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mL 10 000 µg/mL Be stock standard solution [(
i
) above] to obtain a 10 µg/mL Be internal
standard concentration.
(m)
4 M Hydrochloric acid digestion solution
.—Add approx. 500 mL deionized (or equivalent)
water to a water to a 1 L volumetric flask. Slowly add 333 mL of concentrated hydrochloric acid
[(
a
) above], then bring to volume with deionized water and mix.
C.
Calibration (Alternative B)
(a)
Standard solution.
—Prepare calibration standards from ammonium dihydrogen
phosphate [Alternative B, B(
b
)] and potassium chloride [Alternative B, B(
c
)] as recommended in
Table
2015.18E
. As with Alternative A, many calibration standards are required since multiple
ICP-OES wavelengths are used, since some wavelengths are split into multiple calibration
segments, and since a minimum of five points/curve is recommended. Table
2015.18E
provides
the P and K concentrations expressed as µg/mL and their percent oxide forms.
Better P recoveries were obtained using weighed salts [Alternative B, B(
b
)], so commercially
available stock standard solutions are not recommended.
(b)
ICP-OES calibration.—
Emission intensity for each of the calibration standards is plotted
against concentration. A minimum of five calibration standards are used for each wavelength.
Use an internal standard [Alternative B, B(
l
)] to adjust the concentration of the calibration
standards and test solutions. The wavelengths, standards used, concentration ranges, curve fit,
and wavelengths that may require spectral deconvolution are listed in Table
2015.18F
. The data
in Table
2015.18F
are based on a radial view for K. If linear regression to 1000 µg/mL of K is not
possible, one or more of the following will be necessary: selecting quadratic curve fit (provided
the curvature is not excessive), utilizing wavelength 404.721 nm for the five highest K calibration
standards listed in Table
2015.18E
, dropping one or more of the top K standards listed in Table
2015.18E
and/or conducting dilutions of the test solutions using 0.16 M HCl.
The test solution and internal standard/ionic buffer solutions are blended using a reagent “T”
connector (Part No. 116-0522-01, Bran+Luebbe, Mequon, WI) just prior to the nebulizer using
the conditions described in Table
2015.18G
.
D.
Sample Preparation
Candidates for 2016 Method of the Year
253