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INTRODUCTION Ion Chromatography. In the past, in order to quantitatively measure anionic species in water samples, many analytical methods were employed. For one sample of water, one may have had to perform many tests including spectrophotometry, gravimetry, turbidity, and ion-selective electrode potentiometry. Of course this is labour intensive as well as being costly for analysis of many different samples. One principle advantage of using ion chromatography is the simultaneous determination of many inorganic anionic species along with some organic ones in a relatively short period of time. Another advantage of the system is the minimal sample preparation required.
In the first part of the experiment, water samples will be analyzed
for commonly found anionic species such as nitrates, chlorides,
nitrites, fluorides, bromides, phosphates, sulphites, and sulphates.
Anionic species determination can be important in studying oxidation-reduction
potentials of environmental waters, and can provide clues to the
marine system. Nitrates are the principle form of nitrogen found
in natural waters and are the result of complete oxidation of
nitrogen compounds. Sources of nitrates can be found in industrial
discharges, and municipal sewage (especially those containing
human excrement). Chlorides can also come from many sources,
natural ones such as leaching of sedimentary rocks to industrial
sources such as disinfection of domestic sewage. Sulphates can
be leached from sedimentary rocks and from sulphate deposits such
as gypsum and anhydrite.
ICP-AES/GFAAS. The second portion of the experiment examines
two core sediment samples. An analysis of soil sedimentation
over time can reveal insight of past natural and anthropogenic
environmental conditions and changes. Core samples provide an
accurate account of the surrounding history by creating a "closed
system" that prevents components from further contamination
by continual covering with more sediment. The changes in lead
concentrations in the soil are a good example of how changes in
the anthropogenic environment can be seen in core sediments.
A decrease in lead concentrations can be attributed to the discontinued
use of leaded gasoline. Both graphite furnace atomic absorption
spectrometry (GFAAS) and inductively coupled plasma (ICP) are
used to quantify the lead concentrations in core samples. However,
ICP has the added advantage, albeit at a much higher expense,
to simultaneously analyze for several metals. Thus for the ICP,
in addition to trace lead analysis, manganese, iron, copper,
aluminum, and cadmium will also be analyzed. LAKES
Sediment cores from two lakes in the Arctic have been taken by
colleagues in Geology with a "cold finger" coring device.
Those of you who go on the sampling expedition to Crawford Lake
will be able to see this activity firsthand. A cold finger corer
is basically a steel tube, having a flat surface on at least one
side, that is weighted on the bottom and filled with dry ice and
ethanol, attached to a rope long enough to reach the bottom of
the lake. The corer is gently lowered through the water column
(while carefully balancing the boat!) until it is about 1 meter
from the sediment (pre-measured indication on the rope) from which
it is allowed to drop directly to the sediment and bury itself
there. The sediment is then allowed to freeze onto the cold finger
for 20 minutes when it raised to the surface. The flat surface
containing the sediment "record" is then carefully returned
to the lab for segmenting.
The lake chosen for your sampling expedition, Crawford Lake is
meromictic which means it does not turn over during the year and
thus the bottom waters are anoxic and have very little biological
activity. These conditions result in an annually detailed sediment
record of yearly activities in the lake with each annual "ring"
observed in the sediment white/dark layers. This allows a very
efficient and inexpensive dating of the sediment core. Specific lake conditions are listed below:
1Three samples from Colour Lake
will be done in 1997 in prep for 1998.
PROCEDURE
Part 1: Simultaneous determination of organic and inorganic
anions by ion exchange chromatography. Preparation of sampling containers. Polyethylene sample bottles to be used in sampling of surface waters must be cleaned prior to with 10% HCl followed by thorough rinsing with deionized-distilled water (Type I) and dried at room temperature.
Type I deionized-distilled water is prepared by passing distilled
water through an ion-exchange cartridge. Sampling of surface waters.
Collect water samples in clear polypropylene bottles. Be sure
to "overfill" the bottles so that when the cap is replaced
there is no "headspace". This is particular important
in the depth samples from Crawford Lake as these will be under
anoxic conditions; we want to be able to observe the change in
anions with oxidation state. Refrigerate samples as quickly as
possible, or place in an appropriate cool container. Cleanup.
