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1.
The gravimetric method usually uses an appropriate method to separate the measured component from the sample, and then convert it into a certain weighing form, and finally use the weighing method to determine the content of the component
The gravimetric method is mostly used in the analysis of inorganic substances.
2.
(1) The scope of application
(2) Principle
The drying temperature is generally 105±3℃
When the total dissolved solids of the water sample contains a large amount of calcium chloride , calcium nitrate , and magnesium chloride , these compounds have strong moisture absorption and the weighing cannot be constant.
(3) Instruments
(4) Reagents
(5) Measurement steps
1) Wash the evaporator, put it in an oven at 105±3℃ for 30min, take it out, and cool it in a desiccator for 30min
2) Weigh its weight on the analytical balance, bake it again, and weigh it until a constant weight.
3) Filter the supernatant of the water sample with a filter, use a non-grading pipette to take 100ml of the evenly shaken filtered water sample in an evaporating dish.
4) Put the evaporating dish on a water bath and evaporate to dryness (the surface of the water bath should not touch the bottom of the dish), move the evaporating dish into an oven at 105±3℃, take it out after 1h, put it in a desiccator, cool for 30min, and weigh
5) Put the weighed evaporating dish into an oven at 105±3°C for 30 minutes, and then put it in a drying vessel to cool for 30 minutes, and weigh until constant weight
The total dissolved solids are dried at 180±3℃
.
According to the above steps, dry the evaporating dish at 180±3℃ and weigh it to a constant weight
.
Use a non-grading pipette to draw 100ml of water sample into the evaporating dish, accurately add 25.
0ml of 1% sodium carbonate solution in the evaporating dish, mix well, and make a pair of blanks where only 25.
0ml of 1% sodium carbonate solution is added
.
The weight of the sodium carbonate blank should be subtracted when calculating the water sample results
.
(6) Calculation
.
In the formula, C—— total dissolved solids in water sample, mg/L;
W 1 ——weight of empty evaporating dish, g;
W 2 ——The total weight of evaporating dish and dissolved solids, g;
V—Volume of water sample, ml
.
Related link: Water quality analysis turbidity method