5
CORTECS and CORTECS Premier 2.7
µ
m Columns
[ CARE AND USE MANUAL ]
Table 2. Buffer Recommendations for Using CORTECS Columns
Additive/Buffer
pK
a
Buffer
Range
Volatility
(±1 pH Unit)
Used for
Mass
Spec
Comments
TFA
0.3
—
Volatile
Yes
Ion pair additive, can suppress MS signal,
used in the 0.02–0.1% range.
Acetic acid
4.76
—
Volatile
Yes
Maximum buffering obtained when used with
ammonium acetate salt. Used in 0.1–1.0% range.
Formic acid
3.75
—
Volatile
Yes
Maximum buffering obtained when used with
ammonium formate salt. Used in 0.1–1.0% range.
Acetate (NH
4
CH
3
CO
2
)
4.76
3.76–5.76
Volatile
Yes
Used in the 1–10 mM range.
Note: Sodium or potassium salts are not volatile.
Formate (NH
4
HCO
2
)
3.75
2.75–4.75
Volatile
Yes
Used in the 1–10 mM range.
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
7.2
6.20–8.20 Non-volatile
No
Above pH 7, reduce temperature/concentration
and use a guard column to maximize lifetime.
Phosphate 3
12.3
11.3–13.3 Non-volatile
No
Above pH 7, reduce temperature/concentration
and use a guard column to maximize lifetime.
4-Methylmorpholine
~8.4
7.4–9.4
Volatile
Yes
Generally used at 10 mM or less.
Ammonia (NH
4
OH)
Ammonium
bicarbonate
9.2
10.3 (HCO
3
-
)
9.2 (NH
4
+
)
8.2–10.2
8.2–11.3
Volatile
Volatile
Yes
Yes
Used in the 5–10 mM range (for MS work keep
source >150 ˚C). Adjust pH with ammonium
hydroxide or acetic acid. Good buffering
capacity at pH 10.
Note: Use ammonium bicarbonate (NH
4
HCO
3
),
not ammonium carbonate ((NH
4
)
2
CO
3
).
Ammonium (Acetate)
9.2
8.2–10.2
Volatile
Yes
Used in the 1–10 mM range.
Ammonium (Formate)
9.2
8.2–10.2
Volatile
Yes
Used in the 1–10 mM range.
Borate
9.2
8.2–10.2 Non-volatile
No
Reduce temperature/concentration and use a
guard column to maximize lifetime.
CAPSO
9.7
8.7–10.7
Non-volatile
No
Zwitterionic buffer, compatible with acetonitrile,
used in the 1–10 mM range. Low odor.
Glycine
2.4, 9.8
8.8–10.8 Non-volatile
No
Zwitterionic buffer, can give longer
lifetimes than borate buffer.
1-Methylpiperidine
10.2
9.3–11.3
Volatile
Yes
Used in the 1–10 mM range.
CAPS
10.4
9.5–11.5
Non-volatile
No
Zwitterionic buffer, compatible with acetonitrile,
used in the 1–10 mM range. Low odor.
Triethylamine
(as acetate salt)
10.7
9.7–11.7
Volatile
Yes
Used in the 0.1-1.0% range. Volatile only when
titrated with acetic acid (not hydrochloric
or phosphoric). Used as ion-pair for DNA
analysis at pH 7–9.
Pyrrolidine
11.3
10.3–12.3
Volatile
Yes
Mild buffer, gives long lifetime.
Note: Working at the extremes of pH, temperature, and/or pressure will result in shorter column lifetimes.