United States
Environmental Protection
Agency
^ _
Research and Development
Environmental Monitoring
Systems Laboratory
P.O. Box 93478
Las Vegas NV 89193-3478
EPA/600/4-90/025
September 1990
Determination of Trace
Elements in Hazardous
Wastes by Ion
Chromatography
Project Report
-------
DETERMINATION OF TRACE ELEMENTS IN HAZARDOUS WASTES
BY ION CHROMATOGRAPHY
by
J. T. Rowan
Lockheed Engineering and Sciences Company
1050 E. Flamingo Road, Las Vegas, Nevada 89119
and
E. M. Heithmar
U.S. Environmental Protection Agency
P.O. Box 93478, Las Vegas, Nevada 89193-3478
Contract 68-03-3249
Project Officer
E. M. Heithmar
Quality Assurance and Methods Development Division
Environmental Monitoring Systems Laboratory
Las Vegas, NV 89193-3478
OFFICE OF MODELING, MONITORING SYSTEMS AND QUALITY ASSURANCE
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
-------
NOTICE
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under Contract 68-03-3249 to Lockheed Engineering and Sciences Company.
It has been subjected to the Agency's peer and administrative review, and it has been approved for publication
as an EPA document Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
11
-------
ABSTRACT
An ion chromatographic method is evaluated for the determination of cadmium, cobalt, copper, iron,
manganese, nickel, and zinc. This procedure combines the features of preconcentration and matrix
modification with ion chromatography for the analysis of acidic aqueous samples, such as digests of hazardous
wastes or preserved water samples. The system is able to separate alkali and alkaline-earth metals, as well as
many anions, from the sample matrix prior to loading of the sample on the analytical separator column.
Detection limits for 6.5-mL samples are generally below 1 jig/L. The calibration curves in terms of
both peak area and peak height are linear for at least 2.5 orders of magnitude. Quantification on the basis
of peak height is recommended to reduce inter-element effects on peaks that are not completely resolved.
Precision, measured as relative standard deviation, is generally better than 2% at 250 ng/L. The technique
is evaluated on synthetic seawater and three reference materials. There is no effect from high salt
concentrations, and recoveries are generally within acceptable quality-control limits.
This report was submitted in fulfillment of contract number 68-03-3249 by Lockheed Engineering and
Sciences Company under the sponsorship of the U.S. Environmental Protection Agency. This report covers
a period from January 1, 1990 to August 24, 1990. Work is on-going.
111
-------
IV
-------
CONTENTS
Notice ii
Abstract iii
Figures vi
Tables vii
1. Introduction 1
2. Conclusions 3
3. Recommendations 4
4. Materials and Methods 5
5. Experimental Procedures • 12
6. Results and Discussion 14
References 26
Appendix
A. Method 6060: Ion Chromatography of Transition Metals 27
-------
FIGURES
Number Page
l(a) Chelation ion chroma tograph in sample loading configuration. PI = high-
pressure gradient pump, P2 <= two-channel peristaltic pump, P3 =
reciprocating single-piston pump, P4 = pneumatic pump ............................. 6
l(b) Chelation ion chromatograph in trace-element chelation configuration ................... 7
l(c) Chelation ion chromatograph configuration for elution of analytes to
interface column [[[ 8
\
l(d) Chelation ion chromatograph configuration for conversion of interface
column to ammonium form [[[ 9
l(e) Chelation ion chromatograph configuration for analyte separation and
chelator-column clean-up [[[ 10
2 Chelation ion chromatogram of 80 jig/L cobalt, copper, iron, manganese,
nickel, and zinc, and 250 |ig/L cadmium ......................................... 15
3 Chelation ion chromatogram of synthetic seawater spiked with 80
cobalt, copper, iron, manganese, nickel, and zinc, and 250 pg/L cadmium. ............... 19
1A Chelation ion chromatograph in sample loading configuration. PI =
high-pressure gradient pump, P2 = two-channel peristaltic pump, P3 =
-------
TABLES
Number Page
1 DETECTION LIMITS (jig/L, 3a CRITERION, N=7) BASED ON
HEIGHT, AREA, AND SAMPLE SIZE 16
2 PRECISION AS A FUNCTION OF SAMPLE CONCENTRATION
AND QUANTITATION METHOD 18
3 RECOVERY OF ANALYTES FROM SYNTHETIC SEAWATER 20
4 ANALYSIS OF ICAP-19 22
5 ANALYSIS OF NIST 1643B 23
6 ANALYSIS OF QB390W2 24
1A METALS DETERMINED BY METHOD 6060 27
2A STOCK STANDARD 34
3A CALIBRATION STANDARD CONCENTRATIONS (|ig/L) 35
4A ION CHROMATOGRAPHY SEQUENCE 37
Vll
-------
Vlll
-------
SECTION 1
INTRODUCTION
Trace-metal analysis of environmental samples is generally performed by some type of atomic
spectroscopy: graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma-atomic
emission spectrometry (ICP-AES), or inductively coupled plasma-mass spectrometry (ICP-MS). These
techniques allow rapid, sensitive, accurate, and precise determination of metal concentration in a wide variety
of matrices.
While ion chromatography (1C) is not expected to replace the spectroscopic methods, it has attributes
that make it attractive in some applications. It uses relau\ dy inexpensive instrumentation which is not limited
to just metal determinations. It can be configured in various ways to determine the gamut of inorganic and
organic ionic species in aqueous samples. This versatility would be very valuable for a laboratory of limited
capital resources. 1C instrumentation is significantly more rugged than atomic spectrometry equipment,
making field-transportable instruments feasible. 1C offers the potential for element speciation, while atomic
spectrometry is generally limited to total element determinations.
All these factors make the recent development of a sensitive, reliable 1C method for the determination
of trace metals by workers at the National Institute of Science and Technology (NIST) and Dionex
Corporation (1) important They used chelation preconcentration of the trace metals to enhance the
sensitivity of 1C separation with post-column derivatization and spectrophotometric detection. This report
describes an evaluation of a modified form of that method for the analysis of acidic aqueous samples with
matrices similar to hazardous-waste digests.
The application of chelation preconcentration to ion chromatography offers the same advantages
which are provided by its implementation with ICP-AES and ICP-MS (2,3). Most important, the ability to
concentrate several milliliters of sample lowers 1C detection limits to the point that they are competitive with
atomic spectroscopic techniques. Also, the removal of interfering alkali and alkaline-earth metals allows the
analysis of complex samples of the type that might be expected of hazardous wastes.
-------
In the method evaluated in this report, a preconcentration column is interfaced with an analytical
separator column via a high-capacity cation-exchange column for the determination of cadmium, cobalt,
copper, iron, manganese, nickel, and zinc The preconcentration column contains a macroporous
polystyrene/divinylbenzene resin functionalized with iminodiacetate, which has a high affinity for many
transition metals and lower affinity for alkaline-earth metals. Alkali metals and anions are not retained by
the column, and alkaline-earth metals can be selectively removed by exchange with ammonium ion. The
concentrated trace metals are then eluted by nitric acid to the high-capacity interface column. The excess
hydronium ion concentration in the interface column after exposure to the acid matrix is removed by exchange
with ammonium ion. The interface column is then switched into the analytical eluant stream. The metals are
separated in the analytical column, and they are detected photometrically after post-column derivatization
with a chromophoric reagent.
-------
SECTION 2
CONCLUSIONS
The 1C method evaluated in this report has been shown to be applicable to six trace metals: cobalt,
copper, iron, manganese, nickel, and zinc. Accurate determinations of cadmium are also possible in samples
containing substantially more cadmium than cobalt. The appropriateness of this method for cadmium
determinations will depend on sample composition and data quality objectives.
