Marine Chemistry, 14 (1983) 43--48 43 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands

MERCOS - - A SIMPLE TEFLON SAMPLER FOR ULTRATRACE METAL ANALYSIS IN SEAWATER

PETER FREIMANN, DIETHER SCHMIDT and KARL SCHOMAKER

Deutsches Hydrographisches Institut, Laboratorium Siilldorf, W~stland 2, 2000 Hamburg 55 (Federal Republic of Germany)

(Received September 6, 1982; accepted 4 July 1983)

ABSTRACT Freimann, P., Schmidt, D. and Schomaker, K., 1983. Mercos -- a simple Teflon sampler

for ultratrace metal analysis in seawater. Mar. Chem., 14: 43--48.

This paper describes an uncomplicated sampling technique for ultratrace element analysis of coastal and surface seawaters (maximum depth 100 m). The sampler system is very easy to operate. To prevent contamination problems, interchangeable 500-ml Teflon bottles are used as both sampling and storage vessels. The seawater samples are stabilized in situ by preacidifying the sampling bottles. For the determination of mercury in seawater the desired system has been developed: sampling bottle ---- storage bottle -- reaction vessel.

INTRODUCTION

The concentrat ions of heavy metals in seawater are in trace (~ 10 -3 g I-I ) and ultratrace ( ~ 1 0 - 6 g l - ' ) levels. For copper, iron, manganese, nickel and zinc, values in the range 10-s - -10-7 g 1-1 are of ten found, while for cad- mium, mercury and lead 10-7--10-9 g l -I have been reported. Because of these low concentrat ions, the prevention of contaminat ion of the seawater samples during the processes of sampling, storage and analysis is of paramount importance (Bothner and Robertson, 1975; Fitzgerald and Lyons, 1975; Patterson and Settle, 1976; Mart, 1979). Another problem is the depletion of trace elements by adsorption onto the container wails at the natural pH of the seawater sample. The hi ther to used Transparent Plastic Nansen samplers (Fischer, 1968) and Close-Open~lose (COC) samplers (both • f rom Hydro-Bios Apparatebau GmbH, Kiel) do no t meet all of these require- ments. The materials used in these samplers contain large amounts of heavy metals, and adequate cleaning procedures are difficult or impossible to perform. For these reasons a new and uncomplicated Teflon sampler "Mercos" (Mercury close open sampler) has been constructed and tested.

DESIGN REQUIREMENTS FOR A WATER SAMPLER FOR ULTRATRACE ELEMENT ANALYSIS OF SEAWATER

Preven t ion o f con taminat ion

(1) The sampler should cross the sea surface as well as the contaminated water surrounding the research vessel in a closed configuration.

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(2) The number of metal parts necessary should be as low as possible. (3) Sampling and storage bottle should be the same vessel, to avoid pouring the sample from one vessel to another. (4) One should be able to clean all parts of the sampling device in a simple and effective way.

Prevention of losses of the elements investigated

{1) The surface of the material used should be neither porous nor rough. (2) After soaking all parts of the sampler in concentrated acids, surface properties of the material should not change. (3) The design of the sampler should allow for in-situ acidifying of the sample.

Handling

(1 )The sampler should be mechanically stable and uncomplicated to guarantee its operation under rough sea conditions. (2) The releasing device should allow for serial operation using polyethylene- coated hydrowire and Teflon-coated messengers. (3) All parts of the sampler should be interchangeable.

Integration into existing sampling and analytical systems

(1) In our laboratory we have obtained good results using 500-ml Teflon bottles as storage vessels for seawater samples. A substantial supply is avail- able. Therefore, these bottles should be incorporated into the new sampler. (2) Collection of our surface samples for the determination of mercury is carried out by means of the same type of 500-ml Teflon bottles attached to a sampling gear. (3) Since we also use these Teflon bott les as storage and reaction vessels for the determination of mercury in seawater (Freimann and Schmidt, 1982) it is desirable to integrate the sampler into the system: sampling bott le = storage bott le = reaction vessel.

