Round Robin Samples Research Articles

Transport Property Measurements on the IUPAC Sample of 1,1,1,2-Tetrafluoroethane (R134a)

This paper reports the results of an international project coordinated by the Subcommittee on Transport Properties of Commission I.2 of the International Union of Pure and Applied Chemistry. The project has been conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of R134a and culminates the effort which was initially described in 1995. The project has involved the remeasurement of the transport properties of a single sample of R134a in nine laboratories throughout the world in order to test the hypothesis that at least part of the discrepancy could be attributed to the purity of the samples. This paper provides an intercomparison of the new experimental results obtained for the viscosity and thermal conductivity in the vapor, liquid, and supercritical gas phases. The viscosity measurements were made with a variety of techniques including the vibrating wire, oscillating disk, capillary flow, and falling body. Thermal conductivity was measured using transient bare and anodized hot wires, steady-state anodized hot wires, and light scattering. Agreement between a variety of experimental techniques using the standard round-robin sample is necessary to demonstrate that some of the discrepancies in earlier results were due to sample impurities. Identification of disagreement between data using one experimental technique relative to other techniques may suggest modifications that would lead to more accurate measurements on these highly polar refrigerant materials. It is anticipated that the new data which have been measured on this IUPAC round-robin sample will aid in the identification of the reliable data sets in the literature and ultimately allow the refinement of the IUPAC reference-data correlations for the transport properties of R134a.

Development of methods for the determination of bisphenol A in food simulants

Epoxy resins based on bisphenol A (BPA) have been used as components of food and beverage can coatings for more than 50 years. The recent interest in analysis of extractable BPA from these resins has made it necessary to develop validated methods with performance characteristics necessary for successful analyses in regulatory food simulants. The present study was conducted to develop analytical methodology so that suitably equipped laboratories could confidently perform these analyses. Two methods were developed and validated through round-robin sampling. A historical treatment of the method development challenges, round-robin studies, and results are described here.

The thermal conductivity of liquid 1,1,1,2-tetrafluoroethane (HFC 134a)

The thermal conductivity of HFC 134a was measured in the liquid phase with the polarized transient hot-wire technique. The experiments were performed at temperatures from 213 to 293 K at pressures up to 20 MPa. The data were analyzed to obtain correlations in terms of density and pressure. This study is part of an international project coordinated by the Subcommittee on Transport Properties of Commission 1.2 of IUPAC, conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of HFC 134a, using samples of different origin. Two samples of HFC 134a from different sources have been used. The thermal conductivity of the first sample was measured along the saturation line as a function of temperature and the data were presented earlier. The thermal conductivity of the second one, the round-robin sample was measured as a function of pressure and temperature. These data were extrapolated to the saturation line and compared with the data obtained, previously in order to demonstrate the importance of the sample origin and their real purity. The accuracy of the measurements is estimated to be 0.5%. Finally, the results are compared with the existing literature data.

True Auger spectral shapes (standards)

A novel cylindrical mirror analyzer (CMA) has been developed to obtain standard spectra in Auger electron spectroscopy. The spectra were obtained absolutely by using an electrometer. The measured energy resolution is 0.24% and the transmission was estimated to be 5.6%. The primary energy and current were set with an accuracy within ±0.01% and ±1%, respectively. The sweep energy was directly measured with a precise high voltage divider. Thus the spectra can be calibrated with an accuracy of 0.1 eV. Auger spectra of nickel (the round robin sample) were obtained. Total range of spectra are reported for the primary accelerating voltages ranging 1.0–5000.0 V. We can quantitatively identify every spectrum except a broad peak at 18.5 eV. The L-loss spectrum was observed as a critical bend of background rather than a peak. The LVV Auger peaks which are very small then usually having been missed were obtained as well. Very small fractions of carbon contamination on the Ni showed atomic like KLL (triplet or quintuplet) transitions.

