The antibody used in cell experiments has excessive endotoxin. Is there an endotoxin removal kit suitable for small-volume samples?

Both imported and domestic options are available. Imported brands such as Thermo Pierce and GenScript offer dedicated spin columns with strong batch-to-batch consistency and comprehensive validation documentation, but at a higher unit price. Domestic polymyxin B magnetic beads or histamine affinity resins have also become sufficiently reliable in recent years; the key is to have the manufacturer provide antibody recovery data, at minimum with IgG or BSA case studies. I recommend first running parallel tests with small-pack sizes from two or three brands: load the same 0.1 mg of antibody onto each column and measure endotoxin clearance rate, A280 recovery rate, and SEC aggregate content. Also clarify whether pre-equilibration with endotoxin-free buffer is required and whether the columns can be reused. Domestic small packs generally ship quickly and are well suited for preliminary experiments.

For 1 mL or more, the antibody amount of 0.5 mg/mL is very small. Prioritize 0.2–1 mL spin columns or magnetic bead formats; do not use large-volume gravity columns, otherwise the sample will be heavily diluted by the dead volume. To reduce from 2 EU/mL to below 0.1 EU/mL, theoretically at least 1.3 logs of removal are required. Conventional polymyxin B or histamine affinity media can usually achieve this, but only if the antibody does not undergo significant nonspecific adsorption to the medium. When selecting a product, ask clearly about the binding capacity: some small columns are labeled with the number of EU bound per mL of resin, not the total column capacity. For low-concentration samples, if the column capacity is too small, a single treatment may not be sufficient. You can first buy the smallest package for testing, pass 100–200 μL through the column, and measure endotoxin and concentration. If the results are good, then process the entire sample.

Before treatment, always retain at least 50–100 μL of the original sample as a control and measure it together with the treated samples. For endotoxin testing, recombinant Factor C or dynamic LAL is recommended, with spike recovery performed, because antibodies, detergents, or buffer components may inhibit the Limulus amebocyte lysate reaction, leading to falsely low results. For activity, use SEC-HPLC to monitor aggregate changes and ELISA or flow cytometry to assess binding activity, confirming that the treatment process does not cause significant damage. Use pyrogen-free consumables throughout; pipette tips, centrifuge tubes, and buffers must all be depyrogenated, otherwise the levels will be recontaminated immediately after being reduced. For small-volume samples, losses at each step are significant, so minimize the number of transfers and collect directly into the final storage tube.

Antibody activity is sensitive to extreme conditions; operationally, avoid low-pH elution, high salt, or organic solvents as much as possible. First confirm whether your storage buffer contains sodium azide, glycerol, trehalose, or low-pH buffer, as these may affect endotoxin binding. If conditions permit, first exchange into neutral PBS or Tris buffer, pH 7.0–7.4, and operate at 2–8°C. When passing through the column, do not repeatedly pipette up and down or vortex vigorously; use the lower limit of centrifugal force according to the instructions to reduce aggregation. After treatment, if the level does not drop below 0.1 EU/mL in one pass, rather than repeatedly passing through the same column, it is better to use a new column or reduce the loading amount/increase incubation time to avoid endotoxin that has already dissociated from returning to the sample.