Experimental Standard Uncertainty Research Articles

Simultaneous extraction/derivatization for the analysis of sulfite by capillary electrophoresis: A high-throughput reference method to meet the demand of seafood inspection

Sulfite is widely used to prevent enzymatic browning in shrimp and lobster processing. However, sulfite may cause allergy in sensitive consumers. Thus, regulatory agencies set limits for its use. Sulfite is usually controlled by the normalized Monier-Williams (MW) titrimetric method that allows a limited number of samples to be analyzed. This manuscript consolidates an innovative method for sulfite inspection in seafood by capillary zone electrophoresis with diode array detector (CZE-DAD). A simple, fast, and simultaneous extraction and derivatization method was developed to provide high throughput for analytical routine. The high instability of the sulfite was suppressed by its derivatization with formaldehyde producing hydroxymethylsulfonate. The evaluation of its analytical performance yielded excellent results in compliance with the strict parameters required for metrological accreditation. The CZE-DAD method was selective and specific when submitted to confirmatory evaluations by liquid chromatography coupled to mass spectrometry. The limit of detection (3.50 mg kg−1), limit of quantitation (11.7 mg kg−1) and recoveries (99–103%) were adequate for sample analysis. The measurement uncertainty was estimated by the propagation of errors and experimental standard uncertainties (precision, accuracy, and analytical curves) and type B uncertainties from traceable measurement instruments. The low relative uncertainty (10%) and the adequate reproducibility demonstrated method suitability. The CZE-DAD results were compared to the MW method through the respective expanded standard uncertainties and normalized error. This new method is promising to be used in seafood inspection and continuous laboratory evaluations using instrumentation not very expensive to acquire and maintain.

Phase equilibria of hydrates from ternary mixtures of methane + ethane + propane and methane + propane + carbon dioxide

AbstractHydrate–liquid–vapour (HLV) equilibrium of aqueous clathrates formed from gas mixtures can be complex compared to hydrates formed with single guests. Typically, pressure and temperature are controlled to obtain these data, but for multicomponent systems, it is necessary to control/report more intensive variables, namely, composition. Metastability, manifested as impractically long experimental times, has been reported to be a challenge with some multicomponent systems. We present HLV equilibrium conditions of two ternary gas mixtures: methane + ethane + propane (90:7:3 molar ratio) and methane + propane + carbon dioxide (55:5:40 molar ratio). Conditions varied in the temperature range of 275–285 K and the pressure range of 1.24–4.75 MPa. Experimental standard uncertainties were on average 0.10 K and 0.005 MPa for methane + ethane + propane and 0.19 K and 0.005 MPa for methane + propane + carbon dioxide. Our technique allowed us to bypass the limitations reported in the literature and provided fast, reproducible HLV equilibria for gas‐dominated systems.

Vapor-liquid equilibrium measurements for the binary mixtures of 1,1-difluoroethane (R152a) with trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) and 3,3,3-trifluoropropene (R1243zf)

In this work, vapor-liquid equilibrium (VLE) of R152a + R1234ze(E) and R152a + R1243zf systems were measured by using a recirculation analytical apparatus from 273.15 to 313.15 K. The maximum experimental standard uncertainties of the temperature, pressure, and composition were 5 mK, 0.6 kPa, and 0.0024, respectively. The Peng-Robinson (PR) equation combined with the van der Waals (vdW) mixing rule was used to correlate the VLE data for the two systems. The average relative deviation of pressure (ARD(p)) and the average absolute deviation of vapor phase mole fraction (AAD(y)) were 0.16% and 0.0012 for the R152a + R1234ze(E) system. The ARD(p) and AAD(y) were 0.11% and 0.0012 for the R152a + R1243zf system. The VLE data and correlation results showed that the R152a + R1234ze(E) system is zeotropic and the R152a + R1243zf system is azeotropic in the measured temperature range.

