Average Relative Standard Deviation Research Articles

Dependence of matrix effect on ionization polarity during LC-ESI-MS analysis of derivatized amino acids in some natural samples.

Matrix effect, the influence of co-eluting components on the ionization efficiency of the analyte, affects the trueness and precision of the LC-ESI-MS analysis. Derivatization can reduce or eliminate matrix effect, for example, diethyl ethoxymethylenemalonate (DEEMM) derivatives have shown less matrix effect compared to other derivatives. Moreover, the use of negative ion mode can further reduce matrix effect. In order to investigate the combination of derivatization and different ionization modes, an LC-ESI-MS/MS method using alternating positive/negative ion mode was developed and validated. The analyses in positive and negative ion modes had comparable limit of quantitation values. The influence of ESI polarity on matrix effect was investigated during the analysis of 22 DEEMM-derivatized amino acids in herbal extracts and honeys. Sample dilution approach was used for the evaluation of the presence of matrix effect. Altogether, 4 honeys and 11 herbal extracts were analyzed, and the concentrations of 22 amino acids in the samples are presented. In the positive ion mode, matrix effect was observed for several amino acid derivatives and the matrix effect was stronger in honey samples compared to the herbal extracts. The negative ion mode was free from matrix effect, with only few exceptions in honeys (average relative standard deviation over all analytes and matrices was 8%; SD = 7%). The matrix effect was eliminated in the positive ion mode by sample dilution and agreement between concentrations from the two ion modes was achieved for most amino acids. In conclusion, it was shown that the combination of derivatization and negative ion mode can be a powerful tool for minimizing matrix effect in more complicated applications.

Detecting kinematic boundary surfaces in phase space: particle mass measurements in SUSY-like events

We critically examine the classic endpoint method for particle mass determination, focusing on difficult corners of parameter space, where some of the measurements are not independent, while others are adversely affected by the experimental resolution. In such scenarios, mass differences can be measured relatively well, but the overall mass scale remains poorly constrained. Using the example of the standard SUSY decay chain tilde{q}to {tilde{chi}}_2^0to tilde{ell}to {tilde{chi}}_1^0 , we demonstrate that sensitivity to the remaining mass scale parameter can be recovered by measuring the two-dimensional kinematical boundary in the relevant three-dimensional phase space of invariant masses squared. We develop an algorithm for detecting this boundary, which uses the geometric properties of the Voronoi tessellation of the data, and in particular, the relative standard deviation (RSD) of the volumes of the neighbors for each Voronoi cell in the tessellation. We propose a new observable, overline{Sigma} , which is the average RSD per unit area, calculated over the hypothesized boundary. We show that the location of the overline{Sigma} maximum correlates very well with the true values of the new particle masses. Our approach represents the natural extension of the one-dimensional kinematic endpoint method to the relevant three dimensions of invariant mass phase space.

Indirect competitive electrochemical immunosensor for hepatitis A virus antigen detection

Indirect competitive electrochemical immunosensor for hepatitis A virus antigen (HAV) detection was developed by immobilizing HAV on the surface of carbon nanopowder paste electrode. The monitoring of the target HAV antigen was performed using a secondary antibody labeled with peroxidase. The analytical signal corresponds to an amperometric current resulting from the addition of hydrogen peroxide and hydroquinone as a redox mediator. A calibration curve was obtained by plotting the intensity of the amperometric signal versus the concentrations of HAV antigens. A low detection limit for HAV antigen was attained and estimated to be 26·10−5IU·mL−1. The sensitivity was also investigated and compared with indirect competitive ELISA. Moreover, the immunosensor provides exact results over a broad linear range from 2·10−4 to 5·10−3IU·mL−1, (R2=0.998). The average relative standard deviation (RSD) of this method was less than 3% for the assays performed on the same day and 7% for the measurements made on different days. The immunosensor exhibits a good stability and high biological selectivity for HAV antigen detection and was successfully applied for the determination of HAV in water samples.

