High-Performance Anion Analysis in Drinking and Surface Waters with the Ion Chromatograph IONUS

Author: Jeff Brewer and Dr. Thorsten Heinlein

Introduction

The analysis of anions in drinking and surface water is a critical and universally recognized component of water quality monitoring. While nations worldwide have adopted stringent regulations to protect public health, the specific requirements and maximum contaminant levels for common anions – such as fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate – vary from country to country.

Cations are equally important in water analysis and will be addressed in a separate application note. In addition, many global regulations do not explicitly cover species such as chlorite, chlorate, bromate, or organic acids like formate and acetate, which are also of analytical interest. These compounds will therefore be discussed in a dedicated application note as well.

Even now, many countries do not have or enforce regulations related to water quality. Whether adhering to standards set by the World Health Organization (WHO), the U.S. Environmental Protection Agency (EPA), the European Union, or national bodies in regions spanning South America, Africa, and the Middle East, laboratories require an analytical solution that is both reliable and adaptable.

Ion Chromatography (IC) has become the gold-standard technique for this purpose, offering the sensitivity and selectivity needed to handle diverse water matrices. The Ion Chromatograph IONUS of membraPure is a high-performance ion chromatograph engineered to meet these global challenges. With its proven suppressor technology, universal column compatibility, and advanced automation, the IONUS delivers high-precision results across a wide dynamic range, allowing laboratories to achieve compliance with both trace-level and high-concentration regulatory limits.

The Ion Chromatograph IONUS as the ideal workhorse

The ion chromatograph IONUS offers a range of features that make it ideally suited for water analysis applications. Its precise eluent delivery system ensures consistent and reproducible operation without the need for helium pressurization, while the integrated suppressor technology significantly enhances sensitivity for reliable trace anion detection. The system supports all standard IC columns, giving laboratories maximum flexibility in method development. A heated column compartment maintains stable conditions to deliver reproducible results with optimized peak resolution. With an autosampler capable of handling up to 96 vials, IONUS enables high-throughput analysis while minimizing manual effort. Designed for ease of use and robustness in routine laboratory work, it requires minimal training and ensures dependable long-term performance. Furthermore, its compliance with global regulatory standards makes IONUS a future-proof choice for environmental testing in any region

Advantages of the IONUS IC:

Reliable Eluent Delivery: Consistent and reproducible eluent delivery without helium pressurization.
Suppressor Technology: Enhanced sensitivity by reducing background conductivity, ideal for trace anion detection.
Universal Column Compatibility: Supports all standard IC columns, offering method flexibility.
Heated Column Compartment: Delivers stable temperature for reproducible results and optimized peak resolution.
Autosampler: High-throughput analysis (96 vials) minimizes manual intervention.
User-Friendly Design: Minimal training required, with robust construction for routine lab use.
Regulatory Compliance: Ensures regulatory acceptance for environmental testing regardless of where your lab is located.

This application note provides a validated method for quantifying anions in drinking and surface water. It demonstrates IONUS’s exceptional performance and presents its capability to function within the varied regulatory frameworks found around the globe, proving it is a reliable solution for any laboratory, anywhere. We will address the analyses of monovalent and divalent cations in a separate application.

Global Regulatory Overview for Anions in Drinking and Surface Water

Given the complexity of water quality regulations and the international focus of this application note, a comprehensive understanding of the regulatory environment is essential. The following section provides a non-exhaustive overview of the key regulatory bodies and their requirements for common anions in drinking and surface water, that point to the universal need for a reliable and flexible analytical solution like the IONUS Ion Chromatograph. This information summarizes the specific limits and guidelines that analytical laboratories must meet, reinforcing the importance of the technical data presented in this paper.

World Health Organization (WHO)
The WHO provides the Guidelines for Drinking-Water Quality, which is a framework for managing water safety globally, and are designed for drinking and surface water. The WHO do not dictate specific analytical methods but rather advises that methods used should be capable of achieving the required detection limits.

Fluoride – 1.5 mg/L
Nitrate – 50 mg/L or 10 mg/L as nitrogen (N)
Nitrite – 3 mg/L
Sulfate – 500mg/L is suggested as a limit for taste
Chloride – there is no health-based guideline value

Canada
Health Canada does not provide a published numbered method for Anions in Drinking and Surface water. They do publish maximum acceptable concentrations (MACs) or Aesthetic Objectives (AOs) for various parameters. Laboratories generally use EPA or ISO Standard Methods to meet the performance criteria.

