Cation Analysis

Analyzing cations in municipal water and industrial wastewater

Common cations in group I and II of the periodic table (dissolved alkali and alkaline earth metals) are not on the National Primary or Secondary Drinking Water Regulations (NPDWR or NSDWR) list. However, these cations are routinely monitored in public water systems in the US and some are regulated in the EU and Japan. For instance, sodium is required to be monitored by the Safe Drinking Water Act; calcium and magnesium are regularly measured for evaluating water hardness.

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Ammonia gas produced from agriculture and wastewater treatment plants poses a severe threat to aquatic life by breaking the balance of sensitive habitats. When dissolved in water, ammonia exists in an equilibrium between its molecular form associated with water and ammonium cation. The extent of its toxicity to aquatic life depends upon the extent of dissociation. Monitoring of ammonium cations provides information on the amount of ammonia dissolved in water, and is required for the National Pollutant Discharge Elimination Program (NPDES) permit during the wastewater treatment process. Ammonium ion is also monitored in the EU and Japan in both wastewater and drinking water.

In addition, small polar amines are often used as additives in power plant waters, such as ethanolamines. Several disparate small polar amines are often analyzed in industrial wastewaters.

Cation analysis techniques

Cation analysis techniques, Integrion HPIC

While alkali and alkaline earth cations are commonly determined by spectroscopic techniques such as AA or ICP-OES, and ICP-MS as described in EPA 200.5, 200.7, 200.8, and 200.9, ammonium cation cannot be measured by atomic absorption techniques.

One technique used to analyze ammonium cations is discrete analysis. The technique provides accurate analysis for a particular analyte through a colormetric, enzymatic, or electrochemical measurement. ISO 15923-1 uses a discrete analyzer to determine ammonium and common anions in potable water, surface, ground and wastewater.

Discrete analyzers can simultaneously analyze various parameters. Testing is efficient, hands-on time is significantly reduced, and waste is minimized.

Ion chromatography (IC), specifically cation chromatography, is another technique that is often used to separate and quantify alkalai and alkaline earth metals, as well as ammonium cation in a single analytical run in less than 30 min at ppt or lower detection limits.

For the past 20 years ion chromatography with suppressed conductivity detection has proven to be a robust and reliable technique for the determination of cations. The advantages that cation suppression provides justify the investment. In fact, the use of suppressor systems is mandatory for employing high-capacity columns or gradient elution techniques. The higher capacity improves performance for trace level determinations of cations in high ionic strength matrices by extending the linear range and resolving higher concentration ratios of sodium and ammonium cations. The problems associated with cation suppression identified in the past―low sensitivity and nonlinear calibration for weakly dissociated cations―are no longer an issue.

Cations in drinking water, environmental water, and wastewater

Cations in drinking water, environmental water and wastewater

Analysis of dissolved alkaline and alkaline earth cations

Dissolved alkali, alkaline earth cations, and ammonium cations are often analyzed in drinking water, environmental water, and municipal wastewaters. ASTM Method D6919-03 is a reference method approved for use by the U.S. EPA for such analyses. Method D6919 separations can be performed by suppressed conductivity IC using the IonPac CS16 column. Using Reagent-Free Ion Chromatography (RFIC) with suppressed conductivity and isocratic elution, these common cations are well separated in 20 min or less using a CS16-Fast-4µm. Both standard and capillary high pressure ion chromatography (HPIC) systems can be used for routine cation analysis

Analysis of ammonium cation

By ion chromatography: Due to its toxicity, ammonium is a required target analyte monitored in municipal wastewater effluent as part of the NPDES wastewater discharge permit requirements. Additionally, as wastewater samples have high concentrations of sodium, it is often important to separate relatively low concentrations of ammonium in the presence of excess sodium.

By discrete analyzer: As described above, a discrete analyzer is often used for analysis of ammonium in drinking water, environmental water, and wastewater, as demonstrated in ISO 15923-1. The instruments described in below application notes are easy to use and need no additional priming or method changeover time thereby giving fast analyzing results.

Cations in industrial wastewater

Cations in industrial wastewater

Cation analysis in fracking water

Hydraulic fracturing (fracking) is widely used to enhance recovery natural gas and oil. Due to large amount of water needed for fracking, more and more fracking practices use recycled water from the produced water generated from previous fracking activities. Cations such as calcium, barium, and strontium contribute to scaling problems in water pumps and pipes, and result in poor performance of recycled water. Determination of cations in recycled water thus is necessary.

Analysis of cation metal contaminants

In power plants, the buildup of impurities at sub-ppb levels of metal contaminants can result in their accumulation in steam generators or turbines. Therefore, monitoring the presence of ionic impurities in cooling waters, boiler waters, feed waters, and steam condensate in both fossil-fueled and nuclear power plants is of critical importance.

  • These impurities can propagate stress corrosion cracking and other corrosion mechanisms in turbines, steam generator tubing, and other plant components.
  • This corrosion can eventually lead to component failures and plant shutdowns, resulting in millions of dollars of lost revenue.
  • Corrosive ions, such as sodium, chloride, and sulfate, can be minimized by continuously monitoring their respective levels and maintaining these levels as low as possible by taking the appropriate action.

Analysis of ethanolamine

Morpholine was used as an additive in power plant waters because it was less volatile than the commonly used ammonia under all volatile treatment (AVT).

  • However, ammonia was still present from the thermal decomposition of morpholine.
  • Less volatile amines with higher base strengths, such as ethanolamine, eventually replace morpholine
  • Large concentrations of one or more amines can make the determination of trace concentrations of other amines and cations difficult

Analysis of alkanolamines

Analysis of alkanolamines is also important in metal surface finishing and in wastewater effluents. alkanolamines are commonly used in acid gas removal systems (scrubbers) in both oil refineries and natural gas plants.

  • Hydrogen sulfide and carbon dioxide form weak acids when the gases are dissolved in an aqueous medium
  • Amines, weak bases, react with the weak acids to form salts and thereby removing the acid gases from the process stream
  • When the amine solution is overloaded with salts, the scrubbing process is adversely affected

Thus, continuous monitoring of the amine solution can improve amine makeup, improve final product performance, and decrease system maintenance.

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