Square‐wave Voltammetric Determination of Propyphenazone, Paracetamol, and Caffeine: Comparative Study between Batch Injection Analysis and Conventional Electrochemical Systems

AbstractIn this work, the performance of two methods for simultaneous determination of propyphenazone (PRO), paracetamol (PAR), and caffeine (CAF) were compared. One is based on the use of a conventional electrochemical cell (steady‐state condition) and the other on the use of a batch injection analysis (BIA) cell; both systems were associated with square‐wave voltammetric detection (SWV). Three well separated (▵E ≥ 0.25 V) oxidation peaks were obtained for PRO, PAR, and CAF using 0.1 mol L−1 H2SO4 as electrolyte and a boron‐doped diamond (BDD) as working electrode. In addition, the electrochemical oxidation mechanism of PRO is being proposed for the first time. The average relative standard deviations of CB and BIA methods were 4.1 % and 3.1 %, respectively. The conventional system presented better limits of detection and the BIA system a significantly greater throughput (four times faster). Statistical comparison between the results obtained with both proposed methods and those obtained by chromatography was carried out and no significant differences were observed (95 % confidence level).

Testing the efficiency of extraction of incurred residues from soil with optimized multi-residue method

ABSTRACTThe reproducibility of extraction of residues from spiked soil samples and from soils containing incurred residues was tested with 14C-labeled test compounds of different physical-chemical properties. Nearly 100% of the compounds added to the sample before extraction could be recovered with an average reproducibility relative standard deviation (CV) of 5.4%. The additional steps of the determination process (cleanup, evaporation, etc.) contributed to the major part of the variability of the results (CV = 10–20%). The incurred residues were most efficiently extracted with acetone for 30 min followed by the mixture of acetone/ethyl acetate 1:1 for additional 30 min. However, they could only be recovered at various extent (64–90% of total residues), underlying the importance of testing the efficiency of extraction. The residues were identified and quantified by gas chromatography applying thermionic detector. The performance parameters of the method complied with the international method validation guidelines, and they proved to be robust and suitable for determination of pesticide residues in soils of widely different physical–chemical properties.

Solvent bar micro-extraction (SBME) based determination of PAHs in seawater samples

Measuring the impact of PAHs in seawater samples is often difficult due to the low concentrations in which they appear and the complexity of the sample matrix. Traditional methods for sample preparation such as liquid-liquid extraction and solid phase extraction require the use of excessive amounts of solvents and reagents, and sample handling. In this work, hollow fiber liquid phase micro-extraction (HFLPME), in the configuration of solvent bar micro-extraction (SBME), was proposed as an environmentally friendly and more effective tool, for the extraction of the 16 priority PAHs from seawater samples. Extraction was conducted using hexane as a solvent. Enrichment factors from 45 to 163 were obtained after 60min at a stirring rate of 500rpm in the sample. Moreover, a negative linear relationship was observed between the enrichment factor and the molecular weight of the PAHs. Under optimized conditions, the limits of detection were in the range from 0.21 to 0.82ngL−1, the method showed a linear response up to 500μgL−1, and the average relative standard deviation for seawater samples spiked with 5ngL−1 was 11.6%. After calibration, the SBME was applied to extract PAHs in seawater samples from the Bay of Cadiz (SW Spain), showing an average recovery of 99%. In conclusion, the SBME is an environmentally friendly, one-step alternative for sample preparation in the determination of PAHs in seawater samples.

Assessment of Reproducibility of Laser Electrospray Mass Spectrometry using Electrospray Deposition of Analyte.

A nonresonant, femtosecond (fs) laser is employed to desorb samples of Victoria blue deposited on stainless steel or indium tin oxide (ITO) slides using either electrospray deposition (ESD) or dried droplet deposition. The use of ESD resulted in uniform films of Victoria blue whereas the dried droplet method resulted in the formation of a ring pattern of the dye. Laser electrospray mass spectrometry (LEMS) measurements of the ESD-prepared films on either substrate were similar and revealed lower average relative standard deviations for measurements within-film (20.9%) and between-films (8.7%) in comparison to dried droplet (75.5% and 40.2%, respectively). The mass spectral response for ESD samples on both substrates was linear (R2 > 0.99), enabling quantitative measurements over the selected range of 7.0 × 10-11 to 2.8 × 10-9mol, as opposed to the dried droplet samples where quantitation was not possible (R2 = 0.56). The limit of detection was measured to be 210fmol. Graphical Abstract ᅟ.