DETERMINATION OF THE METROLOGICAL CHARACTERISTICS OF PIPE PROVERS BASED ON THE CONCEPT OF UNCERTAINTY

In this paper noted that oil metering units are used to determine the amount of crude oil. The metering units of crude oil that implement the method of dynamic measurements, the amount of oil is determined by the readings of oil meters (turbine or mass flow meters). Such flow rate transducers (flow meters) are subject to verification during operation. The main reference means used for the calibration of flow transducers are pipe provers (TPP). Calibration of such reference units can be performed using reference meters (compact-prover), reference balance and using a reference pipe prover with a comparator. The methods of calibration pipe provers with the use of reference meters (standard volume measure), as well as a reference compact-prover with a comparator have been developed. These methods of calibration approbation during the calibration of reference pipe prover installations operated at the facilities of JSC "Ukrtransnafta". The method is considered, and also the structural scheme of calibration of TPP by means of the reference compact prover with the comparator is resulted. A mathematical model is developed taking into account the influential factors and algorithms for their evaluation, as well as the metrological characteristics of TPP are determined - the uncertainty budget is formed and the uncertainty of measuring the capacity of the pipe prover calibration unit is estimated. According to the results of calibration of TPP BHP -1100 company "VEGYEPSZER", Hungary, operated in the Branch "PDMN" JSC "Ukrtransnafta" (Kremenchuk) using the reference Compact Prover company Brooks Insntrument Division Emerson Electric Co., USA comparator - turbine flow meter Smith Meter series MVTM, USA, the relative extended uncertainty of TPP capacity measurement was 0,03%. The main contributions to the extended measurement uncertainty during TPP calibration were the standard uncertainties due to the influence of liquid volume expansion (liquid temperature measurement) in TPP and compact-prover, the standard uncertainty of the reference compact-prover and the experimental standard uncertainty of pipe prover capacitance measurement result's mean value.

OA153] EBT3 radiochromic film dosimetry in kV X-ray radiation therapy

Purpose To evaluate the suitability of EBT3 radiochromic films for the dosimetry of therapeutic kV X-ray beams and particularly examine their potential energy dependence. Methods Film samples from the same batch were irradiated at dose levels of 0.5, 1, 2 and 3 Gy using seven filters/qualities Q (80 ⩽ kVp ⩽ 220, 2.5mmAl ⩽ HVL ⩽ 2mmCu) of a unit calibrated using the in-air method [1] . Pre- and post-irradiation scanning facilitated the calculation of energy response, S AD , W (Q) = netOD(Q)/ D w (Q) for the red channel. S AD , W (Q) equals the inverse product of the intrinsic energy dependence, k bq (Q) = D film (Q)/netOD(Q), by the absorbed dose to water energy dependence, f(Q) = D w (Q)/ D film (Q). The latter was calculated using MCNP6 [2] employing secondary electron tracking in the experimental geometry with beam spectra from SpekCalc [3] and film composition from the literature [4] . k bq (Q) was calculated from experimental [ S AD , W (Q)] and simulation [f(Q)] results. Results EBT3 film does not exhibit energy dependence in the qualities studied. S AD , W (Q) results relative to the highest quality equal unity within 1%, which is well within experimental standard uncertainty (on the order of 4%). An increase of f - 1 (Q) with decreasing quality was found (up to 1.37 relative to the highest quality) suggesting an almost equal film under-response [ k bq - 1 (Q) 1], in accordance with the literature [4] . While S AD , W (Q) varies with dose due to the known non-linearity of film dose response, relative results are in close agreement regardless of dose level. Conclusions The energy dependence of EBT3 films is negligible in the energy range studied. Future studies will extend the studied energy range and focus on reducing experimental uncertainty, studying batch variability, and application of EBT3 for experimental dosimetry.

Measurements of bubble point pressure and saturated liquid density for ((R1234yf + R290))

In this paper, bubble point pressures and saturated liquid densities of {2,3,3,3-Tetrafluoroprop-1-ene (R1234yf) + propane (R290)} binary mixtures were measured using a compact single-sinker densimeter. Measurements were carried out over temperatures from (255.048 to 300.135) K and mole fractions of R1234yf at (0.113, 0.217, 0.322, 0.422, 0.533, 0.625). The experimental standard uncertainties were estimated to be less than 5 mK for the temperature, 2 kPa for the pressure, 0.003 for the mole fraction and 0.02% for the density. The experimental bubble point pressures were correlated by the Peng-Robinson equation of state, while the experimental saturated liquid densities were represented with the VDNS and our modified Rackett equations. In addition, saturated liquid densities of azeotropy point at temperatures T = (253.150, 263.150, 273.150, 283.150 and 293.150) K were determined based on our previous and present work.

