Average Relative Standard Deviation Research Articles

Electrochemical Characterization and Detection of Lead in Water Using SPCE Modified with BiONPs/PANI.

The need for constant assessment of river water qualities for both aquatic and other biological survival has emerged a top priority, due to increasing exposure to industrial pollutants. A disposable screen print carbon electrode was modified with a conductive polymer (PANI) and Zn and/or Cu oxides NPs, obtained through bioreduction in citrus peel extracts (lemon and orange), for ultra-sensitive detection of PB2+, in the Crocodile River water sample. The synthesized materials were characterized with Fourier-transform infra-red spectroscopy (FTIR), ultra-violet visible spectroscopy (UV-Vis), and scanning electron microscopy (SEM). The SPC-modified electrodes designated as SPCE/LPE/BiONPs/PANI and SPCE/OPE/BiONPs/PANI were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and eventually deployed in the electrochemical detection of PB2+ in water using square wave voltammetry (SWV) technique. The electrochemical responses of the modified electrodes for both CV and EIS in 0.1 M HCl demonstrated enhanced performance relative to the bare SPCE. A detection and quantification limit of 0.494 ppb and 1.647 were obtained at SPCE/LPE/BiONPs/PANI, respectively, while a detection and quantification limit of 2.79 ppb and 8.91 ppb, respectively, were derived from SPCE/OPE/BiONPs/PANI. The relative standard deviations (RSD) for SPC electrode at a 6.04 µM PB2+ analyte concentration was 4.76% and 0.98% at SPCE/LPE/BiONPs/PANI and SPCE/LPE/BiONPs/PANI, respectively. The effect of copper, zinc, iron, cobalt, nickel, and magnesium on the stripping peaks of PB2+ at SPCE/OPE/BiONPs/PANI, showed no significant change except for cobalt, with about 17.67% peak current drop. The sensors were assessed for possible determination of PB2+ in spiked river water samples. The average percentage recovery and RSD calculated were 94.25% and 3.74% (n = 3) at SPCE/LPE/BiONPs/PANI and, 96.70% and 3.71% (n = 3) at SPCE/OPE/BiONPs/PANI, respectively. Therefore, the fabricated sensor material could be used for environmental assessment of this highly toxic heavy metal in the aquatic system

Determination of calorific value in coal by LIBS coupled with acoustic normalization

The low reproducibility is the most critical obstacle to the wide commercial application of laser-induced breakdown spectroscopy (LIBS). In this work, to improve the sample-to-sample reproducibility of LIBS real-time analysis of coal calorific value, we applied the acoustic signal generated by the laser ablation as the reference signal for normalization. First, the correlation between acoustic signal and spectral signal was analyzed and the results showed that the spectral signal from coal pellet samples with 35-ton compaction pressure had a strong correlation with acoustic signal. Second, the influences of shot-to-shot spectral intensities with different normalization methods were analyzed, including total area normalization, channel normalization, background normalization and acoustic normalization. Finally, different normalization models for calorific value were established using the support vector regression (SVR). With the acoustic normalization method, the relative standard deviation (RSD) of shot-to-shot intensities of spectral lines of C (I) 193.1 nm, C (I) 247.8 nm, H (I) 656.3 nm and N (I) 868.1 nm were significantly reduced from 10.16, 6.53, 3.79, 5.21% to 7.01, 4.40, 2.81, 3.54%, respectively. Moreover, compared with model without normalization, the average RSD of sample-to-sample measurements of validation samples based on acoustic normalization method was reduced from 6.25% to 4.16%, and the average relative error (ARE) was reduced from 4.66% to 3.28%. The results demonstrated that the acoustic normalization method can effectively reduce the fluctuations of the shot-to-shot spectral intensities and was an effective method to improve the reproducibility and accuracy of measurement of coal calorific value in LIBS.

Dielectric Polymer Property Prediction Using Recurrent Neural Networks with Optimizations.

