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An in situ pump sampler for trace materials in seawater
Marine Chemistry, 22 (1987) 353-361
353
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
AN IN SITU P U M P SAMPLER FOR TRACE MATERIALS IN SEAWATER*
BRUCE D. JOHNSON, PETER J. WANGERSKY and XIANLIANG ZHOU
Department of Oceanography, Dalhousie University, Halifax, N.S. B3H 4J1 (Canada) (Received January 29, 1987; revision accepted 21 April, 1987)
ABSTRACT Johnson, B.D., Wangersky, P.J. and Zhou, X., 1987. An in situ pump sampler for trace materials in seawater. Mar. Chem., 22: 353-361. A battery-powdered in situ pump sampler, capable of operation at full oceanic depths, has been designed, built and tested. The pump motor, sealed in a pressure-proof housing, is coupled magnetically to the pump head. Water is drawn through a filter then passed successively through an adsorption column and the pumphead and finally through a flowmeter. The unit as a whole is pivoted and vaned so that the intake is always pointed into the current. The selectivity of the sampler depends upon the choice of packing material used in the adsorption column or columns. Column materials specific for different classes of compounds have been tested in the laboratory and at sea. Preliminary results in the collection and measurement of Cu and Cd suggest that the pumping system is free from shipboard contamination. INTRODUCTION
Accurate measurement of trace substances in seawater is vital to our understanding of the geochemistry of the oceans. Such measurements are also essential for environmental monitoring, for physical oceanographic tracer studies and for certain aspects of biological modeling. Recent advances in our understanding of the processes governing the distribution and cycling of various trace substances in the oceans have been made possible largely by improvements in analytical techniques (Wangersky, 1986). However, for an ever-growing number of substances the more recent methods of analysis provide sensitivities far exceeding our ability to deliver contamination-free samples. Nowhere has improvement in analytical techniques spurred a concomitant effort to r e d u c e levels of c o n t a m i n a t i o n m o r e t h a n in the m e a s u r e m e n t of t r a c e m e t a l s in s e a w a t e r . In only ten y e a r s the a c c e p t e d c o n c e n t r a t i o n s of m a n y t r a c e m e t a l s h a v e f a l l e n b y f a c t o r s o f 10-100. T h e m e a s u r e s r e q u i r e d t o r e d u c e c o n t a m i n a t i o n h a v e been extreme, e x c e e d i n g the capabilities of all but the best *Presented at the IX International Symposium 'Chemistry of the Mediterranean' May 1986, Primo~ten, Yugoslavia.
0304-4203/87/$03.50
((~ 1987 Elsevier Science Publishers B.V.
354 funded of laboratories and the most careful and patient of investigators to implement. Such measures include the use of hydrowires encapsulated with polymers or made of Kevlar (Betzer and Pilson, 1975), and specially designed water samplers made from non-contaminating materials such as Teflon (Spencer, et al., 1982) or employing large volume:internal-surface-area ratios (Clark, et al., 1967). Remote sampling buoys have been employed for certain trace substances (Ehrhardt, 1978) and clean rooms or clean modules have been fitted to some research vessels. While all of these strategies have met with some success, they suffer from the limitations of inconvenience, high cost, lack of versatility and the need for large vessels with special winches or deck space large enough to hold bolt-down clean rooms. These measures require resources that few laboratories can commit, and thus exclude a growing proportion of the oceanographic community from such research. Rather than continue in this restrictive approach to the sampling of trace substances, it is now time, perhaps, to seek alternatives to conventional water sampling methods. One such alternative is offered by in situ pumping. With this method, the sample is drawn through columns packed with some form of adsorbent. Because the extraction and concentration steps occur in situ, contamination from sampling bottles and that occurring during sample transfer and shipboard extraction are eliminated. In addition, the pump sampler can be lowered to sampling depth with the column and flow lines filled with effectively ~pure' water and with the inlet plugged, thus eliminating contamination acquired during passage through the surface film or other potentially high concentration regions in transit to the sampling depth. When the pumping system is recovered, the adsorption column can quickly be detached, the ends capped, and the column placed in a freezer or refrigerator for storage. Using this approach, the concentrated sample is exposed to the potentially contaminating atmosphere of the ship for