The authors thank Drs. Bobby J. Presley, Robert Tayloy, Paul Boothe, Mr. Bryan Brattin, and Mr. Mike Metcalf for their assistance during the laborious field sampling and lab work for the practical development and application of "clean techniques".

1. Sampler Preparation
<ol>
	<li>Sampler
	<ol>
		<li>Assemblage of sampler
		<ol>
			<li>Connect a 4 m long fluorinated ethylene propylene (FEP) tubing (I.D. 0.635 cm, O.D. 0.95 cm or similar) to a 1.5-m chemically resistant silicone pumping tube (O.D. 0.635 cm).</li>
			<li>Insert a polypropylene Y-connector into the pumping tube, and connect a 50-cm pumping tube to one outlet, and a 0.45 &#956;m capsule filter (by a 20-cm pumping tube) to the other.</li>
			<li>Assemble the tubings in a clean room (bench) after they ...

<ol>
	<li>Taylor, H. E., Shiller, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mississippi+River+Methods+Comparison+Study:+Implications+for+water+quality+monitoring+of+dissolved+trace+elements.">Mississippi River Methods Comparison Study: Implications for water quality monitoring of dissolved trace elements.</a> Environmental Science and Technology. 29, 1313-1317 (1995).</li><li>Windom, H. L., Byrd, J. T., Smith, R. G., Huan, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inadequacy+of+NASQAN+data+for+assessing+metal+trends+in+the+nation's+rivers.">Inadequacy of NASQAN data for assessing metal trends in the nation's rivers.</a> Environmental Science and Technology. 25 (6), 1137-1142 (1991).</li><li>Mason, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Trace Metals in Aquatic Systems. , (2013).</li><li>Wen, L. -. S., Santschi, P., Gill, G., Paternostro, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estuarine+trace+metal+distributions+in+Galveston+Bay:+importance+of+colloidal+forms+in+the+speciation+of+the+dissolved+phase.">Estuarine trace metal distributions in Galveston Bay: importance of colloidal forms in the speciation of the dissolved phase.</a> Marine Chemistry. 63, 185-212 (1999).</li><li>Wen, L. -. S., Stordal, M. C., Tang, D., Gill, G. A., Santschi, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+ultraclean+cross-flow+ultrafiltration+technique+for+the+study+of+trace+metal+phase+speciation+in+seawater.">An ultraclean cross-flow ultrafiltration technique for the study of trace metal phase speciation in seawater.</a> Marine Chemistry. 55, 129-152 (1996).</li><li>Benoit, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clean+technique+measurement+of+Pb,+Ag,+and+Cd+in+freshwater:+A+redefinition+of+metal+pollution.">Clean technique measurement of Pb, Ag, and Cd in freshwater: A redefinition of metal pollution.</a> Environmental Science and Technology. 28, 1987-1991 (1994).</li><li>Benoit, G., Hunter, K. S., Rozan, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sources+of+trace+metal+contamination+artifacts+during+collection,+handling,+and+analysis+of+freshwater.">Sources of trace metal contamination artifacts during collection, handling, and analysis of freshwater.</a> Analytical Chemistry. 69 (6), 1006-1011 (1997).</li><li>Jiann, K. -. T., Presley, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preservation+and+determination+of+trace+metal+partitioning+in+river+water+by+a+two-column+ion+exchange+method.">Preservation and determination of trace metal partitioning in river water by a two-column ion exchange method.</a> Analytical Chemistry. 74 (18), 4716-4724 (2002).</li><li>Fardy, J. J., Alfassi, Z. B., Wai, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Preconcentration Techniques for Trace Elements. , 181-210 (1992).</li><li>Pai, S. -. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pre-concentration+efficiency+of+Chelex-100+resin+for+heavy+metals+in+seawater.+Part+2.+Distribution+of+heavy+metals+on+a+Chelex-100+column+and+optimization+of+the+column+efficiency+by+a+plate+simulation+method.">Pre-concentration efficiency of Chelex-100 resin for heavy metals in seawater. Part 2. Distribution of heavy metals on a Chelex-100 column and optimization of the column efficiency by a plate simulation method.</a> Analytica Chimica Acta. 211, 271-280 (1988).</li><li>Pai, S. -. C., Fang, T. -. H., Chen, C. -. T. A., Jeng, K. -. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+low+contamination+Chelex-100+technique+for+shipboard+pre-concentration+of+heavy+metals+in+seawater.">A low contamination Chelex-100 technique for shipboard pre-concentration of heavy metals in seawater.