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Lab #4 10/4-10/11/04
Preparation of a Saturated Soil Paste Extract
|1.) Weigh 20
g of soil into a 125 mL polyethylene bottle in duplicate.
|2.) Add 40 mL of deionized distilled water and stir with a spatula.|
|3.) Shake for 1h.|
|4.) Transfer to a Büchner funnel containing filter paper connected to a vacuum flask.|
|5.) Apply a
vacuum and collect the filtrate. You should be able to collect at
least 20mL of filtrate to allow for
characterization of anions and cations. Note: Be careful not to contaminate this “stock soil solution.”
|II. Characterization of Soil Solution|
pH with Metrohm pH meters. Between pH readings, rinse electrode
with DI water. Be careful not
to contaminate your sample.
electrical conductivity (EC).
|3.) Anion Concentration|
| a.) Common
soil anions (chloride, nitrite, nitrate, orthophosphate, and sulfate)
quantified using a Metrohm ion chromatograph, in which anions are separated on a
column packed with an anion exchange resin and detected by a conductivity detector as
eluent is pumped at a constant rate through the system. You will inject approximately
~2 mL of your water sample and depending on the composition of your solution, the
anions will separate. Each will have a characteristic retention time that may be used to
identify components in your sample by comparison with those in a standard solution.
Each injection run time will be 18 min. The chromatogram will be a plot of signal versus
time. The area under the peak is directly proportional to the amount of anion present.
The software will allow you to integrate the peaks to determine anion concentration in
|4.) Cation Concentration|
||a.) You will measure dissolved Fe, Mn, and Zn
concentrations using flame atomic absorption
spectroscopy (FAAS) against a set of standards that you will prepare. Atomic absorption
spectroscopy is based on energy absorbed during transitions between electronic energy levels of an
atom. Atoms of a given element have a diagnostic set of allowed electronic energy levels. Atomic
absorption spectroscopy consists of passing light of a specific wavelength that can be absorbed by
the element of interest through an atomic vapor of the element. By measuring attenuation of the
light intensity as a result of absorption and comparison with standards in the same background
solution, elemental concentrations can be derived. Standards calibration curves plotting
absorbance versus concentration (mg L-1) are prepared. Samples are run against these calibration
curves to measure concentrations of specific elements of interest.
standard solutions for Fe, Mn, and Zn in deionized water from 1000 mg
L-1 stock solutions.
Standard concentrations are 0 (blank), 0.5, 1.0, 5.0, and 10.0 mg L-1 (at total of 15 standards per