Analytica Chimica Acta, 84 (1976) 89-96 0 Etsevier Scientific Publishing Company,
Amsterdam
-
Printed
in The Netherlands
SOME APPLICATIONS OF RAPID SEPARATION OF MERCURY METALLIC COPPER TO ENVIRONlMENTAL SAMPLES WITH DETERMINATION BY FLAMELESS ATOMIC ABSORPTION SPECTROMETRY
S. DOCAN
and W. HAERDI
Department of Inorganic and Analytical CII- 121 I Ccneva 4 (Switzerland) (Received
ON
17th December
Chemistry.
University
of Ceneun, Sciences
II.
1975)
Preconcentration of mercury on a copper micro-column is particularly suitable for determination of mercury in various environmental samples. The micro-column is coupled to the cell for mercury determination by f.a.a.s. To avoid possible interferences by volatile organic compounds adsorbed on the copper together with mercury, an alumina column is placed just before the C.a.a.s. cell. With this method 1 ng of mercury can be determined with a precision of r 13 70. The time required for determinations is 15-120 min for 50--5OGml water samples (several preconcentrations can be done simultaneously). about 2.5 h for liquid biological samples. and lF-50 min for solid samples.
For relatively high mercury concentrations in aqueous media the tin(I1) reduction-aeration method is often preferred because of its simplicity [ 1, 21. For lower mercury concentrations a preconccntration step seems to be necessary [ 1, 3, 41. Another approach, which is rather lengthy, is based on the electrodeposition of mercury on Au, Pt, Ag or Cu, and is particularly convenient for samples of small volume [ 5-71. For solid samples such as sediments, rocks and bio-organics, a preliminary mineralization by combustion is necessary to preconcentratc the mercury vapour on gold metal [7-101. This method is very much faster than wet mineralization ant1 possible contaminations by the reagents are avoided. In the present paper, first the preconcentration technique described recently [ 111 is applied to the determination of mercury in natural waters and waste-waters. Secondly, a very rapid and efficient mineralization technique by combustion or acid digestion is applied to mercury determinations, respectively, in solid samples or liquid biological materials from various sources.
90
EXPERIMENTAL
In a preliminary study, water samples (10-500 ml) from various sources with ‘03Hg (tl = 47 days; C.E.A. France). After ccntrifugation or filtration on milliporc membranes, the pIi values of the samples were adjusted to l-5--2.0 with nitric acid and the mercury was separated on microcolumns of copper powder as described previously [ 111. For total added mercury concentrations in the 1O-6-lO-8 M range, the separation efficiency was greater than 98 %; the efficiency was lower (75-80 ‘%) for lower concentrations such as 10-l’ M (1 ng/500 ml) owing to the adsorption of mercury on the walls of the vessel. The adsorbed mercury could be rclcascd by 1 M IICl [ 121. No apparent interference by the other constituents of water was observed. The copper column on which mercury was retained was used directly for flameless atomic absorption spectrometry (f.a.a.s.). were labclled
Procedure
for aqueous samples
‘I’hc water sample (10-1000 ml) is passed through a milliporc membrane (diameter 47 mm, porosity 0.45 pm) and immediately acidified with nitric acid (Merck G.R.) to pH 1.5-2.0. The ionic mercury is then separated by passage of the sample through a copper micro-column at a flow rate of about 4-5 ml min-‘. It is possible to determine the total mercury content by oxidizing the filtrate in order to free the “bound mercury”. This is done by treating the filtrate with ozone produced by passing oxygen over a high-voltage discharge lamp (131. At a flow rate of oxygen of 100 ml min-‘, the oxidation is complete in about 10 min; even with relatively highly polluted samples oxidation is complete in about 30 min. The excess of ozone which accumulates in the solution is removed by passing a stream of nitrogen. This method of oxidation is unsuitable for samples containing, or which on oxidation liberate, highly volatile organo-mercurials such as (CHs)2Hg and (C2HS)2Hg, since the loss of mercury becomes significant. Hfanlz determination. Separation on copper micro-columns for a given sample is repeated by successive passages until a constant absorbance is reached. This value is taken as blank and subtracted from the absorbance of analytical samples. It should bc noted that it is indispensable to add traces of gold ([Au] ( = lOmy M) as AuCli to the filtrate, to prevent mercury from being adsorbed on the walls of the vessel [ 12]_ Procedure
for solid samples
The dried solid into a quartz tube burnt at 900-950 carries the volatile
sample (10-100 mg) in a quartz crucible is introduced placed in a tubular furnace (see Fig. 1). The sample is “C in an osygcn stream (flow rate 45 ml min-‘) which combustion products including mercury to and through
91
Fig. 1. Combustion and separation apparatus. a, tubular furnace; b, combustion tube (quartz); c, quartz crucible; d, quartz wool; e. copper powder micro-column; f, copper powder; g, ice bath. Dimensions in mm.
