Hollow Cathode Lamp (HCL)
Definition
A sealed lamp whose cathode is made of the element being analysed, filled with argon or neon at low pressure. Strikes a discharge that emits the element's sharp atomic emission lines as the light source for AAS.
- Cathode composition
- Made of the element being analyzed (element-specific)
- Fill gas
- Argon or neon at low pressure
- Primary application
- Light source for atomic absorption spectrometry (AAS)
Common questions
What is a hollow-cathode lamp and why is it used in forensic analysis?+
A hollow-cathode lamp is a specialized light source with a cathode made of the element being tested. When filled with argon or neon gas and energized, it produces sharp atomic emission lines specific to that element. In atomic absorption spectrometry, this element-specific light allows forensic labs to detect and measure trace elements in evidence samples like soil, glass, or biological material.
How does an HCL work in atomic absorption spectrometry?+
The lamp emits exactly the wavelengths that the target element will absorb. When light from the HCL passes through a vaporized sample, the atoms in the sample absorb some of that light proportional to their concentration. Measuring how much light is absorbed tells the analyst how much of that element is present in the evidence.
Why must the cathode be made of the specific element being analyzed?+
The cathode element determines which wavelengths the lamp emits. If you're testing for lead, you use a lead cathode; for copper, a copper cathode. This ensures the light source and analyte element are matched, producing precise, element-specific results needed to identify materials in forensic evidence.
Related terms
- AAS
- Atomic absorption spectrometry. Free ground-state atoms in a vapour absorb a characteristic resonance wavelength from a hollow-cathode lamp, and Beer-Lambert converts the...
- Atomisation
- Conversion of a sample into free gaseous atoms in the ground state (AAS) or excited state (AES). The mandatory first step of...
- Background Correction
- A method (deuterium continuum, Zeeman effect, Smith-Hieftje self-reversal, or high-resolution continuum-source) that subtracts non-atomic absorption (molecular bands, scatter) from the raw absorbance...
- Beer-Lambert Law
- A = εbc. Absorbance equals molar absorptivity times path length times concentration. The linear relation between absorbance and concentration that makes UV-Vis...
- Chromophore
- The molecular subunit responsible for a dye's colour, typically a conjugated double-bond system; chemical erasure destroys the chromophore while leaving the decolourised...
- CVAAS
- Cold-vapour AAS. Mercuric ions are reduced by stannous chloride or sodium borohydride to elemental mercury vapour, swept by argon into a quartz...
- Fingerprint Region (IR)
- 1500 to 400 cm⁻¹. The complex lower-wavenumber zone where the whole-molecule pattern is unique enough to identify a substance by overlay.
- GFAAS
- Graphite-furnace AAS, also called electrothermal AAS. A graphite tube heated electrically through a programmed ramp atomises a microlitre aliquot, giving roughly 100...
- HG-AAS
- Hydride-generation AAS for hydride-forming elements (As, Sb, Se, Bi, Te, Sn, Ge). Sodium borohydride in acid generates the volatile hydride, which is...
- ICP Source
- Inductively coupled argon plasma at 6000 to 10000 K. The hottest practical excitation source for AES, giving simultaneous multi-element analysis (ICP-OES, ICP-MS).
- Molar Absorptivity (ε)
- The proportionality constant in the Beer-Lambert law, in L mol⁻¹ cm⁻¹. A property of the analyte at a given wavelength, solvent and...
- Stokes Shift (Raman)
- The Raman-scattered photon at lower energy than the incident photon. The Stokes line is the one routinely measured because it is stronger...
Explained in these topics
- Atomic Absorption Spectrometry: Flame, Graphite Furnace, Cold VapourA sealed lamp whose cathode is made of the element being analysed, filled with argon or neon at low pressure. Strikes a discharge that emits the element's shar...
- Spectrophotometry for Forensic Science: UV, Visible, IR, Raman, AAS and AESElement-specific line source used in AAS. The cathode is made of the analyte element, so the lamp emits exactly the wavelengths that element will reabsorb.