Reference materials for marine trace analysis

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quantitative analysis of mixtures13. In many cases, however, such as the analysis of mixtures of isomers (Fig. 2), the value of techniques of selected fragmentation monitoring will lie in their ability to enhance the specificity of analyses based on tandem chromatography-mass spectrometry. Further refinements of this general approach in quantitative mass spectrometry may be expected, based on the use of multiple analyser instruments, where unit to high resolution of both parent and daughter ion beams is simultaneously achieved.

Conclusions Many developments in quantitative mass spectrometry have contributed to the utility of the technique. Advances in computerized data handling, for example, have encouraged the development of automated procedures and may enhance analytical precision. The more widespread availability of stable isotopically-labelled internal standards also contributes to improved precision and lessens the risk of systematic error. This review has concentrated on means of achieving enhanced specificity and sensitivity, features of quantitative mass spectrometry which particularly recommend its application to demanding problems in trace analysis. Such developments, of course, should be viewed as components of overall analytical strategy, and elegant techniques of instrumental analysis should not be used to disguise the inadequacies of poor procedures of sample preparation or sample introduction. Where due attention is paid to all aspects of analysis, however, recent developments in quantitative mass spectrometry open new areas of application and substantially improve the reliability of analytical data.

Reference

materials

References 1 Henneberg, D. (1959) Z. Anal. C&m. 170,369 2 Sweeley, C. C., Elliot, W. A., Fries, I. and Ryhage, R. (1966) Anal. Chem. 38, 1549 3 Dougherty, R. C. (1981) Anal. Gem. 53,625A 4 Markey, S. P., Lewy, A. J. and Colbum, R. W. in A. P. De Leenheer, Roncucci, R. R. and Van Peteghem, C. (eds) (1978) Quantitative Mass Spectrometry in Life Sciences II, p. 17, Elsevier, Amsterdam 5 Miwa, B. J., Garland, W. A. and Blumenthal, P. (1981) Anal. them. 53, 793 6 Barber, M., Bordoli, R. S., Sedgewick, R. D. and Tyler, A. N. (198l)J. Chem. Sot., Chem. Commun. 325 7 Millington, D. S. (1975) J. Steroid Biochem. 6, 239 8 Hummel, R. A. and Shadoff, L. A. (1980) Anal. C&n. 52, 191 9 Gaskell, S. J. and Millington, D. S. (1978) Biomed. Mass Spectrom. 5,557 10 Gaskell, S. J., Finney, R. W. and Harper, M. E. (1979) Biomed. Mass Spcctrom. 6, 113 11 Gaskell, S. J. and Millington, D. S., in De Leenheer, A. P., Roncucci, R. R. and Van Peteghem, C. (eds) ( 1978) Quantitative Mass Spcctrometry in Life Sciznces II, p. 135, Elsevier, Amsterdam 12 Beynon, J. H., Cooks, R. G., Amy, J. W., Baitinger, W. E. and Ridley, T. Y. (1973) Anal. Chem. 45, 1023A 13 Kondrat, R. W. and Cooks, R. G. (1978) Anal. Chum. 50,81A Simon Gaskell obtained his undergraduate andgraduate degrees jiom tke University of Bristol, U.K. Following a post-doctoral fclowship at t/u University of Glasgow, he took up his present position in 1977 as head of the Mass Spectrometry Unit at the TenovusIn&u& for Cancer Research, Welsh National School of Medicine, Car&z CF4 4Xx, U.K.

for marine

trace analvsis _

_____~_

l

___

As we intensify our use of marine resourc&, accurate analysis of marine materials becomes kweaslrigJy important and reference materials are reqtiiied.

