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INDUCTIVELY COUPLED PLASMA-MASS
SPECTROMETRIC METHOD FOR THE
DETERMINATION OF DISSOLVED TRACE
ELEMENTS IN NATURAL WATER

U.S. GEOLOGICAL SURVEY

Open-File Report 94-358

INDUCTIVELY COUPLED PLASMA-MASS
SPECTROMETRIC METHOD FOR THE
DETERMINATION OF DISSOLVED TRACE
ELEMENTS IN NATURAL WATER

By J.R. Garbarino and H.E. Taylor

_____________________________________________________________________

U.S. GEOLOGICAL SURVEY

Open-File Report 94-358

Boulder, Colorado

1996

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement
by the U.S. Government.

For additional information write to: Copies of this report can be purchased from:

Chief, Branch of Regional Research
U.S. Geological Survey
Box 25046, MS 418
Denver Federal Center
Denver, CO 80225

U.S. Geological Survey
Branch of Information Services
Box 25286
Denver, CO 80225

CONTENTS

CONVERSION FACTORS……………………………………………………………………………………………….v
ABSTRACT…………………………………………………………………………………………………………………….1
INTRODUCTION ……………………………………………………………………………………………………………1
INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRIC METHOD ……………………..3
Application of method ………………………………………………………………………………………………………3
Summary of Method …………………………………………………………………………………………………………3
Interferences…………………………………………………………………………………………………………………….3
ANALYTICAL PROCEDURE FOR THE DETERMINATION OF TRACE ELEMENTS IN

WATER………………………………………………………………………………………………………………………5
Calibration and Sample Analysis………………………………………………………………………………………..5
Processing analytical data………………………………………………………………………………………………….5
Accuracy and Precision …………………………………………………………………………………………………….6
SUMMARY…………………………………………………………………………………………………………………….7
REFERENCES ………………………………………………………………………………………………………………..8

FIGURES
1. Diagram showing manifold system for internal standards introduction………………………………15
2.-18. Graphs showing measured concentrations determined by inductively coupled plasma-mass

spectrometry and certified concentrations in selected reference water standards for:
2. Aluminum. …………………………………………………………………………………………………………..16
3. Arsenic………………………………………………………………………………………………………………..16
4. Barium ………………………………………………………………………………………………………………..17
5. Beryllium …………………………………………………………………………………………………………….17
6. Cadmium……………………………………………………………………………………………………………..18
7. Chromium ……………………………………………………………………………………………………………18
8. Cobalt………………………………………………………………………………………………………………….19
9. Copper…………………………………………………………………………………………………………………19
10. Lead ………………………………………………………………………………………………………………….20
11. LIthium ……………………………………………………………………………………………………………..20
12. Manganese …………………………………………………………………………………………………………21
13. Molybdenum………………………………………………………………………………………………………21
14. Nickel………………………………………………………………………………………………………………..22
15. Strontium …………………………………………………………………………………………………………..22
16. Thallium…………………………………………………………………………………………………………….23
17. Vanadium…………………………………………………………………………………………………………..23
18. Zinc …………………………………………………………………………………………………………………..24

Table 1. Detection and quantitation limits, in micrograms per liter, for inductively coupled

plasma-mass spectrometry using internal standard manifold injection ……………………………..9

Table 2: Instrumental operating parameters and accesssory specifications for inductively

coupled plasma-mass spectrometry determination of trace metals in natural waters…………10

Table 3: Quality assurance parameter set for inductively coupled plasma-mass spectrometry

quantitative analysis…………………………………………………………………………………………………11

TABLES

iii

Table 4: Interelement interference corrections for inductively coupled plasma-mass

spectrometry method………………………………………………………………………………………………..12

Table 5: Potential interferences that could affect accuracy for selected elements in inductively

coupled plasma-mass spectrometry ……………………………………………………………………………12

Table 6: Calibration concentrations of multielement standards in micrograms per liter for

inductively coupled plasma-mass spectrometry …………………………………………………………..13

Table 7. Linear regression statistics for values versus published values determined by

inductively coupled plasma-mass spectrometry …………………………………………………………..13

Table 8. Analytical precision for inductively coupled plasma-mass spectrometric determinations14

iv

CONVERSION FACTORS
By

To obtain

Multiply

milliliter (mL)
liter (L)

0.03382
0.2642

ounces, fluid
gallon

Volume

Mass

picogram (pg)
microgram (µg)
milligram (mg)
gram (g)

0.00000000003527
0.00000003527
0.00003527
0.03527

ounce, avoirdupois
ounce, avoirdupois
ounce, avoirdupois
ounce, avoirdupois

The following abbreviations were also used in this report:

Unit

Abbreviation

Concentration

milligram per liter
microgram per liter

millimeters

Liters per minute

kilowatts

pounds per square inch

Counts per second

seconds
milliseconds

Distance

Flow

Power

Pressure

Intensity

Time

mg/L
µg/L

mm

L/min

kW

psi

cps

s
ms

v

Inductively Coupled Plasma-Mass Spectrometric Method for the
Determination of Dissolved Trace Elements in Natural Water

