TOTAL DISSOLVED SOLIDS (TDS)

TOTAL DISSOLVED SOLIDS (TDS):

Principle 
A well-mixed sample is filtered through a standard glass filter; the filtrate is evaporated to dryness in a weighed dish and dried to a constant weight at 180^oC. The increase in dish weight represents the total dissolved solids.

Interference 
Highly mineralized waters with a considerable calcium, magnesium, chloride and sulphate content may be hygroscopic and as such requires prolong drying proper desiccation and rapid weighing.

APPARATUS

• ·        Beaker

• ·      Measuring cylinder

• ·      Drying oven

• ·      Weighing balance

• ·      Filter paper

• ·      Desiccator

PROCEDURE

•        Weigh the empty dry beaker

•        Measure 100ml of the well mixed sample.

•        Filter the measured sample through the filter paper into a weighed beaker.

•        Evaporate to dryness on an oven.

•        Remove the beaker from the oven and place in a desiccator to cool.

•        Measure the dry beaker.

•        Repeat drying, cooling and weighing until weight loss is less than 4% of previous weight.

CALCULATION

Mg/l  =       (A – B) x 1000

                   Vol of sample

Where

          A       = weight of residue + dish

          B       = weight of dish

PRECAUTION

•        Make use of clean apparatus

•        Measurement of sample should be correct

•        Beaker should be well washed and dry for use