Inorganic Chemical Analysis of Environmental Materials—A Lecture Series

Inorganic Chemical Analysis of Environmental Materials—A Lecture Series Open-File Report 2011–1193 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia 2011 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Crock, J.G., and Lamothe, P.J., 2011, Inorganic chemical analysis of environmental materials—A lecture series: U.S. Geological Survey Open-File Report 2011-1193, 117 p. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. ii Contents Abstract ......................................................................................................................................................................... 1 Introduction .................................................................................................................................................................... 1 Standard Reference Materials ....................................................................................................................................... 3 Development of QC materials matrix matched to a project study area - an example ................................................. 4 Slides and Lecture Notes ............................................................................................................................................... 7 Acknowledgments ......................................................................................................................................................111 Selected References ..................................................................................................................................................111 Figures 1. Major element comparisons in QC material versus median element concentrations in Pebble Deposit study... ..... 5 2. Minor and trace element comparison in QC material versus median element concentrations in Pebble Deposit study. ................................................................................................................................................................ 5 3. Minor and trace element comparison in QC material versus median element concentrations in Pebble Deposit study. ................................................................................................................................................................ 6 4. Minor and trace element comparison in QC material versus median element concentrations in Pebble Deposit study..……... ......................................................................................................................................................6 Table 1. Atomic Spectroscopy detection limits (ppb or micrograms/liter). ..........................................................................108 iii Inorganic Chemical Analysis of Environmental Materials—A Lecture Series By J.G. Crock and P.J. Lamothe Abstract At the request of the faculty of the Colorado School of Mines, Golden, Colorado, the authors prepared and presented a lecture series to the students of a graduate level advanced instrumental analysis class. The slides and text presented in this report are a compilation and condensation of this series of lectures. The purpose of this report is to present the slides and notes and to emphasize the thought processes that should be used by a scientist submitting samples for analyses in order to procure analytical data to answer a research question. First and foremost, the analytical data generated can be no better than the samples submitted. The questions to be answered must first be well defined and the appropriate samples collected from the population that will answer the question. The proper methods of analysis, including proper sample preparation and digestion techniques, must then be applied. Care must be taken to achieve the required limits of detection of the critical analytes to yield detectable analyte concentration (above “action” levels) for the majority of the study’s samples and to address what portion of those analytes answer the research question—total or partial concentrations. To guarantee a robust analytical result that answers the research question(s), a well-defined quality assurance and quality control (QA/QC) plan must be employed. This QA/QC plan must include the collection and analysis of field and laboratory blanks, sample duplicates, and matrix-matched standard reference materials (SRMs). The proper SRMs may include in-house materials and/or a selection of widely available commercial materials. A discussion of the preparation and applicability of in-house reference materials is also presented. Only when all these analytical issues are sufficiently addressed can the research questions be answered with known certainty. Introduction The precise and accurate analyses of environmental materials, including geological, biological, and man-made matrices, form the basis for most environmental studies. The analysis of environmental materials, including fresh and weathered metal-mining waste products, includes both laboratory-based determinations of the stable or stabilized analytes, as well as the in-field determination of the non-stable analytes. Difficulties in providing such analyses include the large range of analyte and matrix element concentrations, phase associations of the analyte elements, sample size (too small or too large), sample homogeneity, analyte volatility or stability, and contamination. Current trends in analytical chemistry focus on: lower detection limits (at least in the low µg/kg range) and smaller sample sizes for simultaneous multi-element determinations; automation of the sample digestion/preparation methods; automation of data handling; and species characterization (phase association and/or valence) state. The growth in environmental analytical 1 chemistry has also given rise to increased awareness of the need for a wide range of appropriate standard reference materials, both for total analyses and for operationally defined extraction procedures or speciated analyses. There are many complete references for the analysis of environmental and geological materials available. Some of the more noteworthy are Carter (1993), Jeffery and Hutchison (1983), Ingamells and Pitard (1986), Keith (1992), Potts (1987), Smith (1994), Smoley (1992), Sparks (1996), Stoch (1986), and Westerman (1990). One of the most important aspects to the analysis of environmental materials is the digestion/decomposition of the material prior to presenting the sample to the individual instrumental method. Excellent references for the total dissolution of environmental materials include Bock (1979) and Sulcek and Povondra (1989). Chao (1984) addresses in detail the application of partial and sequential dissolution schemes. Chao and Sanzolone (1992) discuss both total and partial dissolution techniques, as well as their application. Often, a method of determination is not sensitive enough, either because the original concentration of the analyte is too low or the required dilution of the resulting digestate is too high. Often, the separation and (or) preconcentration of the analyte from the matrix is required. Minczewski and others (1982) present a comprehensive overview of these useful techniques. Sample dissolution is usually the most tedious, time-consuming, and limiting factor in chemical analyses. A multi-acid digestion, combining hydrofluoric, hydrochloric, nitric, and perchloric acids at low temperatures and pressures (Crock and others, 1983; Taggart, 2002), is a common dissolution method. Many of the common rock-forming alumino-silicate minerals can be dissolved by this method. The advantages of acid digestion are the ease of the method, use of large samples (as much as 2 g, although 0.2 g is more common), low reagent blanks, and low total dissolved salts in the analytical solution. With an acid digestion, the final dilution factor commonly is less than 100, allowing many elements to be determined at or near their crustal abundance. One disadvantage of acid digestion using hydrofluoric acid is the volatilization of some elements, such as silicon and boron, as fluoride compounds. Commonly, a higher pressure, closed-vessel “bomb” digestion used in conjunction with a complexing agent (for the excess fluoride) is used to avoid volatilization of silicon and boron. Some minerals are resistant to routine acid digestions and require a more rigorous digestion. These minerals include spinels, beryl, tourmalines, chromite, zircon, monazite, niobates, tungstates, topaz, and cassiterite. These minerals can be completely dissolved by the proper choice of a sinter or fusion digestion procedure. A sodium peroxide sinter will dissolve most resistant minerals (for example, Sulcek and Povondra, 1989). For example, boron and silicon are routinely determined in tourmaline by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) following a sodium peroxide sinter

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