External Calibration Procedure Research Articles

Improved method of estimating temperatures at meteor peak heights

Abstract. For 2 decades, meteor radars have been routinely used to monitor atmospheric temperature around 90 km altitude. A common method, based on a temperature gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by fitting a linear regression model in the scattered plot of log⁡10(1/τ) and height, where τ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such a bias is that it produces a systematic offset in the estimated temperature, thus requiring calibration with other co-located measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in τ and the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. To incorporate various error terms in the statistical model, an appropriate regression analysis for these data is the errors-in-variables model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log⁡10(1/τ). This solution is found to be a good prior estimate for the core of this bivariate distribution. Further improvement is achieved by defining density contours of this bivariate distribution and restricting the data selection process within higher contour levels. With this solution, meteor radar temperatures can be obtained independently without needing any external calibration procedure. When compared with co-located lidar measurements, the systematic offset in the estimated temperature is shown to have reduced to 5 % or better on average.

A Technique for Improving the Precision of the Direct Measurement of Junction Temperature in Power Light-Emitting Diodes.

Extending the lifetime of power light-emitting diodes (LEDs) is achievable if proper control methods are implemented to reduce the side effects of an excessive junction temperature, TJ. The accuracy of state-of-the-art LED junction temperature monitoring techniques is negatively affected by several factors, such as the use of external sensors, calibration procedures, devices aging, and technological diversity among samples with the same part number. Here, a novel method is proposed, indeed based on the well-known technique consisting in tracking the LED forward voltage drop when a fixed forward current is imposed but exploiting the voltage variation with respect to room temperature. This method, which limits the effects of sample heterogeneity, is applied to a set of ten commercial devices. The method led to an effective reduction of the measurement error, which was below 1 °C.

Assessment of the Biorisk Status of Veterinary Laboratories in Southwest Nigeria: Application of the Food and Agriculture Organization Laboratory Mapping Tool-Safety Module.

Because of the nature of work conducted in veterinary laboratories and potential exposures to pathogenic microorganisms, good laboratory practices, risk assessments, biosafety, and biosecurity capacity is becoming vital. In this study, the Food and Agriculture Organization Laboratory Mapping Tool-Safety Module was applied to demonstrate its practical implementation in the assessment of biosafety and biosecurity statuses of veterinary laboratories in Nigeria. The Laboratory Mapping Tool-Safety Module, a standardized questionnaire, systematically and semiquantitatively gathered data on 98 subcategories covering 4 areas of biosafety and biosecurity capabilities: administrative, operational, engineering, and personal protective equipment. Overall, the various areas and categories covered by the Laboratory Mapping Tool-Safety Module were weak across the board, with a mean performance of 19.5% (95% confidence interval, 14.0%-25.1%; range, 0.8%-29.6%). The weakest functionality was in emergency preparedness (0.8%; ie, emergency responses and exercises such as fire drills, spill cleanup, and biological spill kit availability). Also, many laboratories were deficient in metrology procedures, biosafety cabinets, chemical hazard containment, regular maintenance and external calibration procedures for laboratory equipment, and personnel health and safety. However, a few functionalities within individual laboratories scored above average (50%), for example, a university microbiology laboratory animal facility (100%). Interlaboratory comparison indicated that biosafety and biosecurity performance was similar across laboratories (P = .07) and did not vary by location (P = .37). Significant biosafety and biosecurity improvements are needed to guarantee the health and safety of workers and the global community, efficient responses to infectious disease containment, and compliance with the Global Health Security Agenda.

