Chemistry: analytical and immunological testing – Metal or metal containing – Ti – zr – hf – va – nb – ta – cr – mo – w
Reexamination Certificate
2000-10-10
2004-10-26
Snay, Jeffrey (Department: 1743)
Chemistry: analytical and immunological testing
Metal or metal containing
Ti, zr, hf, va, nb, ta, cr, mo, w
C436S073000, C436S161000, C436S175000, C436S178000
Reexamination Certificate
active
06808931
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the determination of hexavalent chromium (Cr
VI
). More specifically, the present invention relates to a simple, fast, sensitive, and economical method for the determination of Cr
VI
which is especially adapted for environmental and work place samples (including solid and air samples). The present method can be used in both laboratory and field analysis.
BACKGROUND OF THE INVENTION
Chromium exists primarily in two valence states, trivalent (Cr
III
) and hexavalent (Cr
VI
). The trivalent state is relatively non-toxic, and is an essential nutrient in the human diet. On the other hand, Cr
VI
has been shown to be a human respiratory carcinogen in epidemiological studies of workplace exposures, and has been classified by the U.S. Environmental Protection Agency (EPA) as a Group A inhalation carcinogen. Hence, analytical methods are desired which can be used to easily speciate chromium so that human exposures to Cr
VI
can be monitored and, thus, better controlled.
Workplace exposure to Cr
VI
has been associated with a number of industrial sources, such as metal plating, spray painting, welding, tanning, and abrasive blasting operations. Environmental sources of Cr
VI
include, for example, deteriorated or disturbed chromate-containing paint, combustion sources such as automobiles and incinerators, and fugitive dusts from contaminated solid. Because of the desire to accurately measure Cr
VI
at low levels, the development of analytical methods for the determination of Cr
VI
has been a subject of significant interest in occupational and environmental health.
Chromium has been detected using atomic absorption spectrometry (Mehra et al., Talanta, 1989, 36(9), 889; Fong et al., Spectrosc. Lett. 1991, 24, 931), atomic absorption spectrometry (Jarvis et al., Analyst, 1987, 122, 19; Arar et al., Environ. Sci. Technol., 1992, 29, 1944); atomic emission spectrometry (Boumans, Line Coincidence Tables for Inductively Coupled Plasma Atomic Emission Spectrometry, Oxford University Press, Oxford, 2nd ed., 1984; Giglio et al., Anal. Chim. Acta, 1991, 254, 109; Roychowdhury et al., Anal. Chem., 1990, 62, 484), X-ray fluorescence (Arber et al., Analyst, 1988, 113, 779), charged-particle X-ray emission spectrometry and neutron activation analysis. National Institute for Occupational Safety and Health (NIOSH) Methods 7024 and 7300 (NIOSH Manual of Analytical Methods, Eller & Cassinelli (eds)., National Institute for Occupational Safety and Health, Cincinnati, Ohio, 4
th
ed, 1994) use atomic absorption spectrometry and atomic absorption spectrometry, respectively, for the determination of chromium in workplace air samples. These methods, however, generally determine only total. Moreover, these methods generally involve expensive and complex instrumentation and are not, therefore, generally suitable for monitoring directly in the field.