Fluoride – MAC of 1.5 mg/L
Nitrate (as N) – MAC of 10 mg/L
Nitrite (as N) – MAC of 1 mg/L
Chloride – AO of 250 mg/L to minimize consumer complaints about taste
Sulfate – AO of 500 mg/L is recommended for taste

European Union
EU’s Drinking Water Directive sets mandatory parameters for the quality of water intended for human consumption.

Nitrate – maximum limit of 50 mg/L
Nitrite – maximum limit of 0.5 mg/L
Fluoride – maximum limit of 1.5 mg/L
Sulfate – maximum limit of 250 mg/L
Chloride – maximum limit of 250 mg/L

United States – Environmental Protection Agency (EPA)
The US EPA has both legally enforceable Primary and non-enforceable Secondary standards for drinking water. Maximum Contaminant Level (MCL).

Primary Standards (Enforceable)
- Nitrate as (N) – MCL of 10 mg/L
- Nitrite as (N) – MCL of 1 mg/L
- Fluoride – MCL of 4.0 mg/L
Secondary Standards (Non-enforceable, aesthetic based)
- Chloride – 250 mg/L for taste
- Sulfate – 250 mg/L taste and laxative effect
- Fluoride – 2.0 mg/L to protect against tooth discoloration

The International Organization for Standardization (ISO) Methods
The ISO has established ISO 10304-1 for the determination of anions in water with low to moderately high contamination. They have also established ISO-15061 for the determination of dissolved bromate in water using Ion Chromatography.

Other Regions and Regulations:

China – GB 5749-2022 is a comprehensive legal document that sets limits for a wide range of water quality indices.
Japan – The Ministry of Health, Labour, and Welfare established a list of regulated substances and limits. Anions are on this list.
South Korea – The Ministry of Environment implemented the Water Environment Conservation Act that governs water quality and aquatic ecosystems. An official research paper from the The National Institute of Environmental Research provides explicit limits for several anions which have become part of the country’s ‘Mandatory Drinking Water Norms.’ Ion Chromatography in South Korea is a standard analytical method for anions.

Fluoride – 1.5 mg/L
Chloride – 250 mg/L
Nitrate – 10 mg/L
Sulfate – 2000 mg/L

India – IS 10500:2012 specification from the Bureau of Indian Standards prescribes requirements and test methods for drinking water from any source.
Africa – many countries adopt the WHO or US EPA guidelines or reference them in creating their own national standards.
Middle East – the United Arab Emirates references the US EPA and EC/DWD limits for regulations in bottled water.
South and Central America – The WHO guidelines have been referenced, but discrepancies exist, suggesting regulations need to be updated to a more consistent, health-based approach.

Columbia – Ministry of Health and Social Protection and Ministry of Environment and Sustainable Development have key oversight from the Potable Water and Basic Sanitation Regulation Commission.

Key Regulation: Decree 1575 of 2007 established a limit of 1.5 mg/L for Fluoride but there are no limits on Sulfate or Chloride.

Experimental

Sample Collection
Samples were collected in pre-cleaned polypropylene bottles. Because of our sample collection process we have found the pre-cleaned polypropylene bottles to be more durable, less weight, cost-effective, and the polypropylene has low reactivity or leaching of inorganic ions. Each bottle was again rinsed multiple times onsite using the water source, and filled to the top of the bottle. Caps were immediately tightened, and the samples were placed in a cooler on ice. Once back at the laboratory, the samples were transferred to a refrigerator with a temperature held at 4∞C.

The samples collected were from local lakes and from different drinking water sources, for the sake of discussion and to divide the collection points, north of the city dividing line and south of the city dividing line. The drinking water was sourced from a North location and a South location, each area supplied by different sources. The lakes were also divided by the region and include lakes north of the city, mid-city, around a golf course, and south of the city. Each lake has runoff water flowing into it from a different source. The IC was prepared for the analysis with fresh eluent, fresh ultra-pure water, and fresh sulfuric acid. The system was started and equilibration started.

Operating Conditions of the Method

Reagents and Standards

Reagents: Ultra pure water (18.2 MΩ·cm, membraPure Aquinity²P10 water purification system), analytical-grade Sodium Carbonate, Sodium Bicarbonate, Sulfuric Acid were purchased from Millipore-Sigma Chemicals, United States.