Interference-free, green microanalytical method for total mercury and methylmercury determination in biological and environmental samples using small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry

An analytical method for the quantification of total Hg and CH3Hg+ in biological tissues (fish, mushroom) and water sediment was developed based on small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry using a low-resolution microspectrometer as detector. Sample preparation was carried out according to the procedure recommended by JRC Technical Report of European Commission for the determination of CH3Hg+ in seafood and adapted by us for lower consumption of reagents. Amounts of 0.1 – 0.5 g sample were subjected to extraction in 5 ml of 47% HBr then CH3Hg+ was extracted in 2 × 1 ml toluene and back-extracted in 2 ml aqueous solution of 1% l-cysteine. Total Hg/CH3Hg+ were quantified in 10 μl of acidic extract/l-cysteine solution after electrothermal vaporization and measurement of 253.652 nm Hg signal in the episodic emission spectra. Under the optimal working conditions of system (70 °C sample drying, 1300 °C sample vaporization, 10 W plasma power and 150 ml min−1 Ar flow) the limits of detection were 7.0 μg kg−1 total Hg and 3.5 μg kg−1 CH3Hg+. Comparison of slopes in external calibration and standard addition procedure revealed the lack of non-spectral interferences of multimineral matrix, so that the calibration against Hg2+ standards was adopted. Pooled recovery of total mercury/methylmercury was 101 ± 7%/100 ± 7%, while precision assessed from measurements of real samples was in the range 1.6-9.6%/2.7-12.8%. The proposed method validated according to Eurachem Guide 2014 is selective and complies with demands in European legislation (Decisions 657/2002; 333/2007; 836/2011) and Association of Official Analytical Chemists Guide in terms of performances for food control. The method displays a high degree of greenness by circumventing cold vapor generation, use of small amounts of reagents and full-miniaturized instrumentation resulting in low analytical costs without reducing results quality. Besides, the method is simple and rapid, since it uses external calibration curves prepared from Hg2+standard solutions both for total Hg and CH3Hg+ determination.

Scout-multiple reaction monitoring: A liquid chromatography tandem mass spectrometry approach for multi-residue pesticide analysis without time scheduling

In this work, an innovative method is described for multi-residue pesticide analysis by liquid chromatography coupled to targeted mass spectrometry, called “Scout-MRM, this new acquisition mode relies on the monitoring by either endogenous or spiked Scout compounds, hence fully releasing the monitoring of target molecules from time scheduling. As a proof of concept, a Scout-MRM method was built where 5 transitions groups tracking a total of 191 pesticides where successively triggered under the control of 5 spiked-in deuterated pesticides. As expected from its retention time independency, Scout-MRM demonstrates strong detection robustness towards modifications of gradient parameters, as well as easy method transfer between distinct analytical platforms with nearly 100% recovery after a single run. Finally, Scout-MRM was used for the multi-residue screening and quantification of pesticides in real surface water samples, by applying an external calibration procedure and comparing it with classical scheduled reaction monitoring methods.

Odorants quantitation in high-quality cocoa by multiple headspace solid phase micro-extraction: Adoption of FID-predicted response factors to extend method capabilities and information potential

This paper focuses on several methodological aspects in the quantitation of volatiles in solid samples by headspace solid phase micro-extraction (HS-SPME) combined with gas chromatography and parallel detection by flame ionization detector and mass spectrometry (GC-FID/MS). Informative volatiles, including key odorants and process markers, from single-origin cocoa samples (Colombia, Ecuador, Mexico, Sao Tomè, and Venezuela) were captured at two processing stages along the chocolate production chain (nibs and cocoa mass). Accurate quantitation was achieved by multiple headspace extraction (MHE) in headspace linearity conditions and by external calibration. Quantitative results on selected analytes (3-hydroxy-2-butanone, 2-heptanol, 2,3,5-trimethylpyrazine, 2-ethyl-3,6-dimethylpyrazine, ethyl octanoate, benzaldehyde, 2-methylpropionic acid, 3-methylbutyric acid, ethyl phenylacetate, 2-phenylethyl acetate, guaiacol, 2-phenylethanol, and (E)-2-phenyl-2-butenal) provided reliable information about the key sensory notes of cocoa intermediates (odor activity values) and their origin specificities. Additional information about analytes release by the solid environment (cocoa nibs, mass, and powders) was achieved by modeling decay curves. Parallel detection by MS and FID enabled quantitative cross-validation, and FID-predicted relative response factors (RRFs) extended method quantitation capabilities to additional compounds that were not subjected to an external calibration procedure: 3-methylbutyl acetate (isoamyl acetate), 2-heptanone, heptanal, 2-nonanone, γ-butyrolactone, octanoic acid, 2-ethyl-5(6)-methylpyrazine, phenylacetic acid, phenol, 2-acetyl pyrrole, and 2,3-dihydro-3,5-dihydroxy-6-methyl(4H)-pyran-4-one. This procedure extends method capabilities and information potential with great consistency.