Spectrophotometric and colorimetric methods have been developed for the determination of Cr
VI
. See, for example, Alvarez et al., Talanta, 1989, 36(9), 919; Haukka, analyst, 1991, 116, 1055; Abel et al., Am. Ind. Hyg. Assoc. J., 1974, 35, 229. The most prevalent colorimetric method uses the selective reaction of Cr
VI
with 1,5-diphenylcarbazide (DPC) under acidic conditions to yield a red-violet Cr
VI
-diphenylcarbazone complex. A variation of this colorimetric method is used in NIOSH method 7600 (NIOSH Manual of Analytical Methods, Eller & Cassinelli (eds.), National Institute for Occupational Safety and Health, Cincinnati, Ohio, 4
th
ed, 1994) where alkaline extraction is used to help stabilize the Cr
VI
species. Stripping voltammetry (Wang et al., Analyst, 1992, 117, 1913; Elleouet et al., Anal. Chim. Acta, 1992, 257, 301) and ion chromatographic assays (Powell et al., Anal. Chem., 1995, 67, 2474; Vercoutere et al., Mikrochim. Acta., 1996, 123, 109; Molina et al., Am. Ind. Hyg. Associ. J., 1987, 48, 830; ASTM D 5281-92, “Standard Test Method for Collection and Analysis of Hexavalent Chromium,” in Annual Books of ASTM Standards, American Society for Testing and Materials, vol. 11.01, Philadelphia, Pa., 1992; U.S. Environmental Agency, Method 218.6. Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Waste Water Effects by Ion Chromatography, EPA Office of Research and Development, Cincinnati, Ohio, 1990; U.S. Environmental Agency, Method 3060A, “Alkaline Digestion for Hexavalent Chromium” in Test Methods for Evaluating Solid Wastes, EPA, Washington, D.C., 1995) have also been used to determine Cr
VI
in various samples. Many of these techniques are limited to laboratory-based analysis and cannot, therefore, be used in field monitoring and/or real-time evaluations.
Over the past decade, solid phase extraction (SPE) has been established in the analytical chemistry laboratory and has become increasingly popular. The use of SPE for the separation and preconcentration of trace polar or non-polar target analytes has been widely investigated, and the advantages of such a technique over a conventional liquid-liquid extraction, coprecipitation, electrochemical deposition and evaporation have been well documented. See, for example, Masque et al., Analyst, 1997, 122, 425-428; Corcla et al., Environ. Sci. Technol., 1994, 28, 850-858; Shahteri et al., J. Chromatogr., 1995, 697, 131-136. Some of the advantages of SPE over classical analytical methods include: (1) efficiency and simplicity; (2) solvent minimization and enhanced safety with respect to hazardous samples; (3) high preconcentration factors; (4) good recoveries; (5) flexibility; and (6) low cost.
Both off-line and on-line SPE methodologies have been employed for the preseparation and preconcentration of a variety of analytes. Off-line SPE methodologies involve the use of packing materials that may contain functional groups of different polarity such as C
8
or C
18
bonded silica phases (Falco et al.,
Analyst,
1997, 122, 673-677). With on-line SPE, followed by high pressure liquid chromatography, a critical parameter is the selection of an adequate precolumn in order to avoid band broadening of the first eluded peaks, and to allow for the percolation of large sample volumes (Kiss et al., J. Chromatogr., 1996, 725, 261-272). Numerous solid-phase extractants, such as pure or modified silica, alumina, magnesia, activated carbon, polyurethane, and cellulose and its derivatives, have been used in SPD techniques. Consequently, solid phase extraction has largely replaced classical liquid-liquid extraction in the analytical laboratory.
More recently, innovative new cartridges for SPE, such as reversed-phase and ion-exchange of target analytes in a single resin, are being developed and many are commercially available. These resins cartridges allow for sorption of the analyte of interest while removing non-sorbed interferents, with fast, quantitative adsorption and high elution capacities. These cartridges can improve the overall specificity and sensitivity of trace analysis. Furthermore, the use of commercially available, low cost vacuum manifolds for SPE allows for up to, and even greater than, 24 samples to be processed simultaneously. Complete automation of procedures based on SPE are also available with commercial instrumentation. Despite these advantages, there have been relatively few applications of SPE to inorganic materials, including heavy metals.
Ultrasonic extraction (UE) for the purpose of dissolving target heavy metal analytes in environmental samples is also a technique that has not been used extensively, although it offers great promise (Lugue de Castro et al., Trends Anal. Chem., 1997, 16, 16-24). UE has been demonstrated to perform well for the quantitative dissolution of several heavy metals in a variety of environmental matrices (Harper et al., Anal. Chem., 1983, 55, 1553-1557; Sanchez et al., Analysis, 1994, 22, 222-225; Ashley, Electroanalysis, 1995, 7, 1189-1192z), including hexavalent chromium (James et al., Environ. Sci. Technol., 1995, 29, 2377-2381).
Nonetheless, there remains a need for a
Ashley Kevin
Wang Jin
Gakh Yelena
Needle & Rosenberg P.C.
Snay Jeffrey
The United States of America as represented by the Secretary of
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