By J.R. Garbarino and H.E. Taylor

ABSTRACT

An inductively coupled plasma-mass spectrometry method was developed for the determination of

dissolved Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sr, Tl, U, V, and Zn in natural waters. Detection
limits are generally in the 50-100 picogram per milliliter (pg/mL) range, with the exception of As which is in the 1
microgram per liter (µg/L) range. Interferences associated with spectral overlap from concomitant isotopes or
molecular ions and sample matrix composition have been identified. Procedures for interference correction and
reduction related to isotope selection, instrumental operating conditions, and mathematical data processing
techniques are described. Internal standards are used to minimize instrumental drift. The average analytical
precision attainable for 5 times the detection limit is about 16 percent. The accuracy of the method was tested using
a series of U.S. Geological Survey Standard Reference Water Standards (SWRS), National Research Council
Canada Riverine Water Standard, and National Institute of Standards and Technology (NIST) Trace Elements in
Water Standards. Average accuracies range from 90 to 110 percent of the published mean values.

INTRODUCTION

Inductively coupled plasma-mass spectrometry (ICP-MS) combines the ionization efficiency of the

argon plasma with the sensitivity and selectivity of mass spectrometric separation. Greater than 80 percent of the
elements have primary ionization potentials that are attainable using an argon plasma as the ionization source;
therefore, absolute detection limits are consistently in the 0.1 µg/L range.

Analyte ions produced in the plasma are sampled at the instrument-plasma interface through concentric

orifices in a pair of nickel sampling cones. Electrostatic lenses accelerate and focus the ion beam into the
quadrupole mass analyzer. By applying a pair of radio frequencies and direct-current potentials to the quadrupole
rods, only ions with a specific mass-to-charge ratio (m/z) are transmitted to the detector; ions with other m/z ratios
collide with the rods and are lost. The ions impinge on a Channeltron-type detector where a current pulse is
generated and counted. The detector is mounted 90 degrees off-axis to minimize background signal contributions
from photons emitted by the plasma. Inherent to the technique is the capability of selectively measuring all isotopes
of a given element, thereby providing isotopic ratio information and allowing isotope dilution analysis to be
performed.

Spectral interferences result in the analysis of an element primarily from spectral overlap of isotopes

from other elements or molecular ion species that cannot be resolved from the analyte ion. Concurrent elemental
isotopic interferences may be eliminated or reduced by a chemical separation to remove the interfering element, by
mathematical correction, or by selection of an alternative isotope, whenever possible. In this case of direct spectral
overlap from a concomitant ion, use of a different analytical isotope is the best alternative for eliminating
interferences. When the analyte is monoisotopic, chemical separation or mathematical correction are the only
alternatives.

Spectral interferences attributable to molecular ions, for example, 43Ca16O+ interference on 59Co+,

require a combination of compensation procedures for elimination of interference. First, the degree of oxide
formation is directly affected by the operating conditions associated with the introduction of aqueous sample
aerosol. Oxide formation can be reduced by optimizing nebulizer argon flow rates, by applying solvent desolvation
techniques to reduce water entering the plasma, or by the addition of small quantities of nitrogen to the argon gas
stream. When determining analyte concentrations in the µg/L range, an additional mathematical correction may be
required by calibrating the apparent analyte concentration as a function of oxide interferent. Molecular ion

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interferences associated with other combinations of elements, for example, 35Cl16O+ interference on 51V, can either
be eliminated through the chemical separation of chloride in the sample or through mathematical corrections based
on natural isotopic abundances. These mathematical corrections are only accurate to 10-20 percent.

Spectral interferences from multiple charged ions are not generally found. Most elements have second

ionization potentials greater than what is attainable through plasma ionization (that is, greater than 16 electron
volts).

Sample matrix composition affects the magnitude of analyte signals. Analyte signal intensities are

suppressed with increasing concentration of many matrix elements. Generally, lighter mass analytes are subject to
greater suppressions than heavier mass analytes, and heavier matrix elements cause more severe suppression effects.
These suppression effects are thought to result from changes in ion transmission through the ion optics preceding
the mass analyzer (Gillson and others, 1988). Suppression effects can be reduced by adjusting the potentials applied
to the electrostatic lenses, by altering the matrix through chemical separations, or by modifying the sample-
introduction procedure. Compensation for signal suppressions using standard additions, isotope dilution analysis, or
internal standards is also effective. However, due to the mass relationship of the suppression phenomena, multiple
internal standard elements are required to span the entire mass range.

The purpose of this report is to describe methodology using a Perkin Elmer-Sciex, Model 250, modified inductively
coupled plasma-mass spectrometer for the simultaneous determination of dissolved trace metals in natural water,
including Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sr, Tl, U, V, and Zn.

research and development work: R.C. Antweiler, T.I. Brinton, D.B. Peart, and D.A. Roth.

Gratitude is expressed to the following coworkers for their suggestions and assistance in performing this

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