Spectrochimica Acta Part B 57 (2002) 513–524
Determination of Cd and Pb in seawater by graphite furnace
atomic absorption spectrometry with the use of hydrofluoric acid
as a chemical modifier夞
J.Y. Cabon*
UMR CNRS 6521-UBO, 6 Avenue Le Gorgeu, BP 809, 29285 Brest-Cedex, France
Received 12 June 2001; accepted 11 December 2001
Abstract
High concentration of added hydrogen fluoride converted the seawater chloride to the corresponding fluoride
matrix, and the liberated hydrochloric acid could be removed during the drying step. The atomization of cadmium
and lead could be performed at a relatively low temperature (;1300 8C) at which the vaporization of the fluoride
matrix was relatively slow, and the corresponding weak background signals could be separated from the analytical
signals in time. Experimental conditions for the determination of Cd and Pb in seawater in the presence of HF were
optimized with the use of the a priori calculation of the limit of detection. The experimental limit of detection
obtained for Cd and Pb were, respectively, 0.007 and 0.25 mg ly1 for a 15-ml seawater sample (3s, 20 replicates).
The concentrations of Cd determined in a SLEW-1 estuarine water and a CASS-2 seawater were 0.020"0.002 and
0.016"0.002 mg ly1 Cd, respectively, in good agreement with the 0.018"0.003 and 0.019"0.004 mg ly1 Cd
certified values (At the 95% confident level, 10 replicates). 䊚 2002 Elsevier Science B.V. All rights reserved.
Keywords: Atomic spectrometry; Graphite furnace; Seawater; Cd; Pb; HF; Chemical modification
1. Introduction
The determination of anthropogenic trace metal
pollutants, like Cd and Pb, in natural waters is of
great importance because they are involved in
biological cycles and present a high toxicity.
夞 This paper was presented at Colloquium Spectroscopicum
Internationale XXXII, held in Pretoria, South Africa, 8–13
July 2001 and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference.
*Tel.: q33-2-9801-6594; fax: q33-2-9801-7001.
E-mail address: [email protected] (J.Y. Cabon).
Graphite furnace atomic absorption spectrometry
(GFAAS) has been widely used for trace metal
determinations in various types of environmental
samples. However, direct determination of Cd and
Pb by GFAAS is difficult in seawater as the saline
matrix can cause both spectral (high background
absorption) and non-spectral interference effects.
To overcome these problems, different preconcentrationyseparation procedures have been generally
used. However, most of these analytical procedures
are generally specific of only one chemical form
and, to determine total concentrations, different
pretreatment procedures have to be applied. Con-
0584-8547/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 5 8 4 - 8 5 4 7 Ž 0 2 . 0 0 0 0 5 - 8
514
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
sequently, these analytical procedures are generally
time-consuming and subject to contamination.
In the case of direct determination of trace
metals in seawater by GFAAS, it is necessary to
minimize both the interference effects and the
magnitude of the background absorption signal at
the atomization stage to improve the baseline noise
and to reduce errors. This can be generally
achieved through a chemical modification of the
chloride matrix leading to less interfering species
having different absorbance spectra and volatilities.
To minimize the simultaneous background absorption signal, two ways can be considered: one way,
by delaying sufficiently the vaporization of the
element in order to eliminate the major part of the
salts before atomization (mainly sodium species
and volatile decomposition products). In the case
of Pb, chemical modifiers like Pd introduced under
different forms have been used for this purpose
w1–4x. This procedure cannot be used in the case
of Cd because the delaying effect is not sufficient
to eliminate sodium species without important
losses of analyte. Therefore, a second way has to
be used by increasing the volatility of the element
and selecting a low atomization temperature in
order to obtain a good separation of the analyte
and the vaporization of sodium species. This can
be generally achieved with the use of organic acids
like ascorbic or oxalic acid w5–8x; these acids
promote a lower atomization temperature of Cd
and Pb in seawater and a decrease of the NaCl
background absorption signal, particularly with the
use of oxalic acid w3,8x. However, organic acids
also lead to decomposition products and eventually
to the production of carbon residues in the atomizer. Sodium hydroxide has also been used in the
case of Cd w9x, but the mass of sodium species in
the atomizer is obviously increased and the sodium
chloride absorption signal cannot be reduced. A
HNO3 –(NH4)2HPO4 modification has been also
used, but in this case the optimization of pyrolysis
conditions appeared relatively difficult w10–12x.
