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Is 1 ppb equal to 1 μg/kg?

15

$begingroup$

In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I thought that 1 μg/kg = 1 ppb.

Is 1 ppb equal to 1 μg/kg ? What is a reason to consider ppb as incorrect ?

concentration notation units

share|improve this question

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

New contributor

Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  $begingroup$
  Just using ppb is ambiguous unless you state the basis (eg w/w for mass %). ppb could also be referring to molar proportion or volume proportion.
  $endgroup$
  – matt_black
  20 hours ago
  

  
  
  
  

add a comment | 

15

$begingroup$

In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I thought that 1 μg/kg = 1 ppb.

Is 1 ppb equal to 1 μg/kg ? What is a reason to consider ppb as incorrect ?

concentration notation units

share|improve this question

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

New contributor

Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  $begingroup$
  Just using ppb is ambiguous unless you state the basis (eg w/w for mass %). ppb could also be referring to molar proportion or volume proportion.
  $endgroup$
  – matt_black
  20 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I thought that 1 μg/kg = 1 ppb.

Is 1 ppb equal to 1 μg/kg ? What is a reason to consider ppb as incorrect ?

concentration notation units

share|improve this question

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

New contributor

Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

New contributor

Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

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Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited yesterday

andselisk

19.5k664127

edited yesterday

andselisk

19.5k664127

asked yesterday

NakxNakx

1816

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Nakx is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked yesterday

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1 Answer
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33

$begingroup$

You are correct suggesting that 1 μg/kg implies 1 ppb, however the reverse is not true. For instance, 1 ppb can also be 1 nmol/mol, and the reader will never have a chance to deduce which one is it unless you explicitly define the usage of the "parts per something" in the text.
This clutters the manuscript with redundant notes and causes overall confusion.

IUPAC also lists all similar symbols (ppm, ppt, ppb etc.) as deprecated; from IUPAC's “Green Book” [1, p. 98]:

Although ppm, ppb, ppt and alike are widely used in various applications of
analytical and environmental chemistry, it is suggested to abandon completely their use because of the ambiguities involved. These units are unnecessary and can be easily replaced by SI-compatible quantities such as pmol/mol (picomole per mole), which are unambiguous. The last column contains suggested replacements (similar replacements can be formulated as mg/g, μg/g, pg/g etc.).

$$
begin{array}{lllll}
hline
text{Name} & text{Symbol} & text{Value} & text{Examples} & text{Replacement} \
hline
ldots & & & & \
text{part per billion} & text{ppb} & 10^{-9} & text{The air quality standard for ozone is a} & pu{nmol/mol} \
& & & text{volume fraction of}~varphi = 120~text{ppb} & \
ldots & & & & \
hline
end{array}
$$

References

1. IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. (PDF)

share|improve this answer

edited 17 hours ago

answered yesterday

andseliskandselisk

19.5k664127

$endgroup$

• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  $begingroup$
  Similarly in the related standard ISO 80000: "Abbreviations such as ppm, pphm, ppb and ppt are language-dependent and ambiguous and shall not be used. Instead, the use of powers of 10 is recommended."
  $endgroup$
  – Loong♦
  22 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This difficulty with "parts-per" notations should probably be extended to percentages as well (given that, really, 'percent' is just 'parts per hundred'). I can't tell you how many times I've struggled to identify what kind of percentage is meant: % w/w? % w/v? at. %? % v/v? For % v/v, what are the bases? Is 10% one volume A for every 9 volumes of B? For every 10 volumes of B? For 10 volumes of final mixture/solution? Headaches, headaches, headaches, every dang time.
  $endgroup$
  – hBy2Py
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ andselisk, I am slightly confused by this new recommendation. My question is related to the denominator in nmol/mols. Suppose I prepare 100 ppb NaCl in water. Do I have 100 nmol of NaCl in 1 mol of water? How we practically prepare it. What if my solvent is a mixture such as air. How will we calculate moles of air? This new definition does not seem to be any better than the previous ones.
  $endgroup$
  – M. Farooq
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @M.Farooq I'm not sure I understand, and this is not a novel directive, part-per-somehing has never been a favored/preferred notation as long as I remember myself. ppb is just a fraction, use whatever quantities of the same dimensions; you have to find out the amounts to calculate ppb anyways, why is this suddenly a problem?
  $endgroup$
  – andselisk
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @andselisk, I am actually wondering about different scenarios. There is a very subtle difference in using nmol/mol vs. ug/kg. The typical definition of ppb is ug X in a kg of solution not the solvent. 100 ppb NaCl in water mean 100 ug NaCl "in" 1 liter of water solution. The total volume is 1 L. The analyte is a part of the solvent weight. With 100 ppm NaCl as 100 nmol NaCl dissolved in 1 mol water. In this case, NaCl is not a part of solvent. Similarly if I have a mixture as a solvent, whose moles should we use? The 1 L and kg definition do not care about the identity of the solvent system.
  $endgroup$
  – M. Farooq
  9 hours ago
  

