Nitric acid trace metal grade

The trace element profile of teeth at the opening of this chapter was obtained by inductively coupled plasma-mass spectrometry. Figure 21-28 shows an example in which coffee beans were extracted with trace-metal-grade nitric acid and the aqueous extract was analyzed by inductively coupled plasma—mass spectrometry. Coffee brewed from either bean contains —15 ngPb/mL. However, the Cuban beans also contain Hg at a concentration similar to that of Pb. 

The ICP was a Perkin-Elmer 3000DV with an AS90 Autosampler, which has an instrument detection limit of about 1 ppb (for most elements) with a linear calibration up to 100 ppm (for most elements). Solid samples were prepared via microwave digestion in concentrated nitric and hydrochloric acids, then diluted to volume. The ICP was calibrated and verified with two independent, certified standard sets. Spikes and dilutions were done for each batch of samples to check for and/or mitigate any matrix effects. The ICP process ran a constant pump rate of 1.5 mL/min for all samples and standards during analysis. A 3 mL/min rinse and initial sample flush were used to switch between each sample and standard. The plasma was run at 1450 W with argon flow. Trace metal-grade (sub-ppb) acids and two independently NIST-certified calibration standard sets were used for calibration and method verification. 

All water used is 18 Mil de-ionized water polished by a Simplicity ion exchange system available from Millipore Coiporation, USA. Trace Metal Grade sulfuric, nitric, and perchloric acids that were used in the procedures are available from Fisher Scientific, Pittsburgh, Peimsylvania, USA. Commercially prepared, multi-element, aqueous ICP-AES standards and the blank acid matrix were obtained from VHG Labs, Inc., Manchester, New Hampshire, USA. The multi-element, oil standards used for validation are available from Conostan Division, Conoco Specialty Products, Ponca City, Oklahoma, USA. 

A stock standard aqueous solution of mercury chloride, 997 mg T (Wako) was used to prepare a series of working standard solutions. The working standards are prepared in an aqueous i-Cysteine, 10 mg l in 0.2 % nitric acid. The i-Cysteine, 97 % was obtained from Aldrich Chemical Company, Inc. Milwaukee, WI, USA. The nitric acid, concentrated. Trace Metal Grade was obtained from Fisher Scientific, Pittsburgh, PA, USA. 

Total elemental concentrations-Total concentration of each metal in an unfiltered sample was determined after digestion. The unfiltered sample was carefully mixed, and a known amount (approximately 10 g) was weighed into the Teflon bomb of the microwave digestion system. Five milliliters of concentrated ( 36N) trace-metal grade nitric acid were added to each sample and the mixture was digested at high temperature and pressure in a microwave digestion unit... 

For the total dissolved metal fraction, the wastewater sample was filtered through a 0.45 /rm membrane filter immediately after collection, acidified with trace-metal grade nitric acid to a pH of approximately 2.0 and then stored. 

In elemental analysis by ICP-MS, ICP-AES, GFAA, and Flame AA, dilute nitric acid (0.5 to 5.0 %) is used as a matrix compound for determining metal traces in solutions. Ultrapure trace metal grade acid is required for such determination, because small amounts of metal ions could affect the result of the analysis. 

The fire assay, the antecedents of which date to ancient Egypt, remains the most rehable method for the accurate quantitative determination of precious metals ia any mixture for concentrations from 5 ppm to 100%. A sample is folded iato silver-free lead foil cones, which are placed ia bone-ash cupels (cups) and heated to between 1000 and 1200°C to oxidize the noimoble metals. The oxides are then absorbed iato a bone-ash cupel (ca 99%) and a shiny, uniformly metaUic-colored bead remains. The bead is bmshed clean, roUed fiat, and treated with CP grade nitric acid to dissolve the silver. The presence of trace metals ia that solution is then determined by iastmmental techniques and the purity of the silver determined by difference. 

MetaUic impurities in beryUium metal were formerly determined by d-c arc emission spectrography, foUowing dissolution of the sample in sulfuric acid and calcination to the oxide (16) and this technique is stUl used to determine less common trace elements in nuclear-grade beryUium. However, the common metallic impurities are more conveniently and accurately determined by d-c plasma emission spectrometry, foUowing dissolution of the sample in a hydrochloric—nitric—hydrofluoric acid mixture. Thermal neutron activation analysis has been used to complement d-c plasma and d-c arc emission spectrometry in the analysis of nuclear-grade beryUium. 

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