the copper micro-column, which is cooled in an ice bath, to ensure a quantitative separation of mercury. (This combustion can also be done with a Bunsen burner.) The micro-column is joined to the combustion tube by means of a length of short PVC tubing. A little quartz wool (d) acts as a filter for any particulate matter that may be carried along. It should be removed before f.a.a.s. For this procedure, the blank is similarly prepared, but without the. sample. In order to prevent possible clogging, the micro-column must be loosely filled with copper_
Procedure for liquid biological samples Wet mineralization under pressure is well suited for mercury determinations in biological liquids such as blood and milk. For this purpose a slightly modified decomposition vessel ( Uni-Seal decomposition vessels, Israel) was used (Fig. 2). It was necessary to make some modifications to the original vessel, to make it airtight and avoid deformation of the teflon crucible (b). The teflon disk (e) and viton “0” ring (d) must be renewed before each mineralization About 1 g of blood and 2 ml of concentrated nitric acid (hlcrck suprapur) are introduced into the vessel which is sealed and left at 150 “C for 2 h. The sealed vessel is cooled in liquid nitrogen or dry ice before it is opened. Its contents are transferred to a beaker and the pH is adjusted to 1.5-20 with solid sodium hydroxide (Merck suprapur). The mercury in solution is then separated on a copper micro-column as described previously [ 111.
F.a.a.s. analysis Once the mercury has been separated,
the micro-column is rinsed two or three times with methanol (Merck G.R.) and is incorporated in the analytical apparatus as shown in Fig. 3 (see also ref. 11).
Fig. 2. Mineralization vessel. a. stainless 5 ml); c. stainless steel retaining screws; less steel cap. RESIJI.‘K
ANI)
steel container; b, tcflon crucible (total volume, d. viton “0” ring; c, teflon disk (0.6 mm); f, stain-
DISCUSSION
Determination of mercury in water The described method proved to be very satisfactory for determinations of mercury in environmental water samples of various origins (lake, river, sea and tap-water) as well as in industrial waste-waters which do not contain a large amount of organic compounds and especially chlorinated organic or mineral compounds. Significant interference by volatile species absorbing in the 253.7-nm region was eliminated by passing the effluent gas over a O-53-cm alumina column before its entrance into the f.a.a.s. cell (Fig. 3). The detection limit was 1 ng absolute as can be seen from the results in Table 1 (in a sample of the Rhbne river at Geneva). Table 2 shows the results obtained for lake, river and sea-water samples. It is important to note that during the ozonization of sea water to liberate “bound mercury”, some chlorine is also produced and causes very serious interference with the analysis. ‘This osidation procedure is therefore not recommended for sea-water samples. Determination of mercury in bloocl samples By labelling blood samples with *“.‘Hg, efficiencies
of 9s % in the combined
93
Fig. 3. F.a.a.s. measuring system. 3, ;t’, quartz windows (2 mm); b, alumina micro-column (h = 0.5-3.0 cm; A&Q, stand-d&d for chromatogrnphic adsorption analysis xc. to Brockman); c, heating coil; d, copper micro-column; e, c.m.f. cell (O-5 A); f, flowmeter. Dimensions in mm.