Direct determination of copper and zinc in alcoholic and non-alcoholic drinks using high-resolution continuum source flame atomic absorption spectrometry and internal standardization

A simple, rapid, direct and multi-element method based on high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was developed to analyse a large variety of beverages with successful results. The use of the internal standard (IS) calibration method was explored to carry out the direct analysis of drinks with different sugar and/or alcohol content using only one calibration curve. The main absorption lines for the analytes (Cu, Zn and Pb) and the possible ISs (Ag, Co, Ni and Bi) were chosen to perform the analysis. In addition, the possibility of introducing the sample in the spectrometer in a continuous or discontinuous mode was investigated. The limits of quantification (LOQs) obtained using Ag as IS and the continuous sample introduction mode were 0.040 mg L−1 for Zn, 0.016 mg L−1 for Cu, and 0.099 mg L−1 for Pb. In addition, the precision, expressed as the relative standard deviation (RSD), was lower than 4% for the three elements. The developed IS method was applied to analyse different commercial beverages: an apple juice, a ready-to-drink beverage containing fruit juices, an isotonic drink, a lemon and lime flavoured soft drink, a beer, a wine, a gin, a whisky, a rum, and an apple liqueur. For comparison, these beverages were also analysed using a conventional external calibration procedure. The Cu concentration was lower than 1.28 mg L−1 and 0.15 mg L−1 in alcoholic and non-alcoholic drinks, respectively, and Zn concentration was lower than 0.37 mg L−1 in alcoholic and 12.3 mg L−1 in non-alcoholic drinks. The Pb concentration in all the analysed samples was below the limit of detection (LOD). The recoveries in the validation studies were within 92–109% for Cu, 93–111% for Zn and 94–110% for Pb.

Analysis of human cerebrospinal fluid monoamines and their cofactors by HPLC.

The presence of monoamines and their cofactors (the pterins and vitamin B6 (pyridoxal phosphate (PLP))) in human cerebrospinal fluid (CSF) can be used as indicators of the biosynthesis and turnover of dopamine and serotonin in the brain. In addition, abnormalities in the CSF levels of these molecules are associated with various neurological diseases, including genetic diseases leading to dopamine and serotonin deficiency. Here, we provide a set of quantitative high-performance liquid-chromatography (HPLC) approaches to determine CSF levels of monoamines and their cofactors. This protocol describes step-by-step procedures for CSF sample preparation for the analysis of different molecules, HPLC calibration and analysis, and data quantification and interpretation. Unlike plasma/tissue/blood samples, CSF requires minimal sample preparation: in this protocol, only the analysis of PLP requires mixing with trichloroacetic acid to release the protein-bound vitamin, centrifugation, and mixing of the supernatant with phosphate buffer and sodium cyanide for derivatization in alkaline conditions. Monoamines are analyzed by HPLC with coulometric electrochemical detection (ED), pterins are analyzed by HPLC with coupled coulometric electrochemical and fluorescence detection, and PLP is analyzed by HPLC with fluorescence detection. The quantification of all compounds is achieved by external calibration procedures, and internal quality control and standards are analyzed in each run. We anticipate that investigation of dopamine and serotonin disturbances will be facilitated by measurements of these compounds in human CSF and other biological samples. The estimated time for the different procedures primarily depends on the electrochemical detector stabilization. Overnight stabilization of this detector is advised, and, after that step, preanalytical equilibration rarely exceeds 3 h.

