Determination of Metals in Alumina
Using ICP-OES
Application Note
Inductively Coupled Plasma-Optical Emission Spectrometers
Author
Introduction
Deen Johnson
The use of alumina is very common in the petroleum, petrochemcial and pharmaceutical manufacturing. Alumina is used as a substrate for many of the catalysts
used in the refining or manufacturing process. The alumina is chemically bound to,
or coated with, active catalytic agents to produce the desired reactions. Typical catalytic agents are; platinum, palladium, rhodium, titanium, tungsten and tantalum
[1,2]. As substrate material, the alumina must be sufficiently pure. The alumina may
contain other metals in the lattices of the structure which can result in contamination [3]. It is not desirable to have such contaminates in the alumina reacting with
the catalytic agent or the products. These metallic impurities could alter desired
reaction rates, or contaminate the final product. It is therefore necessary to analyze
the alumina to determine the major and minor metallic components.
The scope of this study was to determine six metals in alumina. The metals determined are; lanthanum, silicon, iron, sodium, titanium and lead. The primary elements
of interest in the alumina are Si, Fe, Na and Ti.
Additionally, the study looked at three different acid mixes for the digestion of the
alumina. The acid mixtures used were; 1:1 HNO3, 1:1 HCl and a mix called the Alcoa
#1 mix. The Alcoa #1 mix contained 350 mL water, 250 mL of 1:1 sulfuric acid,
200 mL concentrated hydrochloric acid and 200 mL concentrated nitric acid. The
results were checked against both colorimetric and atomic absorption analysis.
A 3% lanthanum nitrate solution was also analyzed for lead. All the samples were
analyzed in the same analytical sequence.
Experimental
Table 1.
Instrumentation
Nebulizer pressure (kPa)
Stabilization time (sec)
Sample delay time (sec)
Rinse time (sec)
Snout purge
200
15
12
10
OFF
Integration time (sec)
Replicates
3
3
PMT (V)
Power (kW)
Plasma (L/Min)
Auxiliary (L/Min)
Pump speed (rpm)
650
1.20
12.0
1.50
10
Background correction mode
Dynamic
Concentration units
Max curve order
C.C. limit
mg/L
4
0.9950
The Liberty 200 ICP-OES was used in this study. The instrument was optimized for the viewing height, scan and search
windows, power, plasma flow, auxiliary plasma flow, pump
speed and nebulizer pressure. The use of dynamic background
correction was used for all the wavelengths in the determination.
Analytical Procedure
The samples were received in solution having already been
prepared in the three acid mixtures. Approximately 0.20 grams
of sample had been weighed. 10 mL of the selected acid was
added for digestion. The overall dilution ratio was approximately 1:1000. The analytical blank was analyzed for each
acid mixture to correct for any contaminates present.
The samples were analyzed using standards prepared in both
0.014 M (1% v/v) nitric acid and 0.1 M (1% v/v) hydrochloric
acid. The samples were also analyzed with 10,000 mg/L aluminum spiked into each standard to determine whether
matrix matching of samples and standards is required.
Table 2.
Parameters Common to All Elements in the Alumina Analysis
Element Specific Parameters for the Metals
La
Wavelength (nm)
View height (mm) 8
The common parameters used in the analysis of the alumina
are presented in Table 1.
Si
Fe
Na
Ti
Pb
379.478 251.611 259.940 589.592 323.904 220.353
6
6
12
8
8
0.040
0.080
0.026
0.027
Windows
Search (nm)
0.080
0.040
Scan (nm)
0.120
0.060
0.060
0.120
0.030
0.040
Filter position
6
6
6
7
6
1
Order
1
2
2
1
2
3
Results
Standard 1
(units mg/L)
50.00
5.000
5.000
5.000
5.000
5.000
The results for the analysis of the alumina using the different acid mixtures are shown in Table 3. The results have
been corrected for the blank contribution.
Standard 2
(units mg/L)
100.0
10.00
10.00
10.00
10.00
10.00
The titanium was the element of primary interest in this
analysis. The sample digested with the nitric acid exhibited
the highest recovery for titanium. The hydrochloric acid gave
the next best recovery, followed by the Alcoa #1 acid mixture.
The recovery may vary with the acid mixture, due to the possibility of interferences in the plasma [4]. Titanium, silicon and
lanthanum are refractory in nature which may affect the
recoveries for the different acid mixtures used in digestion.