only a very short time. While in situ pumping provides a means for eliminating many major sources of contamination, another of its advantages can be seen where large and variable blanks or low concentrations dictate the processing of large samples; the volume sampled is limited only by the capacity of the power source and the efficiency and capacity of the adsorbent. A large and ever-growing list of adsorbents for concentrating a wide range of trace substances can be found in the chemical literature. Examples include XAD-2 (Ehrhardt, et al., 1980) and reverse-phase C18 for lipids (Saner, et al., 1979), Chromosorb-T for hydrocarbons (Josefson, et al., 1984), and immobilized 8-hydroxyquinoline for trace metals (Sturgeon, et al., 1981). With continued research in the area of specialized adsorbents, column packings which are specific for single classes of trace substances will ultimately emerge. One such example is the cation exchange resin charged with 2,4-dinitrophenylhydrazine, specific for aldehydes and ketones (Takami, et al., 1985). Many reports of pumping systems, both onboard and in situ, have appeared in the literature, but none has emerged as the system of choice for routine sampling. The in situ pumping systems which have been described are typically large and heavy and are powered either by specially prepared and pressurized
355 lead-acid storage batteries or by ship's power, using winches with slip rings and conductor cable. These samplers can neither be deployed from ships of opportunity nor, typically, can more than one pump be attached to the wire for the purpose of obtaining profiles. We have developed a pump sampler that provides the versatility required for pumping volumes of a few to hundreds of litres, combined with the capability of operation at full oceanic pressures. In addition, the sampler operates on rechargeable NiCad batteries, and is of a size and weight permitting easy deployment from ships of opportunity. THE PUMP SAMPLER The primary impediment to the development of in situ pumps has been the difficulty in coupling the pump and motor shafts. Several designs that have been described in the literature incorporate waterproof seals or oil-filled motors to provide protection against pressure. However, the former strategy is limited to use in relatively shallow waters while the latter requires the expenditure of large amounts of energy to overcome dissipation in the viscous oil. An alternative approach, chosen for our sampler, is magnetic coupling. This approach allows the motor and electronics to be sealed in a pressure-proof housing, requiring that only the flowmeter and pumphead be maintained at ambient pressure. Two versions of the pump sampler have been developed. One version (Fig. la) was specifically designed to sample trace substances for which the hydrowire or the construction materials of the pump may be a source of contamination. This version consists of the battery housing, 4 cm in diameter by 130 cm long; the pump housing, 10 cm in diameter by 25 cm long; a flowmeter; a trigger mechanism; and clamps for attaching the adsorption column and filter holder. Weighing ~ 11 kg in air, the sampler features a pivot mechanism which allows the battery housing to occupy three positions in the vertical plane. Two near vertical positions permit easy deployment and recovery, while a horizontal position places the inlet port at a maximum distance from the hydrowire. The sampler is lowered in a position such that the main axes of the pump and battery housing are oriented at 14° to the vertical, with the forward end of the sampler pointing upward (Fig. la). The inlet to the sampler extends beyond this forward end of the battery housing. When the sampling depth has been reached, a messenger dropped down the hydrowire releases the locking mechanism and allows the battery housing and attached pump to pivot into a horizontal position where the mechanism again locks (Fig. lb). In this horizontal position the pump is activated by a magnetic switch. Fins on the battery housing and specially designed wire clamps allow the system to rotate about the wire and align with the direction of water advection. The inlet port then faces upstream. Termination of pumping occurs either automatically, when a preset volume of water has passed through the column, or manually, when a second messenger is dropped down the hydrowire. In either case, the second messenger
356
Inlet
Pump q
F
25cm
\\ ~Battery
I
housing
Fins
I
j
(Z)
"
~
To
auxiliary
Fig. 1. Pump sampler (a) in position for lowering, (b) in operating position.
again releases the locking mechanism, allowing the battery housing to pivot to a position 14° to the vertical, but with the forward end pointing down. The mechanism then locks, and the system is ready for recovery.
357
Impact plate I
Handle
Fig. 2. Pump sampler, simplified version.
