The ELS detector will detect all nonvolatile components in the mobile phase, which includes column-packing material. Column-packing material will become chemically and mechanically broken down over the lifetime of the column, causing particles to enter the ELSD. This column “shedding” will lead to extremely high baseline.
Amino columns used with aqueous mobile phase are particularly prone to this type of shedding and should be checked regularly. To minimize column breakdown, always follow the manufacturer's instruction supplied with the column.
Mobile Phase Additive | pKa | pKb | pH Range | Bp (°C) | Mp (°C) |
|---|---|---|---|---|---|
Acids | |||||
Trifluoroacetic Acid (TFA) | 0.3 | 13.70 |
| 72.4 | -15.4 |
Formic Acid | 3.75 | 10.25 |
| 100.7 | 8.3 |
Acetic Acid | 4.75 | 9.25 |
| 116.0 | 16.6 |
Bases | |||||
Ammonia | 9.25 | 4.75 |
| -33.4 | -77.7 |
Methylamine | 10.66 | 3.34 |
| -6.6 | -94.0 |
Ethylamine | 10.81 | 3.19 |
| 16.6 | -81.0 |
Triethylamine | 11.01 | 2.99 |
| 89.3 | -114.7 |
Buffers | |||||
Ammonium Formate | 3.8 9.2 |
| 3.0 – 5.0 8.2 – 10.2 |
| 120 |
Ammonium Acetate | 4.8 9.2 |
| 3.8 – 5.8 8.2 – 10.2 |
| 111 |
Ammonium Bicarbonate | 6.3 9.2 10.3 |
| 6.8 – 11.3 |
| 106 |
Ion-Pair Reagent | |||||
Pentafluoropropionic acid (PFPA) | ~0.6 |
|
| 97 |
|
Heptafluorobutyric acid (HFBA) | ~0.6 |
|
| 120 |
|
Nonafluoropropionic acid (NFPA) | ~0.6 |
|
| 140 |
|
Tridecafluoroheptanoic acid | ~0.6 |
|
| 175 |
|
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