Measurement of Calcium in Drinking Water

LAQUAtwin is a series of pocket ION meters. Using Ion Selective Electrode (ISE) technology, they are available for measuring Conductivity, Calcium, Nitrate, Potassium, Sodium, Salt concentration and pH measurement. Using just a tiny amount of sample, the LAQUAtwin proprietary flat sensors can quickly and accurately measure the values of the chemical parameters in the field.

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 the water (if drinking water) 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 tris-hydroxy-aminomethane buffer solution with a pH of 6.95 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.

A small sample of this solution is placed on the sensor of the LAQUAtwin Ca2+  and measured. To repeat sampling, wash 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.

The LAQUAtwin Ca2+ pocket meter is small and compact; convenient to carry around for on-site testing. Its easy-to-use interface is simple for anyone to use the LAQUATwin Ca2+ pocket meter.

1For 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 Internal study by HORIBA labs, 2013

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