To filter the solution (if necessary) of any undissolved matter,
pull 25 mL of the sampled water into a plastic syringe. Proceed
by fitting a LC PVDF 0.2 µm Gelman Acrodisc over the tip.
Evenly, expel all of the water into a clean Erlenmeyer flask.
The filtered solution is then ready for injection. Make duplicate
or if time allows, triplicate 250 µL injections. Preparation of standard curve. Mixed standards of the following concentrations are to be made, 10, 20, 50, 250, and 1000 ng/g. Take one mL of the stock 1000 mg/L and dilute to mark in a 100 mL volumetric flask with 18 ½ deionized water. Take 10 mL of this solution and dilute to mark in a 100 mL volumetric flask (1000 ng/g). For the 250 ng/g solution, take 25 mL of the 1000 ng/g solution and dilute to mark in a 100 mL volumetric flask. For the 50 ng/g solution, take 5 mL of the 1000 ng/g solution and dilute to mark in a 100 mL volumetric flask. For the 20 and 10 ng/g solutions, take 2 and 1 mL of the 1000 ng/g solution and fill to mark in 100 mL volumetric flasks respectively. For the standard curve, inject 200 µL of the standards. 1997: Anions targeted for analysis are: F-, Cl-, SO4-, PO43-, and NO32-.
A water blank should be injected to test for any anions that
may not be accounted for in the standard solutions. Ion chromatographic conditions.
Analytical reagent grade Na2CO3 and NaHCO3 will be used as the
eluent in the following concentrations : 1.8 mM Na2CO3 and 1.7
mM NaHCO3; flow rate will be between 1 and 1.5 ml/min ~ check
with your TA.
BACKGROUND REFERENCES A.A. Ammann and T.B. Rüttimann. 1995. Simultaneous determination of small organic and inorganic anions in environmental water samples by ion-exchange chromatography. J. Chromat. A. 706:259-269. W. Shotyk. 1993. Ion chromatography of organic-rich natural waters from peatlands. J. Chromat. 640:309-316.
National Laboratory for Environmental Testing. Manual of Analytical
Methods, Vol. I.
Part 2: Analysis of trace metals by means of ICP-AES and GFAAS.
Preparation of core sediment. (To be performed ahead of time by TA's and students) Core samples will be collected and cut to specified portions. Each portion will represent a time period (e.g. the first 0.3 centimetres may be accumulated from 1996-1997). Dry the samples for 48 hrs in an oven at 65°C. Each sample will then be ground in a mortar to pass a 40 mesh screen and then thoroughly mixed before removing a subsample. Weigh 0.25 g of each sample into labeled digestion tubes.
QA/QC. You will be running a large number of spike/recovery,
replicates, and blanks during this experiment. Please check the
added "info" sheet for this experiment for specifics.
Digestion of sample. 1) Weight 0.25 gram of sample and place into the ACV vessel liner. 2) Add 8 mL of Nitric Acid and 1 mL of Hydrochloric Acid. 3) Mix the sample and acid until all of the sample has been wetted with acid. 4) Assemble the vessel. Put vessel in the carousel and place in the microwave. 5) Program the MultiWave as follows and allow the sample to heat.
6) Allow the sample to cool, vent, and remove the vessel cap.
The sample should be colorless and contain white solids.
7) Transfer your extracted sample to labeled 25 ml volumetric
flasks. Dilute to the mark with 2% Nitric Acid. Preparation of standards.
Two sets of standards are to be prepared for the ICP-AES and
GFAAS portions of the experiment. For the ICP-AES, Pb, Mn, Fe,
Cu, and Cd standards will be made. For the GFAAS, only Pb standards
will be made. GFAAS &ICP-AES standards. Standards will be prepared ahead of time by the TAs by serially diluting from certified 1000 ppm solutions of each of the metals. You will find mixed standards for the target metals available for your use. GFAAS: 0, 4, 6, 20, 50 ppb as Pb ICP: 1, 10, 100, 1000, 10000, and 100000 ppb of Pb, Mn, Fe, Cu, and Cd
ICP/GFAAS Operation
TAs will instruct you in how to operate the graphite-furnace
and the ICP. Please review the theory from lecture prior to coming
to lab so that the basic concepts will be familiar. Basic operation
conditions are found below; see the TAs for any other specific
parameters you might need. GFAAS.
