Standard Methods for the Examination of Water and Wastewater
© Copyright 1999 by American Public Health Association, American Water Works Association, Water Environment Federation
water of acceptable quality. Other water preparation regimes may be used, provided that the
water produced is metal-free. Reagent water containing trace amounts of analyte elements will
cause erroneous results.
Produce reagent water using a softener/reverse osmosis unit with subsequent UV
sterilization. After the general deionization system use a dual-column strong acid/strong base ion
exchange system to polish laboratory reagent water before production of metal-free water. Use a
multi-stage reagent water system, with two strong acid/strong base ion exchange columns and an
activated carbon filter for organics removal for final polishing of laboratory reagent water. Use
only high-purity water for preparation of samples and standards.
c. Stock, standard, and other required solutions: See Section 3120B.3d for preparation of
standard stock solutions from elemental materials (pure metals, salts). Preferably, purchase
high-purity commercially prepared stock solutions and dilute to required concentrations. Single-
or multi-element stock solutions (1000 mg/L) of the following elements are required: aluminum,
antimony, arsenic, barium, beryllium, cerium, cadmium, chromium, cobalt, copper, germanium,
indium, lead, magnesium, manganese, molybdenum, nickel, rhodium, scandium, selenium,
silver, strontium, terbium, thallium, thorium, uranium, vanadium, and zinc. Prepare internal
standard stock separately from target element stock solution. The potential for incompatibility
between target elements and/or internal standards exists, and could cause precipitation or other
solution instability.
1) Internal standard stock solution: Lithium, scandium, germanium, indium, and thorium
are suggested as internal standards. The following masses are monitored:
6
Li,
45
Sc,
72
Ge,
115
In,
and
232
Th. Add to all samples, standards, and quality control (QC) samples a level of internal
standard that will give a suitable counts/second (cps) signal (for most internal standards, 200 000
to 500 000 cps; for lithium, 20 000 to 70 000 cps). Minimize error introduced by dilution during
this addition by using an appropriately high concentration of internal standard mix solution.
Maintain volume ratio for all internal standard additions.
Prepare internal standard mix as follows: Prepare a nominal 50-mg/L solution of
6
Li by
dissolving 0.15 g
6
Li
2
CO
3
(isotopically pure, i.e., 95% or greater purity†#(88)) in a minimal
amount of 1:1 HNO
3
. Pipet 5.0 mL 1000-mg/L scandium, germanium, indium, and thorium
standards into the lithium solution, dilute resulting solution to 500.0 mL, and mix thoroughly.
The resultant concentration of Sc, Ge, In, and Th will be 10 mg/L. Older instruments may
require higher levels of internal standard to achieve acceptable levels of precision.
Other internal standards, such as rhodium, yttrium, terbium, holmium, and bismuth may also
be used in this method. Ensure that internal standard mix used is stable and that there are no
undesired interactions between elements.
Screen all samples for internal standard elements before analysis. The analysis of a few
representative samples for internal standards should be sufficient. Analyze samples ‘‘as
received’’ or ‘‘as digested’’ (before addition of internal standard), then add internal standard mix
and reanalyze. Monitor counts at the internal standard masses. If the ‘‘as received’’ or ‘‘as