Calibrated cryo-cell UV-LA-ICPMS elemental concentrations from the NGRIP ice core reveal abrupt, sub-annual variability in dust across the GI-21.2 interstadial period

Abstract. Several abrupt shifts from periods of extreme cold (Greenland stadials, GS) to relatively warmer conditions (Greenland interstadials, GI) called Dansgaard–Oeschger events are recorded in the Greenland ice cores. Using cryo-cell UV-laser-ablation inductively coupled-plasma mass spectrometry (UV-LA-ICPMS), we analysed a 2.85 m NGRIP ice core section (2691.50–2688.65 m depth, age interval 84.86–85.09 ka b2k, thus covering ∼ 230 years) across the transitions of GI-21.2, a short-lived interstadial prior to interstadial GI-21.1. GI-21.2 is a ∼ 100-year long period with δ18O values 3–4 ‰ higher than the following ∼ 200 years of stadial conditions (GS-21.2), which precede the major GI-21.1 warming. We report concentrations of major elements indicative of dust and/or sea salt (Na, Fe, Al, Ca, Mg) at a spatial resolution of ∼ 200 µm, while maintaining detection limits in the low-ppb range, thereby achieving sub-annual time resolution even in deep NGRIP ice. We present an improved external calibration and quantification procedure using a set of five ice standards made from aqueous (international) standard solutions. Our results show that element concentrations decrease drastically (more than 10-fold) at the warming onset of GI-21.2 at the scale of a single year, followed by relatively low concentrations characterizing the interstadial part before gradually reaching again typical stadial values.

“Virtual IED sensor” at an rf-biased electrode in low-pressure plasma

Energy distribution and the flux of the ions coming on a surface are considered as the key-parameters in anisotropic plasma etching. Since direct ion energy distribution (IED) measurements at the treated surface during plasma processing are often hardly possible, there is an opportunity for virtual ones. This work is devoted to the possibility of such indirect IED and ion flux measurements at an rf-biased electrode in low-pressure rf plasma by using a “virtual IED sensor” which represents “in-situ” IED calculations on the absolute scale in accordance with a plasma sheath model containing a set of measurable external parameters. The “virtual IED sensor” should also involve some external calibration procedure. Applicability and accuracy of the “virtual IED sensor” are validated for a dual-frequency reactive ion etching (RIE) inductively coupled plasma (ICP) reactor with a capacitively coupled rf-biased electrode. The validation is carried out for heavy (Ar) and light (H2) gases under different discharge conditions (different ICP powers, rf-bias frequencies, and voltages). An EQP mass-spectrometer and an rf-compensated Langmuir probe (LP) are used to characterize plasma, while an rf-compensated retarded field energy analyzer (RFEA) is applied to measure IED and ion flux at the rf-biased electrode. Besides, the pulsed selfbias method is used as an external calibration procedure for ion flux estimating at the rf-biased electrode. It is shown that pulsed selfbias method allows calibrating the IED absolute scale quite accurately. It is also shown that the “virtual IED sensor” based on the simplest collisionless sheath model allows reproducing well enough the experimental IEDs at the pressures when the sheath thickness s is less than the ion mean free path λi (s < λi). At higher pressure (when s > λi), the difference between calculated and experimental IEDs due to ion collisions in the sheath is observed in the low energy range. The effect of electron impact ionization in the sheath on the origin and intensity of low-energy peaks in IED is discussed compared to ion charge-exchange collisions. Obviously, the extrapolation of the “virtual IED sensor” approach to higher pressures requires developing some other sheath models, taking into account both ion and electron collisions and probably including even a model of the whole plasma volume instead of plasma sheath one.

Automatic detection of a one dimensional ranging pole for robust external camera calibration in mobile mapping

A mobile mapping system (MMS) is the answer of the geoinformation community to the exponentially growing demand for various geospatial data with increasingly higher accuracies, captured by multiple sensors. As the mobile mapping technology is pushed to explore its use for various applications on water, rail, or road, the need emerges to have an external sensor calibration procedure that is portable, fast and easy to perform. This way, sensors can be mounted and demounted depending on the application requirements without the need for time consuming calibration procedures. A new methodology is presented to provide a high quality external calibration of cameras which is automatic, robust and fool proof. The method uses a portable, standard ranging pole which needs to be positioned on a known ground control point. While the literature focuses on solving the absolute orientation problem of the calibration, an automatic method to detect the calibration object is missing. Here, we present a mutual information based image registration technique for automatic sub-pixel localization of the ranging pole under realistic outdoor conditions. We include several robust error detection rules to allow the calibration to run without human intervention, giving as little outliers as possible, to ensure a correct calibration. Several tests are performed under various lighting and noise conditions which prove the methodology’s robustness.

