A novel derivatization-based liquid chromatography tandem mass spectrometry method for quantitative characterization of naphthenic acid isomer profiles in environmental waters
Journal of Chromatography A, Volume 1293, 7 June 2013, Pages 36–43
Million B. Woudneh, M. Coreen Hamilton, Jonathan P. Benskin, Guanghui Wang, Preston McEachern, John R. Cosgrove
Entry by Matthew S. MacLennan
There are lots of interesting things about the approach described in this paper.
Woudneh et al.'s method is mentioned as attempting to quantify NAs based on "equivalents of pyrenebutyric acid (PYB)" (image of PYB below from ChemSpider)
I find the setup here is a bit convoluted, so I will try to clarify it:
1. Grab sample of OSPW/water filtered, spiked with d19-C10 acid and d31-C16 acid standards, then SPE to isolate NAs.
d19-C10 acid and d31-C16 acid act as surrogate standards for extraction efficiency.
2. NAs derivatized with EDC become amines, and were then spiked with 13C3-atrazine.
3C3-atrazine acts as a recovery standard: monitoring instrument performance and quantifying surrogate recovery values.
3. Merichem NAs mixture was used as the quantification standard (calibration curve) for the OSPW samples. Yet, the quantity of the Merichem NAs mixture was translated to units of PYB. It was noted in the paper that the slope of the Merichem NAs calibration curve was 38% of the slope of the PYB curve. PYB was not added to any OSPW samples.
I feel that the analytical issues involved in quantifying complex unknown mixtures as a bulk material ("total NAs") are important. This study uses a few strategies.
1. Using two surrogate standards for extraction efficiency is a good approach. I feel like they are trying to "bound" the space of SPE binding so that we have a range of recoveries we could reasonably apply to the components of a complex sample.
2. Derivatization using EDC carbodiimide is an important contribution to these types of methods because, in my opinion, it is an attempt to restrict the kinds of fragmentations that could occur in ESI. The assumption is that by doing so, the response factor (ionization efficiency) is almost the same for every type of naphthenic acid species, permitting less error in quantification.
3. The third approach used could be quantifying Merichem NAs in terms of pyrenebutyric acid units. Essentially, the Merichem signal is interpreted on a PYB calibration curve (I hope I have understood this correctly)! Standards are needed, definitely. However, because Merichem NAs calibration curve has a much lower slope (lower ESI-MS sensitivity?) the Merichem NAs concentrations will be squished together on the PYB calibration curve, underestimating the NAs concentrations in solution. Perhaps an improvement would be to interpret toxicity values in terms of units PYB (since toxicity is arguably the most important industrial endpoint) to provide some perspective.
This paper comes out of the context of the quantification of total naphthenic acids. The approach outlined here is fantastic but not without its limits. Are the limits enough to discredit the method? I don't think so. That's why I chose it for the journal club's first paper!
Journal of Great Lakes Research, Volume 40, Issue 2, June 2014, Pages 226–246
Posted by Chris Mallon,
Of all the Laurentian Great Lakes, Lake Erie is the most sensitive to eutrophication. Its sensitivity arises from its shallow depth, making the water warmer and more amenable to algae growth. Lake Erie also receives direct runoff from major cities and intensely-managed agricultural landscapes in Canada and the United States. Lake Erie has therefore been one focal point for the study of eutrophication in freshwater ecosystems.
This article focuses on phosphorus as the main causal factor of eutrophication in Lake Erie. The article covers the history of phosphorus loading, explains the difference between total phosphorus (TP) and dissolved reactive phosphorus (DRP), and explains the impacts these nutrients have on algal growth, dissolved oxygen, and ecosystem health. It also provides a summary of agricultural best management practices (BMPs) that influence the release of TP and DRP into the Lake Erie ecosystem. A summary of the implications of climate change is provided, explaining the impact of more extreme weather events on the phosphorus loading trends already noted. The article concludes with a section describing policy and management implications.
This article offers value in several ways. Firstly, it provides an effective summary from many different disciplines to explain the overall impacts that phosphorus loading is having on the Lake Erie basin. In doing so, it also functions as an annotated bibliography for anyone interested in discussing or learning about the impacts of phosphorus on freshwater ecosystems. Secondly, it provides rare clarity on the historical progression of phosphorus contributions to the Lake Erie ecosystem, synthesizing many different datasets. The context and difference between point source and non-point source pollution is explained, with the overall message being that eutrophication is recurring now because of an increase in non-point source pollution. Thirdly, it very clearly outlines the different sources, both spatially and by industry, of the P loading. This enables one to get a sense of both the volume and nature of the phosphorus entering Lake Erie. Finally, it explains the basic difference between DRP and other types of P in light of the management challenges. The reader can gain a clear understanding that the re-eutrophication of Lake Erie is occurring largely due to the increase in dissolved reactive phosphorus.
In summary, this is a multi-disciplinary introduction to freshwater eutrophication in the Great Lakes as a result of phosphorus loading.