CONSTRUCTION OF THE SAMPLER

Following the preceding criteria we have developed the new "Close/Open" Teflon sampler shown in Fig. 1. The main part of the sampler is a polyethyl- ene T-shaped frame (1) with two Teflon screw caps (2). The latter contain two sockets each, one to fix the sample inlet tube (silicone rubber tubing, 8 mm i.d.) and the other the air outlet tube {silicone rubber tubing, 3 mm i.d.). Two 500-ml Teflon bottles from standard commercial s tock (Berghof GmbH, Tfibingen) axe used as sampling vessels (3). The release mechanism consists of a polyethylene anvil (4) with a screwed-on stainless-steel piston. When the messenger hits the anvil, the sampler is opened and a secondary

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(a)

(b)

(c)

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;~ ~ •

150ram I

Fig. 1. Schematic diagram of the Mercos Teflon sampler: (a) left-side view; (b) top view; (c) front view. (1) T-shaped frame. (2) Teflon screw cap. (3) 500-ml Teflon bottle. (4) Anvil. (5) Releasing mechanism of the secondary messenger. (6) Wing-nut. (7) Clamp. (8) Groove. (9) Teflon lever. (10) Bent inlet tubing.

messenger is released (5). To prevent unwanted release of the sampler (e.g., by rough seas) a stainless-steel spring is placed at the lower end of the piston. The sampler can be at tached to a 6-mm polyethylene-coated hydrowire using a stainless-steel wing-nut (6) and clamp (7). To place the sampler in a safe condition the T-shaped frame contains a groove (8) and a Teflon lever (9).

HANDLING AND OPERATION

Cleaning procedure

The Teflon bottles are cleaned by means of the simple two-bot t le still described by Mattinson (1972), using concentrated HNOa (Baker Instra grade) followed by rinsing with ultrapure water. The silicone rubber tubes are first soaked under stirring in 10% (v/v) HNO3, rinsed with ultrapure water and dried under an infrared lamp. All other parts of the sampler are first soaked in concentrated HNOa, then rinsed and dried as described above. All cleaning procedures are carried out, wearing polyethylene gloves, in a laminar air f low clean bench.

Sampling procedure

In order to avoid contamination risks on board a research vessel all pre- parative steps should be carried out in a clean bench, preferably installed in a special shipboard laboratory container (Wong et al., 1977).

Fig. 2. The sampler Mereos in the closed configuration in which it passes the sea :~urface: the water inlet tubes and the air outlet tubes are bent. The messenger (Teflon filled with glass fibre) for release of the following sampler is still attached.

Fig. 3. The sampler (reverse side) in the open configuration after sampling: the messenger has hit the anvil, the tubes have sprung up to allow water to move into and the air to leave the bottles.

The 500-ml Tef lon bo t t l e s are p rov ided wi th HNO3 (Baker Ins t ra grade) where the vo lum e o f the acid added depends on the pH needed for the s tabi l iza t ion o f the seawate r sample . The bot t les are sc rewed to the sample r and the p rec leaned si l icone r u b b e r tubes a t t a ched to the socke t s are ben t and held in place by the anvil (see No. 10, Fig. 1). For the co l lec t ion of seawate r samples we use a 4 - m m h y d r o w i r e coa ted wi th p o l y e t h y l e n e (6 m m o.d.) , a p o l y e t h y l e n e sheave, and a 25-kg Te f lon -coa t ed b o t t o m weight . Since Mercos weighs on ly a b o u t 0.5 kg in wa te r it is possible to a t t ach ten or m o r e samplers per hois t .

The samplers are released by means o f Tef lon messengers (Fig. 2). The first messenger running d o w n the h y d r o w i r e hits the anvil and presses it down ; in this way the tubes are released, and their o w n e las t ic i ty causes t h e m to erect . At the same m o m e n t , the small m o v a b l e h o o k (Fig. 1, No. 5) t ha t holds the plast ic co rd o f the second Te f lon messenger is opened and releases this messenger (in a s imilar w a y to the m o r e conven t iona l H y d r o b i o s TPN samplers) . One m i n u t e later , the bo t t l e s are c o m p l e t e l y filled (Fig. 3). Af t e r raising the sample rs and de tach ing t h e m f r o m the hyd rowi re , the sea- wa te r in the tubes is d iscarded by shaking the sample rs and the Tef lon bo t t l e s are r e m o v e d and c a p p e d t ight ly wi th the original screw caps. The

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TABLE I

Compar i son o f samples col lec ted by d i f fe ren t samplers

E lement

Close-Open-Close sampler Mercos sampler Sampling gear

Concen t ra t ion Dep th Concen t ra t ion Dep th Concen t r a t i on Dep th (pg 1-1 ) (m) (pg 1-1 ) (m) (pg 1-1 ) (m)

Mn 22.6 + 3.5 a 30 13.3 +- 3.1 25 Mn 16.8 + 3.2 40 9.5 + 1.3 35 Cd 0.07 + 0.02 30 0.04 + 0.01 25 Cd 0.11 + 0.03 40 0.08 + 0.03 35 Cu 1.18 + 0.20 30 1.06 + 0.24 25 Cu 1.53 + 0.13 40 0.51 + 0.17 35 Ni 0.86 + 0.57 30 0.42 + 0.28 25 Ni 0.46 + 0.12 40 0.26 + 0.21 35 Fe 27.5 + 3.5 30 23.7 + 3.9 25 Fe 28.2 + 4.5 40 15.0 + 3.0 35 Hg(reac t ive) 0.5 x 10 -3 2 1.0 × 10 -3 2 1.4 × 10 -3 Hg( to ta l ) 1.1 × 10 -3 2 3.6 × 10 -3 2 3.7 × 10 -3

aS tanda rd deviat ion at 95% conf idence level.