A simpler version of the pump sampler has been developed to collect those trace substances for which the hydrowire and the construction materials of the sampler do not represent serious sources of contamination. This version of the sampler (Fig. 2) consists of a waterproof housing 10 cm in diameter by 34 cm long, containing the electronics, batteries, pump motor, and drive magnet. Attached to the outside of this housing are the pumphead, flowmeter and trigger mechanism. In addition, there are provisions for attaching a filter holder and an adsorption column. The sampler weighs < 10 kg in air, or about as much as a full 51 Niskin bottle. This general version of the sampler is also activated by messenger and like the first version, pumping is terminated either when a preset volume of water has passed through the adsorption column or when a second messenger is dropped. When the sampler is recovered, pressing the activating trigger displays, through a window in the bottom plate, the actual volume of water
358 pumped. Pressing the trigger again resets the electronics and after the absorption column has been changed the sampler is ready for redeployment. Construction materials of the pump samplers include polymers such as Delrin and polyethylene, with housings made typically of aluminum and stainless steel. For resistance to full ocean pressures the housings are made of titanium. The samplers are powered by rechargeable NiCad batteries, chosen because of the reduced long-term cost of operation and the reduced storage space needed on long cruises. With the 6V 7A-h batteries now in use, the samplers are capable of sustained operation for 7 1 4 h, depending upon the type of pumphead chosen and the pressure drop of the combined column and filter. Three different pumpheads have been used with the samplers to provide a range of flow rates and pressure capabilities. Of these pumpheads, the one with the highest flow rate permits a single deployment total flow capacity of ~ 5001. This capacity can be increased by the use of auxiliary battery packs or batteries of higher capacity such as alkalines. A major problem in developing the pump sampler was that of devising a means of measuring the amount of water pumped. Commercially available flow meters are expensive, limited in range, and are generally not capable of submersion in seawater at high pressures. Also, the flowmeter information must be transmitted to the electronic module in the pressure housing, a function normally requiring an electrical connection. Therefore, we developed our own positive displacement mechanical flowmeter capable of measuring a wide range of flow rates and which passes information for processing through the pressure housing to the electronics module by means of magnetic pulses. In addition to counting pulses from the flowmeter and comparing this total to the preset value corresponding to the desired sample volume, the sampler electronics perform other functions. The electronics protect the batteries by turning the pump off when battery voltage falls below a safe level and they also turn the motor off if the pump and motor shafts decouple. In this latter case, the motor is reactivated when coupling has been re-established. Further details of construction and availability can be learned from Manna Marine Enterprises Ltd., P.O. Box 790, Station ~M', Halifax, N.S., B3J 2V2, Canada.
RESULTS AND DISCUSSION The pump samplers have been used on numerous one day sampling trips in coastal areas of Nova Scotia and on longer cruises aboard the C.S.S. ~Baffin" and C.S.S. "Dawson" at stations across the Scotian Shelf and into the Gulf Stream. On these cruises the pump samplers, with appropriate columns, have been used effectively for sampling lipids, hydrocarbons and a number of trace metals. Examples of typical profiles for Cd and Cu, collected on an immobilized 8-hydroxyquinoline column are shown in Figs. 3, 4, and 5. These profiles were determined from samples collected from Gulf Stream Station 3 on cruises
359
AICopper Cadrniu(ng/Kg) m(ng/Kg)l
3C ,
I
Silicate
""
-
t i L
%
o zc
',
/
l
F
"
""
•
(,u. M)
"'t, .I
y
iy O - -
i
~
200
~ b
I
L
I
400 600 DEPTH(m)
i
-
h
800
.~L=
IOOO
Fig. 3. Cu, Cd and silicate concentrations from Gulf Stream Station 3, May 1986.
-
40
3C /
(~ 20
L &Cc~dmiurn ( ng/Kg)]
/ .mm
..........
• . . . . . . . . . . . . . . . . . .
I0
200
400 600 DEPTH(m)
8OO
IOOO
Fig. 4. Cd and silicate concentrations from Gulf Stream Station 3, August 1986.
I00i !60 i BO
o~ v
y
L
QTotoICopper I @OrgonK:Copper ~ @InorgonicCopper
~
L 200
'
~ 400
, --L__ 600 DEPTH (m)
,
B~)O
'
IO00
Fig. 5. Total, organic and inorganic Cu concentrations from Gulf Stream Station 3, August 1986.