Roger Guevremont and W. D. Jamieson Halifax, Nova Scotia, Canada The establishment and implementation of regulations designed to control pollution ultimately requires accurate analytical data. Questions such as ‘how much of a certain toxic substance can safely be added to the marine environment?‘, must be answered in order to fix realistic safe limits for the disposal of toxic wastes. Are accurate chemical analytical methods available to measure the concentrations of such substances? Will 0 165.9936/82/0000-0/$02.75

available methods be used cqgsistently and conscientiously to ensure that Unsafe materiils are not unwittingly (or deliberately) dumped int6 the marine environment? To ensure these questions are adequately answered and as part of its role in fulfilling the International Convention on the Prevention of Marine Pollution by Dumping Wastes and Other Matter, the Canadian government established an Ocean Dumping Control Act and Regional Ocean Dumping Advisory Committee’**J. The regulations require that debris to be dumped at sea, most commonly the dredge spoils @ 1962 Elscvicr Scientific Publishing Company

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from a harbour, be analysed for certain toxic substances before permission to dump is granted. How can an analytical laboratory provide high quality data on these marine sediments? One way is to carry out the analysis of a marine sediment of known composition along with the samples. If the results for the standard material agree with its expected composition, accurate analysis of the unknown samples is probable. The Marine Analytical Chemistry Standards Program was established by the National Research Council of Canada to meet the present and future needs for marine standards. It is the goal of the program to supply reference materials or analytical standards which will represent marine samples for which there are, as yet, no standards. Current projects include the preparation of standards of marine sediments with known compositions of trace metals and marine sediments containing known levels of polychlorinated biphenyls. Neither is available at the time of writing, but factors relevant to the preparation of these materials will be outlined. Table I summarizes the steps in their preparation which have occurred since 1978.

Reference materials A reference material is a substance which has been characterized to the extent required to make it useful for establishing the accuracy of analytical data. Because the problems encountered in an analysis often result from some characteristic of the bulk composition of the sample - its matrix - a reference material with a matrix closely resembling that of the sample is needed to obtain a true assessment of accuracy. All reference materials are different as are the words used to describe them, thus the user must be aware of the limitations. The U.S. National Bureau of Standards clearly defines the terms it uses to describe materials*. Certification of a reference material for the composition of a particular component in a given matrix implies a certain effort and approach in defining the material. A limited number of compilations of types and sources of reference materialss, and catalogs*lsJ are available. Sydney Abbey’s comments (Ref. 7, pages l-4) concerning the reliability of data on

standard silicate rocks and minerals relevant and informative.

are particularly

What is a marine sediment? Many processes lead to the accumulation of material on the ocean floor. Near coasts the most notable include settling of organic and mineral debris from rivers. These may include particles of eroded rock or clay, and particles arising from the precipitation of river water components which are insoluble in sea water. a marine sediment is not By definition homogeneous. It is stratified by seasonal processes, partly mixed by hydraulic and biological activity and changes with depth as a result of the availability of oxygen. The main problems in the preparation of the sediment are therefore concerned with sampling, homogenization and preservation.

Sampling Since a reference material is not collected to define properties of the site, some contamination can be tolerated. For example, the level of cadmium in the final reference material will not necessarily be identical to that of the location from which it was collected. However, cadmium contamination is a minor problem when compared to possible effects such as the changes

TABLE I. Preparation of marine sediment reference materials 1978

1979

1980

1981

Define needs

Collection ofbulk sample

Trace metals Available for distribution

Feasibility study

Freeze drying

Trace metals Sieving, homogenizing Bottling (30 g) Sterilization (y-radiation) Homogeneity tests Analysis by independent methods PCB’s Pilot preparations Preliminary analyses Sieving, homogenizing Canning (250 g) Homogeneity tests

PCB’s Analysis by different laboratories

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in the chemistry of sediment components caused by factors such as oxygenation, fluctuating temperatures and microbiological activity. It is nearly impossible to collect hundreds of kilos of soggy wet sediment and preserve it from these changes. A typical practical sampling will include (a) several grabs of mud from the bottom with a large steel sampler; (b) transfer of these into 200 1 plastic barrels; (c) a delay of several hours during settling time and removal of the excess sea water; and (d) refrigeration of the barrels as soon as possible. The total mass of material involved may be one or two tons.