Measurements of isothermal vapour–liquid equilibrium for the 2,3,3,3-tetrafluoroprop-1-ene + propane system at temperatures from 253.150 to 293.150 K

The vapour–liquid phase equilibrium was measured using an apparatus based on the recirculation method for the 2,3,3,3-tetrafluoroprop-1-ene + propane binary system. A total of 55 data points were obtained over the temperature range from 253.150 to 293.150 K. The experimental standard uncertainties were less than 5 mK for the temperature, 800 Pa for the pressure, and 0.005 for the mole fraction. The experimental data were correlated by the PR-VDW model and PR-HV-NRTL model. Both models can present the experimental data well and the PR-HV-NRTL model achieves a higher degree of precision. The relative deviations of pressure are within ±0.50% and the maximum absolute deviation of vapour mole fraction is 0.006 for the PR-HV-NRTL model. A positive azeotropic behaviour can be observed for the binary system.

Experimental study on the gaseous pρTx properties for (HFO1234yf + HC290)

Values of gaseous pρTx were measured with a compact single-sinker densimeter for {2,3,3,3-tetrafluoroprop-1-ene (HFO1234yf)+propane (HC290)} mixtures. A total of 168 data points was obtained at temperatures from (265.460 to 300.268) K, pressure up to 0.70252MPa, and mole fractions of HFO1234yf at (0.0906, 0.2546, 0.5830, 0.8116, and 1.0000). For the densimeter, values of the experimental standard uncertainty were less than 5mK for the temperature, 200Pa for the pressure, and 0.0003 for the mole fraction. When all the experimental standard uncertainties are considered, the relative uncertainty in density was estimated to be less than 0.13%. The experimental results were correlated using a truncated virial equation of state (EOS) and the Patel-Teja (PT) EOS. The virial model gives the best description of the experimental pρTx values with average absolute relative deviations of 0.080% in pressure and 0.085% in density.

Investigation of pρTx properties for R1234ze(E) + R134a mixtures in the gas phase

In this work, 101 gaseous pressure–density–temperature–mole fraction (pρTx) measurements for trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) + 1,1,1,2-tetrafluoroethane (R134a) binary mixtures were measured along with seven isotherms from 270.351 to 300.276 K by using a compact single-sinker densimeter. The mixtures consisted of four mole fractions of R1234ze(E) from 0.4338 to 0.6356, corresponding to mass fractions of R1234ze(E) from 0.4613 to 0.6610. The experimental standard uncertainties in temperature, pressure, mole fraction, and density were estimated to be less than 5 mK, 200 Pa, 0.0003, and 0.05%, respectively. The Peng–Robinson (PR) equation of state with vdW one-fluid mixing rules and a truncated virial equation of state were employed to correlate the experimental data. The correlated results from different models are consistent with each other, and the virial model gives the best description of the experimental pρTx data with average absolute relative pressure and density deviations of 0.088% and 0.093%, respectively.

Thermal Conductivity of Aqueous Solvents Used in CO2 Capture

The growing CO2 concentration in the atmosphere forces researchers to work on improving existing carbon dioxide capture technologies. This technology is energy-intensive and consumes significant amount of heat for solvent regeneration. Thermal conductivity is a key property for the estimation of the heat required for solvents regeneration. Accordingly, in the present work thermal conductivity is measured for six aqueous solvent used for this purpose; monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2methyl-1-propanol (AMP), sodium hydroxide (NaOH), potassium carbonate (K2CO3), and potassium glycinate (PG) aqueous solutions for mole fraction range from 0.00 to 0.0825. The measurements were carried out at constant temperature (294.82K) and pressure (102.02kPa). The total experimental standard uncertainty of thermal conductivity, pressure, temperature, and mole fraction measurements were estimated to be ± 0.001 Wm-1K-1, ± 0.02kPa, ± 0.1K, and ± 0.0002, respectively. The measured values of thermal conductivity were compared with data and correlations reported in the literature. The average absolute deviation between measured and calculated values from available correlation equations for the thermal conductivity was lease than 0.5%.