TABLE
1
Analysis of river water and recovery
.
-
TotaI volume (ml)
_-.-
Hg added (ng) -. --_
100
_
“After
0.0 3.0 5.0 100.0 -_-blank subtraction.
- _--.
___-...__
_
.._--
-
Absorbance
-. _--_.
0.0 1.0 2.0 4.0 10.0
500
of added mercury
_-
._.-, _‘..
0.005 (blank)
-
0.011 0.017 O.OSG 0.056
1.2 2.4 4.2 lo.‘?
0.010 0.024 0.035 0.101 (on 100 ml)
1.0 3.8 6.0 98.0
. -__
-
_._ ._,-
I-& found ( ng)a
-...._._._.----
.. .-_.-
.._-
94 TABLE
2
Mercury in natural -. - - -.-
water samples3 ---.---_
Origin
Ionic
- ---
-
-
-
-_
(ng I-‘) .-. - .-_
-.-
-..-.-..-.----_
Iig -
Total Hg (ng I”‘) _.-___ _.-
Rhbne river (at Geneva)
3.1 t 0.8
11.3 f 1.2
Arve riverb (at Geneva)
1.8 I 1.0
2.8 _c 1.0
Lake of Geneva (surface)
2.5 f 1.2
8.9 t 1.5
Lake
of Geneva=
4.3 ? 1.0
Lake
of Genevad
Adriatic
Sea
(at Rovinj/YU) -.___.-
-
..-.-
.-
-
11.6
? 1.6
5.3 ? 1.2
15.4
f 2.5
4.6 + 1.1
-
-
-
-_-
-.-----.-
‘Experiments done on one sample only. bSandy water. ‘Water pumped at about 30 m depth before dSame water filtered over sand for domestic TABLE
3
Mercury in a blood _-__-.--_-.Sample weight ____.__ Blank 0.968 1.007 0.981 _--.-.‘After
sand filtration. use.
(g)
sample -.__-_
-.-
---.------
Hg added (ng) ..__ _ _ __._ -_ -
10 10 -.--_-..-_---------.-----.--.-.-.---.subtracting
blank
and added
mercury.
-.-.-.Absorbance --.-----.-.-.-. 0.007 0.036 0.030 0.081 0.058 hlean:
---._---
--
.-
I ig found (p.p.b.)” - .- .--5.8 4.4 4.5 10.0
4.9 t 0.9.
mineralization and separation steps were found for l-2 ng of added mercury. The results for a blood sample are presented in Table 3. Determination of mercury in plants The accuracy of the method as applied to samples of vegetable origin was checked by analyzing the mercury content of standard orchard leaves (NBS reference material 1571) alone and mised with flour to obtain lower amounts. As shown in Table 4, the results are in very good agreement with certified values and with those obtained by other workers [ 141. In the analysis of such samples, the regularity of combustion and the flow
95
TABLE
4
Mercury content
in standard orchard leaves (NBS
- .-
..
..-...-
-.._.-
.
Orchard leaves Flour (pure) Mixture 1 hlixture 2 -
- --
---
1571)
..-.-.. ~-
Hg found (p.p.b.)
Hg certified
154.0 7.2 40.5 55.9
155 ? 15 40.2” 56.7b
---.-.
-_.---_.-...
_ _. ..-.-.--
+ t f ?
13.0 2.2 4.P 4.P
--_..
.(p.p.b.)
.---
..___ .-_- _.-----..
“After blank subtraction (flour). bValues calculated from the certified TABLE
--
_-
value.
5
Mercury in some vegetation samples ___.______ _._....----._. . ..----.. Sample ---.-__--.
Origin”
_--__
Hg (p.p.b.)b
-_ ----
- --
Apple tree leaves
A B
96-l 64’ 275-i2dc
Pine leaves
A B
54.2 f 2.0 252.6 * 4.5
Larch leaves
H
730-860=
Ripe wheat
A B
10.6 * 0.6 13.6 + 0.4
Zooplankton Phytoplankton
C C
268.2 f 12.0 87.3 + 4.0
Mixed ---
plankton
.._.
