Minerals standards

In the analysis of solid samples (e.g., LA-ICP-MS, SEM), synthetic standards cannot easily be prepared to the required concentrations, and accurate calibration of such techniques is often challenging. In some cases (e.g., SEM) pure element or single mineral standards are used, ideally with an appropriate standard for each element to be quantified. (It is possible in SEM, within limits, to use fewer standards than the number of elements to be determined, with the calibration for other elements being predicted from the response of the nearest element.) More often, however, multielement primary standards are used as the means of calibrating the instrument, e.g., for LA-ICP-MS of glasses, volcanics, and ceramics, two glass standards, NIST 610 and 612 (Pearce et al. 1996), are often used. It is always advisable to use more than one multielement standard in order to cover as wide a range of concentrations as possible, and to use at least one additional independent reference material as an unknown, for quality assurance purposes (see below). 

Mineral standards were hand crushed to -1/4 inch, then ground to a fine powder in a ball mill (alumina elements) or Bleuler Model 526/LFS678 puck mill. The resultant powder was aerodynamically classified in a Bahco Model 6000 micro particle classifier and the finest fraction ( 18 throttle) was collected. A size criterion of 90% or more by weight of particles 5 micron and smaller in diameter was used for the mineral standards. Sizes were verified by Coulter Counter. Duplicate 13 mm KBr pellets were prepared and the spectra were weight-scaled by techniques similar to those reported by Painter (3) and Elliot (4). With one exception, all the mineral standard spectra were averages of spectra from duplicate pellets. The one exception was the iron sulfate spectrum, which was obtained as the difference spectrum by subtracting the spectrum of HCl-washed weathered pyrite from that of the weathered pyrite. A weight correction was applied to the difference spectrum. 

Figure 17.15. Phosphorus (Is) fluorescence spectra from chemical and mineral standards. The dashed line represents the edge position (2152 eV) of inorganic phosphorus (V) compounds (redrawn after Brandes et al., 2007).

The accuracy of the method was considered by determination of the concentration of chloride, nitrate and sulphate in an EPA nutrient/ mineral standard. The results are shown in Table 2.10. The proximity of the chromatographic values to the EPA values indicates that corrections for matrix effects, due to additional constituents present in this standard, are unnecessaiy. 

As an example of thin-foil analysis in the SEM, samples of the mineral standard kaolinite (<2 pm fraction, KGa-2, Source Clay Minerals Repository) were dispersed on TEM grids and analyzed using a JEOL JSM 6400 SEM under the control of an automated Noran Voyager EDS system equipped with a thin-window EDS detector.93 For comparison, EDS spectra were also collected using the same instrument for the kaolinite size fractions deposited on polycarbonate filters, fixed to SEM... 

Abstract Solid-state NMR studies on bone, bone mineral standards and collagen are reviewed. NMR spectroscopy was mostly applied to the bone mineral and confirmed that the structure resembles that of calcium carbonatoapatite of type B. Apatite in bone was found to be deficient in structural hydroxyl groups. Concentration and distribution of hydrogen-phosphate and carbonate ions, and of water in apatite crystals (interior vs surface and crystal defects vs structural positions) were closely investigated. The NMR characterization of the organic matrix still remains a challenge for future research. 

Following the first procedure, mineral standards were synthesized and characterized by P MAS NMR [31,42]. BD, CP and DD spectra of mineral standards and bone samples were compared, giving particular attention to chemical shifts (Table 2),linewidths and rotational sideband patterns [35]. A typical set of spectra, acquired for mineral standards, is given in Fig. 7. Each BD spectrum comes from all P-sites, while its CP counterpart exposes a fraction of the P-sites capable of obtaining polarization from surrounding protons. The DD experiment is performed with a time interval without proton decoupling inserted just after CP. This is called a dipolar suppression period (DS), because... 

Fig. 20 NMR spectra of various mineral standards recorded with MAS at 40 kHz (833 MHz spectrometer) [20]. HAh and HAc denote hydrated (as-prepared) and calcined HA, respectively. CHA-B contained 9 wt% of COf ...

Chapter 1 General Food Standards, Part 1.3 Substances Added to Food, Standard 1.3.1 Food additives. The purpose of which is any substance not normally consumed as a food in itself and not normally used as an ingredient of food, but which is intentionally added to a food to achieve one or more of the technological functions specified in Schedule 5. It or its by-products may remain in the food. Food additives are distinguishable from processing aids (Standard 1.3.3) and vitamins and minerals (Standard 1.3.2). 