Detection limits for a 6.5-mL sample loop have been estimated to range from 60 ng/L for cobalt to
1.3 Mg/L for zinc. The estimates are probably higher than the actual limits in the cases of cadmium, cobalt
and manganese, due to software limitations in evaluating baseline noise for these elements.
Long-term precision (over several hours), for a 2.5 /ig/L sample, ranges from 0.6% to 7.1% relative
standard deviation (RSD) for measurements based on chromatographic peak height and from 1.2 to 14% RSD
for quantitation based on area. The long-term precision for a 250 /ig/L sample ranges from 0.4% to 2.1%
RSD based on height and from 0.6% to 2.1% RSD based on area. Sequential analyses of sample duplicates
generally agree within ± 2% of the mean concentration using either quantitation method.
An analysis of a synthetic seawater sample spiked with analytes verifies that the matrix modification
system effectively eliminates interferences from alkali and alkaline-earth metals, as well as interferences from
anions. Recoveries from three reference materials are within ± 10% of the reference values for all analytes
except cadmium, which exhibits low recoveries in samples with large differences between the sizes of the
overlapping cadmium and cobalt peaks. This problem is more severe when quantitation is based on area
measurement, because the software overestimates the contribution of the tailing cobalt peak to the cadmium
peak area. Quantification of cadmium on the basis of peak height is therefore preferable.
The 1C method which is evaluated in this report has been designated Method 6060 and is presented
in SW-846 format in Appendix A.
-------
SECTION 3
RECOMMENDATIONS
In the current geometry, the preconcentration eluants must be directed through the sample loop in
order to pass the chelator column. Depending on the size of the sample loop, this may require large volumes
of eluant. Mixing between ammonium acetate and nitric acid eluants in the sample loop is another problem
that may degrade method performance and makes selection of appropriate elution times difficult The
geometry of the apparatus can and should be altered so that eluant passes through the sample loop only long
enough to inject the entire sample. This would be a more efficient ion chromatographic system that would
consume less eluant and probably improve analytical performance. •
This study and similar work on preconcentration applied to ICP-MS has demonstrated that the eluants
contribute to the blank levels. The ICP-MS work has shown that blanks can be reduced for some elements
by passing the ammonium acetate eluant through a preliminary chelator column in order to remove impurities.
The blank values, and therefore the detection limits, may be reduced by further alteration of the 1C
configuration to include on-line polishing of some of the ammonium acetate eluant.
Lead and cadmium are two important target analytes for 1C Cadmium was evaluated in this study,
but suffered peak-overlap interference from cobalt This situation may be slightly ameliorated by further
optimization of the integration algorithm. Results for all of the metals would probably benefit from
refinement of this aspect of the software. Preliminary efforts have been made to determine lead by
modification of the present method, but sensitivity for that metal is low, and the lead peak splits under some
conditions. Further experimentation, including alteration of the eluant chemistry and modification of the
detection scheme, is required to adapt this procedure for lead.
-------
SECTION 4
MATERIALS AND METHODS
INSTRUMENTATION
The ion chromatograph used in this work is shown schematically in Figure l(a). The sample pump,
P2 in the Figure, is a two-channel peristaltic pump (Gilson Minipuls II, Gilson Medical Electronics,
Middleton, WI). The rest of the apparatus is an ion chromatograph that consists entirely of equipment from
Dionex Corporation, Sunnyvale, CA. The eluant paths in the apparatus are metal-free.
The chromatographic system is based on three columns. The first is an iminodiacetate chelating resin
column (MetPac CC-1). The second column is a high-capacity, fully sulfonated, cation-exchange resin column
(TMC-1) with a capacity of 0.3 meq. This column serves as an interface between the chelator column and the
analytical separator column, which is a low-capacity, mixed-bed, ion-exchange column (lonPac HPIC-CS5).
The eluants used in the preconcentration and matrix modification steps are delivered by a
programmable, high-pressure, gradient pump, PI (Model GPM-II). The gradient pump controls two
independent sets of column-switching valves, VI and V2, that direct the flow of eluants throughout the
procedure. A reciprocating single-piston pump, P3 (Model DQP), is used to pump eluant through the
analytical column. The post-column derivatization reagent is introduced to the eluant in a post-column reactor
with a reagent delivery system (Model RDM) driven by a pneumatic pump, P4. The post-column reactor is
connected to a flow-through, variable-wavelength detector (Model VDM-II) via a knitted reaction coil. The
detector monitors at 530 nm. Data acquisition and integration are accomplished with the Dionex Autoion 450
chromatography software on an 80386-based computer via a computer interface (Model ACI).
REAGENTS AND SAMPLE PREPARATION
In-house deionized water, prepared using a Milli-Q Reagent Water System (Millipore Corporation,
Bedford, MA) and feed water purified by reverse osmosis, was used for all solutions. Sub-boiling, distilled-in-
-------
Sample Buffered with Ammonium Acetate
PDCA Eluant
PAR
Derivatized Eluant
Chelator Column
Post-column Reactor
Analytical Column
yariable-wavelencjth Detector
Ammonium
Acetate Buffer
Interface Column
Figure l(a). Chelation ion chromatograph in sample loading configuration. PI = high-pressure gradient pump, P2 = two-channel peristaltic pump,
P3 = reciprocating single-piston pump, P4 = pneumatic pump.
-------
Post-column Reactor
Ammonium Acetate
PDCA Eluant
PAR
Derivatized Eluant
P4
Variable-wavelength Detector
>—P>
Figure l(b). Chelation ion chromatograph in trace-element chelation configuration.
-------
00
Post-column Reactor
Nitric Acid + Water
PDCAEIuant
PAR
Derivatized Eluant
P4
yariable-^vayelength Detector
^H>
Figure l(c). Chelation ion chromatograph configuration for elution of analyies to interface column.
-------
Post-co umn Reactor
Ammonium Nitrate
PDCA Eluant
PAR
Derivatized Eluant
P4
Variable-wavelength Detector
---;:^^4_
Figure l(d). Chelation ion chromatograph configuration for conversion of interface column to ammonium form.
-------
Ammon. Acet. alternating with
Nitric Acid (clean-up procedure - see text)
PDCA Eluant
PAR
Derivatized Eluant
Post-column Reactor
Variable-wavelength Detector
Fieurc l(c). Chcluiion ion chromatograph configuration for analyic separation and chclator-column clean-up.
-------
quartz concentrated nitric acid, acetic acid, and ammonia (Seastar, Sydney, B.C., Canada) was used throughout
the study. 1.5 M nitric acid, 0.1 M ammonium nitrate, and approximately 2 M ammonium acetate (pH 5.5)
were all prepared from the Seastar reagents. The ammonium acetate serves as both an eluant and as an on-
line buffer solution in the method. This buffer, when mixed in a 1:1 ratio with samples of up to 3% (w)
nitric acid, produces a sample solution with a pH of between 5 and 5.5. The eluant for the analytical column
is 6'IQ"4 M pyridine-2,6-dicarboxylic acid (PDCA) (Dionex, Sunnyvale, CA), 0.040 M sodium hydroxide
(Aldrich Chemicals, Milwaukee, WI), and 0.090 M acetic acid. The post-column derivatization reagent
contains SxlO"4 M 4-(2-pyridylazo)resorcinol (PAR) monosodium salt, monohydrate (Dionex, Sunnyvale, CA),
1.0 M 2-dimethylamino ethanol (Aldrich Chemicals, Milwaukee, WI), 0.30 M sodium bicarbonate (Aldrich
Chemicals, Milwaukee, WI), and 0.50 M ammonia.