Improving the thermal, radial, and temporal accuracy of the analytical ultracentrifuge through external references

Sedimentation velocity (SV) is a method based on first principles that provides a precise hydrodynamic characterization of macromolecules in solution. Due to recent improvements in data analysis, the accuracy of experimental SV data emerges as a limiting factor in its interpretation. Our goal was to unravel the sources of experimental error and develop improved calibration procedures. We implemented the use of a Thermochron iButton temperature logger to directly measure the temperature of a spinning rotor and detected deviations that can translate into an error of as much as 10% in the sedimentation coefficient. We further designed a precision mask with equidistant markers to correct for instrumental errors in the radial calibration that were observed to span a range of 8.6%. The need for an independent time calibration emerged with use of the current data acquisition software (Zhao et al., Anal. Biochem., 437 (2013) 104–108), and we now show that smaller but significant time errors of up to 2% also occur with earlier versions. After application of these calibration corrections, the sedimentation coefficients obtained from 11 instruments displayed a significantly reduced standard deviation of approximately 0.7%. This study demonstrates the need for external calibration procedures and regular control experiments with a sedimentation coefficient standard.

Application of laser ablation-ICP-mass spectrometry for 2-dimensional mapping of element distributions in a Late Archean impact spherule layer

ser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has been successfully applied to visualize the 2-dimensional distribution of various major (Mg, Mn, Fe) and trace (Cr, Co, Ni, Ir, Pt) elements in the Late Archaean Paraburdoo impact spherule layer (PB SL). As this spherule layer is highly enriched in meteoritic material, this study particularly focuses on the distribution of siderophile elements. Multi-elemental maps with a lateral resolution of 15 μm, covering surface areas of approximately 1.5 mm × 1.5 mm and multiple impact spherules, were acquired by LA-ICP-MS using two different ablation – standard (circular) and teardrop – cells. It was observed that with the teardrop cell, the elemental maps follow the mineralogy as displayed by the optical microscopy image more closely, with limited memory and washout effects in comparison to the standard cell. In order to acquire representative quantitative data, 100 μm diameter spot LA-ICP-MS analysis in a vertical transect through the SL was performed additionally. Quantification of element concentrations in the PB SL was carried out using external calibration procedures. The validity of this approach was evaluated by comparison of the averages of the determined transect spot concentrations to bulk rock geochemical data and it was found that the mean concentrations fall within the uncertainty of the bulk geochemical analysis, but the results show biases of 5.9% for Pt, 16% for Ir, 11% for Cr and 38% for Ni. In addition, the bulk rock Pt/Ir elemental ratio obtained upon transect LA-ICP-MS analysis was reported and it was observed that the slope of the regression line (1.06) and the mean value (1.23) for all data points measured with LA-ICP-MS equal the bulk rock Pt/Ir value of 1.08–1.43 measured by fire assay/solution ICP-MS for all PB SL outcrops at the Governor site.

Development of a method for the determination of advanced glycation end products precursors by liquid chromatography and its application in human urine samples

A liquid chromatographic method with fluorimetric detection has been developed to determine the most abundant α-dicarbonyl compounds, generated as intermediates in the Maillard's reaction, previous derivatization to high fluorescent pteridinic derivatives. Hence, the biomarkers D-glucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, diacetyl, 2,3-pentanedione, and phenylglyoxal were quantified using a gradient elution mode. The experimental conditions of the derivatization reaction and mobile phase composition were optimized. Linearity ranges (peak area versus α-dicarbonyl compound concentration) from 1.0 to 100.0 ng mL(-1) were obtained. Detection limits were comprised between 0.3 and 11.0 ng mL(-1). The high sensitivity of the method allows the determination of α-dicarbonyl compounds present in human urine, such as D-glucosone, 3-deoxyglucosone, glyoxal, and methylglyoxal, that are used as biomarkers, in order to investigate their roles in several diseases, with special emphasis in diabetes mellitus. With the aim of avoiding the interferences due to pteridinic compounds present in urine, a cleanup step with an ISOLUTE ENV+ cartridge was carried out. The concentrations of these urinary biomarkers have been reported as a normalized ratio to urinary creatinine, and determined in healthy and in diabetic volunteers, of different ages and sex. In all urine samples, standard addition and external calibration procedures were applied and compared.

