To CLASS PAGE:
Preparation of a Saturated Soil Paste Extract
|1.) Weigh 20
g of soil into a 125 mL polyethylene bottle.
|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. Standards calibration
curves plotting absorbance versus concentration (mg L-1) are prepared. Samples are run
gainst these calibration curves to measure concentrations of specific elements of interest.