  
  
  
  

 | 
show 1 more comment

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33

$begingroup$

You are correct suggesting that 1 μg/kg implies 1 ppb, however the reverse is not true. For instance, 1 ppb can also be 1 nmol/mol, and the reader will never have a chance to deduce which one is it unless you explicitly define the usage of the "parts per something" in the text.
This clutters the manuscript with redundant notes and causes overall confusion.

IUPAC also lists all similar symbols (ppm, ppt, ppb etc.) as deprecated; from IUPAC's “Green Book” [1, p. 98]:

Although ppm, ppb, ppt and alike are widely used in various applications of
analytical and environmental chemistry, it is suggested to abandon completely their use because of the ambiguities involved. These units are unnecessary and can be easily replaced by SI-compatible quantities such as pmol/mol (picomole per mole), which are unambiguous. The last column contains suggested replacements (similar replacements can be formulated as mg/g, μg/g, pg/g etc.).

$$
begin{array}{lllll}
hline
text{Name} & text{Symbol} & text{Value} & text{Examples} & text{Replacement} \
hline
ldots & & & & \
text{part per billion} & text{ppb} & 10^{-9} & text{The air quality standard for ozone is a} & pu{nmol/mol} \
& & & text{volume fraction of}~varphi = 120~text{ppb} & \
ldots & & & & \
hline
end{array}
$$

References

1. IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. (PDF)

share|improve this answer

edited 17 hours ago

answered yesterday

andseliskandselisk

19.5k664127

$endgroup$

• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  $begingroup$
  Similarly in the related standard ISO 80000: "Abbreviations such as ppm, pphm, ppb and ppt are language-dependent and ambiguous and shall not be used. Instead, the use of powers of 10 is recommended."
  $endgroup$
  – Loong♦
  22 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This difficulty with "parts-per" notations should probably be extended to percentages as well (given that, really, 'percent' is just 'parts per hundred'). I can't tell you how many times I've struggled to identify what kind of percentage is meant: % w/w? % w/v? at. %? % v/v? For % v/v, what are the bases? Is 10% one volume A for every 9 volumes of B? For every 10 volumes of B? For 10 volumes of final mixture/solution? Headaches, headaches, headaches, every dang time.
  $endgroup$
  – hBy2Py
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ andselisk, I am slightly confused by this new recommendation. My question is related to the denominator in nmol/mols. Suppose I prepare 100 ppb NaCl in water. Do I have 100 nmol of NaCl in 1 mol of water? How we practically prepare it. What if my solvent is a mixture such as air. How will we calculate moles of air? This new definition does not seem to be any better than the previous ones.
  $endgroup$
  – M. Farooq
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @M.Farooq I'm not sure I understand, and this is not a novel directive, part-per-somehing has never been a favored/preferred notation as long as I remember myself. ppb is just a fraction, use whatever quantities of the same dimensions; you have to find out the amounts to calculate ppb anyways, why is this suddenly a problem?
  $endgroup$
  – andselisk
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @andselisk, I am actually wondering about different scenarios. There is a very subtle difference in using nmol/mol vs. ug/kg. The typical definition of ppb is ug X in a kg of solution not the solvent. 100 ppb NaCl in water mean 100 ug NaCl "in" 1 liter of water solution. The total volume is 1 L. The analyte is a part of the solvent weight. With 100 ppm NaCl as 100 nmol NaCl dissolved in 1 mol water. In this case, NaCl is not a part of solvent. Similarly if I have a mixture as a solvent, whose moles should we use? The 1 L and kg definition do not care about the identity of the solvent system.
  $endgroup$
  – M. Farooq
  9 hours ago
  

  
  
  
  

 | 
show 1 more comment

33

$begingroup$

You are correct suggesting that 1 μg/kg implies 1 ppb, however the reverse is not true. For instance, 1 ppb can also be 1 nmol/mol, and the reader will never have a chance to deduce which one is it unless you explicitly define the usage of the "parts per something" in the text.
This clutters the manuscript with redundant notes and causes overall confusion.

