⚗️ Calcium and magnesium in water
In short
Determination of calcium and magnesium in water by flame atomic absorption spectrometry (FAAS) at wavelengths 422. The test is performed according to PN-EN ISO 7980:2002; Range—calcium: 0.1–50 mg/L Ca (without dilution). The procedure comprises 8 steps (about 52–54 min in total); it is used for: Drinking water quality control (Ca, Mg—optional parameters), Water hardness (Ca²⁺ + Mg²⁺) and Langelier index calculation, Mineral and therapeutic water monitoring.
At a glance
- Standard: PN-EN ISO 7980:2002
- Category: Physicochemistry
- Procedure steps: 8
- Total time of stages: 52 min–54 min
- Range—calcium: 0.1–50 mg/L Ca (without dilution)
- Range—magnesium: 0.01–5 mg/L Mg (without dilution)
- Wavelength—Ca: 422.7 nm
Overview
Calcium and magnesium are the main cations responsible for water hardness. Their determination is crucial for drinking water quality assessment, groundwater and surface water mineralization, and treatment process control. Calcium is important for bone and tooth health, and magnesium participates in over 300 enzymatic processes in the body.
The PN-EN ISO 7980 standard describes a flame atomic absorption spectrometry (FAAS) method for determining calcium (up to 50 mg/L) and magnesium (up to 5 mg/L) in raw and drinking water. The method is selective, accurate, and fast—it enables determination of each element separately, which is an advantage over the complexometric method (EDTA).
Calcium and magnesium are optional parameters in drinking water monitoring. Recommended concentrations in drinking water: Ca 30–80 mg/L, Mg 10–30 mg/L. They are crucial for calculating the Langelier index (water stability) and calcium-carbonate equilibrium.
Method principle
In the FAAS method, the water sample is aspirated by a nebulizer (atomizer), which creates an aerosol. The aerosol is introduced into an acetylene-air flame (~2300°C), where atomization occurs—chemical compounds break down into free element atoms. A light beam from a hollow cathode lamp (HCL) at appropriate wavelength passes through the flame. Free Ca or Mg atoms absorb radiation at 422.7 nm (Ca) and 285.2 nm (Mg), respectively. Absorbance is proportional to element concentration in the sample (Beer-Lambert law). To eliminate phosphate interferences, lanthanum chloride (LaCl₃) is added.
Applications
- Drinking water quality control (Ca, Mg—optional parameters)
- Water hardness (Ca²⁺ + Mg²⁺) and Langelier index calculation
- Mineral and therapeutic water monitoring
- Water control in industrial installations and boilers
- Groundwater testing—mineralization
- Surface water and wastewater monitoring
Key parameters
| Parameter | Value |
|---|---|
| Range—calcium | 0.1–50 mg/L Ca (without dilution) |
| Range—magnesium | 0.01–5 mg/L Mg (without dilution) |
| Wavelength—Ca | 422.7 nm |
| Wavelength—Mg | 285.2 nm |
| Flame | Acetylene–air (oxidizing) |
| Analysis time | 10–15 seconds per reading |
Standard
- Standard number
- PN-EN ISO 7980:2002
- Title (PL)
- Jakość wody — Oznaczanie wapnia i magnezu — Metoda atomowej spektrometrii absorpcyjnej
- Title (EN)
- Water quality — Determination of calcium and magnesium — Atomic absorption spectrometric method
Step-by-step procedure
-
AAS startup
Turn on spectrometer, air compressor, open acetylene. Install HCL lamp (Ca 422.7 nm). Ignite flame and adjust parameters (fuel/oxidizer ratio, burner height).
-
Standard preparation—calcium
From 1000 mg/L Ca standard solution, prepare series: 0.5; 1; 2; 5; 10; 20; 50 mg/L in HNO₃ 1%. To each flask add LaCl₃ (final concentration 0.5% La).
-
Sample preparation
Acidify samples with HNO₃ to pH <2. Add LaCl₃ (0.5% La). Dilute if concentration exceeds linear range.
-
Calibration and Ca measurement
Aspirate successive standards—record absorbance. Plot calibration curve. Then measure samples. Repeat each reading 3×, report mean.
-
Lamp change to Mg
Turn off flame. Replace HCL lamp with magnesium (285.2 nm). Re-ignite flame and optimize.
-
Calibration and Mg measurement
Prepare Mg standards (0.02–5 mg/L) with LaCl₃. Calibration and measurement analogous to Ca. Note: Mg linear range is narrower.
-
Quality control
Blank (HNO₃ 1% + LaCl₃), CRM every 10 samples, duplicates, spiked sample. Recovery 90–110%. Correlation coefficient r² > 0.999.