In this work, we examine the use of HF as a
new chemical modifier for the seawater matrix. In
marine environments, this acid has been currently
used for the solubilization of sediments or particulate matter and eventually, for slurry sampling
w13x. This acid has been also shown to reduce the
background absorption signal of NaCl w14x. Consequently, it appeared interesting to us to examine
the modification of the seawater matrix with the
use of this chemical modifier. The removal of
chloride by HF at the drying step was followed
by ion chromatography. Its influence on the atomization signal of Pb and Cd in seawater was then
examined. The experimental conditions for the
determination of Cd and Pb in seawater have been
optimized with the use of the a priori calculation
of the detection limit w15,16x.
2. Experimental
2.1. Instrument parameters and operation
A Perkin-Elmer 4100ZL was used for all atomic
absorption measurements (Frequency measurements f s54 Hz). End-capped pyrolytic graphite
coated tubes equipped with integrated platforms
(Perkin-Elmer) were used. Samples were delivered
to the furnace using a Perkin-Elmer AS-70 and
stored in acid washed polypropylene cups prior to
injection. The light sources were Perkin-Elmer
EDL2 lamps operating at 480 mA for Pb and 230
mA for Cd using the respective resonance lines at
283.3 and 228.8 nm, with a 2 nm spectral bandwidth. The inert gas was argon. Dilutions were
carried out with calibrated Gilson Pipetman pneumatic syringes. Typical operating conditions were
as follows: 10 ml of sample solution was introduced into the furnace with 10 ml HF solution and
heated according to the electrothermal program
presented in Table 1. After a drying step at
approximately 130 8C, followed by a cooling step
at 20 8C for 10 s (1 s ramp) under 250 mlymin
argon flow, no pyrolysis was used and the atomization occurred in the max-power mode at the
selected atomization temperature with the gas flow
interrupted. A final cleaning step with a slow
heating rate to 2500 8C was used to gently remove
the remaining saline matrix after the atomization
step. A 5 s (270 points) baseline offset compensation (boc) time was used. One ‘read’ measurement was performed and the signal was recorded
during the atomization step; the atomization time
being chosen longer than the duration of the atomic
signal. The data recorded on a floppy disk were
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
515
Table 1
Graphite atomizer program
Step
Drying
Temp. (8C)
Ramp time (s)
Hold time (s)
Read
Ar flow rate (ml miny1)
130
5
30
20
1
10
250
250
then converted to ASCII format with the ‘peak
data reformat’ Perkin-Elmer software, and then
transferred to Microsoft Excel 5 for mathematical
post-treatments of the signal: smoothing; determination of the integrated absorbance by determining
the beginning and the end of the integration (3s
threshold), or by using a moving sum of a fixed
number of points; determination of the weighted
mean background absorbance; summation of signals, etc.
2.2. Ion chromatographic study
The removal of chloride was followed by analyzing by ion chromatography the residue left on
the platform after the drying step. Ten microliters
of salt solution were pipetted onto the platform
together with 10 ml of HF solution, and then dried.
The residue remaining on the platform was dissolved by adding 30 ml of ultrapure water with
the use of the autosampler. The resulting solution
was then pipetted from the platform with a pneumatic syringe. The operation was repeated three
times. The pipetted solutions were diluted to a
final volume of 4 ml with ultrapure water. A
Dionex DX-100 was used for ion chromatograph
measurements. The ion chromatograph was
equipped with an AS9-SC column and an ASPRSII anion self-regenerating suppressor; the eluent
being 1.8 mM Na2CO3 y1.7 mM NaHCO3. The
concentration of chloride was determined by calibration of the instrument with a chloride standard
solution (1 g ly1 Merck).
2.3. Reagents
The standard solutions were prepared by dilution
from 1 g ly1 Pb or Cd in 0.5 M HNO3 Merck
Cooling
step
Atomization
Cleaning
Variable
0
Variable
On
0
2500
10
5
250
standard. Hydrofluoric acid 40% was suprapur
grade Merck. Magnesium chloride was pro analysi
grade Merck. Seawater was a Mediterranean sample. National Research Council of Canada certified
CASS-2 and SLEW-1 reference materials were
analyzed for Cd. Ultrapure water from a Millipore
milliro-MQ system was used.