</a> Marine Chemistry. 29, 295-306 (1990).</li><li>Pai, S. -. C., Whung, P. -. Y., Lai, R. -. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pre-concentration+efficiency+of+Chelex-100+resin+for+heavy+metals+in+seawater.+Part+1.+Effects+of+pH+and+salts+on+the+distribution+ratios+of+heavy+metals.">Pre-concentration efficiency of Chelex-100 resin for heavy metals in seawater. Part 1. Effects of pH and salts on the distribution ratios of heavy metals.</a> Analytica Chimica Acta. 211, 257-270 (1988).</li><li>Salbu, B., Oughton, D. H., Salbu, B., Steinnes, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Trace Elements in Natural Waters. , 41-69 (1995).</li><li>. U.S. Environmental Protection Agency. Method 1669. Sampling ambient water for trace metals at EPA Water Quality criteria levels Available from: <a target="_blank" href="https://www3.epa.gov/caddis/pdf/Metals_Sampling_EPA_method_1669.pdf">https://www3.epa.gov/caddis/pdf/Metals_Sampling_EPA_method_1669.pdf</a> (1996)</li><li>Horowitz, A. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Problems+associated+with+using+filtration+to+define+dissolved+trace+metal+concentrations+in+natural+water+samples.">Problems associated with using filtration to define dissolved trace metal concentrations in natural water samples.</a> Environmental Science and Technology. 30, 954-963 (1996).</li><li>Cortecci, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Geochemistry+of+trace+elements+in+surface+waters+of+the+Arno+River+Basin,+northern+Tuscany,+Italy.">Geochemistry of trace elements in surface waters of the Arno River Basin, northern Tuscany, Italy.</a> Applied Geochemistry. 24 (5), 1005-1022 (2009).</li><li>Markich, S. J., Brown, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relative+importance+of+natural+and+anthropogenic+influences+on+the+fresh+surface+water+chemistry+of+the+Hawkesbury-Nepean+River,+south-eastern+Australia.">Relative importance of natural and anthropogenic influences on the fresh surface water chemistry of the Hawkesbury-Nepean River, south-eastern Australia.</a> The Science of the Total Environment. 217, 201-230 (1998).</li><li>Shafer, M. M., Overdier, J. T., Hurley, J. P., Armstrong, D., Webb, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+dissolved+organic+carbon,+suspended+particles,+and+hydrology+on+the+concentration,+partitioning+and+variability+of+trace+metals+in+two+contrasting+Wisconsin+watersheds+(U.S.A.).">The influence of dissolved organic carbon, suspended particles, and hydrology on the concentration, partitioning and variability of trace metals in two contrasting Wisconsin watersheds (U.S.A.).</a> Chemical Geology. 136, 71-97 (1997).</li><li>Warren, L. A., Haack, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biogeochemical+controls+on+metal+behaviour+in+freshwater+environments.">Biogeochemical controls on metal behaviour in freshwater environments.</a> Earth-Science Reviews. 54, 261-320 (2001).</li><li>Jiann, K. -. T., Santschi, P. H., Presley, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationships+between+geochemical+parameters+(pH,+DOC,+SPM,+EDTA+Concentrations)+and+trace+metal+(Cd,+Co,+Cu,+Fe,+Mn,+Ni,+Pb,+Zn)+concentrations+in+river+waters+of+Texas+(USA).">Relationships between geochemical parameters (pH, DOC, SPM, EDTA Concentrations) and trace metal (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) concentrations in river waters of Texas (USA).</a> Aquatic Geochemistry. 19 (2), 173-193 (2013).</li><li>Peltzer, E. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparison+of+methods+for+the+measurement+of+dissolved+organic+carbon+in+natural+waters.">A comparison of methods for the measurement of dissolved organic carbon in natural waters.</a> Marine Chemistry. 54, 85-96 (1996).</li><li>Nowack, B., Kari, F., Hilger, S. U., Sigg, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+dissolved+and+adsorbed+EDTA+species+in+water+and+sediments+by+HPLC.">Determination of dissolved and adsorbed EDTA species in water and sediments by HPLC.</a> Analytical Chemistry. 68 (3), 561-566 (1996).</li><li>Bergers, P. J. M., de Groot, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+analysis+of+EDTA+in+water+by+HPLC.">The analysis of EDTA in water by HPLC.</a> Water Research. 28 (3), 639-642 (1994).</li></ol>