Preservation Since the wet sediment cannot be stored at room temperature, some procedure is needed to stabilize the material. Freezing would be an excellent way to stabilize the material but is difficult to maintain while shipping (at least in Canada) and virtually useless if the analyst wants small portions of his material at The freeze-thaw cycles involved regular intervals. would certainly induce changes in the sediment. In fact, the sediment is best preserved by drying and distributing it as a fine powder in sealed glass bottles. The sea water and its heavy load of salts should not be washed out. Drying in open air would allow undue exposure to atmospheric oxygen (and exposure of people to sediment stench). Heating in an oven is likewise unsuitable. The rather energy-intensive method of freeze drying is the most satisfactory alternative, and is the only method the Marine Analytical Chemistry Standards Program uses to dry marine sediments.

Homogenization and bottling It is essential that each bottle of sediment resembles every other. Certain particulate matter deposited on the ocean floor is large in size (e.g. the ‘Titanic’) and must be sieved out. This will alter the overall character of the sediment (e.g. the average iron content) but this is probably preferable to the grinding of the sediment, with its inherent problems of crushed particles and the loss of fine material as dust. A gentle sieving to remove large particles is practical. After drying a ton of wet sediment and removing large particulates, perhaps 75 kg of material will remain. This must be mixed and blended, then bottled or canned. These procedures give rise to many potential problems, including those associated with the segregation and separation of particles based on their differences in shape and density, electrostatic and magnetic force. It is theoretically possible that even after thorough mixing in a cement mixer the sediments coming to rest near the bottom are rich in some very dense mineral. Another class of problem exists. It is possible that a large quantity of a particular analyte, for example a very insoluble pollutant, may have been dumped in the sea at some location and come to rest at extremely high concentrations on a small mass of sediment. This

material could subsequently be dispersed by storms and currents, but nevertheless, each polluted particle would contain massive levels of this analyte. Should a potential reference material be collected and prepared, the analysis of each sub-sample could give quite different results depending upon whether the sub-sample contained zero, one, or two of these polluted particles. Such problems can and will arise in the analysis of pollutants present at low concentrations in sediment.

Analysis The analytical work must answer two major questions. Is the material homogeneous from bottle to bottle? What are the true levels of analytes in the samples? In neither case is an unequivocal answer possible. The result is a qualified statement, which is, in the case of homogeneity, based on statistical considerations, and in the case of analytical data, based on procedure. The role of analysis is to establish the true composition of the sample, be it for trace metals or trace organic pollutants. This will usually involve a comparison of analyses carried out using several different methods. In principle, if agreement is achieved this is good evidence that the result is near the truth. One of the major problems facing those wishing to control pollution of the environment is establishment of allowable or safe levels of pollutants. What is toxic? This leads to the question of the availability of the toxic component to living systems; but how can bioavailability be defined in terms of a chemical analysis? Present regulation of pollution generally deals with total concentrations of pollutants, simply because there are no well-defined answers to questions of toxicity and bio-availability. Modern chemical industrial processes often produce complex mixtures of products and byproducts. For example, polychlorinated biphenyls (PCB’s), which were once used widely as coolants within electrical

. . . ‘a referencematerial with a matrix closc(yresemblingthat of the sample is needed to obtain a tme assessment of accuracy.’

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transformers, are a mixture of up to 200 compounds, differing from one another only slightly in chemical structure. How does one define the ‘amount’ of PCB’s when it is difficult to measure the concentration of any one of the numerous components? Moreover, how can the toxicity of a given mixture be evaluated if each of those components differs in its toxic characteristics? Marine sediments are now being prepared which contain known levels of PCB’s. One of these will be a marine sediment containing a known addition of standard ‘Aroclor 1254’ (Monsanto). This will have an accurately determined load ofPCB’s. Feasibility studies have shown that this can be done successfully on a small scale. Clearly, certain qualities peculiar to a natural marine mud with equivalent PCB content will be sacrificed. Other sediments will be taken from the sea floor, and analysed for their PCB content based on equivalent amounts of the commercial mixture ‘Aroclor 1254’. TABLE II. Concentrations