Stock analyte solutions of cadmium, cobalt, copper, iron, manganese, nickel, and zinc were prepared
from commercial standards (Spex Industries, Metuchen, NJ) in 1% (v/v) nitric acid.
A synthetic seawater solution prepared for a previous investigation (2) was used in this study. It had
been prepared from sub-boiling, distilled-in-quartz sulfuric acid (J.T. Baker Chemicals, Phillipsburg, NJ),
chloride salts of sodium, potassium, magnesium, and calcium with minimum purities of 99.99+% (Aldrich
Chemicals, Milwaukee, WI), and nitric acid. This solution contains 10,560 mg/L sodium, 1270 mg/L
magnesium, 400 mg/L calcium, 380 mg/L potassium, 21,000 mg/L chloride, and 880 mg/L sulfur, the matrix
of a seawater sample acidified with 0.5% hydrochloric acid and 1% nitric acid. It was spiked with cadmium
at a concentration of 250 /ng/L and cobalt, copper, iron, manganese, nickel and zinc at 80
A working solution of ICAP-19 quality control sample (U. S. Environmental Protection Agency,
Cincinnati, OH) was prepared by diluting 0.5 mL of the stock to 100 mL with 1% nitric acid. This sample
contains 50 /xg/L of each of the target analytes in a 1% nitric acid matrix. A Contract Laboratory Program
Quarterly Blind Sample, QB390 Water II (U. S. Environmental Protection Agency, Las Vegas, NV) was
diluted 10-fold with 0.8% nitric acid. The resulting solution has a matrix of 1% nitric acid. Standard
Reference Material 1643b (National Institute of Standards and Technology, Gaithersburg, MD) was analyzed
as received. It has a matrix of 3% w) nitric acid.
11
-------
SECTION 5
EXPERIMENTAL PROCEDURES
. When valves VI and V2 are in the "A" position [Figure l(a)J, acidified samples are pumped, at 4.0
mL/min., through one channel of a two-channel peristaltic pump. At the same time, 2 M ammonium acetate
is pumped, at 4.0 mL/min., through the other channel of the peristaltic pump. The two solutions are combined
in a mixing tee in a 1:1 ratio. This buffers the sample solution to a pH between 5 and 5.5. The buffered
sample flows from the mixing tee, fills the sample loop (L), and flows to waste. The PDCA eluant flows
continuously, at 1.0 mL/min., through the interface column to the analytical column.
Once the sample is loaded, at t = 0.0 minutes, the program on the gradient pump is initiated [Figure
l(b)]. Valve VI is switched into the *B" position and the gradient pump sweeps the buffered sample onto the
chelator column by passing 2 M ammonium acetate, at 3.0 mL/min., through the sample loop for 1.5 minutes.
The transition metals and alkaline-earth metals are chelated by the iminodiacetate functional group in the
chelator column. The 4.5 mL of ammonium acetate following the sample replaces most calcium and
magnesium ions in the column with ammonium ions and passes to waste.
At t = 1.5 minutes, the gradient pump begins to pump a combination of 1.5 M nitric acid and water
in a 1:2 ratio so that the final eluant solution is 0.5 M nitric acid. Nitric acid is pumped for 3.5 minutes. The
nitric acid front reaches the chelator column at t = 3.7 minutes. At this time, valve V2 is switched to the "B"
position [Figure l(c)]. The nitric acid elutes the concentrated metals to the interface column. While valve
V2 is in the "B" position, the PDCA eluant is diverted into a by-pass which sends it directly to the analytical
column. At t = 5.0 minutes, 10.5 mL of 0.5 M nitric acid have been pumped into the sample loop. Now the
gradient pump begins to pump ammonium nitrate in order to carry all of the nitric acid through the loop and
chelator column to the interface column. Once this is accomplished, the analytes have been collected on the
interface column, and that column has been converted to the hydronium form by the acid matrix used to elute
the metals from the chelator column.
At t = 8.2 minutes, when all of the nitric acid has passed through the chelator column, valve VI
12
-------
switches to the "A" position [Figure l(d)]. The gradient pump continues to pump ammonium nitrate, but now
it bypasses the chelator column and flows directly onto the interface column. The interface column is
converted from the hydronium form to the ammonium form. This continues for 1.5 minutes.
With the interface column in the ammonium form, valve VI switches to the *B* position and valve
V2 switches back to the "A" position at t = 9.7 minutes. This occurs at t=9.7 minutes [Figure l(e)]. The
PDCA eluant returns to its route through the interface column, at which time it chelates the concentrated
metals and carries them to the analytical column, where the chelates are separated. The separated metals are
derivatized with 4-(2-pyridylazo)resorcinol (PAR), flowing at 0.5 mL/min., in the post-column reactor and are
detected and quantified at 525 ± 5 nm using an absorbance detector.
At the same time, the gradient program begins a chelator column clean-up procedure in which the
chelator column is flushed with 3 mL portions of 2 M ammonium acetate, 1.5 M nitric acid, 2 M ammonium
acetate, and 1.5 M nitric acid. Finally, the gradient pump passes enough 2 M ammonium acetate (12.9 mL)
through the loop and chelator column so that the column receives a minimum rinse of 6-mL of 2 M
ammonium acetate. The program then terminates and the gradient pump ceases to pump. At the same time,
the pump switches valve VI to the "A" position so that a new sample may be loaded.
13
-------
SECTION 6
RESULTS AND DISCUSSION
GENERAL METHOD PERFORMANCE
A representative chromatogram of a solution containing cobalt, copper, iron, manganese, nickel and
zinc at a concentration of 80 jig/L and cadmium at 250 \ig/L is shown in Figure 2. The separation requires
approximately 12 minutes (allowing time for large manganese peaks to return to baseline), after slightly less
than 10 minutes for preconcentration and matrix modification. An analysis sequence run with an autosampler
would perform the chelator clean-up and the preconcentration and matrix modification of each sample during
the separation of the previous sample. A separation could thus begin every 12 minutes.
The nickel and zinc peaks are not completely resolved in Figure 2, nor are the cobalt and cadmium
peaks. The latter overlap is more problematic, because the later-eluting analyte of the pair, cadmium, is much
less sensitive than cobalt. The implications of the overlap of the cobalt and cadmium peaks will be discussed
in detail in the section on accuracy.
LINEARITY
The tested calibration range for all metals except cadmium was 0.8 to 250 pg/L using a 6.5-mL
sample loop. The evaluated calibration range for cadmium was 2.5 to 800 (ig/L. The curves are linear for
each metal over the entire concentration range, which spans greater than two orders of magnitude.
Calibrations by peak height yield correlation coefficients ranging from 0.9971 to 0.9999. Peak area calibrations
have correlation coefficients ranging from 0.9991 to 0.9999. In all but the case of cobalt, calibration by area
provide slightly higher correlation.
DETECTION LIMITS
The detection limits of the method were estimated using the 3a criterion by analyzing seven acidified
14
-------
0.35000
0.30000
0.25000
0.20000
*U°
.15000
0.10000
0.05000
0.00000
Mn
-0.05000
0.00
Ninutc
I 1 , I
10.00
Figure 2. Chelation ion chromatogram of 80 jig/L cobalt, copper, iron, manganese, nickel, and zinc, and
250 ng/L cadmium.