Despite the growing success of machine learning for predicting structure-property relationships in molecules and materials, such as predicting the dielectric properties of polymers, it is still in its infancy. We report on the effectiveness of solving structure-property relationships for a computer-generated database of dielectric polymers using recurrent neural network (RNN) models. The implementation of a series of optimization strategies was crucial to achieving high learning speeds and sufficient accuracy: (1) binary and nonbinary representations of SMILES (Simplified Molecular Input Line System) fingerprints and (2) backpropagation with affine transformation of the input sequence (ATransformedBP) and resilient backpropagation with initial weight update parameter optimizations (iRPROP- optimized). For the investigated database of polymers, the binary SMILES representation was found to be superior to the decimal representation with respect to the training and prediction performance. All developed and optimized Elman-type RNN algorithms outperformed nonoptimized RNN models in the efficient prediction of nonlinear structure-activity relationships. The average relative standard deviation (RSD) remained well below 5%, and the maximum RSD did not exceed 30%. Moreover, we provide a C++ codebase as a testbed for a new generation of open programming languages that target increasingly diverse computer architectures.

Variation in chemical composition of MSWI fly ash and dry scrubber residues

Our society generates extensive amounts of municipal solid waste (MSW), which are mainly incinerated for volume reduction and energy recovery. Though, MSW incineration generates hazardous air pollution control (APC) residues that must be treated and deposited in appropriate landfills. An alternative to landfilling is material recovery, leading to regeneration of valuable products and reducing hazardous waste amounts. The chemical composition of APC residues, stemming from MSW, makes the waste attractive for metal and salt recovery, but its variation makes the development of material recovery processes challenging. This study investigates results from 895 X-ray fluorescence analyses of fly ash and dry scrubber residue samples originating from Norway and Sweden between 2006 and 2020 to explore variation in chemical composition within and between different incineration plants. The average relative standard deviation of elemental concentration in APC residue was estimated to 30% within plants. The variation in elemental concentration between grate fired incineration plants is about half of the average variation within the plants. The study also clarifies compositional differences from APC residues originating from fluidized bed incinerators and grate incinerators. Also, reported concentrations of APC residues from other countries than Sweden and Norway showed significant differences in chemical composition. The presented variations clarifies the importance of holistic approaches for waste valorization processes which can substitute stabilization processes for landfilling.

Electrochemical Detection of Electrolytes Using a Solid-State Ion-Selective Electrode of Single-Piece Type Membrane.

This study aimed to develop simple electrochemical electrodes for the fast detection of chloride, sodium and potassium ions in human serum. A flat thin-film gold electrode was used as the detection electrode for chloride ions; a single-piece type membrane based solid-state ion-selective electrode (ISE), which was formed by covering a flat thin-film gold electrode with a mixture of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and ion-selective membrane (ISM), was developed for sodium and potassium ions detection. Through cyclic voltammetry (CV) and square-wave voltammetry (SWV), the detection data can be obtained within two minutes. The linear detection ranges in the standard samples of chloride, sodium, and potassium ions were 25–200 mM, 50–200 mM, and 2–10 mM, with the average relative standard deviation (RSD) of 0.79%, 1.65%, and 0.47% and the average recovery rates of 101%, 100% and 96%, respectively. Interference experiments with Na+, K+, Cl−, Ca2+, and Mg2+ ions demonstrated that the proposed detection electrodes have good selectivity. Moreover, the proposed detection electrodes have characteristics such as the ability to be prepared under relatively simple process conditions, excellent detection sensitivity, and low RSD, and the detection linear range is suitable for the Cl−, Na+ and K+ concentrations in human serum.