Analyte

DDTa PCB’sa Cyclodienesa (endrin, dieldrin) PAH’s, totalh Hydrocarbons,” total

of some typical pollutants in marine sediments

Reported Analyte Concentrations Distance from Source Moderate Very Near Remote (>lOO km) > 1 mg/kg > 10 mg/kg

‘1 ug/kg > 10 pg/kg

100 ug/kg 100 pg./kg

<5 pg/kg 18 ug/kg

200 pg/kg

120 mglkg

1.3 mg/kg

I5 mg/kg

2900 mg/kg

10&kg

aRef. 3, and references contained therein. “Ref. 8, and references contained therein. PAH-polyaromatic hydrocarbon.

Other reference materials Though reference materials for numerous analytes, based on many kinds of sediments, can be prepared and analytical reference materials for marine plants and animals may eventually be prepared, a major problem still lies ahead: the preparation of standards for sea water itself. Despite man’s efforts to pollute the oceans, sea water remains one of the purest materials known, both from the point of view of levels of toxic metals and of toxic man-made chemicals. Airborne lead has invaded the surfaces of every sea on our globe, but miles below the waves the water has, in many places, sat undisturbed for thousands of years. The concentrations of metals such as lead, mercury and cadmium are in the order of nanograms per kilogram of water (10-a/1000 g of water). The problems of collection, storage and analysis are enormous. Unfortunately, it is probable that given time man will pollute the oceans. From an environmental point of view alone, it is essential that the present state of the oceans be assessed, so that future changes can be detected. Because of the extreme dificulties involved in

the accurate analysis of sea water, reference sea water samples are clearly required and thus should be given high priority.

Acknowledgements This work was done with the aid of NRCC No. 19533.

grant

References 1 Walton, A. (ed.) Ocean Dumping Report 1. Methods for Sampling and Analysis of Marine Sediments and Dredged Materials, Government of Canada, Ottawa 2 Bezanson, D. S., Moyse, C. M. and Byers, S. C. Ocean Dumping Report 2. Research and Related Work on Ocean Dumping, An Annotated Bibliography, Government of Canada, Ottawa 3 Swiss, J. J., Addison, R. F., McLeese, D. W. and Payne, J. F. Ocean Dumping Report 3. Regulated Levels of ScheduleI Substancesin the Ocean Dumping Control Act - A Review, Government of Canada, Ottawa 4 NBS Standard ReferenceMaterials Catalog 197988, National Bureau of Standards Special Publication 260, U.S. Government Printing Office, Washington 5 Koch, 0. G. (1978) Pure and A#. Chem. 50, 1531-1699 6 Faye, G. H. (1978) Certified and Provisional Reference Materials Available from the Canada Centre for Mineral and Energy Technology, Printing and Publishing, Supply and Services Canada, Ottawa 7 Abbey, Sydney (1979) Studies in ‘Standard Samples'for use in the General Analysis of Silicate Rocks and Minerals Part 6, Canadian Government Publishing Center, Quebec 8 Wakeham, S. G. and Farrington, J. W. (1980) Contaminants and Sediments, Volume 1, Ann Arbor Science Publishers Inc., Michigan, Ch. 1, pp. 3-32

Roger Guevremontgainedhis Ph.D. in Analytical Chemistryfrom~the UniversityofAlberta in 1978. He is presently an Assistant Research Oflcer in the Marine Analytical Chemistry Standards Program at the Atlantic Research Laboratory of the National Research Counn’lof Canada, 1411 OxfordStreet, Halifti, N.S., Canada B3H3ZI.

W. D. Jamieson receivedhis Ph.D. in Physical Chemistryjom the University of Cambridge in 1954, and is presently a Senior Research OfjfGcr in the Marine Analytical Chemistry Standards Program at the Atlantic ResearchLaboratory of the National Research Council of Canada