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Estimation of inorganic nutrients comparing Turner Designs Trilogy with absorbance modules to a Bran & Luebbe Auto Analyzer

October 28, 2011

Parameters: Absorbance

 

Introduction
Auto Analyzer determination of nutrient concentrations utilizing absorbance have been used for water monitoring and water quality studies, ecosystem and phytoplankton research. The Turner Designs Trilogy with absorbance modules and a Bran & Luebbe Auto Analyzer were used to estimate nutrient concentrations of split water samples. Tests were conducted at the Romberg Tiburon Center for Environmental Studies in an effort to compare the Trilogy’s absorbance estimates to a nutrient specific auto analyzer. 


Study Site

Established in 1978, the Romberg Tiburon Center (RTC) is operated by San Francisco State University (SFSU) for marine studies and research. Scientists at RTC are involved in a broad range of projects, such as San Francisco Bay monitoring, food web studies, salmon restoration, assessment of global productivity, climate variability, and nutrient fluctuations. Our comparison was performed at the Dugdale-Wilkerson laboratory http://online.sfsu.edu/~phytopl/. The laboratory’s main focus is inorganic nutrient inputs and fluxes and how they affect phytoplankton populations. A Senior Oceanographic Research Technician for the lab, Al Marchi, aided us in performing the comparative analyses.

 

Figure 1: Dugdale-Wilkerson laboratory at RTC where samples were collected and analyzed.

 


Sampling Protocol
The Bran & Luebbe Auto Analyzer is highly sensitive utilizing a lamp and photomultiplier tube platform to detect nutrient absorbance. Turner Designs Trilogy uses nutrient specific absorbance modules each fitted with an LED, excitation filter, and photodiode that maximize the accuracy for estimating nutrient concentrations. Al Marchi prepared standards and collected samples for Trilogy comparisons on November 3, 2006 at RTC, in Tiburon, CA. Standards of known phosphate and silicate concentrations were used for simultaneous calibration of the Auto Analyzer and Turner Designs Trilogy. A five-point calibration curve was created for each nutrient in the analysis per instrument. Phosphate and silicate concentrations were calculated using regression equations from their respective calibration curves (figure 2).

 


Results
Turner Designs Trilogy and Bran & Luebbe Auto Analyzer estimated nutrient concentration comparisons for phosphate (figure 3) and silicate (figure 4).

 

Conclusions
Inorganic nutrient concentrations estimated by the Turner Designs Trilogy Absorbance Modules result in a very low percent difference from Auto Analyzer’s that are specifically designed for nutrient analyses. The Trilogy Absorbance Modules will produce accurate estimates of phosphate and silicate concentrations.

 

Figure 2: Five point calibration curves characterizing Turner Designs Trilogy correlation of µM concentration per absorbance units (Au) for phosphate and silicate.

 

 

 
Figure 3: Comparison between Turner Designs Trilogy and Bran & Luebbe Auto Analyzer µM phosphate concentrations for five natural water samples.

 

Figure 4: Comparison between Turner Designs Trilogy and Bran & Luebbe Auto Analyzer µM silicate concentrations for five natural water samples.

 

 

Authors: Al Marchi

Institution:  Romberg Tiburon Center for Environmental Studies

Location:  Tiburon, California, USA

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