3500-Li LITHIUM* 3500-Li A. Introduction 1. Occurrence and Significance minerals of soils. Lithium is considered nonessential for plants and animals, but it is essential for some microorganisms. Some lithium salts are toxic by ingestion. The United Nations Food and Agriculture Organization recommended maximum level for lithium in irrigation waters is 2.5 mg/L. Lithium (Li) is the second element in Group IA of the periodic table; it has an atomic number of 3, an atomic weight of 6.94, and a valence of 1. The average abundance of Li in the earth’s crust is 18 ppm; in soils it is 14 to 32 ppm; in streams it is 3 g/L, and in groundwaters it is ⬍0.1 mg/L. The more important minerals containing lithium are lepidolite, spodumene, petalite, and amblygonite. Lithium compounds are used in pharmaceuticals, soaps, batteries, welding flux, ceramics, reducing agents (e.g., lithium aluminum hydride), and cosmetics. Many lithium salts are only slightly soluble, and the metal’s concentration in water is controlled by incorporation in clay 2. Selection of Method The atomic absorption spectrometric method (3111B) and the inductively coupled plasma method (3120) are preferred. The flame emission photometric method (B) also is available for laboratories not equipped to use preferred methods. The inductively coupled plasma/mass spectrometric method (3125) may be applied successfully in most cases (with lower detection levels), even though lithium is not specifically listed as an analyte in the method. * Approved by Standard Methods Committee, 2004. Editorial revisions, 2011. Joint Task Group: 20th Edition—See Section 3500-Al. 3500-Li B. Flame Emission Photometric Method 1. General Discussion a. Potassium ionization suppressant: Dissolve 95.35 g KCl dried at 110°C and dilute to 1000 mL with water; 1.00 mL ⫽ 50 mg K. b. Stock lithium solution: Dissolve 152.7 mg high-purity anhydrous lithium chloride, LiCl, in water and dilute to 250 mL; 1.00 mL ⫽ 100 g Li. Dry salt overnight in an oven at 105°C. Cool in a desiccator and weigh immediately after removal from desiccator. Alternatively, purchase prepared stock from a reputable supplier. c. Standard lithium solution: Dilute 10.00 mL stock LiCl solution to 500 mL with water; 1.00 mL ⫽ 2.0 g Li. a. Principle: Lithium can be determined in trace amounts by flame photometric methods at a wavelength of 670.8 nm. b. Interference: A molecular band of strontium hydroxide with an absorption maximum at 671.0 nm interferes in the flame photometric determination of lithium. Ionization of lithium can be significant in both the air-acetylene and nitrous oxide-acetylene flames and can be suppressed by adding potassium. See Section 3500-Na.B.1b for additional information on minimizing interferences in flame photometry. c. Minimum detectable concentration: The minimum lithium concentration detectable is approximately 0.1 g/L for reagent water analyzed on an atomic absorption spectrophotometer in the emission mode with an air-acetylene flame, or 0.03 g/L with a nitrous oxide-acetylene flame. d. Sampling and storage: Preferably collect sample in a polyethylene bottle, although borosilicate glass containers also may be used. At time of collection adjust sample to pH ⬍2 with nitric acid (HNO3). 4. Procedure a. Pretreatment of polluted water and wastewater samples: Choose digestion method appropriate to matrix (see Section 3030). b. Suppressing ionization: If necessary, filter sample through medium-porosity paper, add 1.0 mL potassium ionization suppressant to 50 mL volumetric flask, and dilute with sample for flame photometric determination. Sample solution will be in a 0.1% K matrix. c. Treatment of standard solutions: Prepare dilutions of the Li standard solution to bracket sample concentration or to establish at least three points on a calibration curve of emission intensity against Li concentration. Prepare standards by adding appropriate volumes of standard lithium solution to 25 mL water ⫹ 1.0 mL potassium ionization suppressant reagent in a 50-mL volumetric flask. Dilute to 50.0 mL and mix. Both samples and standards will be in a 0.1% K matrix to suppress ionization of lithium. d. Flame photometric measurement: Determine lithium concentration by direct intensity measurements at a wavelength of 2. Apparatus Flame photometer: A flame photometer or an atomic absorption spectrometer operating in the emission mode using a lean air-acetylene flame is recommended. 3. Reagents Use reagent water (see 3111B.3c) in reagent preparation and analysis. 1 LITHIUM (3500-Li)/Flame Emission Photometric Method and 10.0 g/L were 4.09 ⫾ 0.056 g/L and 9.96 ⫾ 0.094 g/L, respectively. The single-operator RSD was 1.38% for a lithium solution containing 10 g/L. See Part 1000 and Section 3020 for specific quality control procedures and acceptance limits to be followed during sample preparation and analysis. 670.8 nm. The bracketing method (Section 3500-Na.B.4d) can be used with some photometric instruments, while the construction of a calibration curve is necessary with others. Run sample, water, and lithium standard as nearly simultaneously as possible. For best results, average several readings on each solution. Follow the manufacturer’s instructions for instrument operation. 7. Bibliography 5. Calculation FISHMAN, M.J. 1962. Flame photometric determination of lithium in water. J. Amer. Water Works Assoc. 54:228. PICKETT, E.E. & S.R. KOIRTYOHANN. 1968. The nitrous oxide-acetylene flame in emission analysis-I. General characteristics. Spectrochem. Acta. 23B:235. KOIRTYOHANN, S.R. & E.E. PICKETT. 1968. The nitrous oxide-acetylene flame in emission analysis-II. Lithium and the alkaline earths. Spectrochem. Acta, 23B:673. URE, A.M. & R.L. MITCHELL. 1975. Lithium, sodium, potassium, rubidium, and cesium. In J.A. Dean & T.C. Rains, eds. Flame Emission and Atomic Absorption Spectrometry. Dekker, New York, N.Y. THOMPSON, K.C. & R.J. REYNOLDS. 1978. Atomic Absorption Fluorescence, and Flame Spectroscopy—A Practical Approach, 2nd ed. John Wiley & Sons, New York, N.Y. WILLARD, H.H., L.L. MERRIT, J.A. DEAN & F.A. SETTLE., JR. 1981. Instrumental Methods of Analysis, 6th ed. Wadsworth Publishing Co., Belmont, Calif. g Li/L ⫽ (g Li/L in portion analyzed) ⫻ D where: D ⫽ dilution ratio ⫽ mL sample ⫹ mL water mL sample 6. Quality Control The quality control practices considered to be an integral part of each method can be found in Section 3020. Process a QC standard through entire analytical protocol as a way of determining systematic bias. The control limits for precision of duplicate determinations at concentrations (in water) of 4.0 g/L 2