Standards: A primary stock mixed anion standard (fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate) was prepared from 1000 mg/L certified standards at 0.1–200 mg/L, variable by analyte, prepared from certified reference materials from Inorganic Ventures, Christiansburg, VA United States. Each standard includes a Certificate of Analysis.

Standard Preparation

While the instrument was in the equilibration phase, 8 levels of mixed working standards were prepared by weight using the primary stock mixed standard mentioned above. Each prepared standard, Levels 1 – Levels 8, were all recorded and entered into the method.

Sample Preparation

Samples were filtered through 0.22 µm syringe filters to remove particulates. Drinking water samples were diluted 1:10 after syringe filtration, using UHP Di water. No other pretreatment was performed. The surface water samples were diluted 1:20 after syringe filter pretreatment using UHP Di water. The blanks, standards, pre-quality control check samples, and the prepared samples were loaded into the IONUS Automated Sampler that is chilled to 20∞C. The method was loaded into Clarity 10 software, which controls the operations and data collection of the IONUS.

Calibration Discussion:

The focus of using a broader range of calibrants is to demonstrate the IONUS capability; however, we recommend selecting the range of calibrants that best aligns with the regulations of your country. For instance, a calibration may include levels 1 to 6 or in another country, a calibration may include levels 2 to 7 or in another country, the calibration may include levels 4 to 8. Regardless of your country or regulation, the IONUS can perform the proper calibration range to meet the requirements of your drinking and surface water (see appendix Table 2, Table 3, Figure 2, Figure 3 .

The Context of the Correlation Coefficient

The coefficient of determination (R²) is a statistical measure that represents the proportion of the variance in the dependent variable (Area Counts) that can be predicted from the independent variable (Concentration). While an R² of 1.0 is a perfect fit, it’s virtually impossible in real-world analysis due to normal instrument noise, small variations in sample preparation, and other factors.

A value of 0.999 is generally considered a highly acceptable standard in the industry for most applications, indicating a strong linear relationship.

A value of 0.997 is also very common and well-regarded, especially when analyzing a wide concentration range or with analytes that can show minor non-ideal behavior at the lower or higher ends of the curve.

The results presented in Table 3 present the exceptional linearity of the membraPure IONUS across a wide dynamic range, a critical requirement for water quality analysis. The coefficient of determination (R²) values for all analytes consistently exceed 0.997 and in most cases are above 0.999, demonstrating a durable, repeatable, and reliable linear relationship between concentration and detector response.

This high degree of linearity, maintained across multiple, partially overlapping concentration ranges, is a testament to the instrument’s stability and precision. It confirms that the IONUS can accurately quantify anions from low-level drinking water standards to higher concentrations found in surface water samples, ensuring a single instrument can address the diverse analytical needs of laboratories globally.

Demonstration of Extended Linear Dynamic Range: IONUS

While many regulatory methods specify a narrower calibration range for optimal accuracy at low detection limits, the membraPure IONUS is engineered to deliver exceptional performance across a wider dynamic range. To demonstrate the system’s stability and linearity, an additional calibration curve spanning all eight standard levels was analyzed.

The results, as shown in Table 1 and graphically displayed in Figure 2 (see appendix) , confirm that the IONUS maintains a linear relationship between analyte concentration and peak area throughout this extensive range.

This high degree of linearity across such a broad concentration range (two orders of magnitude for Fluoride) is a testament to the stability of the IONUS pumping, injection, and detection systems. This capability is particularly beneficial for laboratories that handle a diverse range of samples, from low-level drinking water to more concentrated industrial effluents or surface waters, as it can reduce the use of multiple calibration curves or extensive sample dilution. It provides confidence that even unforeseen high-concentration samples will be accurately quantified within a single run.

Table 1: Results of the determination of the Correlation Coeffizient for the different anions and 9 levels of concentration.

Results and Discussion

The general purpose of this application note is to show (1) quality, reproducible results over a wide calibration range for the analysis of drinking and surface water that aren’t directly correlated to any one particular regulatory method, but to show the widest capability for acceptance by multiple regulatory protocols from a global perspective. As membraPure is a global company, to best support our global customer base, we wanted to prove beyond any doubt, the Ion Chromatograph IONUS could meet or exceed the widest general regulatory acceptance.

