Measurement of Calcium in Drinking Water

Introduction

It is  helpful to determine the amount of calcium contained in water, since this will enable one to ascertain whether the water is hard, or if it has minerals. This can be determined using atomic absorption spectroscopy (AA) or inductively coupled plasma atomic emission spectroscopy (ICP). However, a much simpler way is by ionizing acid-bound calcium using acidizing pretreatment. The LAQUAtwin Ca²⁺ can be used to measure the total amount of calcium.

The LAQUAtwin Ca²⁺ meter is used as check to determine the calcium content of water products before selling to consumers. This is an easy, quick method used to check the amount of calcium present in water.

Method

Pretreatment Procedure

1. Place 5 ml of sample solution in a 100 ml beaker.
2. Add 10 to 40 μl of 5M hydrochloric acid to the sample solution and confirm that it has a pH of around 2. Return the sample solution to the beaker.
3. Add 15 to 20 ml of 0.05M tris(hydroxymethyl)aminomethane buffer solution with a pH of 7.00 to the solution created in step 2 (thereby diluting it by a factor of 4 to 5) and confirm its pH has changed to around 6 using LAQUAtwin pH meter.

As a supporting electrolyte, add 0.0375 g potassium chloride to 5 ml pre-treated sample solution and dissolve by stirring. Measure the sample with LAQUAtwin callcium meter that has been calibrated and use the dilution ratio to calculate the result. Wash the sensor with tap water and pat dry with a paper tissue.

Results and Benefits

The use of accurate calcium ion testing in controlling the quality and calcium content of water products ensures that consumers are accurately able to gauge their calcium intake. It also enables one to determine whether or not scaling will occur with boiling of their water.

For each type of sample, the following table shows the labeled value, together with the values measured by various methods.

Figure 1 shows the correlation between LAQUAtwin Ca²⁺ data and that from ion chromotography for pretreated and non pretreated samples. Figure 2 shows the correlation between LAQUAtwin Ca²⁺ data and that from other methods for a pretreated sample. Calcium rich mineral water contains calcium sulfate and calcium carbonate, and these were ionized by pretreatment. The data for total Ca amount obtained by LAQUAtwin Ca²⁺ shows better correlation with other methods when the sample has been pretreated.¹ 

¹ Internal study by HORIBA labs, 2013