360 a b o a r d the C.S.S. ~ D a w s o n " d u r i n g the periods of M a y 1-7 and A u g u s t 1-7, 1986. Profiles of S i Q , also s h o w n in Figs. 3 and 4, suggest t h a t the Cd d i s t r i b u t i o n s are of the n u t r i e n t type. Overall, the v a l u e s for Cd are typical of w h a t are now the a c c e p t e d values for samples t a k e n in n e a r - s h o r e waters. On the A u g u s t cruise, a Sep-Pak C18 c o l u m n was placed in series a h e a d of the 8-hydroxyquinoline column, to collect h y d r o p h o b i c o r g a n o m e t a l l i c compounds. All of the Cd was found on the 8 - h y d r o x y q u i n o l i n e column; a n y C d - o r g a n i c c o m p o u n d s p r e s e n t were below the d e t e c t i o n limit of o u r m e t h o d at all depths sampled. H y d r o p h o b i c organo-Cu compounds, on the o t h e r hand, made up approximately h a l f of the c o p p e r p r e s e n t in samples from this cruise (Fig. 5). The high near-surface t o t a l Cu values r e s u l t from high v a l u e s in both o r g a n i c and i n o r g a n i c Cu. The r e l a t i v e l y close c o r r e s p o n d e n c e suggests an equilibrium between the two kinds of Cu. The d i s t r i b u t i o n s of Cd and Cu in this and o t h e r stations sampled on these cruises will be discussed, along with n u t r i e n t and h y d r o g r a p h i c data, in a l a t e r paper. CONCLUSIONS (i) The in situ pump sampler, as described in this paper, is a useful a d j u n c t and in some cases a n e c e s s a r y r e p l a c e m e n t for the t r a d i t i o n a l w a t e r bottle sampler for t r a c e materials. (ii) Such samplers can p r o d u c e t r a c e metal values c o m p a r a b l e to those o b t a i n e d with clean room techniques. (iii) The utility of such samplers will depend upon the specificity and efficiency of the available adsorbents. ACKNOWLEDGMENTS The in situ pump sampler was developed u n d e r a c o n t r a c t with the M a r i n e A n a l y t i c a l C h e m i s t r y S t a n d a r d s P r o g r a m of the A t l a n t i c R e s e a r c h L a b o r a t o r y , N a t i o n a l R e s e a r c h Council of Canada. The field work was funded by g r a n t s to B.D.J. and P.J.W. from the N a t u r a l Sciences and E n g i n e e r i n g R e s e a r c h Council of Canada. Fellowships from the Killam F o u n d a t i o n and the People's Republic of China helped to s u p p o r t X.Z. REFERENCES Betzer, P.R. and Pilson, M.E.Q., 1975.The effect of corroded hydrographic wire on particulate iron concentrations in seawater. Deep-Sea Res., 22: 117-120. Clark, R.C., Jr., Blumer, M. and Raymond, S.O., 1967. A large water sampler, rupture-disc triggered, for studies of dissolved organic compounds. Deep-Sea Res., 14: 125-128. Ehrhardt, M., 1978.An automatic sampling bouy for the accumulation of dissolved and particulate organic material from seawater. Deep-Sea Res., 25: 11~126. Ehrhardt, M., Osterroht, C. and Petrick, G., 1980. Fatty-acid methyl esters dissolved in seawater and associated with suspended particulate matter. Mar. Chem., 10: 67-76. Josefson, C.M., Johnston, J.B. and Trubey, R., 1984.Adsorption of organic compounds from water with porous poly(tetrafluoroethylene). Anal. Chem., 56:764 768.