-
-- C .-. -~-.
301.7
? 34.3
_.
aA, Urban region; B. industrial region; C. Lake of Geneva. “Values for dried weight. CValues obtained at different periods of the year.
of oxygen are important factors in obtaining good precision. The limit of detection is 1 ng of mercury for lO-lOO-mg samples. Results for various vegetation samples are given in Table 5. REFEKENCES 1 See, e.g. h M. Ure, Anal. Chim. Acta, 76 (1975) 1. 2 R. J. Baltisbcrgcr and C. I,. Knudson, Anal. Chim. Acta, i3 (1974) 3 J. Olafsson. Anal. Chim. 4 D. Voyce and II. Zeitlin,
Acta, 68 (1974) 207. Anal. Chim. Acta, 69 (1974)
5 RI. J. Fishman. Anal. Chem.. 42 (1970) 1462. 6 H. Brandcnberger and H. Bader, At. Absorpt. News]., 7 H. Heinrichs, Z. Anal. Chem., 273 (1975) 197.
265.
27. 6 (1967)
101; 7 (1968)
53.
96
8 P. C. Leong and H. P. Ong, Anal. Chem., 43 (1971) 940. 9 D. Ii. Anderson, J. H. Evans, J. J. Murphy and W. W. White, Anal. Chem.. 43 (1971) 1511. 10 J. W. Wimberley. Anal. Chim. Acta, 76 (1975) 337. 11 S. Dogan and W. Haerdi, Anal. Chim. Acta. 76 (1975) 345. 12 S. Dognn, Thesis. University of C&new. 1976. 13 L. Lopez-Fkcobar and D. N. Hume, Anal. Lctt., 6 (1973) 343. 14 W. E‘. Fitzerald, W. R Lyons and C. D. Hunt, Anal. Chem., 46 (1974) 1882.
Amsterdam
-
Printed
in The Netherlands
SOME APPLICATIONS OF RAPID SEPARATION OF MERCURY METALLIC COPPER TO ENVIRONlMENTAL SAMPLES WITH DETERMINATION BY FLAMELESS ATOMIC ABSORPTION SPECTROMETRY
S. DOCAN
and W. HAERDI
Department of Inorganic and Analytical CII- 121 I Ccneva 4 (Switzerland) (Received
ON
17th December
Chemistry.
University
of Ceneun, Sciences
II.
1975)
Preconcentration of mercury on a copper micro-column is particularly suitable for determination of mercury in various environmental samples. The micro-column is coupled to the cell for mercury determination by f.a.a.s. To avoid possible interferences by volatile organic compounds adsorbed on the copper together with mercury, an alumina column is placed just before the C.a.a.s. cell. With this method 1 ng of mercury can be determined with a precision of r 13 70. The time required for determinations is 15-120 min for 50--5OGml water samples (several preconcentrations can be done simultaneously). about 2.5 h for liquid biological samples. and lF-50 min for solid samples.
For relatively high mercury concentrations in aqueous media the tin(I1) reduction-aeration method is often preferred because of its simplicity [ 1, 21. For lower mercury concentrations a preconccntration step seems to be necessary [ 1, 3, 41. Another approach, which is rather lengthy, is based on the electrodeposition of mercury on Au, Pt, Ag or Cu, and is particularly convenient for samples of small volume [ 5-71. For solid samples such as sediments, rocks and bio-organics, a preliminary mineralization by combustion is necessary to preconcentratc the mercury vapour on gold metal [7-101. This method is very much faster than wet mineralization ant1 possible contaminations by the reagents are avoided. In the present paper, first the preconcentration technique described recently [ 111 is applied to the determination of mercury in natural waters and waste-waters. Secondly, a very rapid and efficient mineralization technique by combustion or acid digestion is applied to mercury determinations, respectively, in solid samples or liquid biological materials from various sources.