Optimization of the Small Glycan Presentation for Binding a Tumor-Associated Antibody: Application to the Construction of an Ultrasensitive Glycan Biosensor.

The main aim of the study was to optimize the interfacial presentation of a small antigen-a Tn antigen (N-acetylgalactosamine)-for binding to its analyte anti-Tn antibody. Three different methods for the interfacial display of a small glycan are compared here, including two methods based on the immobilization of the Tn antigen on a mixed self-assembled monolayer (SAM) (2D biosensor) and the third one utilizing a layer of a human serum albumin (HSA) for the immobilization of a glycan forming a 3D interface. Results showed that the 3D interface with the immobilized Tn antigen is the most effective bioreceptive surface for binding its analyte. The 3D impedimetric glycan biosensor exhibited a limit of detection of 1.4 aM, a wide linear range (6 orders of magnitude), and high assay reproducibility with an average relative standard deviation of 4%. The buildup of an interface was optimized using various techniques with the visualization of the glycans on the biosensor surface by atomic force microscopy. The study showed that the 3D biosensor is not only the most sensitive compared to other two biosensor platforms but that the Tn antigen on the 3D biosensor surface is more accessible for antibody binding with better kinetics of binding (t50% = 137 s, t50% = the time needed to attain 50% of a steady-state signal) compared to the 2D biosensor configuration with t50% = 354 s. The 3D glycan biosensor was finally applied for the analysis of a human serum sample spiked with an analyte.

Quantitative Analysis of Lead in Tea Samples by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is applied at natural atmosphere to compare the quantitative analysis performances of the toxic heavy metal element lead (Pb) in Pu’er tea leaves, determined by three calibration methods: the external standard method, the internal standard method, and the multiple linear regression method. The Pb I line at 405.78 nm is chosen as the analytical spectral line to perform the calibration. The linear correlation coefficients (R 2 ) of the predicted concentrations versus the standard reference concentrations determined by the three methods are 0.97916, 0.98462, and 0.99647, respectively. The multiple linear regression method gives the best performance with respect to average relative errors (ARE = 2.69%), maximum relative errors (MRE = 4.94%), average relative standard deviations (ARSD = 9.69%) and maximum relative standard deviations (MRSD = 24.44%) of the predicted concentrations of Pb in eight samples, compared to the other two methods. It is shown that the multiple linear regression method is more accurate and stable in predicting concentrations of Pb in Pu’er tea leaf samples.

Determination of imidazoles and their metabolites in pork by liquid chromatography-tandem mass spectrometry

A method for the determination of 29 imidazoles and their metabolites in pork by liquid chromatography-tandem mass spectrometry has been developed. The samples were extracted with ethyl acetate, and then defatted with n-hexane after concentration of the extracts. The analytes were separated on a C18 reversed-phase column with 0.3% (v/v) formic acid aqueous solution and acetonitrile as mobile phases, and finally analyzed using electrospray ionization in positive ion mode (ESI+) with multiple reaction monitoring (MRM). The linear ranges of the 29 compounds were from 0.05 to 20.0 μg/L with the correlation coefficients (r2) more than 0.99. The average recoveries and relative standard deviations were 65.4%-103% and 1.3%-6.8% respectively in the spiked ranges of 1.0-5.0 μg/kg. The limits of detection and the limits of quantification were 0.02-0.3 μg/kg and 0.1-1 μg/kg respectively for the 29 imidazoles. The method is simple, rapid and sensitive. It is suitable for the detection of imidazoles and their metabolites in pork.

