Waters SunFire Columns - Manual (Page 4)

[ Care and Use ManUal ]
4
c. pH range
The recommended operating pH range for SunFire columns is 2 to 8. A listing of commonly used buffers and additives is given in Table 2.
Additionally, the column lifetime will vary depending upon the operating temperature, and the type and concentration of buffer used. For
example, the use of phosphate buffer at pH 8 in combination with elevated temperatures will lead to shorter column lifetimes.
table 2: Buffer recommendations for using SunFire Columns from pH 2 to 8
Additive or Buffer pK
a
Buffer Range
(±1 pH unit)
Volatility
Used for
Mass
Spec?
Comments
Formic Acid 3.75 Volatile Yes
Maximum buffering obtained when used with Ammonium Formate salt.
Used in 0.1-1.0% range.
Acetic Acid 4.76 Volatile Yes
Maximum buffering obtained when used with Ammonium Acetate salt.
Used in 0.1-1.0% range.
Ammonium Formate
(NH
4
COOH)
3.75 2.75 - 4.75 Volatile Yes
Used in the 1-10 mM range for LC/MS. Higher concentrations (typically 20 mM)
are recommended for UV applications.
Note: sodium or potassium salts are not volatile.
Trifuoroacetic Acid (TFA) 0.30 Volatile Low conc.
When used in LC/MS, due to signal supression, it is generally recommended to
use TFA at concentrations < 0.1%.
Ammonium Acetate
(NH
4
CH
2
COOH)
4.76 2.75 - 5.76 Volatile Yes
Used in the 1-10 mM range for LC/MS. Higher concentrations (typically 20 mM)
are recommended for UV applications.
Note: sodium or potassium salts are not volatile.
Phosphate 1 2.15 1.15 - 3.15 Non-volatile No Traditional low pH buffer, good UV transparency.
Phosphate 2 7.20 6.20 - 8.20 Non-volatile No
Above pH 7, reduce temperature/concentration and use guard column to
maximize lifetime.
d. Solvents
To maintain maximum column performance, use high quality
chromatography grade solvents. Filter all aqueous buffers prior to
use. Pall Gelman Laboratory Acrodisc
® filters are recommended.
(Please refer to the filtration section of the Waters Chromatography
Columns and Supplies Catalog or the Waters web site (www.waters.
com) for additional product information.) Solvents containing
suspended particulate materials will generally clog the outside
surface of the inlet distribution frit of the column. This will result
in higher operating pressure and poorer performance. Degas all
solvents thoroughly before use to prevent bubble formation in
the pump and detector. The use of an on-line degassing unit is
also recommended. This is especially important when running low
pressure gradients since bubble formation can occur as a result of
aqueous and organic solvent mixing during the gradient.
e. Pressure
SunFire columns can tolerate pressures of up to 6,000 psi (400 bar or
40 MPa) although long-term, routine operating pressures greater than
4,000 – 5,000 psi should be avoided in order to maximize column
and system lifetimes.
f. temperature
Temperatures between 20 ˚C – 50 ˚C are recommended for operating
SunFire columns at low pH in order to enhance selectivity, lower
solvent viscosity and increase mass transfer rates. However, any
temperature above ambient may have a negative effect on lifetime
which will vary depending on the pH and buffer conditions used.