3. Results and discussion
3.1. Removal of chloride with the use of HF
Seawater is a complex medium and the major
elements precipitate at the drying step as various
salts (NaCl, MgCl2, MgSO4, CaSO4, etc.); chloride species representing the major part of the
saline matrix. For the determination of trace metals
in seawater, different matrix modifiers have been
previously used in order to transform the chloride
matrix to a less interfering matrix and, depending
on the analytical line eventually to a less absorbing
matrix. Nitric acid, oxalic acid and ammonium
nitrate have similar efficiencies to remove chloride
as HCl at the drying or at the pretreatment step.
With the use of these chemical modifiers, chloride
could be mainly removed out of the furnace at the
drying step as HCl for modifierychloride mole
concentration ratio of two w17,18x. If total suppression of chloride could not be obtained w19x, a
drastic reduction of chloride interference effects
and of the background absorption magnitude were
generally observed.
As shown in Fig. 1, HF could similarly be used
to remove seawater chloride out of the furnace at
the drying step. However, HF appeared much less
efficient than oxalic or nitric acid and much higher
acid concentrations had to be used. For a HFy
chloride mole concentration ratio higher than 30,
516
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
Fig. 1. Relative amount of chloride (%) remaining in the atomizer after addition of HF and drying in 10 ml seawater or 10 ml 0.05
M MgCl2. wHFxywClyx represents the molar concentration ratio of the mixed solution.
the major part of the seawater chloride was
removed out of the furnace at the drying step.
However, it could be observed that HF was much
more efficient to remove chloride at the drying
step from a MgCl2 solution than from a seawater
solution. Indeed, chloride could be efficiently
removed out of the furnace for a HFychloride
mole concentration ratio of approximately 2 from
a MgCl2 solution. This difference could be attributable to the different solubilities of NaF and
MgF2 in water, respectively, of 4.22 and 0.0076%
myv w20x. Consequently, Mg was precipitated as
MgF2 at the drying step and chloride was more
efficiently removed out of the atomizer as HCl.
Consequently, by using HF as a chemical matrix
modifier for seawater, Mg is mainly precipitated
at the drying step in the atomizer as MgF2 and
MgSO4 salts, instead of MgCl2 and MgSO4 salts.
Therefore, the atomization mechanisms of elements will be subsequently modified, particularly the
interference effects induced by the presence of
MgCl2.
3.2. Effect of HF on atomic absorption signals
Atomic absorption signals of Pb and Cd and
corresponding background signals are shown in
Figs. 2 and 3. Pb and Cd signals are delayed in
seawater as compared to water and the atomization
occurred at the beginning of the background signal,
mainly generated by sodium chloride vaporization.
For a 10-ml seawater, as also previously observed
w3x, a strong chloride interference effect (;90%)
was also noted in the case of Pb; a smaller
interference effect was noted in the case of Cd
(;15%). The interference effect was much more
important in seawater than when NaCl was vaporized alone w21x. This could be attributable to the
presence of MgCl2 in seawater. The hydrolysis of
MgCl2 to MgOHCl and MgO at low temperatures
has been previously observed w21,22x. These
oxides could delay the Cd and Pb signals that
were consequently vaporized simultaneously to
HCl resulting from the decomposition of MgCl2
or MgOHCl and a higher mass of NaCl, particularly in the case of Pb causing an important
chemical interference. Moreover, a simultaneous
background absorption signal was observed, more
important in the case of cadmium (228.8 nm) than
in the case of Pb (283.3 nm), according to the
molecular spectrum of NaCl w23x. This background
absorption induced a spectral interference effect
that was more important at the Cd analytical line
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
517
Fig. 2. Atomic absorption signal of Cd in 10 ml seawater (left) and in 10 ml seawaterq10 ml 23 M HF (right); without spike (a)
and with a 2 ng Cd spike (b). Tatoms1250 8C.
Fig. 3. Atomization signal of Pb in 10 ml seawater (left) and in 10 ml seawaterq10 ml 23 M HF (right), without spike (a) and
with a 100 ng Pb spike (b). Tatoms1250 8C.
518
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
Fig. 4. Influence of addition of HF on the recovery of Pb and Cd in 10 ml seawaterq10 ml HF solution. Tatoms1250 8C.
wHFxywClyx represents molar concentration ratio of the mixed solution.
than at the Pb analytical line; it was dependent on
the background absorption magnitude and probably
mainly due to the molecular absorption of NaCl
w19x. This spectral interference effect induced an
important under-correction susceptible of introducing systematic errors on the determination of these
elements at low concentration levels.
