The following table provides some comparative data for interpretation of results from the more common detectors applied to high-performance liquid chromatography (Refs. 1-6). In general, the operational parameters provided are for optimized systems and represent the maximum obtainable in terms of sensitivity and linearity. In this table, the molar extinction coefficient is represented by ε. Column definitions for the table are as follows.
Column heading | Definition |
Detector | Type of detector |
Sensitivity | Detector sensitivity, in terms of minimum mass detectable, in g |
Linearity | Response linearity with respect to changes of concentration |
Selectivity | Types of compounds for which the detector is most suitable |
Comments | Additional information on the applicability and operation of the detector |
Detector | Sensitivity | Linearity | Selectivity | Comments |
Ultraviolet spectrophotometer | 1 × 10-9 g (for compounds of ε = 10 000 to 20 000) | 1 × 104 | For UV-active functionalities on the basis of absorptivity | Relatively insensitive to flow and temperature fluctuations; non-destructive; useful with gradient elution; use mercury lamp for 254 nm and quartz-iodine lamp for 350 nm to 700 nm; often a diode-array instrument is used to obtain entire UV-vis spectrum; solvents must be transparent in the UV region of interest |
Refractive index detector (RID) | 1 × 10-7 g | 1 × 104 | Universal, dependent on refractive-index difference with mobile phase | Relatively insensitive to flow fluctuations, but sensitive to temperature fluctuations; non-destructive; cannot be used with gradient elution; solvents must be degassed to avoid bubble formations; laser-based RI detectors offer higher sensitivity |
Fluorometric detector | 1 × 10-11 g | 1 × 105 | For fluorescent species with conjugated bonding and/or aromaticity | Relatively insensitive to temperature and flow fluctuations; non-destructive; can be used with gradient elution; often chemical derivatization is done on analytes to form fluorescent species; uses deuterium lamp for 190 nm to 400 nm, tungsten lamp for 350 nm to 600 nm, and the xenon flash lamp for 185 nm to 2000 nm |
Amperometric detector | 1 × 10-9 g | 1 × 104 | Responds to –OH functionalities | Used for aliphatic and aromatic –OH compounds, amines, and indoles; pulsed potential units are most sensitive, can be used with gradient elution and organic mobile phases; senses compounds in oxidative or reductive modes; mobile phases must be highly pure and purged of O2 |
Conductivity detector | 1 × 10-9 g | 2 × 104 | Specific to ionizable compounds | Most common detector for ion chromatography; requires suppression of solvent conductivity; uses post-column derivatization to produce ionic species; especially useful for certain halogen, sulfur, and nitrogen compounds |
Radioactivity detector | 1 × 10-11 g | 103 – 104 | Highly selective to radiolabeled compounds | Based on liquid scintillation counting, either from an added post-column scintillator compound (homogeneous) or a bed of solid state scintillator (heterogeneous); relatively large volume flow cells can cause peak broadening |
Light-scattering detector | 1 × 10-9 g | 103 | Universal toward most nonvolatile solutes | Often called evaporative light-scattering detector (ELSD); universal response with higher sensitivity than the RI detector, response independent of solvent; requires use of volatile buffers to promote nebulization |
Mass spectrometers | Interface dependent | Interface dependent | Universal, within limits imposed by interface | Complex, expensive devices highly dependent on an efficient interface; electrospray and thermospray interfaces are most common; linear response is difficult to achieve |