric detection at the section of chemical pathology, AKU. Statistical analysis was done using Microsoft Excel (Microsoft Corporation, Washington, United States) and EP Evaluator version 10.3.0.556 (Data Innovations, LLC, VT, US). Quantitative variables were represented in terms of mean ± SD. For precision, the computed SD was compared with allowable random error. Furthermore, Cohen’s kappa was applied to observe the agreement between the two methods.ResultsThe Trop-I Precision study on the POCT analyzer showed a coefficient of variation (CV) of 2.4% using a pooled patient sample with a mean Trop-I of 2.15 ± 0.05 ng/ml. Three standards ranging from 0.034 to 1.316 ng/ml were run in triplicate to verify accuracy and linearity. The allowable systematic error (SEa) was 10.0%. The maximum deviation for a mean recovery from 100% was 4.1%. All three of the mean recoveries were accurate and within the allowable error limits. The results were linear with slope 1.04, intercept 0.0. On a method comparison, Trop-I showed good agreement, yielding a kappa value of 0.95.ConclusionThis study has validated the performance of a POCT Trop-I assay against a central laboratory immunoassay and found acceptable results. POCT assays for cTnI should be implanted in emergency settings to ensure the fast triage of patients with chest pain, as well as timely diagnosis.

Exposure of chlorpyrifos in toddlers living in an agricultural area in Sakon Nakhon province, North-East Thailand

Purpose Children living in agricultural areas are exposed to pesticides in their living areas and through activities of daily living. These exposures may lead to adverse health effects. The purpose of this paper is to investigate household environmental and behavioural factors associated with chlorpyrifos exposure and resultant adverse health effects in children living in an agricultural community. Design/methodology/approach A cross-sectional study was conducted including 65 toddlers (age of 12–36 months) and their parents were face-to-face interviewed from January to February 2016. Toddler’s hands and feet, toys and floors were wiped for chlorpyrifos residue analysis. The wipes were extracted and analysed by gas chromatography with a flame photometric detector, and blood cholinesterase activity was measured by the EQM Test-mate (model 400). Findings The average age (± standard deviation) of children was 19.9 (±5.9) months. Chlorpyrifos detections were 61.5 per cent (hands), 57.1 per cent (toys), 53.8 per cent (floors) and 30.8 per cent (feet). The highest chlorpyrifos residue concentration was detected on toy surface (3.022 µg/m2). Chlorpyrifos residues on hands and feet were positively correlated with concentrations on floors and toys (Spearman’s ρ, p&lt;0.01). Multiple linear regression analysis revealed that more frequent hand washing (β=−0.236, p=0.067) and showering (β=−0.240, p=0.056) was negatively associated with chlorpyrifos residue on children’s body. House cleaning frequency was significantly associated with an increase in haemoglobin-adjusted erythrocyte cholinesterase (β=0.251, p&lt;0.05). Originality/value Chlorpyrifos exposures found in the children household area through their activities and behaviours can cause several adverse health effects. The circumstances associated with chlorpyrifos exposure should be mitigated and reduced to improve the household environment of children living agricultural areas.

Representative commodity for six leafy vegetables based on the determination of six pesticide residues by gas chromatography

A residue analytical method was developed for the determination of trichlorfon, chlorpyrifos, dimethoate, β cypermethrin, deltamethrin, and chlorothalonilin in six leafy vegetables by gas chromatography–electron capture detector (GC–ECD) and gas chromatography–flame photometric detector (GC–FPD). The method had a good linearity (R2 ≥ 0.9924) and precision (RSD ≤ 14.0%). The limits of quantification (LOQ) of six pesticides were all 0.01 mg/kg. Average recoveries of six pesticides ranged from 81% to 119%. The developed method was successfully applied to study the initial deposits, degrade characteristics, and terminal residues for six pesticides applied to six leafy vegetables under the same dose of formulation. The half-life of six pesticides was in the range of 0.8–8.8 days. The highest initial deposits, maximal residues, and terminal residues were found on leaf mustard and sweet potato leaves as the same pesticides were applied in different crops. Therefore, leaf mustard can be selected as representative commodity in the same subgroup to realize the residual extrapolation. This conclusion should be considered as a complement on crop classification of China.

Development and validation of an HPLC-UV method for simultaneous determination of sildenafil and tramadol in biological fluids: Application to drug-drug interaction study

The introduction of sildenafil (SDF) to treat erectile dysfunction has solved a widespread condition with negative on the quality of life. Recently, the co-administration of tramadol (TMD) with SDF to manage premature ejaculation has illegally increased and thus drug-drug interaction studies of these drugs became of great importance. Although certain biological functions have been altered upon co-administration of the two drugs, methods for their determination in vivo to understand their interactions have yet to be published. Herein, therefore, an HPLC method with photometric detection was developed for the determination of a binary mixture of TMD and SDF in rabbit plasma after oral administration. In this study, a reversed-phase chromatography was performed at room temperature on a C18 column with a mobile phase composed of 10 mM Na2HPO4 solution (pH 7.5): acetonitrile (45:55, v/v) at a flow rate of 0.8 mL min−1 using caffeine (CAF) as an internal standard. The detector was set at 220 nm. The total analysis time was 6 min. Calibration graphs were linear in the concentration ranges of 0.1–10 and 0.05–10 μg mL−1 with a detection limit of 0.05 and 0.02 μg mL−1 for TMD and SDF, respectively. The method was validated in terms of accuracy, precision, limit of detection and quantitation, recovery, and stability as per US FDA bioanalytical guidelines. In addition, the metabolites N-desmethylsildenafil (UK-103,320) and O-desmethyltramadol were quantified in rabbit plasma after 2 h of oral administration using LC–MS/MS. The simultaneous administration of TMD with SDF has affected peak plasma concentration (Cmax), Tmax, area under the concentration-time curve (AUC), and the elimination rate constant (Kel) of SDF. The present study is the first to give valuable insights into the drug-drug interaction and the pharmacokinetic implications associated with the co-administration of SDF and TMD.