Density and Viscosity Measurements of 1,1,1,2-Tetrafluoroethane (HFC-134a) from 199 K to 298 K and up to 100 MPa

New density results for liquid 1,1,1,2-tetrafluoroethane (HFC-134a) along five isotherms from 199 K to 298 K and at pressures up to 100 MPa are presented. The measurements were performed with a new vibrating-wire instrument operated in the forced mode of oscillation and were carried out on a round-robin sample of refrigerant HFC-134a. The viscosity of the fluid was measured simultaneously with the density, using the same vibrating-wire sensor, at temperatures above 248 K over the entire pressure range. The results are compared with recent literature data. The precision of the present values is ±0.03% for the density and ±0.6% for the viscosity. The corresponding estimated accuracies are ±0.05% and ±2.5%, respectively.

Atmospheric Carbonaceous Species Measurement Methods Comparison Study: General Motors Results

The General Motors Research Laboratories participated in both the field sampling and round-robin portions of the Carbonaceous Species Intercomparison study that was held in Glendora, CA, during the summer of 1986. Five samplers were operated during the field study. The average particulate elemental carbon (EC) concentrations determined from the five samplers agreed to within 12%. Large differences were observed in the concentrations of particulate organic carbon (OC) determined from the five samplers. Some of the differences are attributed to losses of OC from the filters due to volatilization during the collection period. The amount of volatilization varies with the length of the sampling time and the filter face velocity. In addition, the adsorption of gas-phase organic compounds caused a significant positive interference in the determination of OC. Our OC and EC results for the round-robin samples were compared to the values obtained by the other participating laboratories. The average ratio of our res...

Determination of nitro-polynuclear aromatic hydrocarbons in air and diesel particulate matter using liquid chromatography with electrochemical and fluorescence detection

Three different approaches to the liquid chromatographic detection of nitro polynuclear aromatic hydrocarbons in air and diesel particulate extracts are presented, based on differential pulse (LCDPD) and amperometric (LCEC) electrochemical detection and fluorescence detection following online reduction to the amine (LCFI). The particulate extraction/fractionation procedure for each detection approach is discussed. The operational advantages of oxygen removal with a platinum oxygen scrubber (all three types of detection), the use of modulated pulse detection, and wavelength-programmed fluorescence detection are explored. 1-Nitropyrene is determined in Standard Reference Material (SRM) 1650 diesel particulate matter and in several other round robin samples by all three methods. Results are compared to those obtained by other techniques (gas chromatography/mass spectrometry) and by other laboratories (LCFI). Additionally, 2-nitrofluorene, 9-nitroanthracene, 7-nitrobenz(a)anthracene, and 6-nitrobenzo(a)pyrene are determined in SRM 1650 by LCFI. The detection limits for 1-nitropyrene (expressed as picograms) are 5200 (LCDPD), 60 (LCEC), and 10 (LCFI).

Total Arsenic in Foods after Sequential Wet Digestion, Dry Ashing, Coprecipitation with Ammonium Pyrrolidine Dithiocarbamate, and Graphite-Furnace Atomic Absorption Spectrometry

A graphite-furnace atomic absorption (GFAAS) method is described for determining total arsenic (organic and inorganic compounds) in foods. Samples ranging from 1 to 40 g (depending on moisture content) were digested with HNO3 and dry-ashed at 500 degrees C overnight after addition of MgO. After dissolution in HCl, the arsenic was reduced with iodide and ascorbic acid and precipitated with ammonium pyrrolidine dithiocarbamate (APDC) in the presence of nickel carrier. Precipitates were collected on 0.3 micron cellulose acetate filters and dissolved in 10% HNO3 containing modifier. Ba(NO3)2 was added to remove a sulfate interference resulting from decomposition of APDC. Arsenic was determined using GFAAS. Accuracy of the method was good for 7 U.S. National Bureau of Standards (NBS) Standard Reference Materials and 3 National Research Council of Canada (NRCC) round-robin samples. Recovery of arsenic(V) from foods averaged 99.2% for peak heights and 97.1% for peak areas, with relative standard deviations (RSD) of 2.2% for peak heights and 3.3% for peak areas for all NBS and NRCC materials. Detection limit of the method was ca 10 ng arsenic.