90
EXPERIMENTAL
In a preliminary study, water samples (10-500 ml) from various sources with ‘03Hg (tl = 47 days; C.E.A. France). After ccntrifugation or filtration on milliporc membranes, the pIi values of the samples were adjusted to l-5--2.0 with nitric acid and the mercury was separated on microcolumns of copper powder as described previously [ 111. For total added mercury concentrations in the 1O-6-lO-8 M range, the separation efficiency was greater than 98 %; the efficiency was lower (75-80 ‘%) for lower concentrations such as 10-l’ M (1 ng/500 ml) owing to the adsorption of mercury on the walls of the vessel. The adsorbed mercury could be rclcascd by 1 M IICl [ 121. No apparent interference by the other constituents of water was observed. The copper column on which mercury was retained was used directly for flameless atomic absorption spectrometry (f.a.a.s.). were labclled
Procedure
for aqueous samples
‘I’hc water sample (10-1000 ml) is passed through a milliporc membrane (diameter 47 mm, porosity 0.45 pm) and immediately acidified with nitric acid (Merck G.R.) to pH 1.5-2.0. The ionic mercury is then separated by passage of the sample through a copper micro-column at a flow rate of about 4-5 ml min-‘. It is possible to determine the total mercury content by oxidizing the filtrate in order to free the “bound mercury”. This is done by treating the filtrate with ozone produced by passing oxygen over a high-voltage discharge lamp (131. At a flow rate of oxygen of 100 ml min-‘, the oxidation is complete in about 10 min; even with relatively highly polluted samples oxidation is complete in about 30 min. The excess of ozone which accumulates in the solution is removed by passing a stream of nitrogen. This method of oxidation is unsuitable for samples containing, or which on oxidation liberate, highly volatile organo-mercurials such as (CHs)2Hg and (C2HS)2Hg, since the loss of mercury becomes significant. Hfanlz determination. Separation on copper micro-columns for a given sample is repeated by successive passages until a constant absorbance is reached. This value is taken as blank and subtracted from the absorbance of analytical samples. It should bc noted that it is indispensable to add traces of gold ([Au] ( = lOmy M) as AuCli to the filtrate, to prevent mercury from being adsorbed on the walls of the vessel [ 12]_ Procedure
for solid samples
The dried solid into a quartz tube burnt at 900-950 carries the volatile
sample (10-100 mg) in a quartz crucible is introduced placed in a tubular furnace (see Fig. 1). The sample is “C in an osygcn stream (flow rate 45 ml min-‘) which combustion products including mercury to and through
91
Fig. 1. Combustion and separation apparatus. a, tubular furnace; b, combustion tube (quartz); c, quartz crucible; d, quartz wool; e. copper powder micro-column; f, copper powder; g, ice bath. Dimensions in mm.
the copper micro-column, which is cooled in an ice bath, to ensure a quantitative separation of mercury. (This combustion can also be done with a Bunsen burner.) The micro-column is joined to the combustion tube by means of a length of short PVC tubing. A little quartz wool (d) acts as a filter for any particulate matter that may be carried along. It should be removed before f.a.a.s. For this procedure, the blank is similarly prepared, but without the. sample. In order to prevent possible clogging, the micro-column must be loosely filled with copper_
Procedure for liquid biological samples Wet mineralization under pressure is well suited for mercury determinations in biological liquids such as blood and milk. For this purpose a slightly modified decomposition vessel ( Uni-Seal decomposition vessels, Israel) was used (Fig. 2). It was necessary to make some modifications to the original vessel, to make it airtight and avoid deformation of the teflon crucible (b). The teflon disk (e) and viton “0” ring (d) must be renewed before each mineralization About 1 g of blood and 2 ml of concentrated nitric acid (hlcrck suprapur) are introduced into the vessel which is sealed and left at 150 “C for 2 h. The sealed vessel is cooled in liquid nitrogen or dry ice before it is opened. Its contents are transferred to a beaker and the pH is adjusted to 1.5-20 with solid sodium hydroxide (Merck suprapur). The mercury in solution is then separated on a copper micro-column as described previously [ 111.