15
-------
reagent water blanks. Both a 6.5-mL and a 1.0-mL sample loop were used. When the 1.0-mL loop was used,
the on-line buffer was made somewhat more basic and mixed 1+4 with the sample in the sample loop, in order
to maximize the volume of sample concentrated. The resulting detection limits for both arrangements are
given in Table 1.
TABLE 1. DETECTION LIMITS (ng/L, 3a CRITERION, N=7)
BASED ON HEIGHT, AREA, AND SAMPLE SIZE
ANALYTE HEIGHT AREA
1 mL 6.5 mL 1 mL 6.5 mL
Cadmium3
Cobalt3
Copper
Iron
Manganese3
Nickel
Zinc
0.25
0.12
0.15
0.66
0.24
0.37
2.1
0.42
0.06
0.09
0.30
0.14
0.13
1.3b
0.16
0.091
0.37
1.5
0.12
0.089
2.7
0.30
0.05
0.15
0.36
0.07
0.14
1.1"
3 Standard deviation of blank estimated to be the same as that of nickel.
bN = 6
Iron, copper, nickel, and zinc all gave rise to detectable peaks in the blanks. As a result, the detection
limits for these metals are easily determined. Cadmium, cobalt and manganese yielded no measurable peaks
in the blanks. Limitations of the ion chromatographic software make it difficult to determine statistical
detection limits for these analytes. The software requires a detectable peak in order to return a concentration
value for the blank. Ceiling values for detection limits for the elements which did not have measurable blank
peaks are estimated based on their response factors and the standard deviation of the nickel blank. The nickel
blank has been selected because it had the smallest blank, and its standard deviation would be expected to be
more representative of the baseline uncertainty. Calculations based on either peak height or peak area yield
similar detection limits.
The sensitivity of the method for each analyte should increase by a factor of 4 between the 1.0-mL
sample loop and the 6.5-mL loop, taking into account the difference in dilution caused by the buffering
procedures. In fact, the mean sensitivity of all the analytes increase by only 3.4. Also, more nitric acid and
16
-------
ammonium nitrate is required to achieve optimal performance with the 6.5-mL loop. These results may be
indicative of eluant mixing in the larger sample loop.
All of the detection limits in Table are anah/te-blank limited; that is, the standard deviations of the
blanks are determined by fluctuations in the sizes of the analyte peaks, not by base-line noise. This is
supported by the fact that the detection limits for the 6.5-mL sample loop in Table 1 are not significantly
lower than those for the 1.0-mL loop, even though the sensitivity increased by more than a factor of 3. The
detection limits could therefore be improved by minimising the size of the analyte peaks in the blank.
Experimentation in conjunction with preconcentration ICP-MS indicate that the some of the analyte blank
levels can be substantially reduced by directing the ammonium acetate eluant flow through a preliminary
chelator before introduction to the primary chelation column. The implementation of such a system with the
1C instrumentation will require substantial modification of the device configuration. Further work is planned
in this area.
PRECISION
The precision of this technique was evaluated through multiple injections of multi-element standards
at two concentration levels. Calculated concentrations based on both peak height and peak area were
examined with respect to precision. The low concentration standard contained 8.0 /ig/L cadmium and 2.5 /jg/L
of the other target analytes. The high concentration standard contained 800 /ig/L cadmium and 250 /ug/L of
the each of the other six metals. Table 2 gives the precision, expressed as relative standard deviation, obtained
for both standards. One point was rejected using Dixon's outlier test at the 95% confidence level (4), from
the iron and the zinc peak height data, before calculating the standard deviations.
The precisions obtained through the measurement of peak area are inferior to that obtained by
measuring peak height This is attributed, in part, to the inability of the software to adequately define a
representative boundary between some peaks. Further optimization of the integration parameters may
improve this situation.
17
-------
TABLE 2. PRECISION AS A FUNCTION OF SAMPLE CONCENTRATION
AND QUANTITATION METHOD8
ANALYTE
Cadmiumb
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
2.50
HEIGHT
2.3
0.6
4.7
7.1
3.0
3.2
1.2C
Ug/L
AREA
3.9
1.2
8.3
14.2
2.7
2.9
5.7
250
HEIGHT
0.4
0.7
0.4
0.8°
2.1
1.6
1.1
UE/L
AREA
1.3
1.5
0.6
1.3
2.1
1.9
1.2
a Percent relative standard deviation (N = 5).
b Concentrations of cadmium were 8.0 and 800 ftg/L.
CN = 4
EFFECT OF HIGH SALINITY
The analysis of environmental samples is often hindered by the additive (usually spectral) and
multiplicative (usually chemical or physical) interferences caused by high salinity. Chelation preconcentration
has been shown to significantly reduce these interferences by removing most of the matrix elements from saline
samples (7-3). The ability of the present method to minimize these interferences was tested. Seawater was
chosen as the test matrix, since it has a higher total salt content than most waste digests, and since the present
method might also be applied to monitoring ocean or estuarine waters.
A synthetic seawater solution was spiked with 250 /lig/L cadmium and 80 /jg/L of the other metals.
This solution was analyzed to determine the effect of interferences from the alkali and alkaline-earth metals.
The resulting chromatogram is shown in Figure 3. The recoveries are given in Table 3. With the exceptions
of iron and zinc, the recoveries are all within ± 10% of the spike value. As the synthetic seawater solution
was several months old, it is likely that the high values for iron and zinc were caused by contamination.
18
-------
0.45000
0.40000
0.3500)
0.30000
0.25000
^0.20000
0.15000
0.10000
0.05000
0.00000
-0.05000
0.00
Zn
5.00
Minutes
T i r i I 1
10.00
Figure 3.
Chelation ion chromatngram of synthetic seawater spiked with 80 pg/L cobalt, copper, iron,
manganese, nickel, and zinc, and 250 ng/L cadmium.
19
-------
TABLE 3. RECOVERY OF ANALYTES FROM SYNTHETIC SEAWATER*
ANALYTE HEIGHT AREA
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
116
99
106
138
96
103
137
105
103
102
146
94
104
129
a Cadmium = 460 (ig/L, all others = 147
ACCURACY
Three reference samples were analyzed in duplicate to evaluate the accuracy of the 1C method. ICAP-
19 was analyzed at a concentration level of 50 (ig/L of each of the target analytes in a 1% nitric acid matrix.
The results of those analyses are given in Table 4. NIST 1643b was analyzed without dilution, and the data
are presented in Table 5. Each of the duplicate analysis recoveries is included to demonstrate short-term
duplicate precision. The duplicates were analyzed about one hour apart. The results in Table 4 and Table
5 are given for calculations based on both peak height and peak area. Using the mean of the duplicate-pair
results, both the height-based and the area-based recoveries are in the range of 86% to 104% for all analytes
except cadmium and manganese.
Cadmium yields low recoveries for both samples. This is attributed to interference from cobalt, the
peak of which immediately precedes and overlaps that of cadmium (Figure 2). Both ICAP-19 and NIST 1643b
have approximately equal concentrations of cobalt and cadmium. This translates into a cobalt peak
approximately six times higher than that of cadmium, given the greater sensitivity of the detection system for
cobalt When two unresolved peaks have disparate intensities, the chromatography software imposes an
exponential decay of the larger of two peaks into the smaller one. This calculated contribution of cobalt to
the cadmium peak is apparently overestimated in these samples, resulting in a calculated cadmium
concentration that is lower than the actual. Conversely, cobalt concentration calculated on the basis of peak
area is too high. The cobalt peak height and the concentration value derived from it are unaffected, since the
20
-------
software does not extrapolate the cadmium peak to the cobalt retention time. Because the cobalt decay affects
both the apparent height and area of the cadmium peak, the cadmium recovery is too low in either case.
