Phosphate Determination

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Phosphate Determination
Presented by Sarah, Mike, Pete Joshua
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Objectives

• Find a standard curve using different dilutions
  of the standard phosphate solution .
• Our primary goal is to test the absorbance of
  different samples of seawater to find
  concentrations of the seawater within our
  standard curve.

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Glassware
Calibrations
Lab Safety
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Lisa Moore

• As a marine microbial ecologist, my broad
  research interests focus on the phytoplankton
  component of the marine food web, specifically
  what factors influence species composition,
  population dynamics and distributions within a
  variety of marine ecosystems. I am also
  interested in the "flip side", i.e. how
  biodiversity and phytoplankton community
  structure influences ecosystem stability and
  biogeochemical cycles. To this end, my research
  focuses primarily on the physiological ecology of
  the marine phytoplankton Prochlorococcus, the
  recently

discovered, numerically dominant component of the
open ocean phytoplankton community. I employ a
variety of techniques to study the light and
nutrient-dependent physiology of Prochlorococcus,
including cultured isolates, flow cytometry,
genomics, and comparative analyses to other
marine cyanobacteria.
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Lisa's Lab
Prokaryotic microorganisms- those that depend
directly on uptake of dissolved phosphate from
their environment
Lisas goal is to measure the amount of phosphate
utilized by the microorganisms by comparing the
amounts of phosphate in the initial media and the
amount of phosphate in the waste container of a
continuous culture chemostat.
A spectrophotometer measures the absorption due
to phosphate with a color indicator. A
calibration curve given by known concentrations
of phosphate with indicator allow an accurate
determination of concentration in the chemostat
samples.
Result A better understanding of how phosphate
effects phytoplankton growth
Application
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Chemostat in use
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Procedure

• We cleansed the glassware by soaking it in
  sulfuric acid and rinsed several times with
  nanopure water
• We mixed stock reagent (indicator) according to
  the following recipe

• We used 1 mL of stock reagent per 10 mL of a
  sample containing a known concentration of
  phosphate and mixed thoroughly.
• Samples sit for 10-15 minutes
• Absorption is determined using a
  spectrophotometer set at 885 nm wavelength.
• Absorption is plotted against concentration to
  determine a standard curve in the range of
  natural seawater.
• Unknown concentrations of phosphate in seawater
  are determined by comparing absorption values
  with concentration values from our standard
  curve.

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First standard curve data did not produce a
linear regression! GRR!!!
Discussion led our group to believe that a lower
micro molar concentration would be appropriate
for a linear regression, because of the first
three data points on the graph.
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Effective Standard Curve!
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Finding Phosphate Concentration of
Seawater Using Standard Curve Equation
Absorbance Equation
y 0.0023x 0.2902
Concentration Equation
x y 0.2902/0.0023
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Absorbances Concentrations
Natural Seawater
Artificial Seawater
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• Standard curve
• Artificial Seawater
• Natural Seawater