Generation of multiply charged ions from homogeneous MALDI microcrystals

The homogeneity of matrix assisted laser desorption/ionization (MALDI) microcrystals, laser fluence, and the proton affinity (PA) of matrices determine the generation of multiply charged ions. Here we adopt three structurally similar matrices, i.e. α-cyano-4-hydroxycinnamic acid (CHCA), 4-chloro-α-cyanocinnamic acid (Cl-CCA), and (E)-propyl α-cyano-4-hydroxyl cinnamylate (CHCA-C3) to examine the homogeneity of microcrystals by measuring the relative standard deviation (RSD) values of the matrices with the homogeneous sample preparation method, e.g. forced dried droplet (FDD). The average RSD values of CHCA, Cl-CCA, and CHCA-C3 matrices are ∼15%, ∼10%, and ∼20%, respectively. With the same CHCA matrix, we found the charge state of myoglobin ions can obtain more charges (+6) with the FDD method as compared to +5 charges obtained by the inhomogeneous sample preparation method, i.e. dried droplet (DD). The laser fluence also affects the generation of multiply charged ions. For instance, the maximum charge states of myoglobin and cytochrome c ions are +6 with CHCA and +4 with CHCA-C3 at threshold laser fluence and decreases at elevated laser fluence. The charge state of myoglobin ions with Cl-CCA matrix is +3 at threshold laser fluence and increases to the maximum charge state of +6 and eventually reduces to +5 with elevated laser fluence. Moreover, we found low PA value of matrix results in high charge state of analyte ions and vice versa. The matrix PA modulates the proton transfer reaction, leading to the formation of multiply charged ions. The homogeneous samples help control the charge states of ions and generate the multiply charged protein ions which can be used as potential mass calibration standards to search suitable protein samples at high m/z ratios with a MALDI time-of-flight mass spectrometer.

Voltammetric determination of heavy metals in honey bee venom using hanging mercury drop electrode and PLA/carbon conductive filament for 3D printer.

A new method for determination of selected heavy metals (Cd, Pb, Cu, Zn, and Ni) in honey bee venom was developed. Heavy metals are metabolized and incorporated into bee products, including honey and honey bee venom (apitoxin). Their composition reflects contamination of “bee environment”, providing information about heavy metal contamination in the neighborhood of human dwellings. Moreover, assessment of bee products contamination is relevant for medicine, as they are a tool for promising therapeutic and chemoprophylactic strategies against COVID-19 (SARS-CoV-2). Owing to the complicated matrix, the developed method consists of wet mineralization with sulfuric acid, nitric acid, under increased temperature, and pressure and subsequent repeated boiling with concentrated nitric acid. Determination of the selected metals was carried out by anodic or cathodic stripping voltammetry on two types of electrodes: pen-type hanging mercury drop electrode (HMDE) and PLA filament with carbon conductive admixture (PLA-C) for 3D printer. Contents of lead and cadmium in all analyzed bee venom samples were on the level of mg kg−1, of nickel and copper about ten times higher, and of zinc on the level of g kg−1. The results achieved using HMDE were recorded with average relative standard deviation (RSD) 5.4% (from 3.2% to 8.6%) and using PLA-C 11.8% (from 6.5% to 18.0%). The results achieved using both electrodes proved to be equivalent with statistical probability higher than 95%.Graphic abstract

Ultra-high performance supercritical fluid chromatography coupled to tandem mass spectrometry for antidoping analyses: Assessment of the inter-laboratory reproducibility with urine samples.

The aim of this study was to assess the interlaboratory reproducibility of ultra-high performance supercritical fluid chromatography coupled with tandem mass spectrometry method for routine antidoping analyses. To do so, a set of 21 doping agents, spiked in urine and analyzed after dilute and shoot treatment, was used to assess the variability of their retention times between four different laboratories, all equipped with the same chromatographic system and with the same ultra-high performance supercritical fluid chromatography stationary phase chemistry. The average relative standard deviations (RSD%) demonstrated a good reproducibility of the retention times for 19 out of 21 analytes, with RSD% values below 3.0%. Only for two substances, namely fenbutrazate and niketamide, the retention was not repeatable between laboratories, with RSD% of approximately 15% in both cases. This behaviour was associated with (a) the low organic modifier percentage (around 2-4%) in the mobile phase at the corresponding retention times, and (b) the influence of the system volume on poorly retained analytes. An analysis on seven "blind" urines was subsequently carried out in the same four laboratories. In these blind samples, either one, two, or none of the 21 doping agents previously analyzed were present at an unknown concentration. Each laboratory had to perform the identification of the compounds in the samples and estimate their concentrations. All laboratories assigned all target analytes correctly in all blind urine samples and provide a comparable estimation of their concentrations.