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

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

A comparison of very short lived halocarbon (VSLS) and DMS aircraft measurements in the tropical west Pacific from CAST, ATTREX and CONTRAST

Abstract. We present a comparison of aircraft measurements of halogenated very short lived substances (VSLSs) and dimethyl sulphide (DMS, C2H6S) from a co-ordinated campaign in January–February 2014 in the tropical west Pacific. Measurements were made on the NASA Global Hawk, NCAR Gulfstream-V High-performance Instrumented Airborne Platform for Environmental Research (GV HIAPER) and UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 (see Sect. 2.2) using four separate gas chromatography–mass spectrometry (GC-MS) instruments: one operated by the University of Miami (UoM), one from the National Center for Atmospheric Research (NCAR) and two from the University of York (UoY). DMS was measured on the BAe-146 and GV. The instruments were inter-calibrated for halocarbons during the campaign period using two gas standards on separate scales: a National Oceanic and Atmospheric Administration (NOAA) SX-3581 standard representative of clean low-hydrocarbon air, and an Essex canister prepared by UoM, representative of coastal air, which was higher in VSLS and hydrocarbon content. UoY and NCAR use the NOAA scale/standard for VSLS calibration, and UoM uses a scale based on dilutions of primary standards calibrated by GC with FID (flame ionisation detector) and AED (atomic emission detector). Analysis of the NOAA SX-3581 standard resulted in good agreement for CH2Cl2, CHCl3, CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl, CH3I, CH2ICl and CH2I2 (average relative standard deviation (RSD) < 10 %). Agreement was in general slightly poorer for the UoM Essex canister with an RSD of < 13 %. Analyses of CHBrCl2 and CHBr3 in this standard however showed significant variability, most likely due to co-eluting contaminant peaks, and a high concentration of CHBr3, respectively. These issues highlight the importance of calibration at atmospherically relevant concentrations ( ∼ 0.5–5 ppt for VSLSs; see Fig. 5 for individual ranges). The UoY in situ GC-MS measurements on board the BAe-146 compare favourably with ambient data from NCAR and UoM; however the UoY whole-air samples showed a negative bias for some lower-volatility compounds. This systematic bias could be attributed to sample line losses. Considering their large spatial variability, DMS and CH3I displayed good cross-platform agreement without any sampling bias, likely due to their higher volatility. After a correction was performed based upon the UoY in situ vs. whole-air data, all four instrument datasets show good agreement across a range of VSLSs, with combined mean absolute percentage errors (MAPEs) of the four platforms throughout the vertical profiles ranging between 2.2 (CH2Br2) and 15 (CH3I) % across a large geographic area of the tropical west Pacific. This study shows that the international VSLS calibration scales and instrumental techniques discussed here are in generally good agreement (within ∼ 10 % across a range of VSLSs), but that losses in aircraft sampling lines can add a major source of uncertainty. Overall, the measurement uncertainty of bromocarbons during these campaigns is much less than the uncertainty in the quantity of VSLS bromine estimated to reach the stratosphere of between 2 and 8 pptv.

Silver Nanoparticle-Decorated Shape-Memory Polystyrene Sheets as Highly Sensitive Surface-Enhanced Raman Scattering Substrates with a Thermally Inducible Hot Spot Effect.

In this study, an active surface-enhanced Raman scattering (SERS) substrate with a thermally inducible hot spot effect for sensitive measurement of Raman-active molecules was successfully fabricated from silver nanoparticle (AgNP)-decorated shape-memory polystyrene (SMP) sheets. To prepare the SERS substrate, SMP sheets were first pretreated with n-octylamine for effective decoration with AgNPs. By varying the formulation and condition of the reduction reaction, AgNP-decorated SMP (Ag@SMP) substrates were successfully prepared with optimized particle gaps to produce inducible hot spot effects on thermal shrink. High-quality SERS spectra were easily obtained with enhancement factors higher than 108 by probing with aromatic thiols. Several Ag@SMP substrates produced under different reaction conditions were explored for the creation of inducible hot spot effects. The results indicated that AgNP spacing is crucial for strong hot spot effects. The suitability of Ag@SMP substrates for quantification was also evaluated according to the detection of adenine. Results confirmed that prepared Ag@SMP substrates were highly suitable for quantitative analysis because they yielded an estimated limit of detection as low as 120 pg/cm2, a linear range of up to 7 ng/cm2, and a regression coefficient (R2) of 0.9959. Ag@SMP substrates were highly reproducible; the average relative standard deviation for all measurements was less than 10%.

Mass-Spectrometry-Based Quantification of Protein-Bound Fatty Acid Synthesis Intermediates from Escherichia coli.

