ColumnsFAQ

C18A is the general-purpose grade, with high retention and high loading, suited to most reversed-phase applications. C18C tolerates strong acid and base (pH 1.5–12) and suits harsh mobile phases or small peptide separations. C18D is designed for hydrophilic compounds, is highly stable in fully aqueous mobile phases and is directly LC-MS compatible with no ion-pairing reagent. Establish your sample polarity and mobile phase pH first, then choose the grade.

A guard column is strongly recommended when: (1) the sample matrix is complex (serum, urine, food extracts); (2) you run more than 20 injections a day; (3) the sample may contain particulates. A guard column extends analytical column life 3–5×, and replacing a cartridge costs far less than replacing the analytical column.

The base medium is the same (custom-bonded SilicaOne silica in both cases), but the particle size differs: 3 µm or 5 µm for analytical columns, 10 µm or 20 µm for preparative. Larger particles give lower backpressure and suit high-flow preparative work; smaller particles give higher efficiency and suit fine analysis. Choose according to your objective — resolution versus throughput.

Yes. Equilibrate with 10–20 column volumes of mobile phase before injecting. If the column was shipped in methanol, transition to aqueous conditions via 50% methanol/water and then water, rather than flushing directly with a high-aqueous phase, which can cause C18 chain collapse (C18D and Ami C18 are exceptions and can go straight to pure water).

Yes. An arrow on the column marks the flow direction, and the column must be installed accordingly (mobile phase from inlet to outlet). Reversed installation loosens the bed, lowers efficiency, broadens peaks and causes irreversible damage. Check the arrow before installing.

(1) Reversed-phase columns (C18 series): flush with 10 column volumes of neat methanol or acetonitrile to remove all buffer salt, cap both ends and store sealed at room temperature. (2) HILIC columns: store in 90% acetonitrile/water. (3) Shodex SEC/GPC columns: follow the storage solution specified for that medium (usually containing sodium azide as a preservative). Never store a reversed-phase column in pure water for any length of time.

Yes, always. Phosphate, ammonium acetate and similar salts left in the column will crystallize and block the bed head, or corrode stainless steel tubing. The correct sequence: (1) flush for 10 min with 5–10% organic in water; (2) raise the organic proportion to 50%; (3) finish in neat methanol or acetonitrile for storage.

Under normal conditions an HPLCONE analytical column will take 2,000–5,000 injections. The main factors are: (1) how thorough the sample preparation is (the most important); (2) whether the mobile phase pH stays within the permitted range; (3) whether a guard column is used; (4) whether the column is flushed correctly after each run. Good preparation and care extend life considerably.

Common causes: (1) particulates accumulating at the bed head (most common); (2) buffer salt crystallization; (3) protein or lipid deposits at the bed head; (4) bubbles in the mobile phase. Remedies: (1) replace the guard cartridge first; (2) backflush with a strong solvent (isopropanol) for 10 min; (3) review sample preparation. If pressure still does not recover, the inlet frit needs replacing.

(1) Check that column temperature is stable (every 1 °C change shifts retention by roughly 1–2%); (2) check that the mobile phase is prepared consistently (organic proportion, pH); (3) check that the column is fully equilibrated (at least 10 column volumes); (4) confirm the flow rate is accurate (pump calibration); (5) check that column pressure is normal — pressure changes affect retention.

(1) Do not use non-volatile buffers such as phosphate or borate; (2) use formic acid (0.1%), acetic acid (0.1%), ammonium formate or ammonium acetate; (3) use acetonitrile (better ionization efficiency) or methanol as the organic phase; (4) choose a column that needs no ion-pairing reagent (5C18D, HILIC); (5) keep the flow rate typically at 0.2–0.4 mL/min to reduce ion suppression.

Not recommended. Phosphate works well for UV detection but is incompatible with MS; ammonium acetate is MS-compatible but gives a slightly higher UV background. If one method must serve both UV and MS, use ammonium acetate or ammonium formate together with a 5C18D column, which needs no ion-pairing reagent. Do not mix mobile phase batches — differences in composition cause retention time drift.