Manganese, though well resolved from the other analytes, suffers an unidentified interference in the
analysis of NIST 1643b. Since the interference appears in the tailing end of the manganese peak, the recovery
is once again most affected when measuring peak area.
A quarterly blind sample, QB390 Water II, which was prepared at the Environmental Monitoring
Systems Laboratory in Las Vegas, was analyzed in duplicate and a third sample was spiked to a level of 500
lig/L cadmium and 160 (ig/L of the other metals. Table 6 presents the results of those analyses. There is no
cobalt in this sample, so the cadmium recoveries are not affected by the overlapping cobalt peak. All of the
original and spike recoveries in Table 6 are within acceptable quality control limits, except the iron spike
recovery based on peak height. The concentration of iron in the spiked sample is nearly 3 times the tested
upper limit of linearity of the method.
21
-------
TABLE 4. ANALYSIS OF ICAP-19
HEIGHT
ANALYTE
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
TRUE
mg/L
0.94
1
1.03
1.02
1.02
1.02
1.01
FOUND
mg/L
0.69
0.69
0.93
0.94
0.98
1.01
0.90
0.98
0.94
0.%
1.03
1.04
1.03
1.05
RECOVERY
%
73
74
93
94
95
98
88
96
92
94
101
102
102
104
AREA
FOUND
mg/L
0.56
0.58
1.03
1.05
0.95
0.98
0.86
0.93
0.86
0.90
1.03
1.05
0.%
0.98
RECOVERY
%
59
61
103
105
92
95
85
91
84
88
101
103
95
98
22
-------
TABLE 5. ANALYSIS OF NIST 16435
HEIGHT
ANALYTE
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
TRUE
20
26
21.9
99
28
49
66
FOUND
11.4
12.1
26.6
26.5
23.3
22.8
101.2
95.7
30.3
28.6
50.3
51.1
72.4
70.8
RECOVERY
57
60
102
102
106
104
102
97
108
102
103
104
110
107
AREA
FOUND
11.3
11.5
29.1
28.8
23.2
23.0
92.8
91.5
32.0
30.6
48.6
49.6
68.4
67.5
RECOVERY
57
57
112
111
106
105
94
92
114
109
99
101
104
102
23
-------
TABLE 6. ANALYSIS OF QB390W2
ANALYTE
TRUE
a U = undetected
SINGLE COLUMN VARIANT
HEIGHT
SAMPLE SPIKE
AREA
SAMPLE
SPIKE
Cadmium 28
Cobalt 0
Copper 125
Iron • 525
Manganese 74
Nickel 0
Zinc 90
107
105
U3
U
101
103
90
90
94
90
U
U
101
103
115
109
112
66
110
114
103
117
111
U
U
109
110
98
98
85
k 81
U
U
104
104
110
112
108
109
114
112
105
A single-column variation on this method, using only the analytical column, was investigated in order
to efficiently determine the effects of eluant parameters on the separation. A number of common eluant
systems were evaluated with the objective of separating lead and cadmium from the other metals and
increasing the sensitivity for these two analytes. There is also some interest in using the single-column
variation of this technique as a simple, field-transportable method with high sample throughput capability and
high (ig/L detection limits.
Separations were attempted on this column with PDCA, oxalic acid, and mixed tartaric and citric acid
eluant systems. None of these systems performed completely satisfactorily. The oxalic acid eluant precludes
the determination of iron. At the same time, the sensitivity for lead was somewhat improved with such a
24
-------
system. Preliminary work has been done with the tartrate/citrate system. The sensitivity is quite low for some
metals, however, and the analysis time is quite long. The most promising work has centered around the PDCA
system.
Sensitivity for some metals can be improved by varying the concentration of the PDCA and the eluant
pH. Retention times with PDCA eluant decrease with increasing PDCA concentration and with increasing
pH. Some metals are quite sensitive to the concentration ratio of the PAR to PDCA. A decrease in the
PDCA concentration increased response for some metals, including lead. The lower PDCA concentration
resulted in longer analysis times, but this effect was offset by increasing the pH. At low concentrations of
PDCA, however, iron became non-linear and began to tail. This tailing interfered with copper determinations.
Since many analyses require the acid digestion of samples prior to analysis, it is desirable to use an
eluant system which will perform well with acidic samples. The single-column system with the PDCA eluant
used in the three-column system provides reasonably good separations of cobalt, copper, iron, manganese,
nickel, and zinc in 1% nitric acid in samples volumes up to 1 mL. The direct introduction of large volumes
of acid does have deleterious effects on the background, however, and makes data integration difficult The
sensitivity for lead is still quite poor in this system. Additionally, the lead peaks tend to tail and split with
increasing metal concentration.
Other schemes to improve sensitivity for lead and cadmium have not been entirely successful. These
included the addition of various modifiers to the PDCA eluant and changes in the post-column chemistry (5).
The PAR/ZnEDTA approach used by others (6,7) appeared to increase sensitivity somewhat, but the system
was unstable and no further work has been attempted along those lines.
The use of the analytical column without matrix modification was prone to interferences from matrix
elements. While sodium and potassium at 100 mg/L produced little interference, calcium and magnesium did
appear in the chromatograms. Calcium eluted relatively early, and did not directly interfere with any of the
transition metals. Magnesium was more strongly retained and was prone to elute during subsequent analyses.
25
-------
REFERENCES
(1) Siriraks, A.; Kingston, H. M.; Riviello, J. M. Anal Chem. 1990, 62, 1185-1193.
(2) Heithmar, E. M.; Hinners, T. A.; Rowan, J. T.; RivieUo, J. M. Anal Chem. 1990, 62, 857-864.
(3) Rowan, J. T.; Heithmar, E. M. "Preconcentration Method for Inductively Coupled Plasma-Mass
Spectrometry"; EPA 600/4-89/043; U. S. Environmental Protection Agency: Las Vegas, Nevada, 1989.
(4) Wernimont, G. T. In Use of Statistics to Develop and Evaluate Analytical Methods; Spendley, W. Ed.;
Association of Official Analytical Chemists: Arlington, Virginia, 1985; p. 96.
(5) Rubin, R. B.; Heberling, S. S. Am. Lab. 1987,19, 46-55.
(6) Arguello, M. D.; Fritz, J. S. Anal Chem. 1977, 49, 1595-1598.
(7) Jezorek, J. R.; Freiser, H. Anal Chem., 1979, 51, 373-76.
26
-------
APPENDIX A
METHOD 6060
ION CHROMATOGRAPHY OF TRACE METALS
NOTICE
This document is a preliminary draft It has not been formally released by the U.S. Environmental
Protection Agency and should not at this stage be construed to represent Agency policy. It is being circulated
for comments on its technical merit and clarity. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
1.0 SCOPE AND APPLICATION
1.1 Method 6060 is used in the determination of jig/L concentrations of the following trace metals
(Table 1) in aqueous solution.
TABLE 1A METALS DETERMINED BY METHOD 6060
Analyte
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
CAS Number
7440-43-9
7440-48-4
7440-50-8
7439-89-6
7439-96-5
7440-02-0
7440-66-6
Detection Limits3
0.4
0.06
0.09
0.3
0.14
0.13
1.3
a (ig/L, 6.5 mL sample
1.2 The method is limited to the determination of free, hydrated metal ions in aqueous solutions.
Therefore, samples must be digested and the digests filtered prior to analysis. The method is applicable to
acid digests from Methods 3010, 3020, and 3050.