The second general purpose of this application note is to (2) prove that regardless of the calibration range selected, (2a) a narrow low calibration range, (2b) a mid calibration range, (2c) a high calibration range, or (2d) the wide possible calibration range – choice depending on the region and regulatory requirements, the Ion Chromatograph IONUS would deliver reproducible, quantifiable results with minimal sample preparation and minimal user intervention.

The third general purpose of this application note is to (3) prove the membraPure column and suppressor technology would deliver quality and reproducible results across a wide range of calibration levels and various water samples that end users could trust to deliver the sample proven level of results in their laboratories without a failure to perform. With membraPure serving a global community of laboratory professionals tasked with producing quality results for drinking and surface water, the worst possible scenario is to have a premature failure of the column or suppressor that would literally shut down the analytical process. Or worse, if there is a worse scenario, the column or suppressor would develop noise or peak movement that would negatively impact the reporting of quality data.

In order to prove the points selected above, our team collected samples from within a 50-mile radius of our location. This included drinking water produced by two different drinking water treatment facilities, we labeled North and South, and four different lakes of varying sizes, with different types of feedwater from rural streams that have runoff from farms and ranches, to a smaller lake with runoff from a golf course, to drainage from major thoroughfares, to a more urban lake with suburban runoff feeding the lake. In the appendix Table 4, the sampled waters are labeled, analyzed in duplicates, and the results are presented.

In addition, a quality control check step was carried out in which a standard was measured before (Appendix, Table 5) and after (Appendix Table 6) the analysis run of the collected water samples, and then the recovery was determined. The aim was to determine system performance and integrity before and after the analysis.

The Ion Chromatograph IONUS instrument with the 96 position autosampler and the powerful Clarity by Data Apex software, puts the analytical laboratory responsible for the environmental analysis of drinking and/or surface in full control with minimal user intervention to perform a broad range of drinking water or surface water samples after minimal sample preparation because of the precision of the injection by the autosampler, consistent eluent delivery without helium pressurization requirements, and durable suppressor technology that isn’t subject to a membrane rupture.

The ability of an instrument to meet regulatory requirements that vary by region, as shown in this application note, from levels below the most stringent to those equal to or above the most flexible as stated in the regulatory protocol, with a simple sample prep and dilution, are relevant to the calibration range which can be translated to the sensitivity of the instrument detection and the precision of the injector.

In the opinion of the author, the Ion Chromatograph IONUS proves it can deliver quality, reproducible results for drinking water and surface water regardless of the location of the lab or the region of the regulatory protocols employed.

Conclusion

A Global Solution for Water Quality Analysis

The data presented in this application note demonstrates that the membraPure Ion Chromatograph IONUS provides a durable, reliable, and versatile solution for the determination of common anions in both drinking and surface water.

Drinking Water: As an example to show the method is flexible to perform within various regulatory requirements, concentrations complied with US EPA drinking water standards (example: fluoride < 4 mg/L, nitrate < 10 mg/L), confirming safety. When compared to other regulatory requirements in other countries, the method also met or exceeded the regulatory compliance for detection and quantification.

Surface water: The higher chloride and sulfate levels reflected run-off from local streets, the golf courses, and the local industry. The location of the various lakes shows the effect of the surrounding community on the water in the lake. The recent heavy rains and the more frequent changes in the water retention are reflected in the results.

Figure 1: Ion Chromatograph IONUS

The instrument’s exceptional performance, as evidenced by a multi-point calibration curve and consistently high correlation coefficients (R²> 0.9999), confirms its outstanding linearity and accuracy across a wide dynamic range.

This level of performance is critical for analytical labs that must adhere to a diverse set of regulatory requirements. By providing an all-in-one solution that can accurately quantify analytes from sub-parts-per-million levels in drinking water to higher concentrations found in surface water, the IONUS system eliminates the need for multiple analytical methods or extensive sample manipulation. The high percent recoveries observed in the Quality Control samples further validate the instrument’s precision and reproducibility, ensuring results are dependable and defensible.

The IONUS system’s ability to handle varied sample matrices from drinking, surface, bottled, and reagent water, and its proven analytical excellence make it an ideal choice for laboratories operating under a wide array of international regulations. It truly offers a singular, high-performance solution that goes beyond borders, meeting the demands of water quality analysis globally.