US EPA Method 108b - Determination Of Arsenic Content In Ore Samples From Nonferrous Smelters
NOTE: This method does not include all of the specifications (e.g., equipment and supplies) and procedures (e.g., sampling and analytical) essential to its performance. Some material is incorporated by reference from other methods in this appendix and in Appendix A to 40 CFR Part 60. Therefore, to obtain reliable results, persons using this method should have a thorough knowledge of at least the following additional test methods: Method 12 and Method 108A.
|Arsenic compounds as arsenic (As)||7440-38-2||Lower limit 10 μg/ml|
This method applies to the determination of inorganic As content of process ore and reverberatory matte samples from nonferrous smelters and other sources as specified in an applicable subpart of the regulations. Samples resulting in an analytical concentration greater than 10 μg As/ml may be analyzed by this method. For lower level arsenic samples, Method 108C should be used.
Adherence to the requirements of this method will enhance the quality of the data obtained from air pollutant sampling methods.
Arsenic bound in ore samples is liberated by acid digestion and analyzed by flame atomic absorption spectrophotometry (AAS).
Analysis for As by flame AAS is sensitive to the chemical composition and to the physical properties (e.g., viscosity, pH) of the sample. The analytical procedure includes a check for matrix effects (Section 11.4).
This method may involve hazardous materials, operations, and equipment. This test method may not address all of the safety problems associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to performing this test method.
The following reagents are hazardous. Personal protective equipment and safe procedures that prevent chemical splashes are recommended.
If contact occurs, immediately flush with copious amounts of water for at least 15 minutes. Remove clothing under shower and decontaminate. Treat residual chemical burns as thermal burns.
5.2.1 Hydrochloric acid (HCl). Highly corrosive liquid with toxic vapors. Vapors are highly irritating to eyes, skin, nose, and lungs, causing severe damage. May cause bronchitis, pneumonia, or edema of lungs. Exposure to concentrations of 0.13 to 0.2 percent can be lethal to humans in a few minutes. Provide ventilation to limit exposure. Reacts with metals, producing hydrogen gas.
5.2.2 Hydrofluoric Acid (HF). Highly corrosive to eyes, skin, nose, throat, and lungs. Reaction to exposure may be delayed by 24 hours or more. Provide ventilation to limit exposure.
5.2.3 Nitric Acid (HNO3). Highly corrosive to eyes, skin, nose, and lungs. Vapors are highly toxic and can cause bronchitis, pneumonia, or edema of lungs. Reaction to inhalation may be delayed as long as 30 hours and still be fatal. Provide ventilation to limit exposure. Strong oxidizer. Hazardous reaction may occur with organic materials such as solvents.
5.2.4 Perchloric Acid (HClO4). Corrosive to eyes, skin, nose, and throat. Provide ventilation to limit exposure. Very strong oxidizer. Keep separate from water and oxidizable materials to prevent vigorous evolution of heat, spontaneous combustion, or explosion. Heat solutions containing HClO4 only in hoods specifically designed for HClO4.
The following items are required for sample preparation:
6.1.1 Teflon Beakers. 150-ml.
6.1.2 Graduated Pipets. 5-ml disposable.
6.1.3 Graduated Cylinder. 50-ml.
6.1.4 Volumetric Flask. 100-ml.
6.1.5 Analytical Balance. To measure within 0.1 mg.
6.1.6 Hot Plate.
6.1.7 Perchloric Acid Fume Hood.
The following items are required for analysis:
6.2.1 Spectrophotometer. Equipped with an electrodeless discharge lamp and a background corrector to measure absorbance at 193.7 nm.
6.2.2 Beaker and Watch glass. 400-ml.
6.2.3 Volumetric Flask. 1-liter.
6.2.4 Volumetric Pipets. 1-, 5-, 10-, and 25-ml.
Unless otherwise indicated, it is intended that all reagents conform to the specifications established by the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available; otherwise, use the best available grade.