We will be using the autosampler which will automatically add
matrix modifier. The conditions listed below may change so make
sure of each when you are running the instruments.
Furnace conditions
ICP. Plasma parameters:
Wavelengths:
Data Transfer
All data will be shipped electronically directly from the ICP
to your email address given at the beginning of the course. GFAAS
Pb data will be provided in class. Given the very large sample
size it is strongly suggested you down-load the data into a spreadsheet
program for data analysis.
BACKGROUND REFERENCES
S.M. Pyle, J.M. Nocerino, S.N. Deming, J.A. Palasota, J.M. Palasota,
E.L. Miller, D.C. Hillman, C.A. Kuharic, W.H. Cole, P.M. Fitzpatrick,
M.A. Watson, and K.D. Nichols. Comparison of AAS, ICP-AES, PSA,
and XRF in Determining Lead and Cadmium in Soil. Environ. Sci.
Technol. 30(1):204-213, 1996.
X. Wen, L. Wu, Y. Zhang, and Y. Chu. Optimized microwave preparation
procedure for the elemental analysis of aquatic sediment. Fresenius
J. Anal. Chem. 357:1111-1115, 1997.
D.E. Kimborough and J. Wakakuwa. Interlaboratory Comparison of
Instruments Used for the Determination of Elements in Acid Digestates
of Solids. Analyst. 119:383-388, 1994.
M. Baucells, G. Lacort, and M. Roura. Determination of Cadmium
and Molybdenum in Soil Extracts by Graphite Furnace Atomic-absorption
and Inductively Coupled Plasma Spectrometry. Analyst. 110:1423-1429,
1985.
H.R. Von Gunten, M. Sturm, and R.N. Moser. 200-Year Record of
Metals in Lake Sediments and Natural Background Concentrations.
Environ. Sci. Technol. 31(8):2193-2197, 1997.
R.B. Cook, R. G. Kreis, Jr., J.C. Kingston, K.E. Camburn, S.A.
Norton, M.J. Mitchell, B. Fry, and L.C.K. Shane. Paleolimnology
of McNearney Lake: an acidic lake in northern Michigan. J.
Palelimnology. 3:13-34, 1990.
D.R. Engstrom, C. Whitlock, S.C. Fritz, and H.E. Wright, Jr. Recent
environmental changes inferred from the sediments of small lakes
in Yellowstone's northern range. J. Paleolimnology. 5:139-174,
1991.
J.R. White and C.P. Gubala. Sequentially extracted metals in Adirondack
lake sediment cores. J. Paleolimnology. 3:243-252,
1990.
N. Radle, C.M. Keister, and R.W. Battarbee. Diatom, pollen, and
geochemical evidence for the palaeosalinity of Medicine Lake,
S. Dakota, during the Late Wisconsin and early Holocene. J.
Paleolimnology. 2:159-172, 1989.
M.J. Mitchell, J.S. Owen, and S.C. Schindler. Factors affecting
sulfur incorporation into lake sediments: paleoecological implications.
J. Paleolimnology. 4:1-22, 1990. REPORT For both the ion chromatography and GFAAS/ICP portions, plot all standard curves relevant to each portion ~ combine your std curves into one graph for IC, one for ICP, and one for GFAAS. Calculate the anion quantities found in your water sample.
For the GFAAS/ICP, calculate the concentration of metals in the
sediments. Compare the lead concentrations as measured by GFAAS
to those determined by ICP. What differences, if any, can be
attributed to the different instruments? You will need to be
very careful because some samples may be correctly determined
from the data on the GFAAS or the ICP but never both ~ you will
need to determine this. You also need to calculate the spike
& recoveries, replicates, and blanks. Create a way to clearly
show how well we did QA/QC-wise. A good activity would be to
calculate from your blank values the greatest error in possible
in your sample values. Graphically show the changes in metal
concentrations over time, and give plausible explanations to
the reasons for the changes or even, lack of change (e.g. industrial
contamination, environmental catastrophes such as fires or floods).
This experiment will generate a very large amount of data and
part of the exercise is for you to be able to create meaningful
ways of "showing" what you've accomplished and what
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