Team:SVA-NYC/Measurement

SVA-NYC

Measurement

Wavelength scan reading for the iron standard. The most highly concentrated reading is in the front and the lowest in the back. For each concentration in the standard, the highest peak corresponds to the wavelength at which iron absorbs the most light.

Standard curve reading for iron. After the wavelength with the highest absorbance across the board is determined, the number is used to again measure each concentration in the standard to produce an equation for which to apply the soil sample readings.

Soil sample iron concentrations. The absorbance of each sample is read by the spectrophotometer and a concentration is determined by the standard curve equation for iron.

Standard preparation

Run chemical past health and safety board, if approved, calculate molar ratio of ion in solution. Determine the proper chemical stand-in for the ionic compound in question. Ideally this is a chemical which has only one of the compounds per molecule (example: if chloride ion is being tested, prefer NaCl over CaCl2 as the standard material.)

Wavelength sweep

An absorption spectrum reading is performed to determine the wavelength that matches each nutrient’s standard gradient. Using MetaSpec Pro’s UV/VIS spectrophotometer and software, the wavelength profile of each standard is measured from 780nm to 380nm and analyzed in Excel to determine their sensitivity to a particular wavelength. In the “Wavelength Scan” feature, parameters are set as follows:
Concentration units – ppm
Display mode – Absorbance
Start wavelength – 780
End wavelength – 380
Wavelength Interval(nm) – 1.0
Scan times – 21
The machine is then zeroed with the nutrient standard cuvette labeled “0”. The wavelength scan is performed for each cuvette in the nutrient’s standard by first wiping down the cuvette, shaking or vortexing it, then placing it into the spectrophotometer and immediately hitting “start”. After the readings for all 21 of the cuvettes in each standard are measured, the data are then exported into excel. The sum is taken of the absorbance for each wavelength then sorted from largest to smallest. The wavelength corresponding to the greatest absorbance sum is then selected to be used in a standard curve reading.

Standard Curve

The standard curve determines the linear relationship between a nutrient’s absorbance and it’s concentration in a medium. Once a wavelength has been established, it is entered into the “Standard Curve” feature or the Metaspec Pro’s software. The parameters for the standard are set as follows:
No. of WL – 1
Unit – ppm
No. of Std. Samples – 21
In the “Standard Sample List”, “Conc.” Is determined by the concentrations, in parts per million, labeled on the nutrient’s cuvettes. The machine is then zeroed again with the nutrient’s standard cuvette labeled “0.” As the absorbance is measured for each cuvette in the standard (including zero), a scatter plot is created that should increase linearly along with concentration. If the relationship in the standard curve is not linear, the reading should be performed again. The standard may need to be reprocessed and re-analyzed before quantitative analysis.

Quantitative Analysis

MetaSpec Pro’s “Quantitative Analysis” feature is used to determine the concentration of each nutrient in the collected soil samples. Quantitative analysis is performed by measuring the absorbance of each sample for each nutrient and applying the equation from the corresponding standard curve line. The linear equation calculated in the “Standard Curve” feature is transferred over to “Quantitative Analysis” and is selected from the “Standard curve method” option in the parameters. For each nutrient, the machine is zeroed again with the corresponding standard’s “0” and the soil samples’ absorbances are measured by the spectrophotometer. These data are then exported into excel to be graphed.

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Team SVA-NYC

SVA Bio Art Lab
School of Visual Arts

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335 W 16th St.
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