Thermo Fisher Scientific CyberScan CON 400/410 (For units manufactured before March 2010, discontinued) - Manual (Page 52)

Instruction Manual CON 400/410
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14 ADDENDUM 2: CALCULATING TDS CONVERSION
FACTORS
You can calibrate your meter using TDS calibration standard solutions. The calibration
standard only needs to give the TDS value at a standard temperature such as 25 °C. To
determine the conductivity-to-TDS conversion factor use the following formula:
Factor = Actual TDS ÷ Actual Conductivity @ 25 °C
Definitions:
• Actual TDS: Value from the solution bottle label or as a standard you make
using high purity water and precisely weighed salts.
• Actual Conductivity: Value measured using a properly calibrated
Conductivity/Temperature meter.
Both the Actual TDS and the Actual Conductivity values must be in the same magnitude of
units. For example, if the TDS value is in ppm the conductivity value must be in µS; if the TDS
value is in ppt the conductivity value must be in mS.
Check your factor by multiplying the conductivity reading by the factor in the above formula.
The result should be in TDS value.
14.1 “Preparing your own TDS calibration standards”.
If you are trying to measure a concentration of a fertilizer, sea salt, or other sample that uses
multiple salts that may not be relevant to commercially available KCl based standards, it may
be desirable to prepare your own TDS standards.
Since ppm is expressed as milligrams per Liter, the preparation is relatively simple with an
analytical balance. One gram of water = 1 mL = 1 cubic centimeter.
To prepare a TDS calibration standard of 750 ppm, weigh out 750 milligrams (0.75 grams) of
your salt or fertilizer and dissolve into 1000 grams (1 liter) of purified water