Determination of Pyrethroid Residues in Wooden Toys by Gas Chromatography and Gas Chromatography–Mass Spectrometry

A novel method for the determination of pyrethroid pesticide residues in wooden toys was developed. Wooden toy samples were extracted with petroleum ether−acetone (1 : 1, v/v), cleaned up on a florisil solid phase extraction cartridge and determined by gas chromatography equipped with electron capture detector (GC−ECD), followed by validation using gas chromatography−mass spectrometry (GC−MS) with negative chemical ionization. Calibration curves were linear in the range of 0.02–0.5 mg/kg with correlation coefficients exceeding 0.9975 for GC−ECD and GC−MS. At spiked concentrations of 0.1, 0.2 and 0.5 mg/kg, the average recoveries and relative standard deviations were 82–97% and 1.5–7.8%, respectively. The limit of quantification for each analyte was 0.1 mg/kg, which satisfied the current maximum residue limit permitted in wooden toys. Results also showed that the developed method could be successfully applied to determine permethrin, cypermethrin, cyfluthrin, deltamethrin residues in real wooden toy samples.

Enhanced Collision Induced Unfolding and Electron Capture Dissociation of Native-like Protein Ions.

Native ion mobility-mass spectrometry (IM-MS) is capable of revealing much that remains unknown within the structural proteome, promising such information on refractory protein targets. Here, we report the development of a unique drift tube IM-MS (DTIM-MS) platform, which combines high-energy source optics for improved collision induced unfolding (CIU) experiments and an electromagnetostatic cell for electron capture dissociation (ECD). We measured a series of high precision collision cross section (CCS) values for protein and protein complex ions ranging from 6-1600 kDa, exhibiting an average relative standard deviation (RSD) of 0.43 ± 0.20%. Furthermore, we compare our CCS results to previously reported DTIM values, finding strong agreement across similarly configured instrumentation (average RSD of 0.82 ± 0.73%), and systematic differences for DTIM CCS values commonly used to calibrate traveling-wave IM separators (-3% average RSD). Our CIU experiments reveal that the modified DTIM-MS instrument described here achieves enhanced levels of ion activation when compared with any previously reported IM-MS platforms, allowing for comprehensive unfolding of large multiprotein complex ions as well as interplatform CIU comparisons. Using our modified DTIM instrument, we studied two protein complexes. The enhanced CIU capabilities enable us to study the gas phase stability of the GroEL 7-mer and 14-mer complexes. Finally, we report CIU-ECD experiments for the alcohol dehydrogenase tetramer, demonstrating improved sequence coverage by combining ECD fragmentation integrated over multiple CIU intermediates. Further improvements for such native top-down sequencing experiments were possible by leveraging IM separation, which enabled us to separate and analyze CID and ECD fragmentation simultaneously.

Determination of lead, cadmium, chromium, and arsenic in 13 herbs of tocolysis formulation using atomic absorption spectrometry

The contents of Pb, Cd, Cr, and As in 13 herbs of tocolysis formulations were studied using three kinds of sample pretreatment and atomic absorption spectrometry. Thirteen herbs were pretreated with either incineration, wet digestion, or microwave digestion, and the results of recoveries and precision about these elements were compared. The average recoveries of 13 herbs via incineration, wet digestion, and microwave digestion pretreatments were 80 ± 12%, 85.7 ± 3.3%, and 94.5 ± 2.1%, respectively. Among them, microwave digestion pretreatment had the highest recovery and precision. The average relative standard deviations for the four measured elements (Pb, Cd, Cr, and As) from incineration, wet digestion, and microwave digestion pretreatments were 8.8 ± 1.7%, 7.1 ± 3.3%, and 3.4 ± 0.8%, respectively. The detection limits for Pb, Cd, Cr, and As using microwave digestion pretreatment were 0.45 ppb, 0.03 ppb, 0.20 ppb, and 0.64 ppb, respectively. Concentrations of Pb, Cd, Cr, and As measured from the tocolysis formulation using microwave digestion pretreatment were 28.0 ± 0.7 ppb, 1.11 ± 0.03 ppb, 8.5 ± 0.3 ppb, and 1.52 ± 0.04 ppb, respectively. Lead was found to have the highest concentration among the four determined elements in 13 herbs. Schizonepetae Herba contained the highest Pb (60.5 ± 2.1 ppb), Cr (23.3 ± 0.5 ppb), and As (8.8 ± 0.1 ppb) among the 13 herbs. Ligustici Rhizoma contained the highest Cd (3.76 ± 0.04 ppb) among the 13 herbs.