361 Saner, W.A., Jadamec, J.R., Sager, R.W. and Killeen, T.J., 1979. Trace enrichment with handpacked CO:PELL ODS guard columns and Sep-Pak C18 cartridges. Anal. Chem., 51: 2180-2188. Spencer, M.J., Betzer, P.R. and Piotrowicz, S.R., 1982. Concentrations of cadmium, copper, lead and zinc in surface waters of the northwest Atlantic Ocean - - a comparison of Go-Flo and Teflon water samplers. Mar. Chem., 11: 403~410. Sturgeon, R.E., Berman, S.S., Willie, S.N. and DeSaulniers, J.A.H., 1981. Preconcentration of trace elements from seawater with silica-immobilized 8-hydroxyquinoline. Anal. Chem., 53:2337 2340. Takami, K., Kuwata, K., Sugamae, R. and Nakamoto, M., 1985. Trace determinations of aldehydes in water by high-performance liquid chromatography. Anal. Chem., 57:243 245. Wangersky, P.J., 1986. Biological control of trace metal residence time and speciation: a review and synthesis. Mar. Chem., 18: 269-297.
353
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
AN IN SITU P U M P SAMPLER FOR TRACE MATERIALS IN SEAWATER*
BRUCE D. JOHNSON, PETER J. WANGERSKY and XIANLIANG ZHOU
Department of Oceanography, Dalhousie University, Halifax, N.S. B3H 4J1 (Canada) (Received January 29, 1987; revision accepted 21 April, 1987)
ABSTRACT Johnson, B.D., Wangersky, P.J. and Zhou, X., 1987. An in situ pump sampler for trace materials in seawater. Mar. Chem., 22: 353-361. A battery-powdered in situ pump sampler, capable of operation at full oceanic depths, has been designed, built and tested. The pump motor, sealed in a pressure-proof housing, is coupled magnetically to the pump head. Water is drawn through a filter then passed successively through an adsorption column and the pumphead and finally through a flowmeter. The unit as a whole is pivoted and vaned so that the intake is always pointed into the current. The selectivity of the sampler depends upon the choice of packing material used in the adsorption column or columns. Column materials specific for different classes of compounds have been tested in the laboratory and at sea. Preliminary results in the collection and measurement of Cu and Cd suggest that the pumping system is free from shipboard contamination. INTRODUCTION
Accurate measurement of trace substances in seawater is vital to our understanding of the geochemistry of the oceans. Such measurements are also essential for environmental monitoring, for physical oceanographic tracer studies and for certain aspects of biological modeling. Recent advances in our understanding of the processes governing the distribution and cycling of various trace substances in the oceans have been made possible largely by improvements in analytical techniques (Wangersky, 1986). However, for an ever-growing number of substances the more recent methods of analysis provide sensitivities far exceeding our ability to deliver contamination-free samples. Nowhere has improvement in analytical techniques spurred a concomitant effort to r e d u c e levels of c o n t a m i n a t i o n m o r e t h a n in the m e a s u r e m e n t of t r a c e m e t a l s in s e a w a t e r . In only ten y e a r s the a c c e p t e d c o n c e n t r a t i o n s of m a n y t r a c e m e t a l s h a v e f a l l e n b y f a c t o r s o f 10-100. T h e m e a s u r e s r e q u i r e d t o r e d u c e c o n t a m i n a t i o n h a v e been extreme, e x c e e d i n g the capabilities of all but the best *Presented at the IX International Symposium 'Chemistry of the Mediterranean' May 1986, Primo~ten, Yugoslavia.
0304-4203/87/$03.50
((~ 1987 Elsevier Science Publishers B.V.
