The Determination of Inorganic Cations in Samples of Water

This technique1 is used to determine the mass concentration of potassium, ammonium, lithium, sodium, strontium, magnesium, calcium, and barium in samples of waste, natural, and drinking waters, as well as other aqueous matrices, by capillary electrophoresis.

Measurement Method

Capillary zone electrophoresis with indirect UV detection at a wavelength of 267 nm is the basis of the measurement method.

Measurement Range

The table below shows the measurement ranges for the components.

Cations Measurement range, mg/L Cations Measurement range, mg/L
Ammonium 0.5–5000 Magnesium 0.25–2500
Barium 0.1–10.0 Potassium 0.5–5000
Calcium 0.5–5000 Sodium 0.5–5000
Lithium 0.015–2.0 Strontium 0.25–50.0


Potassium and ammonium peak shapes will be distorted by injections of samples with sodium concentrations over 200 mg/L. However, this does not influence the quantitative evaluation of their concentrations.

Equipment and Reagents

To make the measurements, the Lumex Instruments CAPEL capillary electrophoresis system is used. A personal computer which runs under the Window® operating system and has the ELFORUN dedicated software package installed carries out acquisition, collection, processing, and output.

Examples of Real Analyses

BGE: benzimidazole, with tartaric acid and 18-crown-6

Capillary: Leff/Ltot=60/60 cm, ID=75 µm

Injection: 150 mbar x sec

Voltage: 25 kV

Temperature: 20 °C

Detection: 267 nm

Measurement results:

1 – ammonium (0.4 mg/L)

2 – potassium (12.7 mg/L)

3 – sodium (28 mg/L)

4 – lithium (0.1 mg/L)

5 – magnesium (13.7 mg/L)

6 – strontium (3.5 mg/L)

7 – calcium (93 mg/L)

References and Further Reading

¹ Regional Standard GOST 31869-2012.

About Lumex Instruments

For almost 30 years, Lumex Instruments has been developing and manufacturing laboratory and industrial analytical equipment, instruments, and procedures.

Our products are used for environmental control, water and wastewater treatment, agriculture, food and beverage quality and safety control, energy industry, and pharmaceutical and biochemical applications. Lumex Instruments offers more than 120 applications for the measurement of organic and inorganic chemicals in liquid, solid and gas.

We offer both traditional and new ingenious solutions, unique technologies and classical equipment, well-established reliable applications and innovative methods. From the beginning of the company, we have developed, manufactured and sold more than 16,500 instruments.

Our products include:

  • capillary electrophoresis systems
  • PCR analyzers
  • atomic absorption spectrometers (including mercury analyzers and monitors)
  • FTIR and NIR Spectrometers
  • fluorimeters and more

We combine high-quality standards with the flexible customized approach because we care about the efficiency of our customer operations. All our innovations are targeted to make the analyses cost-efficient, easy to run, and the instruments easy to maintain and service. We proudly deliver our products and services all around the world and we enjoy working with our valued customers and partners in many industries and countries.

With customers in more than 90 countries worldwide, Lumex Instruments has several offices and multiple distributors around the world.

A significant number of our applications are developed in accordance with international standards, such as ASTM, ISO, EN and EPA.

Facts and figures:

  • More than 30 models of analytical instruments developed starting from 1991
  • Over 20 patents
  • 20% market share of the portable mercury analyzers
  • Over 120 applications
  • Over 350 employees, and 25% of them are involved in the development of new applications and instruments

The customers who selected Lumex Instruments include: BP, Enel, Royal Dutch Shell, PETRONAS, PetroChina, Chevron, UNIDO, SGS, Carlsberg Group, Unilever, PepsiCo, Nestle, Princeton University, and others.

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Last updated: Jul 24, 2020 at 5:31 AM


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