27
-------
1.3 Detection limits of this method range from 0.2 to 1 ng. The range of concentrations that may
be determined will vary with the volume of sample analyzed, which typically ranges from 1 to 25 mL.
2.0 SUMMARY OF METHOD
2.1 In the chelation step, analytes are concentrated from a neutralized aqueous solution in a column
containing a macroporous iminodiacetate chelating resin. This resin has a high affinity for many metals
existing as polyvalent cations in solution. Matrix modification using ammonium acetate results in the elution
of alkali metals, alkaline-earth metals and anions, for which the resin has relatively low affinity. The trace
elements are then eluted from the chelator column with 0.5 M nitric acid.
2.2 The highly acidic eluate from the chelator column is incompatible with the low-capacity analytical
column. An intermediate, high-capacity column, which contains a fully sulfonated cation-exchange resin with
sufficient capacity to retain metal ions under acidic conditions, is used as an interface between the chelator
column and the analytical column.
2.3 After the analytes are collected on the interface column, the hydronium form of the resin is
converted to the ammonium form by passing ammonium nitrate through the interface column. The analytes
are then eluted from the interface column to the analytical column with pyridine-2,6-dicarboxylic acid (PDCA).
The metal-PDCA complexes are separated on an analytical column with both anion-exchange and cation-
exchange properties.
2.4 The separated metals are derivatized with 4-(2-pyridylazo)resorcinol (PAR) in a post-column
reactor and are detected photometrically with an absorbance detector at 520-530 nm. The metals are identified
by their retention times compared to known standards. Quantitation is based on comparison of the sample
peak height (or area) to a calibration curve generated from standards.
3.0 INTERFERENCES
3.1 The extent of interference from alkali and alkaline-earth metals depends largely on the timing
of the chelation procedure. Sufficient quantity of ammonium acetate must be used for the elution of matrix
ions from the chelator column, prior to the elution of the trace elements to the interface column with nitric
acid.
3.2 Organic ligands native to the sample may interfere with the chelating resin and reduce recovery.
28
-------
The digestion procedure must be adequate to destroy these ligands.
3.3 Interference due to carry-over must be kept at a minimum by running blanks after highly
concentrated samples and by using an efficient rinse procedure on the chelator column.
3.4 Interferences can be caused if one or several components are present at high concentrations.
3.4.1 High concentrations of one or more polyvalent metals can interfere with the chelation
of minor constituents by competing for chelation sites on the chelator resin. This type of interference
may sometimes be reduced by diluting the sample, depending on the concentrations of the other
analytes.
3.4.2 High concentrations of one or more of the metals separated in the analytical column can
make quantitation of nearby small peaks difficult.
3.5 Large variations in acid concentration may result in decreased recovery of some analytes by
affecting the final sample pH after on-line buffering. Samples with very high acid content must be partially
neutralized before loading to a point where the on-line buffer can adjust the final pH to between 5.0 and 5.7.
4.0 APPARATUS AND MATERIALS
4.1 Ion Chromatograph: The Ion Chromatograph should be plumbed with 1/8* teflon, polyethylene
or other inert tubing as shown in Figure 1. There should be no metal in the flow path. Required components
are:
4.1.1 Pumps: Four constant-flow pumps. Where appropriate, the use of pressurized eluant
reservoirs is recommended to aid in pumping.
4.1.1.1 Eluant pump (PI): Constant-flow, programmable, gradient pumping system
capable of delivering eluants (see Table 4) from four reservoirs (denoted E1-E4). The pump
should be capable of operating in the range 0-1000 psi at 0-3 mL/min.
4.1.1.2 Sample pump (P2): Two-channel peristaltic pump with mixing tee (Tl). One
channel of the pump (P2a) is used to pump the sample. A second channel (P2b) is used to
29
-------
Chelator Column
Post-column Reactor
Variable-wavelength Detector
Figure 1A. Chelation ion chromaiograph in sample loading configuration. PI = high-pressure gradient pump, P2 = two-channel peristaltic pump,
P3 = reciprocating single-piston pump, P4 «= pneumatic pump. VI = valve 1, V2 = valve 2. Valves are shown in the 'B' position.
-------
pump an ammonium acetate buffer solution, at a flow equal to that of the sample, to adjust the
sample pH on-line prior to injection.
4.1.1.3 Analytical pump (P3): Isocratic, constant-flow pump used to pump eluant
through the analytical column. The pump should be capable of operating in the range 0-1000
psi at 1 mL/min.
4.1.1.4 Reagent pump (P4): Isocratic, constant-flow pump used to pump post-column
derivatization reagent. The pump should have very little pulsation and be capable of operating
in the range 0-200 psi at 0.5-1 mL/min.
4.1.2 Columns: Three chromatographic columns.
4.1.2.1 Chelator Column (Cl): Macroporous iminodiacetate-functionalized chelating
resin column (Dionex MetPac CC-1 or equivalent).
4.1.2.2 Interface Column (C2): High-capacity, cation-exchange column (DionexTMC-
1 or equivalent).
4.1.2.3 Analytical Column (C3): Low capacity, mixed-bed ion-exchange column
(Dionex CSS or equivalent).
4.1.3 Valves: Two independent column-switching valves.
4.1.3.1 Chelator valve (VI): A twelve-port (or equivalent) column-switching valve that
controls the sample loading and injection, as well as eluant distribution to the chelator and
interface columns.
4.1.3.2 Separator valve (V2): An eight-port (or equivalent) column-switching valve
that controls the separation and detection system.
4.1.4 Sample loop: A length of inert tubing sized to provide the desired sample volume.
4.1.5 Post-column reactor Mixing tee, or membrane reactor, and reaction coil. Must be
compatible with flows from 0 to 2 mL/min.
31
-------
4.1.6 Detector Flow-through, low-volume, absorbance detector capable of monitoring 520-530
nm with a maximum time constant of 1 second.
4.1.7 Control and data acquisition system: At a minimum, recorder or integrator compatible
with the detector output with a full-scale response of two seconds or less, and an automated controller
for the column-switching valves. Alternatively, a computer-based system may be used.
5.0 REAGENTS
.5.1 In the determination of trace elements, containers can introduce either positive errors by
contributing contaminants through leaching or surface desorption, or negative errors by depleting
concentrations through adsorption or absorption. Given the high sensitivity of this technique, it is
recommended that all vessels used for containment of reagent solutions be constructed of linear polyethylene
or Teflon. The use of glass is not recommended. To minimize contamination, these vessels should be treated
in the manner recommended for sample containers in Chapter Three, Section 3.1.3, prior to use.
NOTE: Do not introduce foreign objects (magnetic stirring bars, pH electrodes, pH paper, etc.) into
any solutions to be used in the course of this Method. If solution characteristics, such as pH or
temperature, are required, a small amount of solution should be separated for the measurement and
then discarded.
5.2 All reagents used in the preparation of samples, standards, and eluants should be of the highest
purity available.
5.3 Water: Deionized water prepared from purified (by distillation or reverse osmosis) feed water
is recommended. Conductance of water should be at least 16 megohm-cm.
5.4 Nitric Acid (1% v:v\ HNO3: To 500 mL water, add 10 mL concentrated (65%) HNO3. Dilute
to 1 liter.
5.5 Eluants: Prepare eluants directly in eluant containers.
5.5.1 Nitric Acid (1.5 M), HNO3: Prepare in a fume hood. Dilute 145 g concentrated (65%)
nitric acid to 1000 mL with water.