The authors have no conflict of interests to disclose.

Obtaining reliable trace metal data in natural waters requires great care as emphasized during sample collection, processing, pretreatments, and analysis that aim to reduce contamination. Trace metal concentrations in natural waters obtained using &#34;clean techniques&#34; in the last two decades found that the concentrations can be orders of magnitude lower than previously reported. Water quality criteria for trace metals in waters are now more readily assessed when trace metal levels are accurately measured resulting ...

It has been commonly recognized that some trace metal results obtained for natural waters may be inaccurate owing to artifacts arising from inadequate techniques applied during sample collection, treatments and determination1,2. The true concentrations (in sub-nM to nM range in surface waters 3) of dissolved trace metals are now up to two orders of magnitude lower than previously published values. The same situation has been found in marine chemistry where the accepted dissolved trace metal concentrations in oceanic waters have decreased by orders of magnitude over the last 40 years or so as improved sampling and analytical methods have been introduced. Efforts have been made to improve data quality with the developments of &#34;clean techniques&#34; aiming at the reduction or elimination of trace metal contamination throughout all phases of trace metal analysis 4-8. For the determination of trace metal concentrations at ambient levels, preconcentration is often required. Ion-exchange techniques 8-12 have been commonly applied for efficient preconcentration.
Contamination can arise from the walls of containers, the cleaning of the containers, the sampler, sample handling and storage, and sample preservation and analysis 7,13. All studies using clean methods conducted more recently indicate that trace metal concentrations in natural waters are typically well below the detection limits of routine methods 7. Since the recognition of suspect trace metal data in the early 1990s, clean methods have been incorporated into US EPA (Environmental Protection Agency) Guidelines for trace metal determination 14 and the US Geological Survey has adopted clean methods for their water quality monitoring projects 15. Clean methods for trace metal studies need to be employed in all projects in order to create a firm and accurate data base.
In principle, water samples used for trace metal determination should be collected with appropriate sampling gears of a particular material and composition, stored and treated properly using appropriate containers and apparatus, before proceeding with instrumental analysis. Since suspended particulate matter (SPM) can undergo changes during the sample storage period and alter water composition, rapid separation of SPM from water samples is a common practice for trace metal studies in aquatic environments. For the determination of dissolved trace metal concentrations in natural waters, filtration is necessary and in-line filtration techniques are suitable and efficient.
Distribution and behavior of trace metals in aquatic environments such as surface and ground waters can be affected by natural (e.g., weathering) and anthropogenic (e.g., wastewater effluents) factors, as well as other environmental conditions, such as regional geology, morphology, land use and vegetation, and climate 16-19. This can then lead to differences in physicochemical parameters such as concentrations of suspended particulate matter (SPM), dissolved organic carbon (DOC), anthropogenic ligands (e.g., ethylenediaminetetraacetic acid, EDTA), salt, redox potential and pH 17-20. Therefore, accurate and relevant trace metal studies require appropriate collection of samples for trace metal analysis as well as for the determination of related factors and parameters.