Electrochemical detection of fentanyl with screen-printed carbon electrodes using square-wave adsorptive stripping voltammetry for forensic applications

Square-wave adsorptive stripping voltammetry (SWAdSV) is proposed as a fast, simple, and sensitive approach toward the detection, identification, and semi-quantitation of fentanyl in seized drug samples using screen-printed carbon electrodes. Electrochemical oxidation of fentanyl resulted in the formation of two anodic peaks, one at 0.75 V (peak I) and the second at 0.88 V (peak II) versus a Ag/AgCl pseudo reference electrode. Voltammetric measurements were conducted under optimized experimental conditions using fentanyl standards ranging from 0.076 μg/mL to 6.9 μg/mL, which resulted in a limit of detection of 0.037 μg/mL. Reproducibility was assessed as the average percent relative standard deviation of the slopes of calibration curves and was 2.6% for oxidation peak I and 7.4% for oxidation peak II in cell. Detection capabilities were assessed in a 5-mL cell and in a 100 microliter drop. Interference studies were conducted with cocaine, methamphetamine, quinine, caffeine, and acetaminophen. The mechanism for the electrochemical oxidation of fentanyl to norfentanyl is also described. Accuracy and suitability of the method for seized drug analysis was assessed using 11 simulated samples. Suitability of the method for future analysis of fentanyl in oral fluid was assessed.

Analysis of non-conjugated steroids in water using paper spray mass spectrometry

A novel strategy for the direct analysis of non-conjugated steroids in water using paper spray mass spectrometry (PS-MS) has been developed. PS-MS was used in the identification and quantification of non-conjugated (free) steroids in fish tank water samples. Data shown herein indicates that individual amounts of free steroids can be detected in aqua as low as; 0.17 ng/µL, 0.039 ng/µL, 0.43 ng/µL, 0.0076 ng/µL for aldosterone, corticosterone, cortisol, and β-estrone, respectively, and with an average relative standard deviation of ca. < 10% in the positive ion mode using PS-MS/MS. Direct detection of free steroids in a raw water mixture, from aquaculture, without prior sample preparation is demonstrated. The presence of free steroids released in fish water samples was confirmed via tandem mass spectrometry using collision-induced dissociation. This approach shows promise for rapid and direct water quality monitoring to provide a holistic assessment of non-conjugated steroids in aqua.

EVALUATION OF MS-DIAL AND MZMINE2 SOFTWARES FOR CLINICAL LIPIDOMICS ANALYSIS

Lipidomics covers analysis of all lipid species in an organism. Lipid metabolism is one of the key factors to understand cellular processes at molecular level. Lipidomics has been used to find diagnostic and prognostic biomarkers in clinical sample (plasma, serum, urine, tissue). Today mass spectroscopy based approach dominates lipidomics and several computational platforms have been developed to process raw mass spectra data. However, there is no routine procedure for data processing in lipidomics. In present work, two different bioinformatics platforms, which are MS-DIAL and MZmine2, was compared for lipidomics analysis of plasma sample. Peak detection, identification and quantification parameters were investigated to understand advantages and disadvantages. In peak detection process, it was observed that MZmine2 detected more peak than MS-DIAL at same threshold level. In identification process, Lipidmaps database was used for identification. MZmine2 identifies more lipid than MS-DIAL. Semi-quantification is very important to find differentially expressed lipid species and biomarkers in clinical studies. MS-DIAL and MZmine2 calculated normalized peak intensities and results were compared to understand reproducibility. Average relative standard deviation of all peaks was calculated and results showed that MS-DIAL gives more reproducible results than MZmine2. In conclusion, MZmine2 and MS-DIAL could be used in clinical lipidomics studies.

