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, 11^th edition (1989).

Common pKa Values for ACIDS & BASES used in HPLC and LC/MS Method Development

pKa (25°C)                              ACID

0.3                                           Trifluoroacetic acid

2.15                                          Phosphoric acid (pK#1)

3.13                                          Citric acid (pK#1)

3.75                                          Formic acid

4.76                                          Acetic acid

4.76                                          Citric acid (pK#2)

4.86                                          Propionic acid

6.35                                          Carbonic acid (pK#1)

6.40                                          Citric acid (pK#3)

7.20                                          Phosphoric acid (pK#2)

8.06                                          Tris

9.23                                          Boric acid

9.25                                          Ammonia

9.78                                          Glycine (pK#2)

10.33                                        Carbonic acid (pK#2)

10.72                                        Triethylamine

11.27                                        Pyrrolidine

12.33                                        Phosphoric acid (pK#3)

Notes: (1) This is a general list of commonly used acids & bases for chromatography applications and not meant to be a comprehensive list of all values. (2) TFA is an overused and very strong acid for many chromatography applications. It also has strong ion pairing properties and can result in high UV noise, vacuum degasser and/or MS contamination. If you must use it, try and use the lowest concentration which results in the desired pH. Example: 0.1 % TFA ~ pH 2.0, 0.02% TFA ~ pH 2.7. (3) Formic acid is a popular alternative to TFA for many applications, esp LC/MS. (4) Not all acids/bases provide "buffering" on their own.

Reference: CRC Handbook of Chemistry & Physics.