F.a.a.s. analysis Once the mercury has been separated,
the micro-column is rinsed two or three times with methanol (Merck G.R.) and is incorporated in the analytical apparatus as shown in Fig. 3 (see also ref. 11).
Fig. 2. Mineralization vessel. a. stainless 5 ml); c. stainless steel retaining screws; less steel cap. RESIJI.‘K
ANI)
steel container; b, tcflon crucible (total volume, d. viton “0” ring; c, teflon disk (0.6 mm); f, stain-
DISCUSSION
Determination of mercury in water The described method proved to be very satisfactory for determinations of mercury in environmental water samples of various origins (lake, river, sea and tap-water) as well as in industrial waste-waters which do not contain a large amount of organic compounds and especially chlorinated organic or mineral compounds. Significant interference by volatile species absorbing in the 253.7-nm region was eliminated by passing the effluent gas over a O-53-cm alumina column before its entrance into the f.a.a.s. cell (Fig. 3). The detection limit was 1 ng absolute as can be seen from the results in Table 1 (in a sample of the Rhbne river at Geneva). Table 2 shows the results obtained for lake, river and sea-water samples. It is important to note that during the ozonization of sea water to liberate “bound mercury”, some chlorine is also produced and causes very serious interference with the analysis. ‘This osidation procedure is therefore not recommended for sea-water samples. Determination of mercury in bloocl samples By labelling blood samples with *“.‘Hg, efficiencies
of 9s % in the combined
93
Fig. 3. F.a.a.s. measuring system. 3, ;t’, quartz windows (2 mm); b, alumina micro-column (h = 0.5-3.0 cm; A&Q, stand-d&d for chromatogrnphic adsorption analysis xc. to Brockman); c, heating coil; d, copper micro-column; e, c.m.f. cell (O-5 A); f, flowmeter. Dimensions in mm.
TABLE
1
Analysis of river water and recovery
.
-
TotaI volume (ml)
_-.-
Hg added (ng) -. --_
100
_
“After
0.0 3.0 5.0 100.0 -_-blank subtraction.
- _--.
___-...__
_
.._--
-
Absorbance
-. _--_.
0.0 1.0 2.0 4.0 10.0
500
of added mercury
_-
._.-, _‘..
0.005 (blank)
-
0.011 0.017 O.OSG 0.056
1.2 2.4 4.2 lo.‘?
0.010 0.024 0.035 0.101 (on 100 ml)
1.0 3.8 6.0 98.0
. -__
-
_._ ._,-
I-& found ( ng)a
-...._._._.----
.. .-_.-
.._-
94 TABLE
2
Mercury in natural -. - - -.-
water samples3 ---.---_
Origin
Ionic
- ---
-
-
-
-_
(ng I-‘) .-. - .-_
-.-
-..-.-..-.----_
Iig -
Total Hg (ng I”‘) _.-___ _.-
Rhbne river (at Geneva)
3.1 t 0.8
11.3 f 1.2
Arve riverb (at Geneva)
1.8 I 1.0
2.8 _c 1.0
Lake of Geneva (surface)
2.5 f 1.2
8.9 t 1.5
Lake
of Geneva=
4.3 ? 1.0
Lake
of Genevad
Adriatic
Sea
(at Rovinj/YU) -.___.-
-
..-.-
.-
-
11.6
? 1.6
5.3 ? 1.2
15.4
f 2.5
4.6 + 1.1
-
-
-
-_-
-.-----.-
‘Experiments done on one sample only. bSandy water. ‘Water pumped at about 30 m depth before dSame water filtered over sand for domestic TABLE
3
Mercury in a blood _-__-.--_-.Sample weight ____.__ Blank 0.968 1.007 0.981 _--.-.‘After
sand filtration. use.
