High-sensitivity absorbance determination by laser-induced thermal modulation of electrical conductivity

McLaren, R.; Dovic̀hi, Norman J.

doi:10.1021/ac00158a029

Cited by 4 publications

(7 citation statements)

References 41 publications

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“…An experimental design similar to the refractive index design was used by McLaren and Dovichi to detect the change in conductivity . A modulated helium−neon laser was focused into a Pasture pipet into which electrodes had been inserted.…”

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confidence: 99%

Development of a Conductivity-Based Photothermal Absorbance Detector for Capillary Separations

2006

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A contactless conductivity-based absorbance detector has been developed for use with capillary separations. Detection is based on a photothermal process. As analytes pass through the detector they absorb light, producing a thermal perturbation. This thermal event results in a change in the solution conductivity. The measured change in conductivity is directly related to the absorption of light. The major advantage to this type of detector is that the measured absorbance is, to a first approximation, independent of optical path length, allowing small-diameter capillaries to be used. This approach combines the optical simplicity of traditional transmission-based instruments with the path length independence of similar refraction-based photothermal detectors. In addition to the initial development and characterization of the photothermal absorbance detector, multiphysical modeling of the heat transfer within the conductivity cell was performed.

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confidence: 99%

Development of a Conductivity-Based Photothermal Absorbance Detector for Capillary Separations

2006

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“…Even though the solution is transparent at this wavelength, a small amount of sample heating at this power is detected in the BSI signal for the HSA peak. 37 A HSA solution (10 mg/mL) was incubated with BCG (1 mM) for 2 h and separated in 15 mM boric acid at pH 10.0. The resulting electropherograms as a function of 637 nm excitation power are shown in Figure 8A.…”

Section: Analyticalmentioning

confidence: 99%

“…37−39 It was recognized early that the change in viscosity with temperature for water is orders of magnitude larger than the RI change, suggesting a promising route for enhanced CE detection. 37 In fact, a study integrating photothermal absorbance with C 4 D detection measured an ∼20-fold increase in signal. 39 While clearly enhanced, the magnitude was less than expected.…”

Section: ■ Introductionmentioning

confidence: 99%

Photothermal Backscatter Interferometry for Enhanced Detection in Capillary Electrophoresis

Opallage,

De Silva,

Kariuki

et al. 2024

Anal. Chem.

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Refractive index (RI) detection using backscatter interferometry (BSI) enables universal detection in capillary electrophoresis (CE). BSI detection is a versatile on-capillary approach that is easily integrated with capillary or microfluidic channels, straightforward to miniaturize, and inexpensive. The focused BSI light source can also double as the excitation source for fluorescence, enabling simultaneous universal (BSI) and specific (fluorescence) signals from the same detection volume. To improve BSI detection and expand orthogonal content, we integrate photothermal absorption with BSI detection. Nonradiative relaxation of an excited analyte releases heat into the surroundings, which modifies both the local RI and conductivity (viscosity) of the analyte zone. We recently showed that the BSI signal is sensitive to both RI and conductivity, which makes photothermal absorption a promising route to signal enhancement. Here, we use coaxially delivered BSI and photothermal absorption beams to characterize BSI, photothermal BSI, and fluorescence detection using the separation of test samples. We show that photothermal absorption leads to 3 orders of magnitude improvement in BSI detection limits at the powers studied and provides new opportunities for studying binding interactions with CE.

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“…McLaren and Dovichi focused a 4 mW laser between electrodes 240 μm apart and attained an LOD of 0.2 μM methylene blue (MB) in 0.05 M NaCl flowing therebetween. 13 The authors were prescient in suggesting "electrodeless" conductivity measurement to avoid direct illumination of electrodes; nearly 2 decades later, the Jorgenson group used capacitively coupled contactless conductivity detection. 14 Sub-μM LODs were possible for dabsyl glucosamine with 200 mW illumination.…”

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confidence: 99%

“…Viscosity, and hence electrical conductance (G) of a dilute salt solution (Δ G /Δ t ∼2% /°C), are very sensitive to temperature changes. McLaren and Dovichi focused a 4 mW laser between electrodes 240 μm apart and attained an LOD of 0.2 μM methylene blue (MB) in 0.05 M NaCl flowing therebetween . The authors were prescient in suggesting “electrodeless” conductivity measurement to avoid direct illumination of electrodes; nearly 2 decades later, the Jorgenson group used capacitively coupled contactless conductivity detection .…”

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confidence: 99%

Direct Photothermal Measurement of Optical Absorption in a Flow System

Chouhan

Dasgupta

2019

Anal. Chem.

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We describe here a simple photothermal detection scheme in a flow stream based on the temperature difference upstream and downstream of the point of illumination. We use a single, two-junction 25 μm diameter thermocouple to measure the temperature change. The baseline standard deviation in the dark is ∼0.001 °C that increases up to 0.0016 °C depending on the illumination source. We demonstrate the detection of several chromatographically separated dyes both with a 1.5 mm and a 0.1 mm i.d. detection cell, respectively, with a white LED and a solidstate laser source. With an inexpensive 660 nm, 19 mW laser as the light source, the estimated detection limit for methylene blue (MB) was 30 nM, corresponding to 120 amol in the illuminated volume. The dimerization constant of MB and the quantum efficiency of the monomer was determined.

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High-sensitivity absorbance determination by laser-induced thermal modulation of electrical conductivity

Cited by 4 publications

References 41 publications

Development of a Conductivity-Based Photothermal Absorbance Detector for Capillary Separations

Development of a Conductivity-Based Photothermal Absorbance Detector for Capillary Separations

Photothermal Backscatter Interferometry for Enhanced Detection in Capillary Electrophoresis

Direct Photothermal Measurement of Optical Absorption in a Flow System

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