32
-------
5.5.2 Ammonium Acetate Buffer (approximately 2 M): Prepare in a fume hood. To 600 mL
water, add 115 mL glacial acetic acid and 130 mL 25% ammonia solution. Adjust the pH to 5.5 ±
0.1 with small quantities (3 to 5 mL) of either acetic acid or ammonia, as necessary. Dilute to 1 liter.
5.5.3 Ammonium Nitrate (0.10 M), NH4NO3: To 200 mL water, add 8.9 g concentrated (65%)
nitric acid and 7.0 g 25% ammonia solution. Dilute to 1 liter. Adjust the pH to 3.4 ± 0.3 with small
quantities of either nitric acid or ammonia, as necessary.
5.5.4 Pyridine-2,6-dicarboxylic acid (PDCA) eluant [PDCA (0.006 M), CjHjNO^ Sodium
hydroxide (0.040 M), NaOH; Acetic acid (0.090 M), C2H4O2]: Combine 100 g PDCA stock solution
(5.5.4.1) with 100 g acetic acid stock solution (5.6.4.2). Dilute to 1 liter. The final pH should be 4.6.
5.5.4.1 Pyridine-2,6-dicarboxylic acid (PDCA) stock [PDCA (0.06 M),
Sodium hydroxide (0.40 M), NaOH]: Dissolve 15.9 g sodium hydroxide (NaOH) in 200 mL
water. Add 10.0 g PDCA. Mix until PDCA dissolves. Dilute to 1 liter.
5.5.4.2 Acetic add (0.90 M), C2H4O2: To 200 mL water, add 54.2 g glacial acetic acid.
Dilute to 1 liter.
5.6 Post-column Derivatization Reagent [4-(2-pvridvlazo) resorcinol (PAR) (5x10"* M>. C11H9N3O2:
2-dimethylamino ethanol fl.O M). C1H11NO: Ammonia (0.50 M\ NH3: Sodium Bicarbonate (0.30 M).
NaHCO3): To 200 mL water, add 34.0 g 25% ammonia solution. Add 0.12 g monosodium 4-(2-pyridylazo)
resorcinol mono hydrate and mix When the PAR has completely dissolved, add 500 mL water. Add 89.1 g
2-dimethylamino-ethanoL Finally, add and dissolve 25.2 g sodium bicarbonate, dilute the solution to 1 liter,
and mix thoroughly.
5.7 Stock Solutions: Solutions used for the preparation of calibration standards may be obtained
commercially or prepared as follows.
(CAUTION: Many metal salts are extremely toxic if inhaled or swallowed. Wash hands thoroughly
after handling.)
5.7.1 Cadmium solution, stock, 1000 mg/L: Dissolve 1.142 g CdO in a minimum amount of
(1+1) HNO3. Heat to increase rate of dissolution. Add 10.0 mL concentrated HNO3 and dilute to
1 liter.
33
-------
5.7.2 Cobalt solution, stock, 1000 mg/L: Dissolve 1.000 g of cobalt metal in a minimum
amount of (1+1) HNO3. Add 10.0 niL concentrated HNO3 and dilute to 1 liter.
5.7.3 Copper solution, stock, 1000 mg/L: Dissolve 1.000 g of copper metal in a minimum
amount of (1+1) HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1 liter.
5.7.4 Iron solution, stock, 1000 mg/L: Dissolve 1.000 g of iron metal in a minimum amount
of (1+1) HNO3. Add 10.0 mL concentrated HNO3 and dilute to 1 liter.
5.7.5 Manganese solution, stock, 1000 mg/L: Dissolve 3.149 g of manganese acetate
in water. Add 10.0 mL of concentrated HNO3 and dilute to 1 liter.
5.7.6 Nickel solution, stock, 1000 mg/L: Dissolve 1.000 g of nickel metal in 10 mL hot cone.
HNO3. Cool and dilute to 1 liter.
5.7.7 Zinc solution, stock, 1000 mg/L: Dissolve .1.245 g zinc oxide (ZnO) in a minimum
amount of dilute HNO3. Add 10.0 mL of cone. HNO3 and dilute to 1 liter.
5.8 Working Standards
5.8.1 Stock standards: Prepare a mixed stock standard by adding the volumes of stock
solutions shown in Table 2 to approximately 50 mL water, adding 5.0 mL concentrated HNO3 to each,
and finally diluting each to 100 mL. Fresh mixed stock standard should be prepared each week.
TABLE 2A. STOCK STANDARD
Metal
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
mL Stock
3.3
1.0
1.0
1.0
1.0
1.0
1.0
Concentration3
33
10
10
10
10
10
10
mg/L
5.8.2 Calibration standards: Prepare the six calibration standards in Table 3 from the mixed
34
-------
stock standard. Calibration standards should be prepared daily.
TABLE 3A. CALIBRATION STANDARD CONCENTRATIONS (/ig/L)
Metal
Cadmium
Cobalt
Copper
Iron
Manganese
Nickel
Zinc
Standard
1
2.60
0.80
0.80
0.80
0.80
0.80
0.80
2
8.2
2.5
2.5
2.5
2.5
2.5
2.5
3
26.4
8.0
8.0
8.0
8.0
8.0
8.0
4
82.5
25.0
25.0
25.0
25.0
25.0
25.0
5
264.0
80.0
80.0
80.0
80.0
80.0
80.0
6
825.0
250.0
250.0
250.0
250.0
250.0
250.0
5.8.2.1 Prepare calibration standard 6 by diluting 2.5 mL of the mixed stock standard
to 100 mL with 1% HNO3.
5.8.2.2 Prepare calibration standard 5 by diluting 0.8 mL of the mixed stock standard
to 100 mL with 1% HNO3.
5.8.2.3 Prepare calibration standard 4 by diluting 0.25 mL of the mixed stock standard
to 100 mL with 1% HNO3.
5.8.2.4 Prepare calibration standard 3 by diluting 80 jiL of the stock mixed standard
to 100 mL with 1% HNO3.
5.8.2.5 Prepare calibration standard 2 by diluting 1 mL of standard 6 to 100 mL with
1% HN03.
5.8.2.6 Prepare calibration standard 1 by diluting 1 mL of standard 5 to 100 mL with
1% HN03.
5.9 Calibration blank: Add sufficient concentrated nitric acid to water to match the acid content of
the samples.
35
-------
6.0 SAMPLE COLLECTION, PRESERVATION, AND HANDLING
6.1 All samples must be collected using a sampling plan which addresses the considerations discussed
in Chapter Nine of this Manual, as well as Practice D1066, Specifications D1192, or Practice 3370 of the
ASTM Methods.
6.2 Polyethylene sample containers should be used, since glass can contribute significantly to
increases of blank values. All sample containers should be washed with detergent, acids, and Type II water
prior to use. See Chapter Three, Section 3.1.3, for further details.
6.3 Aqueous samples should be preserved with nitric acid to a pH less than 2 as soon as possible.
If dissolved metal concentrations are desired, the aqueous samples should be filtered through a 0.45 /urn filter
prior to acidification. A suitable digestion procedure should be used for all samples prior to analysis to ensure
that the metals are 'free' in solution and are not bound by organic materials such as fulvic and humic acids.
Methods 3010, 3020, and 3050 of this manual are acceptable digestions. All digests should be filtered prior
to analysis to protect the pre-concentration columns.
6.4 Samples should be analyzed as soon as possible after sampling (See Chapter Three, Section
3.1.3).
7.0 PROCEDURE
7.1 System Start-up:
7.1.1 Activate the data acquisition system.
7.1.2 Turn on the analytical pump and set the PDCA flow to 1.0 mL/min.
7.13 Turn on the reagent pump and set the PAR flow to 0.5 mL/min.
7.1.4 Turn on the absorbance detector. Select a wavelength of 530 nm. Turn on the visible
lamp and set the detector to a full-scale sensitivity of 0.2 Absorbance Units Full Scale (AUFS).