-
Apparatus shutdown
Aspirate deionized water (nebulizer rinse). Turn off flame (close acetylene, then air). Turn off AAS.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Atomic absorption spectrometer (AAS) with flame atomization | Shimadzu AA-7800, Agilent 240FS AA, Thermo iCE 3500, Analytik Jena novAA 800 | 100,000–300,000 PLN |
| Hollow cathode lamps (HCL)—Ca and Mg | Agilent, Photron, S&J Juniper (one lamp per element) | 500–2,000 PLN/piece |
| Oil-free air compressor | Jun-Air, Werther, 6–8 bar, dryer | 5,000–15,000 PLN |
| Acetylene cylinder (dissolved) | 40 L cylinder, operating pressure 0.6–1.0 bar | 200–500 PLN (exchange) |
| Automatic pipettes (100 µL – 10 mL) | Eppendorf Research Plus, Brand Transferpette S | 800–2,500 PLN |
| Volumetric flasks (50, 100, 250 mL) | Class A, borosilicate | 30–100 PLN/piece |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Lanthanum chloride solution (LaCl₃) 10% (w/v) | 10099-58-8 | Phosphate interference suppressor. Dissolve 58.6 g La₂O₃ in 250 mL conc. HCl (carefully!), dilute to 500 mL. Add to samples and standards (final concentration 0.5–1% La). |
| Calcium standard solution 1000 mg/L Ca | 10043-52-4 | Certified CRM (e.g., Merck Certipur, Fluka TraceCERT). Calibration series: 0.5; 1; 2; 5; 10; 20; 50 mg/L Ca. |
| Magnesium standard solution 1000 mg/L Mg | 7791-18-6 | Certified CRM. Calibration series: 0.02; 0.05; 0.1; 0.5; 1; 2; 5 mg/L Mg. |
| Nitric acid (HNO₃) 1% (v/v) | 7697-37-2 | For acidifying samples and preparing standards. Suprapur / TraceSelect purity. |
| Acetylene (C₂H₂)—fuel gas | 74-86-2 | Dissolved in acetone, pressure cylinder. For AAS burner supply. |
| Deionized water | — | Ultrapure, free from Ca and Mg. Conductivity <0.1 mS/m. |
Health and safety (OHS)
- Acetylene—highly flammable and explosive gas (H220). Check connection tightness. Do not approach fire.
- Concentrated HNO₃—strongly corrosive and oxidizing (H272, H314). Work under fume hood.
- Concentrated HCl (for LaCl₃ preparation)—corrosive, irritating vapors (H314, H335). Fume hood.
- La₂O₃—irritating (H315, H319). Use gloves.
- AAS flame (~2300°C)—burn risk. Do not lean over burner.
- Acetylene cylinder—secure against tipping. Do not heat. Store vertically.
- Safety glasses, gloves, and lab coat required.
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 7980:2002 — “Water quality — Determination of calcium and magnesium — Atomic absorption spectrometric method”.
How does this method work?
In the FAAS method, the water sample is aspirated by a nebulizer (atomizer), which creates an aerosol. The aerosol is introduced into an acetylene-air flame (~2300°C), where atomization occurs—chemical compounds break down into free element atoms.
What is the measuring range and accuracy?
Range—calcium: 0.1–50 mg/L Ca (without dilution); Range—magnesium: 0.01–5 mg/L Mg (without dilution); Wavelength—Ca: 422.7 nm; Wavelength—Mg: 285.2 nm.
How long does the test take?
The times given for the individual stages add up to approximately 52 min–54 min. The procedure comprises 8 steps.
What equipment is required?
Atomic absorption spectrometer (AAS) with flame atomization, Hollow cathode lamps (HCL)—Ca and Mg, Oil-free air compressor, Acetylene cylinder (dissolved), Automatic pipettes (100 µL – 10 mL), Volumetric flasks (50, 100, 250 mL). Indicative cost of the core instrument (Atomic absorption spectrometer (AAS) with flame atomization): 100,000–300,000 PLN.
Where is this test used?
Drinking water quality control (Ca, Mg—optional parameters); Water hardness (Ca²⁺ + Mg²⁺) and Langelier index calculation; Mineral and therapeutic water monitoring; Water control in industrial installations and boilers; Groundwater testing—mineralization; Surface water and wastewater monitoring.
What safety precautions apply?
Acetylene—highly flammable and explosive gas (H220). Check connection tightness. Do not approach fire.; Concentrated HNO₃—strongly corrosive and oxidizing (H272, H314). Work under fume hood.; Concentrated HCl (for LaCl₃ preparation)—corrosive, irritating vapors (H314, H335). Fume hood.; La₂O₃—irritating (H315, H319). Use gloves.; AAS flame (~2300°C)—burn risk. Do not lean over burner.; Acetylene cylinder—secure against tipping. Do not heat. Store vertically.; Safety glasses, gloves, and lab coat required.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 7980.