Teflon bottles are sealed in polyethylene bags and stored until the analysis can be carried out in the land-based clean laboratory.

RESULTS AND DISCUSSION

During two recent field experiments in the North Sea on board RV 'Gauss' and RV 'Meteor', the new sampler was tested and compared with other sampling devices.

The tightness of the sampler was checked by lowering a closed sampler to a depth of 40 m. After a period of 30 min it was raised while still closed; not a drop of water had entered the Teflon bottles.

The water pressure stability was tested in the same manner, at different depths. The deformation of the sampling bottle, with atmospheric air pressure inside, was negligible down to 100-m depth but at 300 m the bottle broke. Therefore, we use the new sampler only to a maximum depth of 100 m, sufficient for most estuarine and coastal waters in our research and monitoring areas in the North and Baltic Seas.

The reliability of the release mechanism and all other parts of the sampler was tested by the collection of about 900 water samples at different depths. In no case did a failure occur.

In another study samples from the same body of water were collected using preacidified Mercos samplers as well as Hydrobios Close-Open-Close (COC) samplers (modified version of the Hydrobios Transparent Plastic Nansen sampler). For the determination of mercury, surface samples were collected additionally using 500-ml Teflon bottles attached to an all-plastic sampling gear.

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The samples were ana lyzed for cadmium, copper , iron, manganese and nickel by flameless a tomic absorp t ion s p e c t r o p h o t o m e t r y , while mercury was ana lyzed by cold vapor AAS. The results are summar ized in Table I. It is readily apparen t tha t COC samples show significantly higher values than Mercos samples for manganese, nickel, and to a lesser ex ten t for iron and copper , but comparab le results for cadmium. The Mercos and "sampling gear" values for mercury show good agreement , while COC values are lower, p robab ly due to adsorp t ion on the sampler walls, at natural pH of the sea- water sample.

Owing to the good results ob ta ined and the advantages of elegant and convenien t handling, we now use Mercos in rout ine work for the deter- mina t ion o f ul t ra t race elements in coastal seawater.

ACKNOWLEDGEMENTS

The au thors thank H. Gaul, W. Gerwinski, D. KSrner and H. Zehle for helpful advice and the members o f our workshop for fine machine work.

REFERENCES

Bothner, M.H. and Robertson, D.E., 1975. Mercury contamination of seawater samples stored in polyethylene containers. Anal. Chem., 47: 592--595.

Fischer, H., 1968. The transparent plastic Nansen sampler. Tech. Rep. Hydrobios Apparatebau GmbH, KieI-Holtenau.

Fitzgerald, W.F. and Lyons, W.B., 1975. Mercury concentrations in open ocean waters: sampling procedures, Limnol. Oceanogr., 20: 468--471.

Freimann, P. and Schmidt, D., 1982. Determination of mercury in seawater by cold vapor atomic absorption spectrophotometry. Fresenius' Z. Anal. Chem., 313: 200--202.

Mart, L., 1979. Prevention of contamination and other accuracy risks in voltammetric trace metal analysis of natural waters. Fresenius' Z. Anal. Chem., 299: 97--102.

Mattinson, J.M., 1972. Preparation of hydrofluoric, hydrochloric, and nitric acids at ultra-low lead levels. Anal. Chem., 41: 2088--2089.

Patterson, C.C. and Settle, D.M., 1976. The reduction of orders of magnitude errors in lead analyses of biological materials and natural waters by evaluating and controlling the extent and sources of industrial lead contamination introduced during sample collection, handling, and analysis. In: P.D. LaFleur, (Editor), Accuracy in Trace Analy- sis: Sampling, Sample Handling, Analysis. NBS Spec. Publ. No. 422, pp. 321--351.

Wong, C.S., Cretney, W.J., Piuze, J., Christensen, P. and Berrang, P.G., 1977. Clean laboratory methods to achieve contaminant-free processing and determination of ultra-trace samples in marine environmental studies. In: W.H. Kirchhoff, (Editor), Methods and Standards for Environmental Measurement. NBS Spec. Publ. No. 464, pp. 249--258.