Fig. 5.1 IR spectra of mineral standards (left) and artifacts (right). Because each mineral has an IR spectrum determined by its own chemical bonds, the mineral spectra have different shapes. Thus they can be distinguished and the minerals composing artifacts can be identified by matching the spectra to those of the mineral standards (spectra courtesy of Z.C. ling)...

Bajt et al. (1994 1995) and Sutton et al. (1995) have pushed the practice of pre-edge examination further to reach an effective quantification of the oxidation states for Fe, the atom which most frequently occurs in two oxidation states in the same site of minerals. They have developed, and Galoisy et al. (2001) and Petit et al. (2001) have recently improved upon, a procedure that makes use of the known positions of pre-edge peaks of Fe X-XANES spectra in mineral standards to fit a calibration line giving the Fe /EFe ratios of various minerals (Fig. 16). 

The J value is determined by using mineral standards of known age to monitor the neutron flux. Substituting Equation (6) into Equation (5) and rearranging, yields the Ar-Ar age equation ... 

The Ar-Ar technique is able to achieve higher levels of internal precision than K-Ar dating since it does not depend upon separate absolute measurements but instead requires only the ratios of Ar isotopes and can achieve precision of better than 0.25%. However, external precision and accuracy are affected by the uncertainty in the age of mineral standards, as we will see in the following section. In order to achieve optimum precision in the mass spectrometric measurements, the neutron flux (which affects the magnitude of the J value) must be carefully selected. The flux must be sufficient for precise... 

Analytical procedures, accuracy, precision and mineral standards... 

Hurley PM (1954) The helium age method and the distribution and migration of helium in rocks. In Nuclear Geology. Faul H (ed) John Wiley Sons, New York, p 301-329 Jonckheere R, Mars M, Van den hante P, Rebetez M, Chambandet A (1993) L apatite de Dnrango (Mexique) Analyse d un mineral standard ponr la datation par traces de fission. Chem Geol 103 141-154... 

Next, consider the case where the mineral standard states are of the variable pressure type, that is, the standard states for brucite and periclase are taken to be the pure phase at the system P and T, while water continues to have a standard state of ideal gaseous water at T and one bar. Because there is essentially no mutual solution between the three phases they are essentially pure when at mutual equilibrium, and the mineral activities are therefore 1.0 at all Ps and Ts. This is only an apparent simplification, because now the equilibrium constant varies with pressure. Its value at 2000 bars, 25°C can be calculated from equation (13.42), thus... 

For SEM analysis a Nucleopore poly(carbonate) (PC) membrane filter (diameter 37mm, pore size 0.2 pm) is used. After filtration each piece of the filter is coated with a very thin layer of gold Routine SEM viewing is combined with an energy-dispersive X-ray microanalyzer (EDX). The particles and fibers are identified by their relative elemental peak intensities (based on magnesium, silicon, iron, and calcimn), compared with their respective mineral standards placed in the computer bank (Figures 1-3). 

The Berea sand was obtained from Cleveland Quarries in Amherst, Ohio the montmorillonite was a clay mineral standard from Ward s Natural Science Establishment, Inc. Both solids were characterized well in terms of particle size distribution and surface area. The crushed clay and sand were sieved separately using US sieve series the fractions of sand and clay which passed through sieve No. 170 but not No. 200 were retained for use as adsorbents. The particle size distribution of these fractions is fairly narrow with the majority of particles in the 74-88 ym range (10). The surface areas of these adsorbents as determined by nitrogen adsorption were 2.86 m /g for the sand and 84.7 m 2/g for the clay. 

Fig. 4.4. Release curve of the cinnabar standard compared with sample I 74, and release curve of the incubated clay mineral standard compared with samples I 74 and I 84.2.

The comparison of the samples I 73.1 and I 84.2 with their extracted humic acids (Fig. 4.3) shows that the Hg-release curves of the humic acids are very similar to the first peak of their original samples. In contrast, the thermal release characteristics of natural crystalline cinnabar correspond to the second peak of sample I 74 (Fig. 4.4). The Hg-release curve of the incubated clay mineral standard (Fig. 4.4) displays a very wide irregular release curve in the temperature range from 30° to about 610°C. The curve rises up to a first maximum at about 110°C and continues with some changes to the maximum extinction at about 240°C. 

Solid-state NMR studies of bone, bone mineral standards and collagen have been reviewed by Kolodziejski. In particular, concentration and distribution of hydrogen-phosphate and carbonate ions, and of water in apatite crystals were considered. 

In many cases, the transformation from elements to minerals requires an accurate clay content determination followed by an analysis combining the remaining minerals into groups and more detailed composition. The algorithms use mineral standard samples. 

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