A matrix effect and accuracy evaluation for the determination of elements in milk powder LIBS and laser ablation/ICP-OES spectrometry

Laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES) and laser-induced breakdown spectroscopy (LIBS) were investigated for the determination of Ca, Mg, Zn and Na in milk samples. The accuracy of both methods was evaluated by comparison of the concentration found using LA-ICP-OES and LIBS with classical wet digestion associated with ICP-OES determination. The results were not fully acceptable, with biases from less than 1% to more than 60%. Matrix effects were also investigated. The sample matrix can influence the temperature, electron number density (n (e)) and other excitation characteristics in the ICP. These ICP characteristics were studied and evaluated during ablation of eight milk samples. Differences in n (e) (from 8.9 to 13.8 × 10(14) cm(-3)) and rotational temperature (ranging from 3,400 to 4,400 K) occurred with no correlation with trueness. LIBS results obtained after classical external calibration procedure gave degraded accuracy, indicating a strong matrix effect. The LIBS measurements clearly showed that the major problem in LA-ICP was related to the ablation process and that LIBS spectroscopy is an excellent diagnostic tool for LA-ICP techniques.

Determination of major, minor and trace elements in rock samples by laser ablation inductively coupled plasma mass spectrometry: Progress in the utilization of borate glasses as targets

The present work is a continuation of a research study performed at our laboratory aiming at the multielement analysis of rock samples (basalts and shale) by inductively coupled plasma mass spectrometry in combination with laser ablation using borate glasses as analytical targets. Argon, nitrogen–argon mixtures and helium were evaluated as cell gases, the latter confirming its better performance. Different operational parameters of the laser, such as gas flow, energy, focus, scanning speed and sampling frequency were optimized. External calibration was made with standards prepared by fusion of geological reference materials (basalts 688 and BCR-2, obsidian SRM 278, and shale SGR-1) of different mass fractions in the meta–tetra borate matrix. Coefficients of determination ( R 2) were > 0.99 for 30 elements from o total of 40 determined. Method validation was then performed using additional certified reference materials (BHVO-2, BIR-1, SCo-1) produced as borate targets in a similar way. Accuracies were better than 10% for most of the elements studied and analytical precisions, calculated from the residual standard deviations of calibration curves were, typically, between 6% and 10%. Additionally, the semiquantitative TotalQuant® technique was applied, which gave, within the expected uncertainty for this calibration technique, concordant results when compared to the quantitative external calibration procedure. Both methods were then used for the analysis of marine shale samples, which are of great geological interest in petroleum prospecting.

Spectroscopic analysis (FTIR, Raman) of water in mafic and intermediate glasses and glass inclusions

Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H 2O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH − and molecular H 2O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H 2O content (H 2O T = OH − + H 2O m) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterisation) intensity of the 3550 cm −1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H 2O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H 2O T band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H 2O by Raman spectroscopy irrespective of the procedure, whereas the parameterisation mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H 2O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm −1. We provide new FTIR absorptivity coefficients ( ε 3550) for basalt (62.80 ± 0.8 L mol −1 cm −1) and basanite (43.96 ± 0.6 L mol −1 cm −1). These values, together with an exhaustive review of literature data, confirm the non-linear decline of the FTIR absorptivity coefficient ( ε 3550) as the glass depolymerisation increases. We demonstrate the good agreement between micro-FTIR and micro-Raman determination of H 2O in silicate glasses when the matrix effects are properly considered.