By addition of HF to seawater, chloride was
removed at the drying step and for the different
added HF concentration, the resulting seawater
matrix was modified according to Fig. 1. Consequently, the chloride interference effect observed
for Cd and, particularly for Pb decreased when the
concentration of HF was increased (Fig. 4). The
chloride interference effect was totally suppressed
for small amounts of added HF in the case of Cd,
but for much higher added HF concentrations in
the case of Pb; indeed, a HFychloride mole concentration ratio higher than 10 was necessary to
suppress the chloride interference effect observed
in the case of Pb. As shown in Figs. 2 and 3, the
presence of HF promoted lower atomization temperature for Pb and Cd in seawater. The addition
of HF to seawater led to the precipitation of
MgF2 and prevented the hydrolysis of MgCl2. As
observed when seawater was mixed with HF at
room temperature, Pb was co-precipitated from the
solution with MgF2, indicative of the formation of
Pb fluoride compounds. CdF2 was probably not
formed when HF was added to seawater at room
temperature because it was not similarly co-precipitated from the solution with MgF2. Nevertheless,
it could be also formed when chloride was
removed at the drying step and co-precipitated or
entrapped as CdCl2 oryand CdF2 in the modified
seawater matrix. This probably led to different
atomization mechanisms for Pb and Cd. The trapping effect of MgF2 (Tmps1261 8C, and Tbps
2239 8C) was probably less important than the
trapping effect of magnesium oxides (Tmps2852
8C, and Tbps3600 8C) and consequently, for Cd
and Pb a lower atomization temperature that led
to the suppression of chloride interference effects
was observed. For a high HFychloride mole concentration ratio of approximately 40, well resolved
atomic absorption signals and a drastic decrease
of the background absorption signal were obtained
at the 228.8 nm Cd and the 283.3 nm Pb analytical
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
lines, when heated up to 1250 8C. The lower
background absorption signal was attributable both
to the decrease of the absorbance when NaCl was
modified to NaF according to their molecular
spectra w22x, and to the high vaporization temperature of sodium fluoride; the decrease of the
background absorption signal being accompanied
by a reduction of the error.
3.3. Optimization studies
The standard procedure for the determination of
the detection limit in GFAAS recommended by
IUPAC is time-consuming to optimize experimental conditions, because it requires 20 repeated
measurements of a small absorption signal. In
practice, for optimization studies in GFAAS, the
sensitivity variation has only been monitored, but
this parameter is not adequate to optimize experimental conditions because noise limitations are not
taken into account, particularly in the presence of
a background signal. An interesting tool for the
optimization of experimental conditions has been
proposed in previous papers, that permits a quantification of the limit of detection with the use of
an a priori calculation w15x. The mass detection
limit for our Perkin-Elmer apparatus could be
expressed by the following relation w16x:
ms0.019=10ŽyEy36.=
=
y
m
QA
10ÃBG
1
q
tint
tboc
(1)
where QA is the integrated absorbance; m is the
mass of analyte; tint is the integration time; tboc is
the baseline offset compensation time; the weighted mean background absorption signal A˜ BG is
determined using the expression:
B
D
E
ABGŽmax.qA¯ BGG
C
ÃBGs
F
2
QBG
tint
The baseline noise is dependent on the light
flux intensity and related to the E parameter that
is displayed on Perkin-Elmer spectrometers and
where ĀBGs
519
Ž1000yVPM.
, where VPM is the
10
photomultiplier voltage. The concentration detecmL
tion limit is expressed as cLs
where V is the
V
sample volume introduced into the furnace.