The production of fatty acids from simple nutrients occurs via a complex biosynthetic pathway with dozens of intermediate compounds and multiple branch points. Despite its importance for microbial physiology and biotechnology, critical aspects of fatty acid biosynthesis, especially dynamics of in vivo regulation, remain poorly characterized. We have developed a liquid chromatography/mass spectroscopy (LC-MS) method for relative quantification of fatty acid synthesis intermediates in Escherichia coli, a model organism for studies of fatty acid metabolism. The acyl carrier protein, a vehicle for the substrates and intermediates of fatty acid synthesis, is extracted from E. coli, proteolytically digested, resolved using reverse-phase LC, and detected using electrospray ionization coupled with a tandem MS. Our method reliably resolves 21 intermediates of fatty acid synthesis, with an average relative standard deviation in ratios of individual acyl-ACP species to total ACP concentrations of 20%. We demonstrate that fast sampling and quenching of cells is essential to accurately characterize intracellular concentrations of ACP species. We apply our method to examine the rapid response of fatty acid metabolism to the antibiotic cerulenin. We anticipate that our method will enable the characterization of in vivo regulation and kinetics of microbial fatty acid synthesis at unprecedented detail and will improve integration of fatty acid synthesis into models of microbial metabolism.

Laser-induced breakdown spectroscopy of liquid solutions: a comparative study on the forms of liquid surface and liquid aerosol.

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869 μg/mL, which were close to those of liquid aerosol, 2.847 μg/mL of Cr and 97.635 μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R2 of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Evaluation of a miniaturised single-stage thermal modulator for comprehensive two-dimensional gas chromatography of petroleum contaminated soils

A novel miniaturised single-stage resistively heated thermal modulator was investigated as an alternative to cryogenic modulation for use in comprehensive two-dimensional gas chromatography (GC×GC). The single-stage thermal modulator described herein yielded average retention time relative standard deviations (RSD) of ≤0.2% RSD (first-dimension) and ≤3.4% RSD (second-dimension). The average peak widths generated by the modulator were 72±3ms, and the peak area precision was better than 5.3% RSD for a range of polar and non-polar test analytes. GC×GC analysis can be performed using this modulator without the requirement for cryogenic cooling or additional pressure control modules for flow modulation. The modulator and associated electronics are compact and amenable towards field analysis. The modulator was used for qualitative and quantitative characterisation of petroleum-contaminated soils derived from a sub-Antarctic research station at Macquarie Island. The limit of detection compared to standard 1D GC analysis was improved from 64 to 11mgkg−1. An automated method of analysing and categorising samples using principal component analysis is presented.

Spectrophotometric determination of metoclopramide medicine in bulk form and in pharmaceuticals using orcinol as reagent

Abstract A modern, accurate, simple and sensitive spectrophotometric procedure is tested for the appreciation of metoclopramide medicine as perspicuous form, as well as in various kinds of pharmaceutical dosages. The procedure depends on the interaction of metoclopramide (MCP) medicine and orcinol reagent by utilizing azo coupling reaction. The orcinol in NaOH solution middle to give a latterly ligand which reacts with copper (II) to output the complex with strong yellow color at 50°C. The resulting complex is water soluble, stable and can be determined spectrophotometrically at wavelength 459 nm. The calibration curve absorbance vs. concentration was established in the concentration range 0.6-12 ppm, and the curve followed the Beer’s law in this range. The procedure precision is given by the average recovery of 99.91% sequentially, as well as by the average relative standard deviation 0.70%, related to the amount of drug. The sensitivity is established at molar absorptivity 1.9044×104 l‧cm-1‧mol-1. The Sandell sensitivity is tested as 0.002 μg/cm2. The analytical results for the tested procedure agree with the official procedure. The interferences from medicine additives were tested. The established procedure is successfully examined on the appreciation of MCP in diverse kinds of pharmaceuticals.

Quantitative Detection of Trace Malachite Green in Aquiculture Water Samples by Extractive Electrospray Ionization Mass Spectrometry.