354 funded of laboratories and the most careful and patient of investigators to implement. Such measures include the use of hydrowires encapsulated with polymers or made of Kevlar (Betzer and Pilson, 1975), and specially designed water samplers made from non-contaminating materials such as Teflon (Spencer, et al., 1982) or employing large volume:internal-surface-area ratios (Clark, et al., 1967). Remote sampling buoys have been employed for certain trace substances (Ehrhardt, 1978) and clean rooms or clean modules have been fitted to some research vessels. While all of these strategies have met with some success, they suffer from the limitations of inconvenience, high cost, lack of versatility and the need for large vessels with special winches or deck space large enough to hold bolt-down clean rooms. These measures require resources that few laboratories can commit, and thus exclude a growing proportion of the oceanographic community from such research. Rather than continue in this restrictive approach to the sampling of trace substances, it is now time, perhaps, to seek alternatives to conventional water sampling methods. One such alternative is offered by in situ pumping. With this method, the sample is drawn through columns packed with some form of adsorbent. Because the extraction and concentration steps occur in situ, contamination from sampling bottles and that occurring during sample transfer and shipboard extraction are eliminated. In addition, the pump sampler can be lowered to sampling depth with the column and flow lines filled with effectively ~pure' water and with the inlet plugged, thus eliminating contamination acquired during passage through the surface film or other potentially high concentration regions in transit to the sampling depth. When the pumping system is recovered, the adsorption column can quickly be detached, the ends capped, and the column placed in a freezer or refrigerator for storage. Using this approach, the concentrated sample is exposed to the potentially contaminating atmosphere of the ship for only a very short time. While in situ pumping provides a means for eliminating many major sources of contamination, another of its advantages can be seen where large and variable blanks or low concentrations dictate the processing of large samples; the volume sampled is limited only by the capacity of the power source and the efficiency and capacity of the adsorbent. A large and ever-growing list of adsorbents for concentrating a wide range of trace substances can be found in the chemical literature. Examples include XAD-2 (Ehrhardt, et al., 1980) and reverse-phase C18 for lipids (Saner, et al., 1979), Chromosorb-T for hydrocarbons (Josefson, et al., 1984), and immobilized 8-hydroxyquinoline for trace metals (Sturgeon, et al., 1981). With continued research in the area of specialized adsorbents, column packings which are specific for single classes of trace substances will ultimately emerge. One such example is the cation exchange resin charged with 2,4-dinitrophenylhydrazine, specific for aldehydes and ketones (Takami, et al., 1985). Many reports of pumping systems, both onboard and in situ, have appeared in the literature, but none has emerged as the system of choice for routine sampling. The in situ pumping systems which have been described are typically large and heavy and are powered either by specially prepared and pressurized
355 lead-acid storage batteries or by ship's power, using winches with slip rings and conductor cable. These samplers can neither be deployed from ships of opportunity nor, typically, can more than one pump be attached to the wire for the purpose of obtaining profiles. We have developed a pump sampler that provides the versatility required for pumping volumes of a few to hundreds of litres, combined with the capability of operation at full oceanic pressures. In addition, the sampler operates on rechargeable NiCad batteries, and is of a size and weight permitting easy deployment from ships of opportunity. THE PUMP SAMPLER The primary impediment to the development of in situ pumps has been the difficulty in coupling the pump and motor shafts. Several designs that have been described in the literature incorporate waterproof seals or oil-filled motors to provide protection against pressure. However, the former strategy is limited to use in relatively shallow waters while the latter requires the expenditure of large amounts of energy to overcome dissipation in the viscous oil. An alternative approach, chosen for our sampler, is magnetic coupling. This approach allows the motor and electronics to be sealed in a pressure-proof housing, requiring that only the flowmeter and pumphead be maintained at ambient pressure. Two versions of the pump sampler have been developed. One version (Fig. la) was specifically designed to sample trace substances for which the hydrowire or the construction materials of the pump may be a source of contamination. This version consists of the battery housing, 4 cm in diameter by 130 cm long; the pump housing, 10 cm in diameter by 25 cm long; a flowmeter; a trigger mechanism; and clamps for attaching the adsorption column and filter holder. Weighing ~ 11 kg in air, the sampler features a pivot mechanism which allows the battery housing to occupy three positions in the vertical plane. Two near vertical positions permit easy deployment and recovery, while a horizontal position places the inlet port at a maximum distance from the hydrowire. The sampler is lowered in a position such that the main axes of the pump and battery housing are oriented at 14° to the vertical, with the forward end of the sampler pointing upward (Fig. la). The inlet to the sampler extends beyond this forward end of the battery housing. When the sampling depth has been reached, a messenger dropped down the hydrowire releases the locking mechanism and allows the battery housing and attached pump to pivot into a horizontal position where the mechanism again locks (Fig. lb). In this horizontal position the pump is activated by a magnetic switch. Fins on the battery housing and specially designed wire clamps allow the system to rotate about the wire and align with the direction of water advection. The inlet port then faces upstream. Termination of pumping occurs either automatically, when a preset volume of water has passed through the column, or manually, when a second messenger is dropped down the hydrowire. In either case, the second messenger
356
Inlet
Pump q
F
25cm
\\ ~Battery
I
housing
Fins
I
j
(Z)
"
~
To
auxiliary
Fig. 1. Pump sampler (a) in position for lowering, (b) in operating position.
again releases the locking mechanism, allowing the battery housing to pivot to a position 14° to the vertical, but with the forward end pointing down. The mechanism then locks, and the system is ready for recovery.
