## 1 Introduction
Sulfuric acid can serve as a sufficient preservative for maintaining nitrate-N and total N concentrations for up to seven days [10], but may be unsuitable for samples containing high concentrations of nitrite because sulfuric acid can cause the chemical conversion to nitrate [11]. Furthermore, a study in California, USA, found that long-term freezing can serve as a viable method, as it did not have a significant effect on concentration [12]. A study looking at samples from Lake Ontario found that storage at 4 \({}^{\circ}\)C produced variable results, with orthophosphate concentrations decreasing by as much as 13% and nitrate-N by as much as 7% after eight days [13]. In contrast, a study in New York found that soil water samples maintained stable nitrate-N concentrations for at least one week, with only slight changes after three to 16 weeks of storage at 4 \({}^{\circ}\)C [14]. A study by [PERSON] et al. [15] looked at using slow freezing in addition to chemicals. This study determined that, while room temperature storage can be used for a short period of time, there needs to be an additional preservation method. Sodium omadine is traditionally used as a preservative or additive in manufacturing materials and process fluids. In 1968, the chemical was registered originally as a biocide to reduce the growth of bacteria and fungi in various industrial products. Today, these products include lubricants, latex \begin{table}
\begin{tabular}{c c c} \hline \hline
**Water Quality Indicator** & **Preservation Method** & **Maximum Holding Time** \\ \hline Nitrate-N & Cool 4 \({}^{\circ}\)C & 48 h \\ Nitrite + Nitrate-N & Cool 4 \({}^{\circ}\)C, H\({}_{2}\)SO\({}_{4}\) (pH below 2) & 28 days \\ Orthophosphate & Filter on-site, cool 4 \({}^{\circ}\)C & 48 h \\ \hline \hline \end{tabular}
\end{table} 
Table 1: United States Environmental Protection Agency (US EPA) water sample preservation methods [1]. products, and various cleaners. It has not been used as a preservative for water-based chemicals, or for water concentrations [16]. Since there has been no study focusing on sodium omadine in preserving nitrate-N and orthophosphate levels in water samples, this will be the first study to determine the impacts this chemical has. This research is significant because it (1) compares existing recommended preservation methods for water samples containing both nitrate-N and orthophosphate, and (2) looks at a new preservation option that has not been previously used for this purpose. This study mimics water monitoring that includes collecting samples from a field site, using an automated water sampler and retrieving the samples up to 14 days after initial collection. The objective of this study is to determine the impact of three different preservation methods on nitrate-N and orthophosphate concentrations: (1) Filtration, as it is the US EPA recommended method for preserving water samples for orthophosphate; (2) addition of sulfuric acid to the water sample, as this is the US EPA recommended method for preserving water samples for nitrate-N; and (3) addition of sodium omadine to the water sample, as a possible alternative to currently recommended methods.