Gaseous pVTx measurements for (HFC134a + HC290) by a compact single-sinker densimeter

Comprehensive gaseous pVTx measurements for {1,1,1,2-tetrafluoroethane (HFC134a)+propane (HC290)} were carried out by a compact single-sinker densimeter, based on the Archimedes’ buoyancy principle, at temperatures from (258 to 294)K, pressures up to 0.86MPa, and mole fractions of HFC134a from (0.2391 to 0.7989). The overall experimental standard uncertainty in temperature, pressure, mole fraction and density were estimated to be less than 5mK, 176Pa, (0.02 and 0.05)%, respectively. A truncated virial equation of state was employed to correlate the experimental pVTx data of (HFC134a+HC290) mixtures. This equation represented the experimental pressures and densities with average absolute relative deviations of (0.043 and 0.046)%, respectively.

Is there a fundamental upper limit for the significanceI/σ(I) of observations from X-ray and neutron diffraction experiments?

The answer is yes. A fundamental limit exists, which is not strongly applicable to individual reflections but to a sufficiently large set of reflections such as any set for structure determination. The limit originates from Poisson statistics which gives a minimum (average) error. The proposed limit of significance and a proposed decrease in significance due to data processing are also tested by monitoring W = <I(hkl)(1/2)>/<sigma(I(hkl))> for raw and for Bragg data. Since Poisson statistics are the lower limit for the experimental standard uncertainties, it is expected that W < 1 for raw and Bragg data, and that W decreases upon data processing. W also gives a measure of systematic errors in the experimental data as W ≈ 1 characterizes pure Poisson data, W >> 1 is physically impossible for sufficiently large data sets of unmerged reflections and W < 1 describes the contamination with systematic errors. Systematic differences depending on the software used to process the data were found. Also, the frequency distributions in particular of σ(I) values change considerably depending on the data-processing software used. We have no explanation for these differences in the distributions of σ(I), which lead to distinct changes in the frequency distribution of the significances I/σ(I) compared with the raw data. Another consequence of Poisson statistics is that lower limits also exist for the agreement factors, the internal agreement factor and the goodness of fit. These limits depend on the moments <1/I(o)>, <I(o)>, <I(o)(2)> and <I(o)(1/2)> of the observed set of intensities I(o) about the origin. These agreement factors are theoretically attainable when no systematic sources of error apply. They may be used in future to construct further measures of systematic error in experimental data.

Vapor-Liquid Equilibria of HFC-32/n-Butane Mixtures

The vapor-liquid equilibria of HFC-32 and n-butane mixtures were measured in a temperature range of 283.15 to 313.15 K using a circulation method. The experimental standard uncertainties of temperature, pressure, and composition measurements were estimated to be within 10 mK, 2 kPa, and 0.2% in mole fraction, respectively. The measured data were correlated with the Peng–Robinson (PR) equation of state using Wong and Sandler mixing rules. The relative deviations of the measured bubble-point pressure from the calculated bubble-point pressure as a function of the measured bubble-point pressure were found to be less than 2.5%.

Structural chemistry of a green fluorescent protein Zn biosensor.

We designed a green fluorescent protein mutant (BFPms1) that preferentially binds Zn(II) (enhancing fluorescence intensity) and Cu(II) (quenching fluorescence) directly to a chromophore ligand that resembles a dipyrrole unit of a porphyrin. Crystallographic structure determination of apo, Zn(II)-bound, and Cu(II)-bound BFPms1 to better than 1.5 A resolution allowed us to refine metal centers without geometric restraints, to calculate experimental standard uncertainty errors for bond lengths and angles, and to model thermal displacement parameters anisotropically. The BFPms1 Zn(II) site (KD = 50 muM) displays distorted trigonal bipyrimidal geometry, with Zn(II) binding to Glu222, to a water molecule, and tridentate to the chromophore ligand. In contrast, the BFPms1 Cu(II) site (KD = 24 muM) exhibits square planar geometry similar to metalated porphyrins, with Cu(II) binding to the chromophore chelate and Glu222. The apo structure reveals a large electropositive region near the designed metal insertion channel, suggesting a basis for the measured metal cation binding kinetics. The preorganized tridentate ligand is accommodated in both coordination geometries by a 0.4 A difference between the Zn and Cu positions and by distinct rearrangements of Glu222. The highly accurate metal ligand bond lengths reveal different protonation states for the same oxygen bound to Zn vs Cu, with implications for the observed metal ion specificity. Crystallographic anisotropic thermal factor analysis validates metal ion rigidification of the chromophore in enhancement of fluorescence intensity upon Zn(II) binding. Thus, our high-resolution structures reveal how structure-based design has effectively linked selective metal binding to changes in fluorescent properties. Furthermore, this protein Zn(II) biosensor provides a prototype suitable for further optimization by directed evolution to generate metalloprotein variants with desirable physical or biochemical properties.