Exposure to malachite green (MG) may pose great health risks to humans; thus, it is of prime importance to develop fast and robust methods to quantitatively screen the presence of malachite green in water. Herein the application of extractive electrospray ionization mass spectrometry (EESI-MS) has been extended to the trace detection of MG within lake water and aquiculture water, due to the intensive use of MG as a biocide in fisheries. This method has the advantage of obviating offline liquid-liquid extraction or tedious matrix separation prior to the measurement of malachite green in native aqueous medium. The experimental results indicate that the extrapolated detection limit for MG was ~3.8 μg·L−1 (S/N = 3) in lake water samples and ~0.5 μg·L−1 in ultrapure water under optimized experimental conditions. The signal intensity of MG showed good linearity over the concentration range of 10–1000 μg·L−1. Measurement of practical water samples fortified with MG at 0.01, 0.1 and 1.0 mg·L−1 gave a good validation of the established calibration curve. The average recoveries and relative standard deviation (RSD) of malachite green in lake water and Carassius carassius fish farm effluent water were 115% (6.64% RSD), 85.4% (9.17% RSD) and 96.0% (7.44% RSD), respectively. Overall, the established EESI-MS/MS method has been demonstrated suitable for sensitive and rapid (<2 min per sample) quantitative detection of malachite green in various aqueous media, indicating its potential for online real-time monitoring of real life samples.

High precision pycnometer for volumetric measurement of polymerization shrinkage in light cured dental composites

Abstract Due to the many benefits such as excellent aesthetics, biocompatibility, and wear resistance, the use of light cured composite materials in dentistry has grown in the last few decades. However, the main disadvantage of present composite materials is significant volumetric shrinkage during curing, which leads to void and crack formation that is detrimental to the longevity of the restoration. This work presents a gas pycnometer which was re-designed to achieve high precision measurements of polymerization shrinkage while allowing in-situ curing of small size dental composites. Samples of dentin, enamel and body (DEB) shade of conventionally used restorative nanocomposite material with average mass of ∼141.35 mg were in-situ cured at irradiance of ∼370 mW/cm 2 using various exposure time cycles, which totaled the manufacturer recommended 60 s. The proposed system enhancements allowed measurement of time-dependent polymerization shrinkage of in-situ light cured dental composites. Volumetric measurements had reproducibility of ∼0.005% of nominal full-scale sample cell chamber volume; and the shrinkage measurements did not exceed the average relative standard deviation (RSD) of ∼2.8%, which is ∼4 times better when compared with conventional techniques. Overall, this newly developed high precision and C-factor independent technique provides better understanding of time-dependent volumetric polymerization shrinkage aiding in development of better clinical procedures and materials to improve health and longevity of composite restorations.

Statistical Comparison of Wet and Dry-Ashing Digestion Methods for the Determination of Copper and Iron Species in Orange Peel, Flesh and Tree Leaves by Flame Atomic Absorption Spectroscopy

ABSTRACTIn this study, two methods of wet digestion and dry-ashing digestion are performed and compared statistically for the determination of iron (Fe) and copper (Cu) species in the orange peel, flesh and leaves by means of flame atomic absorption spectroscopy (AAS). In wet digestion, the effects of two reagents and their mixtures were studied. In dry digestion, various factors affecting the digestion were studied and optimal condition established. Based on the average concentration (mg L−1), standard deviation (n = 5) and relative standard deviation (RSD)%, the best conditions of dry digestion and wet digestion to extract Fe and Cu were chosen. Finally, some 12 measurements were performed based on the optimum conditions of dry and wet digestions and the best method was selected with regard to the obtained results. In orange tree leaves because texp (0.016) is smaller than ttheorical (2.18), it shows that there is no difference between the two methods for analysis of Fe. However, the determination of Cu in orange tree leaves was practical with wet digestion in that texp (57.14)˃ ttheorical (2.18) shows there is a difference between the two methods and wet digestion is more suitable than dry-ashing due to obtaining less RSD%. In flesh orange, it is seen that for both texp ˃ ttheorical, showing there is a difference between the two methods and wet digestion is more suitable than dry-ashing one. Furthermore, in both Fe and Cu species, the texp ˃ ttheorical, indicating that the two digestion methods are different and wet digestion was selected as a suitable method because of obtaining smaller values of RSD%. Finally, after comparison of the results, the wet digestion vessel for Fe and Cu extraction in the samples was suggested. The developed digestion methods were validated with certified reference materials.