Equilibrate the system until the baseline is stable.
7.1.5 Set VI and V2 to the 'A' position.
36
-------
7.1.6 Start the sample pump. Select the sample flow rate to equal the on-line buffer flow.
To conserve buffer, both the sample and buffer lines may remain in 1% nitric acid when not loading
sample.
7.2 System operation: The chromatographic procedure is summarized in Table 4. The timing
presented in the Table is specific to the use of a 6.5-mL sample loop and will vary with loop volume. The
timing may also vary slightly with the volume of the tubing used in plumbing the apparatus.
TABLE 4A. ION CHROMATOGRAPHY SEQUENCE3
Time
(min)
18.0+
0.0
1.5
3.7
5.0
8.2
9.7
10.7
11.7
12.7
13.7
18.0
Repeat as
Vlb
A
B
B
B
B
A
B
B
B
B
B
A
necessary (see
V2
A
A
A
B
B
B
A
A
A
A
A
A
Section 7.2.8).
Pump
Channel
P2
El
E2/E3 (1/2)
E2/E3 (1/2)
E4
E4
El
E2
El
E2
El
El
Solution
Sample (P2a) + buffer (P2b)
2 M ammonium acetate
1.5 M nitric acid / water
1.5 M nitric acid / water
0.1 M ammonium nitrate
0.1 M ammonium nitrate
2 M ammonium acetate
1.5 M nitric acid
2 M ammonium acetate
1.5 M nitric acid
2 M ammonium acetate
2 M ammonium acetate
Flow
(mL/min)
4.0/4.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
0.0
Vary as necessary (see Section 7.2).
7.2.1 Load sample: With VI and V2 in the 'A* position, pump sample solution through the
sample loop to waste. Check the pH of the solution as it goes to waste to ensure that the sample pH
is 5.5 ± 0.3. This step is carried out before the analysis sequence is initiated and can be performed
for subsequent samples before the analytes of the previous sample elute.
7.2.2 Inject sample: Switch VI to the 'B' position. Pump 2 M ammonium acetate from the
eluant pump for 1.5 minutes at 3.0 roLAnin, Group LA and IIA metals, as well as anions, are eluted
to waste.
7.2.3 Elute concentrate: Pump 1.5 M HNO3 and water in a ratio of 1:2 (0.5 M HNO3 final
concentration) from the eluant pump at 3.0 mL/min for 3.5 minutes. After 2.2 minutes, switch V2
37
-------
to the 'B* position so that the eluted concentrate will be directed to the interface column.
7.2.4 Flush loop: Pump 0.1 M ammonium nitrate from the eluant pump at 3.0 mL/min to
push the 0.5 M HNO3 through the sample loop to the chelator column. Continue for 3.2 minutes.
7.2.5 Modify interface column: Switch VI to the 'A' position. Pump 0.1 M ammonium nitrate
at 3.0 mL/min for 1.5 minutes. The interface column is converted from the hydronium form to the
ammonium form.
7.2.6 Elute analytes: Switch VI to the 'B' position and V2 to the 'A' position. Begin data
acquisition. Analytes are stripped off the interface column with PDCA and are separated as anionic
chelates on the analytical column. Separation times range from 12 to 16 minutes.
7.2.7 Rinse and recondition chelator column: Cycle the eluants at 3 mL/min through the
chelator column in 1.0-minute increments in the following order: 2 M ammonium acetate, 1 M nitric
acid, 2 M ammonium acetate, and finally 1 M nitric acid. Pump 2 M ammonium acetate at 3.0
mL/min. for 4.3 minutes in order to flush the foregoing eluants through the sample loop and to
recondition the column with 6 mL of 2 M ammonium acetate.
7.2.8 Repeat steps 7.2.1 through 7.2.7 for each solution to be analyzed. The interval between
sample injections must be adjusted so that all sample components traverse the analytical column
before V2 is switched back to the 'B' position.
NOTE: Contamination by carryover can occur if the sample elution time is inadequate.
Whenever an unusually concentrated sample is encountered, it should be followed by the analysis
of a blank to check for cross contamination.
NOTE: Before running samples, or if the analysis is suspended for an extended period of time, flush
the lines and condition the columns by analyzing a sufficient number of blanks to achieve an
acceptable background.
7.3 Calibration: Analyze each of the six calibration standards and a calibration blank according to
the procedure in Section 7.2. The analyte peaks in each chromatogram will appear in the following order:
iron, copper, nickel, zinc, cobalt, cadmium, and manganese. For each analyte, calculate the least squares linear
regression of peak height or area vs. the concentrations given in Table 3. If the correlation coefficient of the
38
-------
regression for any analyte is less than 0.999, either the standards or blank were incorrectly prepared, or the
chromatographic method is out of control. If this is the case, correct the problem and recalibrate.
7.4 Sample Analysis: Analyze the analytical samples and the necessary quality control samples (see
Sections 8.0 - 8.6) according to the procedure in Section 7.2.
7.5 System shutdown: Shut down ion chromatograph.
7.5.1 Clean eluant pump: Disconnect eluant pump from VI. Pump water through each eluant
line at 3 mL/min for 5 minutes.
7.5.2 Clean post-column reactor Disconnect analytical column and post-column derivatization
reagent line from post-column reactor. Drain PAR reagent from reactor. Connect eluant pump
directly to reactor at both vacant inlets. Pump water from the eluant pump at 1.5 mL/min. for 15
minutes.
7.5.3 Clean sample loop: Switch VI to the 'A' position. Pump 1% HNO3 from both channels
of the sample pump through the sample loop to waste for 5 minutes.
7.6 Calculation: Determine the peak height or area of each analyte in the sample. Using the slope
and intercept determined for the linear regression in Section 7.3, calculate the concentration using the
following equation.
concentration (Mg/L) = Peak »*& ' tottgBePt
slope
8.0 QUALITY CONTROL
See Chapter One, Section 1.2 for general quality control requirements.
8.1 All quality control data should be maintained and available for easy reference or inspection.
8.2 Calibration curves must be composed of a minimum of a blank and four standards.
8.3 Samples more concentrated than the highest calibration standard must be diluted and re-analyzed.
39
-------
8.4 A minimum of one reagent blank sample per sample batch should be analyzed to check for
contamination. A reagent blank is reagent water treated according to the procedure in Sections 6.2 and 6.3
of this Method.
8.5 A minimum of one duplicate sample and one matrix spike sample per sample batch should be
analyzed to check for duplicate precision and matrix-spike recovery.
8.6 A minimum of one initial calibration verification sample prepared from an independent source
(EPA or NIST) should be analyzed per sample batch. If an EPA or NIST reference sample is not available,
a mid-range standard, prepared from an independent commercial source, may be used.
9.0 METHOD PERFORMANCE
9.1 Method performance will be evaluated in single-laboratory and multi-laboratory evaluations by
the EPA.
40
-------
METHOD 6060
ION CHROMATOGRAPHY OF TRANSITION METALS
Stan
7.1.1 Activate data
acquisition system
7.1.2 Turn on
analytical pump
7.1.3 Turn on
reagent pump
7.1.4 Turn on
absorbance
detector
7.1.5 VI and V2
in 'A' position
7.16 Start
sample 'pump
7.2 Operate
system
7.3 Calibrate
TA Analyze
Samples
7.5 Terminate
Z6 Calculate
Sample
Concentrations
Stop
41
------- |