A survey of 59 pesticide residues in Turkish chicken eggs using LC-MS/MS

ABSTRACT An LC-MS/MS multi-residue method was validated for the determination of 59 pesticide residue levels in a chicken egg by using QuEChERS extraction method. The validation parameters used were taken from the SANTE/11813/2017 guideline. The calibration curves for each target pesticide had a good linearity in a range of 1.0 or 2.5 to 100.0 µg kg−1 (r2 ≥ 0.995). Ten per cent of the total pesticides had LOQ values less than 5.0 µg kg−1 or LOQ values from 5.0 to 10.0 µg kg−1. The LOQ values were below the MRLs set by the European Commision (EC). Average recoveries (70–120%) and relative standard deviations (RSDs≤20%) were achieved for 59 selected pesticides at different concentrations (5 or 10 and 200 µg kg−1). All expanded measurement uncertainties were lower than 50%. The occurrence of these pesticides was evaluated in 35 commercially available chicken eggs. No MRL exceedance was identified.

Comparison of Directly Suspended Drop Microextraction with Dispersive Liquid-liquid Microextraction Method for Extraction of Doxepin in Water and Biological Samples Prior to UV-Vis Spectrophotometer

The present research describes the use of directly suspended drop microextraction and air-assisted dispersive liquid-liquid microextraction method coupled with UV-Vis spectrophotometer for the analysis of doxepin in water and biological samples. Several important parameters which influence the extraction efficiencies of these two microextraction methods, such as the kind of extracting solvent, volume of the aqueous sample solution (donor phase), the volume of the organic extraction solvent (acceptor phase), pH of the donor phase, salt effect, extraction time, stirring rate and number of the air injection were investigated. Under the optimal conditions, the enrichment factors were above 30. The linearity of the methods has been investigated between the ranges of 0.005-1.5 and 0.003-1 µg/mL. The precisions of two methods which are based on the average relative standard deviations are lower than 6, for three different concentrations of the analyte. Finally, the proposed methods were applied for the determination of doxepin in real samples including environmental water, urine and human plasma samples under the optimal conditions and the reasonable relative recoveries were obtained.

Development of a highly sensitive voltametric sensor for trace determination of melamine residues in milk and water samples

Melamine (MEL) is a key and broadly used trade chemical that is risky to human health and environment. Hence, a method comprising a preanodized glassy carbon electrode (GCE*) for sensitive analysis of MEL has been developed. The electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and surface area data confirmed the preanodization of the GCE. The results highlight the efficacy and the compatibility of the GCE* protocol for sensitive detection of trace levels of MEL. The method was based upon the indirect differential pulse voltammetric (DPV) sensing of MEL depending on its competition with uric acid (UA) as a recognition element at the surface of GCE*. The electrochemical oxidation of UA at GCE* showed one well defined anodic peak at 0.23 V vs. Ag/AgCl electrode. Under the optimized parameters, the linearity range of the method was calculated as 2.0 × 10−9–8.0 × 10−9 M (0.252–1.009 µg.L−1) with an accuracy of 99.21 ± 5.02 (R2 = 0.9969). The lower limits of detection (LOD) and quantization (LOQ) were 6.0 × 10−10 M (0.075 µg.L−1) and 2.0 × 10−9 M (0.252 µg.L−1), respectively. Intra-day and inter-day precisions of the method were in the range 98.46 ± 5.02 and 99.21 ± 5.84%, respectively. The average relative standard deviation (RSD) at 2.0 × 10−7 M of MEL for successive measurements (n = 3) was ± 3.0%. Analysis of MEL in milk powder and water samples determined using the developed DPV procedures gave satisfactorily recoveries ranged from 96.11 to 97.01% for low and high levels of MEL in a variety of milk samples with relative standard deviations (RSDs) over the range of ± 4.1% 0.32%-3.61%. The method offered a significant improvement for trace determination of MEL in a variety of milk and milk powder samples in terms of efficient, rapid, economical, and miniaturized sample preparation methods, which yielded fewer matrix effects compared with SPE method. The established method is expected to be widely applied for analysis of MEL at trace levels in the future.