The following reagents are required for sample preparation:
7.1.1 Water. Deionized distilled to meet ASTM D 1193-77 or 91 Type 3 (incorporated by reference - see 61.18).
7.1.2 Nitric Acid, Concentrated.
7.1.3 Hydrofluoric Acid, Concentrated.
7.1.4 Perchloric Acid, 70 Percent.
7.1.5 Hydrochloric Acid, Concentrated.
The following reagents and standards are required for analysis:
7.2.1 Water. Same as in Section 7.1.1.
7.2.2 Stock Arsenic Standard, 1.0 mg As/ml. Dissolve 1.3203 g of primary grade As203 [dried at 105EC (221 EF)] in a 400-ml beaker with 10 ml of HNO3 and 5 ml of HCl. Cover with a watch glass, and heat gently until dissolution is complete. Add 10 ml of HNO3 and 25 ml of HClO4, evaporate to strong fumes of HClO4, and reduce to about 20 ml volume. Cool, add 100 ml of water and 100 ml of HCl, and transfer quantitatively to a 1-liter volumetric flask. Dilute to volume with water and mix.
7.2.3 Acetylene. Suitable quality for AAS analysis.
7.2.4 Air. Suitable quality for AAS analysis.
7.2.5 Quality Assurance Audit Samples. Same as in Method 108A, Section 7.2.11.
Same as in Method 108A, Sections 8.1 and 8.2.
|Section||Quality Control Measure||Effect|
|10.2||Spectrophotometer calibration||Ensure linearity of spectrophotometer response to standards|
|11.4||Check for matrix effects||Eliminate matrix effects|
|11.5||Audit sample analysis||Evaluate analyst's technique and standards preparation|
NOTE: Maintain a laboratory log of all calibrations.
10.1 Preparation of Standard Solutions. Pipet 1, 5, 10, and 25 ml of the stock As solution into separate 100-ml volumetric flasks. Add 2 ml of HClO4, 10 ml of HCl, and dilute to the mark with water. This will provide standard concentrations of 10, 50, 100, and 250 μg As/ml.
10.2 calibration Curve and Spectrophotometer calibration Quality Control. Same as Method 108A, Sections 10.2 and 10.3..
Weigh 100 to 1000 mg of finely pulverized sample to the nearest 0.1 mg. Transfer the sample to a 150-ml Teflon beaker. Dissolve the sample by adding 15 ml of HNO3, 10 ml of HCl, 10 ml of HF, and 10 ml of HClO4 in the exact order as described, and let stand for 10 minutes. In a HClO4 fume hood, heat on a hot plate until 2-3 ml of HClO4 remain, then cool. Add 20 ml of water and 10 ml of HCl. Cover and warm until the soluble salts are in solution. Cool, and transfer quantitatively to a 100-ml volumetric flask. Dilute to the mark with water.
11.2 Spectrophotometer Preparation. Same as in Method 108A, Section 11.2.
If the sample concentration falls outside the range of the calibration curve, make an appropriate dilution with 2 percent HClO4/10 percent HCl (prepared by diluting 2 ml concentrated HClO4 and 10 ml concentrated HCl to 100 ml with water) so that the final concentration falls within the range of the curve. Using the calibration curve, determine the As concentration in each sample.
NOTE: Because instruments vary between manufacturers, no detailed operating instructions will be given here. Instead, the instrument manufacturer's detailed operating instructions should be followed.
Run a blank and standard at least after every five samples to check the spectrophotometer calibration. The peak height of the blank must pass through a point no further from the origin than ±2 percent of the recorder full scale. The difference between the measured concentration of the standard (the product of the corrected average peak height and the reciprocal of the least squares slope) and the actual concentration of the standard must be less than 7 percent, or recalibration of the analyzer is required.
11.4 Mandatory Check for Matrix Effects on the Arsenic Results. Same as Method 12, Section 11.5.
11.5 Audit Sample Analysis. Same as in Method 108A, Section 11.6.
Same as in Method 108A, Section 12.0.
13.1 Sensitivity. The lower limit of flame AAS is 10 μg As/ml.
Same as in Method 108A, Section 16.0.