Absolute measurement of the hyperfine splittings of six molecular 127I2 lines around the He-Ne/I2 wavelength at λ = 633 nm

With the aid of two diode-laser narrowband spectrometers around 633 nm, we report the measurement of the iodine hyperfine components of the R(60) 8-4, R(125) 9-4 and P(54) 8-4 transitions located −12 GHz from the classical red He-Ne laser stabilized on the R(127) 11-5 transition of 127I2, the P(33) 6-3 transition roughly −1 GHz away, the P(39) 6-3 transition 3.4 GHz above, and the R(59) 8-4 and P(53) 8-4 transitions roughly 19 GHz above. The Doppler-free absorption signals were resolved using a third-harmonic detection technique and hyperfine frequency splittings were measured by beat-frequency techniques. The individual hyperfine transitions were linked to a 633 nm He-Ne laser by direct frequency measurements up to 16 GHz. The experimental standard uncertainty was typically below 5 kHz (i.e. relative uncertainty <1 × 10−11).

How precise are measurements of unit-cell dimensions from single crystals?

The results of single-site and many-site measurements of cell dimensions from single crystals are compared for Bond and four-circle diffractometers using samples of corundum (essentially pure rhombohedral alpha-Al2O3, aluminum oxide) of high diffraction quality, where the effects of small changes in temperature and composition (Cr2O3, chromium oxide, in solid solution) can be taken into account. Similar comparisons are made for four-circle diffractometer measurements on ruby (alpha-Al2O3, with 0.46 wt % Cr in solid solution). The precisions are some parts in 10(5). There is partial support for the Taylor-Kennard [Acta Cryst. (1986), B42, 112-120] dictum that standard uncertainties (s.u.s) of cell parameters from routine four-circle diffractometer measurements are less than those for many-site measurements by factors of 5 for cell lengths and 2.5 for cell angles. For organic crystals, independent repetitions of adequate quality for comparison and analysis of routine four-circle diffractometer measurements are available only for alpha-oxalic acid dihydrate and anthracene. The experimental standard uncertainties given for these two crystals agree reasonably well with the sample s.u.s at room temperature, but appreciably less well at approximately 100 K, again giving partial support to the Taylor-Kennard dictum. The relation between specimen characteristics and attainable precision is emphasized; the precisions for routine measurements on good quality organic crystals are some parts in 10(4). Area-detector measurements of cell dimensions have also been appraised; currently published s.u.s from such measurements appear to be highly unreliable, and this is supported by a recent analysis of the operation of such diffractometers [Paciorek et al. (1999). Acta Cryst. A55, 543-557]. Formulation of a standard protocol for such measurements is badly needed. The dangers inherent in high degrees of replication are illustrated by recounting Kapteyn's Parable of the Chinese Emperor. Attention is drawn to the fact that there has been little improvement in claimed precisions over the past 40-60 years.

Refinement of macromolecular structures by the maximum-likelihood method.

This paper reviews the mathematical basis of maximum likelihood. The likelihood function for macromolecular structures is extended to include prior phase information and experimental standard uncertainties. The assumption that different parts of a structure might have different errors is considered. A method for estimating sigma(A) using 'free' reflections is described and its effects analysed. The derived equations have been implemented in the program REFMAC. This has been tested on several proteins at different stages of refinement (bacterial alpha-amylase, cytochrome c', cross-linked insulin and oligopeptide binding protein). The results derived using the maximum-likelihood residual are consistently better than those obtained from least-squares refinement.