<table border="0" cellpadding="0" cellspacing="0" width="782">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:249px;">Nitric Acid</td>
			<td style="width:216px;">Seastar Chemicals</td>
			<td style="width:129px;"></td>
			<td style="width:188px;">Baseline grade</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:249px;">Ammonium hydroxide</td>
			<td style="width:216px;">Seastar Chemicals</td>
			<td style="width:129px;"></td>
			<td>Baseline grade</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:249px;">Acetic Acid</td>
			<td style="width:216px;">Seastar Chemicals</td>
			<td style="width:129px;"></td>
			<td>Baseline grade</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:249px;">Nitric Acid</td>
			<td style="width:216px;">J. T. Baker</td>
			<td style="width:129px;">9601-05</td>
			<td>Reagent grade</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:249px;">Hydrochloric acid</td>
			<td style="width:216px;">J. T. Baker</td>
			<td style="width:129px;">9530-33</td>
			<td>Reagent grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Chromatographic columns</td>
			<td style="width:216px;">Bio-Rad</td>
			<td>7311550&#160;</td>
			<td>Poly-Prep</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Column stack caps</td>
			<td style="width:216px;">Bio-Rad</td>
			<td>7311555</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Cap connectors (female luers)</td>
			<td style="width:216px;">Bio-Rad</td>
			<td style="width:129px;">7318223</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">2-way stopcocks</td>
			<td style="width:216px;">Bio-Rad</td>
			<td>7328102</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Cation exchange resin</td>
			<td style="width:216px;">Bio-Rad</td>
			<td>1422832&#160;</td>
			<td>Chelex-100</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Portable sampler (sampling pump)</td>
			<td style="width:216px;">Cole Palmer</td>
			<td>EW-07571-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">FEP tube</td>
			<td style="width:216px;">Cole Palmer</td>
			<td>EW-06450-07</td>
			<td>6.4 mm I.D., 9.5 mm O.D.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Pumping tube</td>
			<td style="width:216px;">Cole Palmer</td>
			<td>EW-06424-24</td>
			<td>6.4 mm I.D. C-Flex</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Capsule filter (0.4 mm)</td>
			<td style="width:216px;">Fisher Scientific</td>
			<td>WP4HY410F0</td>
			<td>polypropylene casing</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">1 L low density polyethylene bottle</td>
			<td>NALGE NUNC INTERNATIONAL</td>
			<td>312088-0032</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">1 L (or 500 ml) FEP bottle</td>
			<td>NALGE NUNC INTERNATIONAL</td>
			<td>381600-0032</td>
			<td></td>
		</tr>
	</tbody>
</table>

clean sampling and analysis of river and estuarine waters for trace metal studies

Most of the trace metal concentrations in ambient waters obtained a few decades ago have been considered unreliable owing to the lack of contamination control. Developments of some techniques aiming to reduce trace metal contamination in the last couple of decades have resulted in concentrations reported now being orders of magnitude lower than those in the past. These low concentrations often necessitate preconcentration of water samples prior to instrumental analysis of samples. Since contamination can appear in all phases of trace metal analyses, including sample collection (and during preparation of sampling containers), storage and handling, pretreatments, and instrumental analysis, specific care needs to be taken in order to reduce contamination levels at all steps. The effort to develop and utilize "clean techniques" in trace metal studies allows scientists to investigate trace metal distributions and chemical and biological behavior in greater details. This advancement also provides the required accuracy and precision of trace metal data allowing for environmental conditions to be related to trace metal concentrations in aquatic environments.
This protocol that is presented here details needed materials for sample preparation, sample collection, sample pretreatment including preconcentration, and instrumental analysis. By reducing contamination throughout all phases mentioned above for trace metal analysis, much lower detection limits and thus accuracy can be achieved. The effectiveness of "clean techniques" is further demonstrated using low field blanks and good recoveries for standard reference material. The data quality that can be obtained thus enables the assessment of trace metal distributions and their relationships to environmental parameters.

