Sodium (Na) ions are one of the most important electrolytes along with chloride, calcium and potassium. Sodium ions play vital roles in the maintenance of plasma volume, pH balance, transmission of nerve impulses, and normal cell functions. Healthy individuals can absorb sodium ingested in food, and kidneys maintain proper sodium balance by excreting its excess in urine. Sodium sources include table salt, milk, meat, shellfish, bread, snack food, etc. Hyponatremia (low sodium concentration in blood) can occur in patients with nephrotic syndrome, excessive vomiting and diarrhea, while Hypernatremia (high sodium concentration in blood) is developed in patients suffering from liver diseases, burns, and pregnancy.

Sodium Assay Kit provides a simple, reproducible, and sensitive tool of measuring sodium concentration in serum, saliva, urine, and other biological liquid samples. In this assay, the enzyme β-galactosidase activated by sodium ions can catalyze glycoside analogues to produce glycoside and o-nitrophenol. The product o-nitrophenol produces a yellow color that can be detected at an absorbance of 420 nm. The optical density measured is directly proportional to the sodium level present in the sample.

• Microplate reader capable of measuring absorbance at 420 nm
• Incubator at 37°C
• Precision pipettes to deliver 2 µL to 1 mL volumes
• Tubes to prepare sample dilutions
• 5 mL tubes
• Multi-channel pipettes to deliver 20 µL to 200 µL volumes
• MilliQ water or another type of double distilled water (ddH₂O)

1. Add 20 µL of the diluted Sodium standards or samples to the 96-well microtiter plate.
2. Initiate the reaction by adding 70 µL Working Solution to all wells. Carefully shake the plate for a few seconds to mix.
3. Incubate the plate for 30 minutes at 37°C with mixing in the dark.
4. Add 120 µL of Stop Solution to each well.
5. Measure the absorbance at 420 nm using a plate reader.