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News from the Lab  Articles Online  Analytical Quick Tip  IV Line Humor  ICP Calculations and Equations

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Perform volumetric pipette solution transfer at room temperature. Aqueous standard solutions stored at 'lower' temperature will have a higher density. Weight solution transfers avoid this problem provided the density of the standard solution is known or the concentrations units are in wt./wt. rather than wt./volume.

The difference between ppm and µg/mL is often confused. A common mistake is to refer to the concentration units in ppm as a short cut (parts per million) when we really mean µg/mL. One ppm is in reality equal to 1 µg/g. In similar fashion ppb (parts per billion) is often equated with ng/mL. One ppb is in reality equal to 1 ng/g. To convert between ppm or ppb to µg/mL or ng/mL, the density of the solution must be known. The equation for conversion between wt./wt. and wt./vol. units is:

(µg/g) (density in g/mL) = µg/mL

and/or

(ng/g) (density in g/mL) = ng/mL

Therefore, if we have a solution that is 1000 µg/mL Ca⁺² and know or measure the density to be 1.033 g/mL then the ppm Ca⁺² = (1000 µg/mL) / (1.033 g/mL) = 968 µg/g = 968 ppm.

When making dilutions the following equation is useful:

For example, to determine how much of a 1000 µg/mL solution of Ca⁺² required to prepare 250 mL of a 0.3 µg/mL solution of Ca⁺² we would use the above equation as follows:

(mL_A)(1000 µg/mL) = (250 mL)(0.3 µg/mL)

(mL_A) = [(250 mL)(0.3 µg/mL)]/ (1000 µg/mL)

(mL_A) = 0.075 mL = 75 µL

Exceprt from Inorganic Ventures' ICP Operations Guide.

Articles Online  more articles »

Questions About Mo, Ti, and Hg
Dr. Gaines answers questions from two different chemists -- one concerned with Mo and Ti; the other with Hg.

ICP Operations Guide (complete)
A clear 16-part online guide intended for anyone preparing samples and standards for measurement using ICP. Topics cover many day-to-day tasks required by all operators.

Reliable Measurements: A Guidebook for Trace Analysts (complete)
An essential 17-part online guide for chemical analysts. Topics cover all phases of sample collection, preparation, measurement, and data analysis.

IV Line Humor  more humor »

What's the formula for water?
H₂O

What's the formula for an ice cube?
H₂O³