Analytical Control of Impurities and Active Ingredients in a (–)-Isopulegol Derivative with Highly Potent Analgesic Activity

An HPLC-UV procedure is proposed for identifying processing impurities and determining the contents of active ingredient in the drug substance of the promising non-narcotic analgesic (2R,4R,4aR,7R,8aR)- 4,7-dimethyl-2-(thiophen-2-yl)octahydro-2H-chromen-4-ol (1). Processing impurities including the starting reagents thiophene-2-carbaldehyde and (–)-isopulegol, a related stereoisomer of 1, and intermediates and dehydration products of 1 could be present as a result of the synthesis and isolation. The developed chromatography conditions could separate possible impurities and analyte 1 with the required resolution. The contents of the studied processing impurities were below the established detection limits of 0.056 μg/mL for thiophene-2-carbaldehyde; 0.32, (–)-isopulegol; 0.22, the stereoisomer; and 0.18, 0.22, and 0.37, for the dehydration products. The working range of concentrations for the procedure was 0.50 – 10 μg/mL. The recovery varied from 98.9 to 101.2% in the accuracy evaluation. The procedure was demonstrated to have sufficient accuracy. The average relative standard deviation in the intraday precision evaluation was 0.7%; in the interday precision assessment, 0.8%, which were below the acceptance criteria of 2.0 and 3.0%, respectively.

Quantitative multiple-element simultaneous analysis of seaweed fertilizer by laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy, coupled with advanced chemometric methods, was used to quantitate multiple elements in a seaweed-based fertilizer. The influence of important parameters was determined using partial least squares regression (PLSR), support vector regression (SVR) and random forest (RF) optimizations. Optimal results for Mg, K and P were obtained using PLSR, whereas RF yielded the best results for Mn, Cu, Sr and Ca. The best predictions for Ba levels were obtained with SVR. The lowest root mean square errors in the prediction sets for Mn, Cu, Sr, Ba, Mg, K, P and Ca were 48.27 µg/g, 36.90 µg/g, 0.37 mg/g, 40.32 µg/g, 1.99 mg/g, 2.03 mg/g, 4.81 mg/g and 14.08 mg/g, respectively, with average relative standard deviations of 13.65%, 2.68%, 19.80%, 5.17%, 3.32%, 2.98%, 1.82% and 5.81%. The results showed that the optimal multivariate model depended on the specific element being analyzed. The proposed method provides a rapid means of determining multielement concentrations in seaweed-based fertilizers.

Attomolar SERS detection of organophosphorous pesticides using silver mirror-like micro-pyramids as active substrate.

Surface-enhanced Raman spectroscopy (SERS) is gaining importance as an ultrasensitive analytical tool for routine high-throughput analysis of a variety of molecular compounds. One of the main challenges is the development of robust, reproducible and cost-effective SERS substrates. In this work, we study the SERS activity of 3D silver mirror-like micro-pyramid structures extended in the z-direction up to 3.7μm (G0 type substrate) or 7.7μm (G1 type substrate), prepared by Si-based microfabrication technologies, for trace detection of organophosphorous pesticides, using paraoxon-methyl as probe molecule. The average relative standard deviation (RSD) for the SERS intensity of the peak displayed at 1338cm-1 recorded over a centimetre scale area of the substrate is below 13% for pesticide concentrations in the range 10-6 to 10-15molL-1. This data underlies the spatial uniformity of the SERS response provided by the microfabrication approach. According to finite-difference time-domain (FDTD) simulations, such remarkable feature is mainly due to the contribution on electromagnetic field enhancement of edge plasmon polaritons (EPPs), propagating along the pyramid edges where the pesticide molecules are preferentially adsorbed. Graphical abstract.