Kelly-Ann UR - Making the Right Choices

     When preforming any kind of quantitative analysis, it is important to know how precise you need your data to be, as well as any time and cost constraints that you may have.  Ideally, you would always want to be precise as possible.  However, generally speaking, more precise methods tend to cost more and take more time.  
     Fortunately, my research revolves around nitrate in freshwater bodies.  Determining the level of nitrate in water is something that multiple analytical techniques can accomplish.  I will have the luxury of choosing one that best fits my precision needs while staying within my constraints for this project.
     Nitrate levels can be determined rather quickly, in less than ten minutes after the sample has been prepared, using voltammetry.  This process uses a copper-modified glassy carbon electrode (GCE).  To prepare the sample for this method the sample should be filtered if there is a high level of turbidity and the pH should be adjusted to 1 using sulfuric acid.  Reagents of potassium chloride and copper (II) sulfate are added to the sample as well.  This method has a detection range of 10 to 300 μM.
     Surface-enhanced Raman spectroscopy can also be used to determine nitrate levels in a water sample.  Spectroscopy looks at absorption patters in a series of dilutions of a single sample.  Samples must be thoroughly filtered before analysis.  This method requires more equipment than the GCE, however, it has a longer range of detection (1-00mg/L).

The Ion-Exchange Method

     Yet another method for analyzing nitrate levels in freshwater is the ion-exchange method.  This is one of the most widely used methods due to its high level of reliability and accuracy.  There are six steps to this method: pretreatment, extraction, elution, neutralization, removal of interfering ions, and drying for stable isotope analysis.  Although precise, this process is both lengthy and costly.
     The methods I have covered for quantitative nitrate analysis in freshwater samples are only three of many.  Before I make a decision on which method I am going to use for my analysis I need to determine if any of the equipment I will need is already available for me.  

Works Cited

• Gajaraj, S., Fan, C., Lin, M., & Hu, Z. (2013). Quantitative detection of nitrate in water and wastewater by surface-enhanced Raman spectroscopy. Environ Monit Assess. doi:10.1007/s10661-012-2975-4
• Li, W., Song, Y., Xu, H., Chen, L., Dai, W., & Dong, M. (2015). Ion-exchange method in the collection of nitrate from freshwater ecosystems for nitrogen and oxygen isotope analysis. Enviornmental Science and Pollution Research, 2213, 9575-9588. doi:10.1007/s11356-015-4522-7
• Luo, X., Wu, J., & Ying, Y. (2013). Voltammetric detection of nitrate in water sample based on in situ copper-modified electrode. Ionics, 19(8), 1171-1177. doi:10.1007/s11581-012-0839-0