In our experiment, 10 ml of the modifier solution
were added into the graphite furnace together with
10 ml of seawater spiked with Pb or Cd. Using
fixed spectroscopic parameters (EDL lamps, recommended lamp currents and a 2 nm slit width),
i.e. fixed E parameter, no pyrolysis step and
constant boc time, the only modifiable atomization
parameters were only modifier concentration and
atomization temperature. The integrated absorbance, integration time, and simultaneous background absorption magnitude were dependent both
on the concentration of HF used, and on the
atomization temperature. Therefore, we examined
the variation of the limit of detection with the
atomization temperature for Cd and Pb for three
levels of concentrations: no HF; 5 M HF; and 23
M HF. For the HF concentrations used, the interference effect was minimized (Fig. 4), but different
simultaneous background signal magnitudes were
obtained depending on the HF concentration and
atomization temperature. For this optimization
study, the corresponding integration time was calculated after determining the beginning and the
end of integration of a 11-point smoothed signal
by examining the absorbance values higher than
three times the standard deviation of the baseline
noise. QA and A˜ BG were calculated in this integration window at each atomization temperature, and
for the three HF concentration levels. The limit of
detection was then calculated from Eq. (1).
defined as Es
3.3.1. Cadmium
The variations of the integrated absorbance of
Cd with the atomization temperature are represented in Fig. 5. In unmodified seawater, an
increase of the integrated absorbance was noted
for atomization temperatures up to 1300 8C by
increasing atomization efficiency. However, due to
the dramatic increase of the simultaneous background absorption signal, atomization temperatures
higher than 1300 8C could not practically be used
520
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
Fig. 5. Influence of atomization temperature on the integrated absorbance of Cd in seawater, in 10 ml seawaterq10 ml 5 M HF, in
10 ml seawaterq10 ml 23 M HF (left) and on the mass detection limit in the corresponding media (right).
in unmodified seawater. In the presence of HF, a
higher atomization efficiency of Cd was obtained
at low temperatures. It could be noted the presence
of a plateau for higher atomization temperatures
instead the expected decrease according to the
variation diffusion coefficient of Cd w24x. This
might be partly due to the non-isothermal conditions of the atomization. In Fig. 5 are represented
the variations of the limit of detection with the
atomization temperature. In seawater, the detection
limit was improved when the atomization temperature was increased from 1150 to 1300 8C; the
improvement due the increase in atomization efficiency and reduction of the integration time (9™
3.5 s), was slightly reduced by the increase of the
weighted mean background absorption signal
(0.02™0.7). The dramatic increase of the limit of
detection for atomization temperatures higher than
1300 8C was mainly due to the strong increase of
the simultaneous background absorption signal.
The presence of HF greatly lowered the limit of
detection of Cd in seawater. For a 5 or 23 M HF
concentration, the decrease of the limit of detection
from 1150 to 1300 8C was mainly due to the
reduction of the integration time (;5™2 s). For
higher atomization temperatures, the increase of
the limit of detection in the presence of 5 M HF
was mainly due to the increase of the simultaneous
background absorption signal, generated by the
remaining chloride matrix. For a 23 M HF concentration, the increase of the simultaneous background absorption signal was not important and,
consequently, the increase of the atomization temperature had no important influence on the detection limit.
3.3.2. Lead
The variations in integrated absorbance of Pb
with atomization temperature are represented in
Fig. 6. It clearly appeared that the integrated
absorbance was highly dependent on both HF
concentration and atomization temperature. In
unmodified seawater, an increase of the atomization temperature from 1250 to 1500 8C, improved
only slightly the atomization efficiency. For a
higher atomization temperature, the background
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
521
Fig. 6. Influence of the atomization temperature on the integrated absorbance of Pb in seawater, in 10 ml seawaterq10 ml 5 M HF,
in 10 ml seawaterq10 ml 23 M HF (left) and on the mass detection limit in the corresponding media (right).
absorption signal was very important and atomization temperatures higher than 1500 8C could not
be used. The presence of a high HF concentration
suppressed the chloride interference, and promoted
a much higher atomization efficiency at low atomization temperatures. On the other hand, in this
medium an increase in atomization temperature
induced an important decrease of the integrated
absorbance; this variation appeared in relatively
good agreement with the variation in diffusion
coefficient of Pb with temperature w24x.
From Fig. 6, it appeared clearly that the use of
HF greatly improves the detection limit of Pb in
seawater. In seawater, an important decrease of the
limit of detection from 1250 to 1450 8C was
observed. The improvement was mainly due both
to the increase of the integrated absorbance and
the reduction of the integration time (3.5™2 s).
In the presence of 5 M HF, an increase in atomization temperature from 1150 to 1300 8C led to a
higher atomization efficiency and to a shorter
integration time (;11™4 s); this explained the
important improvement of the detection limit from
1150 to 1300 8C atomization temperature. For
higher atomization temperatures, variations of the
integration time were small, and both the decrease
of the integrated absorbance and the increase in
simultaneous background absorption signal generated by the vaporization of the remaining sodium
chloride, led to an increase in the limit of detection.
