Direct comparison
HPLC Detector Selection: UV vs DAD vs MS
Compare HPLC detectors — UV, DAD, RI, ELSD, FLD, MS — by analyte property, sensitivity, and gradient compatibility to pick the right one for your method.
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How do UV (single/variable-wavelength), Diode-Array (DAD/PDA), Refractive Index (RI), Evaporative Light Scattering (ELSD), Fluorescence (FLD), Mass Spectrometry (MS) compare side by side?
The table below compares UV (single/variable-wavelength), Diode-Array (DAD/PDA), Refractive Index (RI), Evaporative Light Scattering (ELSD), Fluorescence (FLD), Mass Spectrometry (MS) across 9 procurement-relevant dimensions, from what it measures through not suitable for.
Side-by-side comparison
| Dimension | UV (single/variable-wavelength) | Diode-Array (DAD/PDA) | Refractive Index (RI) | Evaporative Light Scattering (ELSD) | Fluorescence (FLD) | Mass Spectrometry (MS) |
|---|---|---|---|---|---|---|
| What it measures | Absorbance at a fixed/selected wavelength | Full UV-Vis spectrum (~190–800 nm) at every data point | Refractive-index difference between eluent and mobile phase | Light scattered off nebulized, evaporated analyte particles | Light emitted after excitation (fluorescence) | Mass-to-charge ratio of ionized analyte |
| Analyte requirement | A chromophore (conjugated π-system, aromatic ring, carbonyl, etc.) | Same as UV, plus reports spectral shape | None — responds to virtually any solute | Non-volatile enough to survive nebulization/evaporation | Native fluorophore, or derivatization (OPA, AQC, dansyl chloride) | Ionizable site (ESI/APCI) and adequate volatility from the eluent |
| Typical sensitivity | Nanogram-level — workhorse sensitivity | Similar to UV, slightly lower per wavelength (light split across the array) | Microgram-level — least sensitive in routine use | Microgram-level | Picogram to low-nanogram — among the most sensitive LC detectors | Picogram-level or lower with MRM on a triple-quad |
| Response linearity | Linear over a wide range (Beer-Lambert) | Linear, same basis as UV | Linear | Nonlinear — power-law response, needs a curved calibration fit | Linear over a narrower range; prone to inner-filter effects at high conc. | Linear over a wide range, subject to matrix-driven ion suppression |
| Gradient compatibility | Yes — blank-gradient subtraction handles baseline drift | Yes, same as UV | No — isocratic only; %B changes swamp the signal | Yes — response is largely independent of mobile-phase composition | Yes, though solvent polarity can shift fluorescence yield | Yes — the dominant LC-MS workflow, but source settings may need re-tuning across the gradient |
| Mobile-phase constraints | Avoid strongly UV-absorbing buffers/additives at your detection wavelength | Same as UV | Must be isocratic; flow cell needs thermostatting (temperature-sensitive) | Must be fully volatile — no nonvolatile phosphate buffers | Fairly tolerant; some solvents quench fluorescence | Volatile buffers only (ammonium formate/acetate, formic/acetic acid) — no phosphate, no nonvolatile ion-pairing reagents |
| Relative cost | Lowest — standard on nearly every HPLC system | Moderate step up from single-wavelength UV | Low-moderate | Moderate | Moderate-high | Highest by a wide margin, plus ongoing consumables and a distinct skill set |
| Best for | Routine quantitation of chromophore-bearing analytes | Same as UV, plus peak-purity confirmation and spectral ID | Sugars, polymers/oligomers, SEC | Lipids, surfactants, non-chromophoric analytes under gradient conditions | Trace-level quantitation of fluorescent or derivatized analytes | Compound identification/confirmation and trace quantitation via MRM |
| Not suitable for | Analytes with no chromophore in the accessible wavelength range | Same limitation as UV | Gradient methods, or trace-level work | Volatile analytes; precise quantitation without a fitted calibration curve | Non-fluorescent analytes that can't be practically derivatized | Methods built around nonvolatile buffers (without reformulation); tight budgets |
Common questions
Common questions about UV (single/variable-wavelength) vs Diode-Array (DAD/PDA) vs Refractive Index (RI) vs Evaporative Light Scattering (ELSD) vs Fluorescence (FLD) vs Mass Spectrometry (MS)
Can I run UV and MS on the same HPLC system at the same time?
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Yes — DAD (or single-wavelength UV) is commonly placed upstream of the MS source in series, since UV is non-destructive and its eluent stream reaches the MS unchanged. This gives quantitation from UV/DAD and structural confirmation from MS in one injection.
Why can't refractive index detection run a gradient?
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RI measures the eluent's own refractive index against a reference. In a gradient method, the changing mobile-phase composition shifts the baseline by far more than any analyte peak, and unlike UV there's no blank-subtraction fix — the interference and the measured property are the same physical quantity.
Is ELSD a replacement for RI?
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For gradient methods on non-chromophoric analytes, largely yes — ELSD tolerates gradients where RI cannot. But ELSD's response is nonlinear (needs a curve-fit calibration, not a straight line) and it can't detect volatile analytes, which RI still can under isocratic conditions.
Does a method validated on UV automatically transfer to LC-MS?
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Not without checking the mobile phase. Many UV methods use nonvolatile buffers (phosphate) or ion-pairing reagents that foul an MS source and suppress ionization. Moving a method to MS typically means reformulating the mobile phase to volatile alternatives (ammonium formate/acetate, formic/acetic acid) and revalidating.
