Determining Inorganic Anions in Drinking Water
Aug 26 2015
Author: by Barbara Van Cann on behalf of Thermo Fisher Scientific (UK) Ltd
Water is essential to maintaining life and as such, drinking water needs to be safe for human consumption. Often sourced from ground, precipitation and surface water, there will inherently be impurities within it, which need to be maintained at concentrations low enough not to pose any risk to human health. Inorganic ions and oxyhalides in drinking water can lead to conditions such as fluorosis and methemoglobinemia, which is why the US Environmental Protection Agency (EPA), and similar health and environmental standards agencies in other industrialised countries, have introduced ion chromatography as an approved method for compliance monitoring . Environmental analysis labs are therefore faced with the challenge of accurately monitoring drinking water in line with these guidelines. However, traditional manual analysis methods using spreadsheets for result calculations can be unsafe and prone to human error. The introduction of chromatography software, where all data is held, analysed and reported using preconfigured and adaptable method specific templates, ensures that compliance is adhered to and data integrity is maintained.
Determining common inorganic ions and oxyhalides in drinking water is an extremely important ion chromatography (IC) application. This technique is approved by the Environmental Protection Agency (EPA Method 300.1) and similar health and environmental standards in other industrialised countries, for compliance monitoring of inorganic anions in drinking water . In addition many standards agencies such as the International Organization for Standardization (ISO), the American Society for Testing and Materials (ASTM) and the American Water Works Association (AWWA) have validated IC methods for this use [2,3].
Due to their toxicity, the concentrations of inorganic anions in drinking water are regulated. For example:
• High levels of fluoride can cause skeletal and dental fluorosis
• Nitrite/nitrate can cause methemoglobinemia, a condition which can be fatal to infants
• Ozonation of drinking water containing bromide can result in the formation of bromate, a potential carcinogen, even at low µg/L concentrations
Even secondary contaminants, such as chloride and sulphate, can affect odour, colour and other aesthetic characteristics of drinking water.
EPA Method 300.1 describes in detail the entire analytical process for the determination of common inorganic anions and oxyhalides in drinking water. To generate reliable, accurate, and repeatable results when adhering to this methodology, quality control (QC) is essential. The QC procedures detailed within EPA Method 300.1 consist of an initial demonstration of performance, assessing laboratory performance within every analysis batch, and assessing analyte recovery and data quality. In addition, the procedures for calibration, standardisation, data analysis and calculations are described. The challenge that environmental analysis laboratories face is to correctly implement these guidelines. First an analytical method, including experimental conditions suitable for instrumentation available in the laboratory, needs to be identified and implemented. Next the guidelines as described in the EPA method, including calculating and assessing the final results, need to be executed correctly. This can prove challenging, since data is often manually transferred to an external spreadsheet, a process which can be both time consuming and open to errors. These spreadsheets are uncontrolled, with no automatic tracking or versioning of changes.
Here we look at how a system, such as an eWorkflow in the Thermo Scientific™ Dionex™ Chromeleon™ 7.2 Chromatography Data System (CDS) software, performs the determination of inorganic anions according to the requirements as described in EPA Method 300.1.
The experimental conditions for the execution of the EPA Method 300.1 are described in detail across several application documents, which can be found in Thermo Scientific™ AppsLab Library of Analytical Applications (Figure 1) and are listed in Table 1 below. Each experiment was performed using Thermo Scientific instruments and columns to meet the different EPA Method Part A or B criteria.
For method execution, an electronic workflow (eWorkflow) was used, to provide guidance throughout an entire analysis batch, from initial sample to final results. The eWorkflow assists in creating an appropriate sequence of actions, with predefined associated files and the correct injection order. The processing method and report templates are included to ensure that the data is processed correctly and final calculations and checks are readily available. A dedicated eWorkflow for the EPA Method 300.1 can be downloaded from the AppsLab Library. This ensures that every step of the EPA specified protocol is undertaken in the correct order, without error.
EPA Method 300.1 provides a detailed description about which order the field samples, standards and other related solutions need to be injected (Figure 2A). This order is also dependent on the total number of field samples and therefore subject to change. The dedicated EPA eWorkflow defines the order of injections (Figure 2B) and if the field number varies, it automatically adjusts to have the correct number of calibration checks and standards. Due to this automatic adjustment functionality, the result is a consistent sequence table with the correct structure that conforms to the EPA requirements (Figure 2C).
The generated sequence contains specific columns to identify the individual injections (analysis type, fortified and duplicate), and the component table of the processing method contains columns to enter parameters specific for the EPA Method 300.1, such as minimum detection and reporting limits. Combining the information present in the sequence and processing method with calculations in the spreadsheet-based report of the software, provides a complete solution that converts all information as described in the EPA Method 300.1 to a final analysis report (Figure 3), eliminating the need to transfer any data to an external spreadsheet. As a result, the likelihood of errors being introduced is minimised and data integrity is ensured.
Figure 3a shows EPA Method 300.1, Chapter 9.4.3, and details the calculation and evaluation of the field or laboratory duplicates. Section 188.8.131.52 defines the calculation for the relative percentage difference (RPD), which can be performed within the software’s reporting tools. Then the RPD limit should be determined, since this depends on the concentration of the analyte relative to its minimum reporting limit (MRL). The calculated RPD for the duplicate injection set is compared to the RPD limit and the evaluation result is reported. To complete the process, a final report can be created, which details the results for each individual section of the EPA Method 300.1 (Figure 4).
The analysis of drinking water in compliance with guidelines such as those set by the US EPA is an important part of environmental analysis, and one which can be greatly simplified through the use of chromatography software. In order to get the full benefit of such software, advanced application expertise is often required to ensure that method development is optimised. There are few online portals offering complete application data and methods, and those that do typically require adaptation to the methods to make them usable in the lab. The AppsLab Library is the only on-line application search engine providing downloadable, ready to run analytical methods, including EPA Method 300.1.
The combination of AppsLab Library and Chromeleon CDS enables analysts to unite their chromatography software with an extensive repository of applications and eWorkflows, simplifying the path to compliance with regulatory requirements. By using the EPA Method 300.1 eWorkflow, environmental analysis laboratories can make sure that analyses are executed according to all guidelines for the determination of inorganic anions and oxyhalides in drinking water, ensuring compliance. The built-in reporting template provides error-free results without the need to export to an external spreadsheet removing time-consuming and error-prone manual transcriptions.
1. Method 300.1: Determination of Inorganic Anions in Drinking Water by Ion Chromatography; U.S. Environmental Protection Agency, National Exposure Research Laboratory, Office of Research and Development: Cincinnati, Ohio, 1997. [Online] http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2007_07_10_methods_method_300_1.pdf (accessed May 19, 2015).
2. Greenberg, A. E.; Clesceri, L. S.; Eaton, A. D., Eds.; Standard Methods for the Examination of Water And Wastewater, 18th ed.; American Public Health Association: Washington, DC, 1992.
3. Standard Test Methods for Anions in Water by Chemically Suppressed Ion Chromatography; American Society for Testing and Materials; West Conshohocken, PA; 1999, D4327-97, Vol. 11.01, 420–427.
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