In the presence of 23 M HF, the interference
effect was minimized and, both a high atomization
efficiency and a very small background absorption
signal were obtained at low atomization temperatures. This led to a much lower detection limit. It
might be noted that the limit of detection was
relatively constant in the atomization temperature
range, despite the important decrease of the integrated absorbance with atomization temperature.
This was mainly due the reduction in integration
time (from ;6 s at 1150 8C to ;1.5 s at 1600
8C) and the decrease in integrated absorbance,
which had opposite effects on the limit of detection. In this medium, the variations of the simultaneous background absorption signal had a
relatively small influence on the detection limit.
522
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
Fig. 7. Single atomic signal of 100 ng ly1 Cd (a), and averaged atomic signal of 20 replicates of 20 ng ly1 Cd (b) in 15 ml
seawaterq15 ml 23 M HF. Single atomic signal of 4 mg ly1 Pb and averaged atomic signal of 20 replicates of 500 ng ly1 Pb (b)
in 15 ml seawaterq15 ml 23 M HF. Tatoms1300 8C.
3.4. Determination of Cd and Pb in seawater in
optimized conditions.
From this study, it appeared that the best limits
of detection for Cd and Pb were obtained with the
use of a 23 M HF concentration. In these conditions, the seawater volume that could be introduced
in the atomizer with a single introduction was
reduced because an equal volume of modifier had
to be introduced and consequently, the limit of
detection was increased by approximately twofold. With the use of the Perkin-Elmer spectrometer, a total volume of 30 ml can be routinely
introduced that limits the seawater volume to 15
ml. Single atomic signals of 4 mg ly1 Pb and 0.1
mg ly1 Cd, obtained in optimized conditions at
1300 8C in 15 ml seawaterq15 ml 23 M HF, are
shown in Fig. 7. As observed, the atomization of
Cd and Pb occurred in the presence of a very low
simultaneous background absorption signal. However, it was noted that a relatively small undercorrection appeared simultaneously to the
vaporization of the modified seawater matrix, particularly in the case of Cd. This under-correction
could represent a significant systematic error for
low absorption signals when the integration window was not carefully chosen. The use of a moving
integration window (fixed number of integration
points) close to the duration of the signal may
significantly improve the detection limit, because
the beginning and end of integration are difficult
to determine for small absorption signals w16x.
Using this data treatment, the experimental detection limits of Cd and Pb were determined by using
a moving window corresponding to the duration
of the respective atomic signals (80 points for Cd;
130 points for Pb). The detection limits obtained
for Cd and Pb were 0.007 and 0.25 mg ly1 (3s,
20 measurements), respectively. In Fig. 7 are also
shown atomic signals of Cd and Pb at the detection
limit concentration level obtained by averaging 20
individual signals. The concentrations of Cd determined by the standard addition method in a SLEW1 estuarine water and a CASS-2 seawater were
0.020"0.002 and 0.017"0.002 mg ly1 Cd,
respectively, in good agreement with the
0.018"0.003 and 0.019"0.004 mg ly1 Cd certified values (At the 95% confident level, 10 meas-
J.Y. Cabon / Spectrochimica Acta Part B 57 (2002) 513–524
urements). The detection limit of Pb was too high
for its determination in these certified samples at
the 0.020 mg ly1 level concentration.
4. Conclusion
From this study, it appears clearly that HF may
be an interesting modifier for the determination of
volatile elements, like Pb and Cd, in seawater and
more generally in chloride matrices. Indeed, it
promotes an efficient atomization at low temperatures, suppresses chloride interference effects and
dramatically reduces the simultaneous background
absorption signal. Moreover, because of the
absence of decomposition products, no pyrolysis
step is necessary. The limit of detection obtained
for Cd permits the direct determination of this
element in seawater; however, the limit of detection of Pb in seawater is too high to permit the
determination of this element in non-polluted seawater. The a priori calculation of the detection
limit appears also very useful to optimize experimental conditions; however, systematic errors like
miscorrections, that may induce important errors
at the limit of detection level, are not included in
the calculation and have to be minimized by a
careful choice of experimental conditions, and an
adequate mathematical data treatment.
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