These trends were similar to those found when the samples were
analyzed by colorimetric and atomic absorption analysis [5].
Table 3.
Element specific parameters, optimized for each of the metals
analyzed, are shown in Table 2.
Analytical Result (in mg/L) with Blank Correction Applied
Acid Mixture
La
Si
Fe
Na
Ti
Pb
HCl
ND
0.104
0.038
0.018
3.81
0.015
HNO3
ND
0.086
0.032
0.028
4.06
0.176
Alcoa
ND
0.102
0.035
0.014
3.16
0.029
La solution
97.34
0.702
1.75
0.033
3.00
0.100
ND = Non detected
Titanium, silicon and lanthanum are refractory in nature
which may affect the recoveries for the different acid mixtures used in digestion. These trends were similar to those
found when the samples were analyzed by colorimetric and
atomic absorption analysis.
2
No problems were found with background or spectral interferences with the sample dilutions used in this procedure, due
to the high resolution of the spectrometer used.
After dilution of the samples by approximately 1:1000, no
problems were found either with background or spectral interferences from the aluminium. The dynamic background more
than adequately compensated for the background levels.
Because there were no problems with background or spectral
interferences, there is the possibility of using a lower dilution
than that used here.
There were no spectral interferences encountered in the samples. For example, the high resolution for Pb in 3rd order
(0.007 nm) easily resolved the very large Al peak near the
Pb 220.353 nm line.
Acknowledgement
A Quality Control Standard (QCS) was analyzed during the
analysis. The QCS, which was the low calibration solution,
was analyzed after every 4 samples. The results of the QCS
are reported in Table 4 and are the mean value of two determinations. The range shown represents plus or minus one
standard deviation. Also shown are typical precision values
(%RSD) for a within run determination of three replicates
(Table 1).
Table 4.
We wish to acknowledge Ken Youngblood and David Bose of
Vista Chemical (Austin, Texas) for supplying the samples.
References
1.
W. L. Leffler “Catalytic Reforming”. Petroleum Refining
for the Non-Technical Person. PennWell Books, Tulsa,
Oklahoma, U.S.A., 1979, p69.
2.
P. Wiley “Catalytic Reforming”. Petrochemicals. John
Wiley & Sons, New York, U.S.A., 1986, p90.
3.
F. A. Cotton and G. Wilkinson “The Group IIIA (13)
Elements: Al, Ga, In, Tl”. Advanced Inorganic Chemistry,
5th Edition,, John Wiley & Sons, New York, U.S.A. 1988,
pp211-212.
4.
G. A. Meyer, and P. N. Keliher “An Overview of Analysis
by Inductively Coupled Plasma - Atomic Emission
Spectrometry”. Inductively Coupled Plasma in Analytical
Atomic Spectrometery. Second Edition, A. Montasser and
D.W. Golightly, VCH Publishers, Inc, New York, U.S.A.
1992, p492.
5.
Personal Communication
Quality Control Standard Results and Recoveries
Found
Metal
Within run
concentration
Recovery
precision
RSD
mg/L %
%
La
49.16 ± 1.35
98.3
0.49
Si
4.85 ± 0.13
97.0
0.84
Fe
4.95 ± 0.09
99.1
0.83
Na
4.85 ± 0.09
97.0
0.71
Ti
5.41 ± 0.13
108.1
0.56
Pb
4.93 ± 0.008
98.5
1.75
Conclusions
For More Information
ICP-OES analysis of metals in alumina using the Liberty 200 is
fast, accurate and precise. The ICP technique is much faster
for this determination than the atomic absorption methods
and considerably faster than the colorimetric methods. The
ICP results were similar to those obtained using the other
techniques. The low concentrations of iron, silicon, sodium
and lead found in the solutions were measured with good
reproducibility.
For more information on our products and services, visit our
Web site at www.agilent.com/chem
Automated analysis with quality control solutions taken
through the procedure, confirms the accuracy of the results.
3
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Agilent shall not be liable for errors contained herein or
for incidental or consequential damages in connection
with the furnishing, performance, or use of this material.
Information, descriptions, and specifications in this
publication are subject to change without notice.
© Agilent Technologies, Inc., 1993
Printed in the USA
November 1, 2010
ICPES-11