A novel second-order standard addition analytical method based on data processing with multidimensional partial least-squares and residual bilinearization

In the presence of analyte–background interactions and a significant background signal, both second-order multivariate calibration and standard addition are required for successful analyte quantitation achieving the second-order advantage. This report discusses a modified second-order standard addition method, in which the test data matrix is subtracted from the standard addition matrices, and quantitation proceeds via the classical external calibration procedure. It is shown that this novel data processing method allows one to apply not only parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least-squares (MCR-ALS), but also the recently introduced and more flexible partial least-squares (PLS) models coupled to residual bilinearization (RBL). In particular, the multidimensional variant N-PLS/RBL is shown to produce the best analytical results. The comparison is carried out with the aid of a set of simulated data, as well as two experimental data sets: one aimed at the determination of salicylate in human serum in the presence of naproxen as an additional interferent, and the second one devoted to the analysis of danofloxacin in human serum in the presence of salicylate.

Comparison of microconcentric and membrane-desolvation sample introduction systems for determination of low rare earth element concentrations in surface and subsurface waters using sector field inductively coupled plasma mass spectrometry

Analytical performances of a microconcentric nebulizer (MCN) and a membrane-desolvation sample introduction system (Aridus) were compared for determination of low concentrations of rare earth elements (REEs) in surface and subsurface waters using a double focusing sector field inductively coupled plasma mass spectrometer. Conventional figures of merit were employed, such as sensitivities, limits of detection (LOD), REE–O + formation, matrix induced interferences, long term signal variations, and recovery from spiked sea water samples and a pristine water CRM. Sensitivity as a function of mass for the MCN was quite flat with the exception of light REE (LREE +) which was dependent on REE–O + generation. Signal responses using the Aridus were enhanced by factors of 4–10. Large sensitivity enhancements were observed for 139La +, 140Ce + and 141Pr +, due to the attenuation of their REE–O + (where the Aridus 140Ce 16O +/ 140Ce + was three orders of magnitude lower than that determined using the MCN) as a result of water analysis reduction in the plasma. Despite higher sensitivities, Aridus LODs were not significantly different from those obtained using the MCN, and values varied from 0.05 to 0.2 ng L − 1 and 0.1 to 0.2 ng L − 1 for the MCN and Aridus systems, respectively. When using the MCN, LREE + signals were closely associated with REE–O bond strengths, implying that LREE–O + production and breakdown are related to the strength of REE–O bonds in REE–O + ions suggesting that medium REE (MREE)–O + and heavy REE (HREE)–O + if formed, were thermally unstable in the plasma. In the presence of conservative Na concentrations, MCN LREE + signal suppressions varied from about 15 to 25% and about 5 to 10% for MREE + and HREE +. In contrast, regular 15% signal suppressions for all REE + were observed for the Aridus. In the case of the MCN, more than one internal standard is required for compensation for these different effects, whereas a single internal standard ( 159Tb +) compensated for REE + signal variations with the Aridus. Long term uncompensated REE + signal % RSDs using the MCN varied from about 2 to 5%, and % recoveries were about 95–110%. With internal standardization, % RSD varied irregularly from about 1 to 3% and % recoveries were not significantly improved. In contrast, with the Aridus, high % RSDs of about 8% and recoveries of about 80% were compensated with 159Tb + as the internal standard (< 0.5% and recoveries of about 100%, respectively). Accuracy was determined by analyzing spiked sea water CRM (NAAS-5) (1:100 v/v) spiked with 1 µg L − 1 REEs and CRM SLRS-4 using an external calibration procedure. With the Aridus system, REE recoveries were about 100% with 159Tb + as the internal standard. REE determinations of SLRS-4 were in good agreement with the reported values indicating that very low REE concentrations can be determined directly without matrix separation and analyte preconcentration.

Comparação entre métodos de quantificação em cromatografia gasosa: um experimento para cursos de química

COMPARISON OF QUANTIFICATION METHODS IN GAS CHROMATOGRAPHY: AN EXPERIMENT FOR CHEMISTRY COURSES. This article describes an experiment designed to teach quantitative determination in gas chromatography (GC) in Organic and Analytical Chemistry practical classes. The experiment consisted of extracting and analyzing eugenol from clove seeds to perform a quantitative approach aimed at comparing results obtained by external and internal calibration procedures. Therefore, this experiment proved to be very effective tool to enhance students awareness on the need to understand different types of calibration in GC and on how to avoid common experimental errors, and to find the best ways to eliminate their interference during the quantitative analysis phase.