# How are the Standard Solutions ppm calculations derived in the manual for Radiometer Analytical ISE25Cu-9 Copper Ion Selective Electrode (ISE) (half-cell, screw cap)?

## Document ID

Document ID TE7322

Version 4.0

Status Published

## Published Date

Published Date 09/28/2018
Question
How are the Standard Solutions ppm calculations derived in the manual for Radiometer Analytical ISE25Cu-9 Copper Ion Selective Electrode (ISE) (half-cell, screw cap)?
Summary
Standard solutions ppm calculations Radiometer Analytical ISE25Cu-9 Copper Ion Selective Electrode (ISE) (half-cell, screw cap)
Answer
The Standard Solutions ppm (parts per million) calculations are found in the  manual   for the Radiometer Analytical ISE25Cu-9 Copper Ion Selective Electrode (ISE) - half-cell, screw cap (Product # E41M006) on page 9.

Assuming row 1 of the table is accurate. 1 M Cu(NO 3) 2 is 5.411*10 4 Cu. That is a 5.41(10 4) Cu/kg solution.

A 1.0 L solution would contain 1.0 moles of Cu or 63.54 g Cu.

Based on the above information:
• 1 L weighs 1,174.5 g and contains 63,540 mg Cu
• 100 mL weighs 117.45 g and contains 6,354.0 mg Cu
• 10 mL weighs 11.745 g and contains 635.40 mg Cu
• 1 mL weighs 1.1745 g and contains 63.540 mg Cu
• .1 mL weighs 0.11745 g and contains 6.354 mg Cu

A 10 fold dilution (0.1 M) would be 100 mL of 1 M and 900 mL of water

Assuming density = 1.0 g/mL
6,354 mg Cu/(117.45 g + 900 g) = 6,354 mg Cu/1017.45 g = 6.245*10 3

Assuming density = .9982 g/mL
6,354 mg Cu/(117.45 g + 898.38 g) = 6,354 mg Cu/1015.83 g = 6.254*10 3

A 10,000 Diltuion (.0001M) = .1 mL of 1 M and 999.9 mL of water

6.354 mg/(0.11745 g + 999.9 g) = 6.354 mg/1000.01745 g = 6.354 ppm

These calculations get us close enough to see what is going on.
The density of solution (for ppm calculations) starts at .174 and approaches 0.9982 as dilution increases.

This shows that column 3, rows 4 & 5 are a misprint.

Column 3 (ppm) Row 4 (10-3) should be 6.37*10 1
Column 3 (ppm) Row 5 (10-4) should be 6.37*10 0

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