3500-Li LITHIUM*
3500-Li A. Introduction
1.
Occurrence and Significance
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 con-
taining 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
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 lith-
ium in irrigation waters is 2.5 mg/L.
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 success-
fully in most cases (with lower detection levels), even though
lithium is not specifically listed as an analyte in the method.
3500-Li B. Flame Emission Photometric Method
1.
General Discussion
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-acety-
lene flames and can be suppressed by adding potassium. See
Section 3500-Na.B.1bfor 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 poly-
ethylene bottle, although borosilicate glass containers also may
be used. At time of collection adjust sample to pH ⬍2 with nitric
acid (HNO
3
).
2.
Apparatus
Flame photometer: A flame photometer or an atomic absorp-
tion 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.
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, pur-
chase 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.
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 sup-
pressant 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 con-
centration by direct intensity measurements at a wavelength of
* Approved by Standard Methods Committee, 2004. Editorial revisions, 2011.
Joint Task Group: 20th Edition—See Section 3500-Al.
1
670.8 nm. The bracketing method (Section 3500-Na.B.4d) can
be used with some photometric instruments, while the construc-
tion 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.
5.
Calculation
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
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.
7. Bibliography
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 Fluores-
cence, 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.
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