IUPAC also lists all similar symbols (ppm, ppt, ppb etc.) as deprecated; from IUPAC's “Green Book” [1, p. 98]:

Although ppm, ppb, ppt and alike are widely used in various applications of
analytical and environmental chemistry, it is suggested to abandon completely their use because of the ambiguities involved. These units are unnecessary and can be easily replaced by SI-compatible quantities such as pmol/mol (picomole per mole), which are unambiguous. The last column contains suggested replacements (similar replacements can be formulated as mg/g, μg/g, pg/g etc.).

$$
begin{array}{lllll}
hline
text{Name} & text{Symbol} & text{Value} & text{Examples} & text{Replacement} \
hline
ldots & & & & \
text{part per billion} & text{ppb} & 10^{-9} & text{The air quality standard for ozone is a} & pu{nmol/mol} \
& & & text{volume fraction of}~varphi = 120~text{ppb} & \
ldots & & & & \
hline
end{array}
$$

References

1. IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. (PDF)

share|improve this answer

edited 17 hours ago

answered yesterday

andseliskandselisk

19.5k664127

$endgroup$

• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  $begingroup$
  Similarly in the related standard ISO 80000: "Abbreviations such as ppm, pphm, ppb and ppt are language-dependent and ambiguous and shall not be used. Instead, the use of powers of 10 is recommended."
  $endgroup$
  – Loong♦
  22 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This difficulty with "parts-per" notations should probably be extended to percentages as well (given that, really, 'percent' is just 'parts per hundred'). I can't tell you how many times I've struggled to identify what kind of percentage is meant: % w/w? % w/v? at. %? % v/v? For % v/v, what are the bases? Is 10% one volume A for every 9 volumes of B? For every 10 volumes of B? For 10 volumes of final mixture/solution? Headaches, headaches, headaches, every dang time.
  $endgroup$
  – hBy2Py
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ andselisk, I am slightly confused by this new recommendation. My question is related to the denominator in nmol/mols. Suppose I prepare 100 ppb NaCl in water. Do I have 100 nmol of NaCl in 1 mol of water? How we practically prepare it. What if my solvent is a mixture such as air. How will we calculate moles of air? This new definition does not seem to be any better than the previous ones.
  $endgroup$
  – M. Farooq
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @M.Farooq I'm not sure I understand, and this is not a novel directive, part-per-somehing has never been a favored/preferred notation as long as I remember myself. ppb is just a fraction, use whatever quantities of the same dimensions; you have to find out the amounts to calculate ppb anyways, why is this suddenly a problem?
  $endgroup$
  – andselisk
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @andselisk, I am actually wondering about different scenarios. There is a very subtle difference in using nmol/mol vs. ug/kg. The typical definition of ppb is ug X in a kg of solution not the solvent. 100 ppb NaCl in water mean 100 ug NaCl "in" 1 liter of water solution. The total volume is 1 L. The analyte is a part of the solvent weight. With 100 ppm NaCl as 100 nmol NaCl dissolved in 1 mol water. In this case, NaCl is not a part of solvent. Similarly if I have a mixture as a solvent, whose moles should we use? The 1 L and kg definition do not care about the identity of the solvent system.
  $endgroup$
  – M. Farooq
  9 hours ago
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

You are correct suggesting that 1 μg/kg implies 1 ppb, however the reverse is not true. For instance, 1 ppb can also be 1 nmol/mol, and the reader will never have a chance to deduce which one is it unless you explicitly define the usage of the "parts per something" in the text.
This clutters the manuscript with redundant notes and causes overall confusion.

IUPAC also lists all similar symbols (ppm, ppt, ppb etc.) as deprecated; from IUPAC's “Green Book” [1, p. 98]:

Although ppm, ppb, ppt and alike are widely used in various applications of
analytical and environmental chemistry, it is suggested to abandon completely their use because of the ambiguities involved. These units are unnecessary and can be easily replaced by SI-compatible quantities such as pmol/mol (picomole per mole), which are unambiguous. The last column contains suggested replacements (similar replacements can be formulated as mg/g, μg/g, pg/g etc.).

$$
begin{array}{lllll}
hline
text{Name} & text{Symbol} & text{Value} & text{Examples} & text{Replacement} \
hline
ldots & & & & \
text{part per billion} & text{ppb} & 10^{-9} & text{The air quality standard for ozone is a} & pu{nmol/mol} \
& & & text{volume fraction of}~varphi = 120~text{ppb} & \
ldots & & & & \
hline
end{array}
$$

References

1. IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. (PDF)

share|improve this answer

edited 17 hours ago

answered yesterday

andseliskandselisk

19.5k664127

$endgroup$

share|improve this answer

edited 17 hours ago

answered yesterday

andseliskandselisk

19.5k664127

answered yesterday

andseliskandselisk

19.5k664127

answered yesterday

andseliskandselisk

19.5k664127