With the development and use of &#34;clean techniques&#34;, it is now well recognized that in order to obtain accurate trace metal concentrations in ambient waters, preconcentration of trace metals in waters samples is a common practice. While most water quality criteria for trace metals in natural waters are in the low &#956;g/L range, lower detection limits are needed to investigate geochemical and biological effects on trace metals at ambient concentrations in aquatic environments....

Watch this Scientific Journal Video about Clean Sampling and Analysis of River and Estuarine Waters for Trace Metal Studies at JoVE.com

Clean Sampling and Analysis of River and Estuarine Waters for Trace Metal Studies

Special care using "clean techniques" is required to properly collect and process water samples for trace metal studies in aquatic environments. A protocol for sampling, processing, and analytical procedures with the aim of obtaining reliable environmental monitoring data and results with high sensitivity for detailed trace metal studies is presented.

Most of the trace metal concentrations in ambient waters obtained a few decades ago have been considered unreliable owing to the lack of contamination ...

The overall goal of this clean sampling and analysis protocol is to provide adequate techniques for obtaining reliable data for trace metal studies, especially when low detection limits are required. This method can help answer key questions in environmental chemistry field, in aquatic environments with dynamic hydrological and geochemical conditions. The advantage of this technique is that under the suggested guidelines, reliable data can be obtained and related to variable key environmental parameters.So this method can provide techniques to obtain information in rivers and estuaries. It can also be applied to other systems, such as lakes, coastal zones, and oceanic environments. Generally, individuals new to this method will struggle due to a lack of knowledge on contamination controls and the inability to recognize proper means to eliminate contamination during trace metal analysis.Demonstrating the procedure will be Chih-Ping Lee and Pei-Yu Lin, students from our labs. To assemble the sampler, connect four meter long fluorinated ethylene propylene tubing to a 1.5 meter chemically-resistant silicone pumping tube. Insert a polypropylene Y-connector into the pumping tube.Connect a 50 centimeter pumping tube to one outlet, and a 0.45 micrometer capsule filter to the other. Assemble the tubings in a clean room after they are cleaned as described in the text protocol and store the assemblage in two layers of polyethylene bags. For sample containers, use polyethylene and FEP bottles for trace metal determination containers.Clean the bottles by soaking them first in 1%detergent solution for 24 hours. After rinsing the bottles with the ionized water, soak them in 50%nitric acid solution for 48 hours. Rinse the bottles a second time and then soak the bottles in 10%hydrochloric acid, or HCl solution for 24 hours.After the final HCl soaking, rinse the bottles thoroughly with the ionized water, abbreviated as DIW. Dry the bottles with the caps sealed in a clean room or class 100 clean bench. Seal the cleaned bottles in polyethylene zippered bags and double bag them in polyethylene bags for transport.At the riverbank or on a boat, have one person open the bag with the sampler and attach the four meter FEP tubing to a cleaned polypropylene pole. Extend the pole as far from the bank as possible and keep the inlet of the FEP tubing approximately 30 centimeters below the surface of the running river water before the pump is turned on. Have a second person attach the pumping tube to the pump-head of a peristaltic pump.Start the pump and drain the water on the downstream side at least three times of the total sampler volume. Have a third person be in charge of opening the inner bags and sample caps, and holding the sampling tube that drains the sample into the bottle. First, collect an unfiltered sample through the outlet without the filter into a 125 milliliter plastic bottle for measurements of conductivity, temperature, and pH in the field.Then, collect a filtered water sample by closing the outlet with a plastic clamp to force the water to go through the capsule filter. Collect filtered samples in 40 milliliter amber glass bottles for DOC and EDTA measurements. For each type of sample, collect extra samples, as well as field blanks at selected locations to serve as quality control aliquots.Place the 40 milliliter glass bottles on ice and store them in an ice chest, and place the polyethylene bottles in ice chests. Finally, collect the suspended particulate matter, or SPM, on 0.4 micrometer polycarbonate membrane filters by vacuum filtration using a plastic filtration funnel and vessel. For