357
Impact plate I
Handle
Fig. 2. Pump sampler, simplified version.
A simpler version of the pump sampler has been developed to collect those trace substances for which the hydrowire and the construction materials of the sampler do not represent serious sources of contamination. This version of the sampler (Fig. 2) consists of a waterproof housing 10 cm in diameter by 34 cm long, containing the electronics, batteries, pump motor, and drive magnet. Attached to the outside of this housing are the pumphead, flowmeter and trigger mechanism. In addition, there are provisions for attaching a filter holder and an adsorption column. The sampler weighs < 10 kg in air, or about as much as a full 51 Niskin bottle. This general version of the sampler is also activated by messenger and like the first version, pumping is terminated either when a preset volume of water has passed through the adsorption column or when a second messenger is dropped. When the sampler is recovered, pressing the activating trigger displays, through a window in the bottom plate, the actual volume of water
358 pumped. Pressing the trigger again resets the electronics and after the absorption column has been changed the sampler is ready for redeployment. Construction materials of the pump samplers include polymers such as Delrin and polyethylene, with housings made typically of aluminum and stainless steel. For resistance to full ocean pressures the housings are made of titanium. The samplers are powered by rechargeable NiCad batteries, chosen because of the reduced long-term cost of operation and the reduced storage space needed on long cruises. With the 6V 7A-h batteries now in use, the samplers are capable of sustained operation for 7 1 4 h, depending upon the type of pumphead chosen and the pressure drop of the combined column and filter. Three different pumpheads have been used with the samplers to provide a range of flow rates and pressure capabilities. Of these pumpheads, the one with the highest flow rate permits a single deployment total flow capacity of ~ 5001. This capacity can be increased by the use of auxiliary battery packs or batteries of higher capacity such as alkalines. A major problem in developing the pump sampler was that of devising a means of measuring the amount of water pumped. Commercially available flow meters are expensive, limited in range, and are generally not capable of submersion in seawater at high pressures. Also, the flowmeter information must be transmitted to the electronic module in the pressure housing, a function normally requiring an electrical connection. Therefore, we developed our own positive displacement mechanical flowmeter capable of measuring a wide range of flow rates and which passes information for processing through the pressure housing to the electronics module by means of magnetic pulses. In addition to counting pulses from the flowmeter and comparing this total to the preset value corresponding to the desired sample volume, the sampler electronics perform other functions. The electronics protect the batteries by turning the pump off when battery voltage falls below a safe level and they also turn the motor off if the pump and motor shafts decouple. In this latter case, the motor is reactivated when coupling has been re-established. Further details of construction and availability can be learned from Manna Marine Enterprises Ltd., P.O. Box 790, Station ~M', Halifax, N.S., B3J 2V2, Canada.
RESULTS AND DISCUSSION The pump samplers have been used on numerous one day sampling trips in coastal areas of Nova Scotia and on longer cruises aboard the C.S.S. ~Baffin" and C.S.S. "Dawson" at stations across the Scotian Shelf and into the Gulf Stream. On these cruises the pump samplers, with appropriate columns, have been used effectively for sampling lipids, hydrocarbons and a number of trace metals. Examples of typical profiles for Cd and Cu, collected on an immobilized 8-hydroxyquinoline column are shown in Figs. 3, 4, and 5. These profiles were determined from samples collected from Gulf Stream Station 3 on cruises
359
AICopper Cadrniu(ng/Kg) m(ng/Kg)l
3C ,
I
Silicate
""
-
t i L
%
o zc
',
/
l
F
"
""
•
(,u. M)
"'t, .I
y
iy O - -
i
~
200
~ b
I
L
I
400 600 DEPTH(m)
i
-
h
800
.~L=
IOOO
Fig. 3. Cu, Cd and silicate concentrations from Gulf Stream Station 3, May 1986.
-
40
3C /
(~ 20
L &Cc~dmiurn ( ng/Kg)]
/ .mm
..........
