A chemical substance is any material
substance used in or obtained by a process of chemistry.
A chemical compound is a substance
consisting of two or more chemical elements that are chemically
combined in fixed proportions.
A chemical element is a substance
that cannot be divided or changed into different substances by
ordinary chemical methods.
Concentration is a very common
concept used in chemistry and related fields. It is the measure
of how much of a given substance there is mixed with another substance.
This can apply to any sort of chemical mixture but most frequently
is used in relation to solutions, where it refers to the amount
of solute dissolved in a solvent.
Parts per notation is a measure of concentration that is
used where low levels of concentration are significant. This is
often used to denote the relative abundance of trace elements
in the Earth's crust, trace elements in forensics or other analyses,
or levels of pollutants in the environment.
| Parts per notation |
Abbreviations |
Examples |
| Parts per hundred |
Denotes one particle of a given substance for every 99 other
particles.
This is the common percent (‘%') = 1 part in 102
Very rarely 'pph' |
|
| Parts per thousand |
Denotes one particle of a given substance for every 999
other particles.
Denoted by '‰' [the per mil symbol] = 1 part in 103
Occasionally 'ppt' |
This is roughly equivalent to one drop of ink in a cup of
water, or one second per 17 minutes.
'Parts per thousand' is often used to record the salinity
of seawater. |
| Parts per million |
Denotes one particle of a given substance for every 999.999
other particles.
1 part in 106
‘ppm’ |
This is roughly equivalent to one drop of ink in a 40 gallon
drum of water, or one second per 280 hours |
| Parts per billion |
Denotes one particle of a given substance for every 999.999.999
other particles.
1 part in 109
‘ppb’ |
This is roughly equivalent to one drop of ink in a canal
lock full of water, or one second per 32 years. |
| Parts per trillion |
Denotes one particle of a given substance for every 999,999,999,999
other particles.
1 part in 1012
‘ppt’
ppt can be confusing as it is sometimes used for parts per
thousand - if you want to use "part per" notation
in this case it is safer to use ppth abbreviation (but rarely
used) or "pro mille" ‰ sign) |
This is roughly equivalent to one drop of ink in an Olympic-sized
swimming pool, or one second every 320 centuries.
To put "parts per trillion" into perspective, one
part per trillion can be considered equal to:
One inch in 1.6 million miles
One second in 32,000 years
One cent in $10 billion
One square foot of the state of Indiana |
| Parts per quadrillion |
Denotes one particle of a given substance for every 999,999,999,999,999
other particles.
1 part in 1015
‘ppq’
ppq is rather a theoretical construct then a useful thing,
chances are you will never see it in use |
This is roughly equivalent to a drop of ink in a medium-sized
lake, or one second every 32,000 millennia.
There are no known analytical techniques that can measure
with this degree of accuracy; nevertheless, it is still used
in some mathematical models of toxicology and epidemiology.
|
Sources:
http://en.wikipedia.org/wiki/Parts_per_million
http://www.chembuddy.com/?left=concentration&right=ppm-ppb-ppt
http://www.dow.com/facilities/namerica/michigan/dioxin/what/trillion.htm