(g)
sample -.__-_
-.-
---.------
Hg added (ng) ..__ _ _ __._ -_ -
10 10 -.--_-..-_---------.-----.--.-.-.---.subtracting
blank
and added
mercury.
-.-.-.Absorbance --.-----.-.-.-. 0.007 0.036 0.030 0.081 0.058 hlean:
---._---
--
.-
I ig found (p.p.b.)” - .- .--5.8 4.4 4.5 10.0
4.9 t 0.9.
mineralization and separation steps were found for l-2 ng of added mercury. The results for a blood sample are presented in Table 3. Determination of mercury in plants The accuracy of the method as applied to samples of vegetable origin was checked by analyzing the mercury content of standard orchard leaves (NBS reference material 1571) alone and mised with flour to obtain lower amounts. As shown in Table 4, the results are in very good agreement with certified values and with those obtained by other workers [ 141. In the analysis of such samples, the regularity of combustion and the flow
95
TABLE
4
Mercury content
in standard orchard leaves (NBS
- .-
..
..-...-
-.._.-
.
Orchard leaves Flour (pure) Mixture 1 hlixture 2 -
- --
---
1571)
..-.-.. ~-
Hg found (p.p.b.)
Hg certified
154.0 7.2 40.5 55.9
155 ? 15 40.2” 56.7b
---.-.
-_.---_.-...
_ _. ..-.-.--
+ t f ?
13.0 2.2 4.P 4.P
--_..
.(p.p.b.)
.---
..___ .-_- _.-----..
“After blank subtraction (flour). bValues calculated from the certified TABLE
--
_-
value.
5
Mercury in some vegetation samples ___.______ _._....----._. . ..----.. Sample ---.-__--.
Origin”
_--__
Hg (p.p.b.)b
-_ ----
- --
Apple tree leaves
A B
96-l 64’ 275-i2dc
Pine leaves
A B
54.2 f 2.0 252.6 * 4.5
Larch leaves
H
730-860=
Ripe wheat
A B
10.6 * 0.6 13.6 + 0.4
Zooplankton Phytoplankton
C C
268.2 f 12.0 87.3 + 4.0
Mixed ---
plankton
.._.
-
-- C .-. -~-.
301.7
? 34.3
_.
aA, Urban region; B. industrial region; C. Lake of Geneva. “Values for dried weight. CValues obtained at different periods of the year.
of oxygen are important factors in obtaining good precision. The limit of detection is 1 ng of mercury for lO-lOO-mg samples. Results for various vegetation samples are given in Table 5. REFEKENCES 1 See, e.g. h M. Ure, Anal. Chim. Acta, 76 (1975) 1. 2 R. J. Baltisbcrgcr and C. I,. Knudson, Anal. Chim. Acta, i3 (1974) 3 J. Olafsson. Anal. Chim. 4 D. Voyce and II. Zeitlin,
Acta, 68 (1974) 207. Anal. Chim. Acta, 69 (1974)
5 RI. J. Fishman. Anal. Chem.. 42 (1970) 1462. 6 H. Brandcnberger and H. Bader, At. Absorpt. News]., 7 H. Heinrichs, Z. Anal. Chem., 273 (1975) 197.
265.
27. 6 (1967)
101; 7 (1968)
53.
96
8 P. C. Leong and H. P. Ong, Anal. Chem., 43 (1971) 940. 9 D. Ii. Anderson, J. H. Evans, J. J. Murphy and W. W. White, Anal. Chem.. 43 (1971) 1511. 10 J. W. Wimberley. Anal. Chim. Acta, 76 (1975) 337. 11 S. Dogan and W. Haerdi, Anal. Chim. Acta. 76 (1975) 345. 12 S. Dognn, Thesis. University of C&new. 1976. 13 L. Lopez-Fkcobar and D. N. Hume, Anal. Lctt., 6 (1973) 343. 14 W. E‘. Fitzerald, W. R Lyons and C. D. Hunt, Anal. Chem., 46 (1974) 1882.