• . . . . . . . . . . . . . . . . . .
I0
200
400 600 DEPTH(m)
8OO
IOOO
Fig. 4. Cd and silicate concentrations from Gulf Stream Station 3, August 1986.
I00i !60 i BO
o~ v
y
L
QTotoICopper I @OrgonK:Copper ~ @InorgonicCopper
~
L 200
'
~ 400
, --L__ 600 DEPTH (m)
,
B~)O
'
IO00
Fig. 5. Total, organic and inorganic Cu concentrations from Gulf Stream Station 3, August 1986.
360 a b o a r d the C.S.S. ~ D a w s o n " d u r i n g the periods of M a y 1-7 and A u g u s t 1-7, 1986. Profiles of S i Q , also s h o w n in Figs. 3 and 4, suggest t h a t the Cd d i s t r i b u t i o n s are of the n u t r i e n t type. Overall, the v a l u e s for Cd are typical of w h a t are now the a c c e p t e d values for samples t a k e n in n e a r - s h o r e waters. On the A u g u s t cruise, a Sep-Pak C18 c o l u m n was placed in series a h e a d of the 8-hydroxyquinoline column, to collect h y d r o p h o b i c o r g a n o m e t a l l i c compounds. All of the Cd was found on the 8 - h y d r o x y q u i n o l i n e column; a n y C d - o r g a n i c c o m p o u n d s p r e s e n t were below the d e t e c t i o n limit of o u r m e t h o d at all depths sampled. H y d r o p h o b i c organo-Cu compounds, on the o t h e r hand, made up approximately h a l f of the c o p p e r p r e s e n t in samples from this cruise (Fig. 5). The high near-surface t o t a l Cu values r e s u l t from high v a l u e s in both o r g a n i c and i n o r g a n i c Cu. The r e l a t i v e l y close c o r r e s p o n d e n c e suggests an equilibrium between the two kinds of Cu. The d i s t r i b u t i o n s of Cd and Cu in this and o t h e r stations sampled on these cruises will be discussed, along with n u t r i e n t and h y d r o g r a p h i c data, in a l a t e r paper. CONCLUSIONS (i) The in situ pump sampler, as described in this paper, is a useful a d j u n c t and in some cases a n e c e s s a r y r e p l a c e m e n t for the t r a d i t i o n a l w a t e r bottle sampler for t r a c e materials. (ii) Such samplers can p r o d u c e t r a c e metal values c o m p a r a b l e to those o b t a i n e d with clean room techniques. (iii) The utility of such samplers will depend upon the specificity and efficiency of the available adsorbents. ACKNOWLEDGMENTS The in situ pump sampler was developed u n d e r a c o n t r a c t with the M a r i n e A n a l y t i c a l C h e m i s t r y S t a n d a r d s P r o g r a m of the A t l a n t i c R e s e a r c h L a b o r a t o r y , N a t i o n a l R e s e a r c h Council of Canada. The field work was funded by g r a n t s to B.D.J. and P.J.W. from the N a t u r a l Sciences and E n g i n e e r i n g R e s e a r c h Council of Canada. Fellowships from the Killam F o u n d a t i o n and the People's Republic of China helped to s u p p o r t X.Z. REFERENCES Betzer, P.R. and Pilson, M.E.Q., 1975.The effect of corroded hydrographic wire on particulate iron concentrations in seawater. Deep-Sea Res., 22: 117-120. Clark, R.C., Jr., Blumer, M. and Raymond, S.O., 1967. A large water sampler, rupture-disc triggered, for studies of dissolved organic compounds. Deep-Sea Res., 14: 125-128. Ehrhardt, M., 1978.An automatic sampling bouy for the accumulation of dissolved and particulate organic material from seawater. Deep-Sea Res., 25: 11~126. Ehrhardt, M., Osterroht, C. and Petrick, G., 1980. Fatty-acid methyl esters dissolved in seawater and associated with suspended particulate matter. Mar. Chem., 10: 67-76. Josefson, C.M., Johnston, J.B. and Trubey, R., 1984.Adsorption of organic compounds from water with porous poly(tetrafluoroethylene). Anal. Chem., 56:764 768.
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