Laser damage test results on Balzers round-robin thin film samples

The pulsed laser damage threshold of several thin film coatings has been assessed using 1.06-μm radiation at a pulse length of 6-nsec FWHM. The irradiation spot size was 360 μm in diameter at the 1/e2 points in intensity. These coatings are part of a well-characterized master set prepared for round-robin testing by Balzers of Liechtenstein, a leading thin film manufacturer. Similar data from eight different laboratories in the United States and Europe have been intercompared to evaluate test procedures and film reproducibility [ K. H. Guenther , Appl. Opt.23, 3743 ( 1984)].

Determination of chromium in human milk, serum and urine by electrothermal atomic absorption spectrometry without preliminary ashing

In the present study a Perkin-Elmer 5000 atomic absorption spectrometer equipped with a tungsten—iodide lamp for improved background correction at the 357.9 nm chromium absorption line and an HGA 500 graphite furnace were employed for the direct determination of chromium in human serum, milk and urine. The method of standard additions was used: 0.25–0.75 ng Cr was added to 1 ml samples. Except for urine samples, a dilution of 1 + 1 to 1 + 2 with H 2O was necessary in order to obtain correct calibration curves. The average concentration of chromium in all the samples of normal subjects was less than 0.5 ng Cr ml −1. The day-to-day variation for all of the pooled samples was around 10% (relative standard deviation). For urine, the accuracy of the method was tested by comparing the results of another laboratory for the same two round robin samples. Excellent agreement was found between the present method and those of the other laboratory that had used isotope dilution—mass spectrometry and continuum source wavelength modulated echelle—atomic absorption spectrometry to define the chromium concentration in the samples. The detection limit of the method, 0.05 ng Cr ml −1 for urine and serum and 0.1 ng Cr ml −1 for human milk, was sufficient for the biological fluids analyzed. The method was employed for the determination of chromium in 24-h urine samples of maturity onset diabetics supplemented with 20 or 200 μg Cr 3+ d −1 for six weeks. It was shown that the 24-h urinary chromium excretion accurately indicates the daily dietary chromium intake of these patients.

Experiments on sputtering of niobium by 14–16 MeV protons and Monte Carlo calculations for proton and neutron sputtering

The sputtering of niobium with 14 MeV neutrons is simulated by 14–16 MeV protons. The targets are cold-rolled niobium foils of 240 μm thickness as prepared by the ANL and PNL (Round Robin samples). The sputtered Nb atoms are collected on Si wafers in forward and backward direction, and then detected by RBS analysis with 300 keV He +, using special features for background suppression. The sputtering yields measured are in the range of 10 −5-10 −4 atoms/proton. A theoretical analysis and comparison of neutron and proton effects is carried out with the realistic Monte Carlo code TRIM, using the Molière repulsive potential and Lindhard-Scharff electronic stopping. The recoil production is based on improved cross sections for elastic scattering and nuclear reactions. The results are the following sputtering yields: neutrons 0.6 × 10 −5 forward, 0.03 × 10 −5 backward; protons 1.5 × 10 −5 forward, 0.9 × 10 −5 backward. The low forward-to-backward ratio for protons, 1.6, is due to the large number of low-energy recoils from Coulomb interactions, starting nearly perpendicular to the proton motion and contributing equally to forward and backward sputtering.

The yields of photonuclear reactions for multielement photon-activation analysis

A comprehensive study on the yields of photonuclear reactions of various types has been performed, and sensitivities and the effects of interferences in multielement photon-activation analysis have been evaluated by bremsstrahlung activation of many elements with maximum energies ranging from 30 to 60 MeV. The applicability and reliability of the method were demonstrated by analyzing standard round-robin samples and then by presenting the elemental abundances in several geological, biological and environmental materials. The method was almost insensitive to matrix effects and was assessed to be promising for nondestructive multielement determination of the materials of wide variety, giving good reproducible results for 20 or more elements.