dissolved trace metal determination, add 2 milliliters of concentrated sub-boiled nitric acid into the one liter sample.UV irradiate the acidified samples in the FEP bottles for 24 hours. Next, weigh 2 grams of cation exchange resin into a small plastic cup and add a small amount of two normal nitric acid solution into the cup. Pour the resin into a 10 milliliter capacity chromatography column.Clean the resin by washing the column with 5 milliliters of two normal nitric acid twice. Then, rinse with high purity water, abbreviated as HPW, three times. Finally, add 10 milliliters of one molar ammonium hydroxide into the column to convert the resin to the ammonium form.Adjust the pH of the acidified UV-irradiated samples to 5.5 plus or minus 0.3, by adding 30 milliliters of one molar ammonium acetate buffer solution and some ammonium hydroxide into the samples. Then, place the sample bottle on a rack approximately 30 centimeters above the column packed with cationic exchange resin. Connect the sample bottle and preconcentration column with a 60 centimeter FEP tube, chromatography cap, and connector.Control the flow rate at three to five milliliters per minute using a two-way stopcock connected above the column. Allow the samples to pass through the preconcentration columns. After the samples have passed through the column, disconnect the tubes and caps from the columns.To separate major cations from other trace metals, treat the columns with 5 milliliters of HPW twice. Then, add 5 milliliters of one molar ammonium acetate, pH 5.5, four times. Finally, treat with an additional 5 milliliters of HPW twice.Place a 30 milliliter acid-washed PE bottle just below the column and wash the column with seven 1 milliliter aliquots of two normal nitric acid into the PE bottle. To digest the suspended particulate matter, freeze-dry the polycarbonate filters with SPM samples and weigh them after drying. Next, place the SPM samples with filters into pre-weighed PFA vessels and add 3 milliliters of concentrated nitric acid into the vessels.Tighten the vessels to a constant torque of 2.5 killogram-meters. Digest the samples in a conventional oven at 130 degrees Celsius for 12 hours. After cooling, open the vessels and add 2 milliliters of hydrogen fluoride.Then, tighten the vessels and digest in a conventional oven, as before. After cooling, open the vessels and add 16 milliliters of 4.5%boric acid solution. Once again, tighten the vessels and digest in a conventional oven in the same manner.Weigh each vessel and determine the specific gravity of each digested solution to yield the final digest volume. Using the presented techniques for low contamination sampling, sample treatments, and analysis, resulted in low detection limits, good recoveries for our referenced standard material, and low field blank concentrations. This indicates the effectiveness of this method.Very good agreement was found between trace metal concentrations determined using two independent methods and separate aliquots of the same sample. One sample was analyzed directly by inductively-coupled plasma atomic emission spectrometry and the other was preconcentrated by ion exchange techniques following determination by inductively-coupled plasma mass spectrometry. The large concentration range implies that these techniques are suitable for trace metal studies and distinctively different environments where trace metal concentrations show significant differences.Obtaining reliable trace metal data in natural waters requires great care during sample collections, processing, pretreatment, and analysis that aim to reduce contamination. The procedure to prepare sampling gear, sample containers, and material used to process and analyze samples are all critical steps toward obtaining high data quality for trace metal in aquatic environments. The techniques and methods demonstrated here can be easily applied to different types of aquatic systems.In addition to river and estuary waters, such as oceans, lakes, and groundwater. After watching this video, you should have a good understanding of how to properly plan and conduct trace metal studies that can be applied to environmental monitoring and geochemical investigation.

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JoVE Journal

Environment

11.3K visualizações.  National Sun Yat-sen University. The overall goal of this clean sampling and analysis protocol is to provide adequate techniques for obtaining reliable data for trace metal studies, especially when low detection limits are required. This method can help answer key questions in environmental chemistry field, in aquatic environments with dynamic hydrological and geochemical conditions. The advantage of this technique is that under the suggested guidelines, reliable data can be obtained and related to variable key environmental...