Translator for HPLC HINTS and TIPS for Chromatographers

Saturday, May 7, 2016

Typical Commercial Strengths of Common Acids and Bases Used in HPLC



CHEMICAL NAME
MOLECULAR WEIGHT
MOLES / LITER
GRAMS / LITER
PERCENT by WEIGHT
SPECIFIC GRAVITY
Acetic Acid
60.05
6.27
376
36
1.045
Acetic Acid, Glacial
60.05
17.4
1045
99.5
1.05
Formic Acid
46.02
23.4
1080
90
1.21
Hydrochloric Acid
36.5
11.6
424
36
1.18
Nitric Acid
63.02
15.99
1008
71
1.42
Perchloric Acid
100.5
11.65
1172
70
1.67
Phosphoric Acid
98
14.7
1445
85
1.70
Sulfuric Acid
98.1
18.0
1766
96
1.84






Ammonia (in H20)
17.0
14.8
252
28
0.898
Potassium Hydroxide
56.1
13.5
757
50
1.52
Sodium Hydroxide
40.0
19.1
763
50
1.53


Data obtained from The Merck Index, 11th edition (1989).

3 comments:

  1. This is great! Thank you for providing it.

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  2. Good morning, I run HPLC methods from the European Pharmacopoeia. Many of these methods (Impurities active ingredients), developed in reverse phase, involving the addition of significant amounts of glacial acetic acid (up to 10%) to the eluent phase in addition to the presence of the organic modifier. Could you explain the utility? These eluents cause much noise. Thank you for your Blog

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    Replies
    1. We sometimes add an acid (to acidify) our mobile phase to help suppress ionization, esp with basic compounds. We want the compound to exist in only one form (*This is a fundamental part of basic HPLC method development, so please read one of the basic introductions to HPLC to learn more about that topic).

      Acids, such as acetic are often used, but for liquid chromatography they should be of the highest purity and quality or they will degrade the signal (esp in the low UV region). A common problem with acetic acid is that it goes bad very quickly when exposed to the air. My advice is to only purchase it in very small bottles, open only when needed, blanket with dry nitrogen gas and always USE FRESH acid acid for HPLC. If you observe any noticeable color in the pure solution, discard it. Alternatively, use a different buffer and "cleaner" high purity acid such as formic or phosphoric acid (if applicable to your method).

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