Optimization of Instrumental Parameters of a Near-Field Thermal-Lens Detector for Capillary Electrophoresis

Abstract

The optical scheme of a near-field dual-beam mode-mismatched thermal-lens detector for capillary electrophoresis with a crossed-beam configuration employing a multimode HeCd laser (325 nm) as an excitation source was optimized. It is shown that a multimode laser can be successfully used as an excitation source in thermal lensing with minimal deviations in thermal responses from Gaussian excitation sources. An equation for diffraction thermal-lens theory for near-field measurements is deduced, and the experimental results agree with the deduced equation. The temperature rise in the capillary was estimated, and the exponential decrease of the signal with time for static conditions and low flow velocities was explained. The optimum configuration of the detector from the viewpoint of the maximum sensitivity and beam sizes was found. The detector provides a significant improvement in the detection limits for model compounds absorbing at 325 nm (nitrophenols) compared to the results obtained with a commercial absorbance detector operating at the same wavelength.

Determination of Trace Cr(VI) with Diphenylcarbazide by μFIA–Thermal Lens Microscopy

“…At higher flow rates, the effects of the flow also affect the heating and the signal start to decrease like in the case of macro-scale flows in thermal lensing. 43 In this study, we obtained the results expected from the viewpoint of this heating model and based on our previous findings. 34,42 For the modulation frequency of 1 kHz, the dissipation time (half-period of the cycle when the excitation beam is closed by the chopper) is 500 μs.…”

Fast Screening Techniques for Neurotoxigenic Substances and Other Toxicants and Pollutants Based on Thermal Lensing and Microfluidic Chips

“…For moderate flows in capillaries (up to 5 cm/s) the thermal-lens effect is significantly enhanced. [46][47][48] This is due to an increased thermal diffusion of the liquid in a capillary accounted for by the edge effects in the flow. Higher thermal diffusion in turn decreases the characteristic time constant of the thermal lens (signal rise time).…”

Thermooptical detection in microchips: From macro‐ to micro‐scale with enhanced analytical parameters

“…A thorough, detailed study of all the factors affecting the accuracy of thermal lensing is still needed. However, a basic verification of the accuracy and bias of TLS, CB-TLS, and TLM was done in detail in previous reports [3,12,17,28]. It was shown that investigations of the thermal-lens signal as a function of the apparent molar absorptivity, excitation-beam wavelength, etc.…”

“…As the main theoretical background, we selected a diffraction theory of thermal lensing, developed by Snook [2,18,19] and later used in capillary electrophoresis [12,29] and in microfluidic systems [16,17,25]. As the main differences between TLS, CB-TLS, and TLM lie in the scaling of the apparatus, we selected the excitation beam diameter as the scale-determining factor.…”

“…We also found that crossed-beam TLS (CB-TLS), the most accepted photothermal-detection technique in capillary electrophoresis [12], and TLM [7,13] have differences in appara-tuses, but have the same advantages of chemistry at the trace level. In this paper, we compare the study of metrology in TLS, CB-TLS and TLM, with the aim of comparing their similarities and differences, and we examine the influence of various factors on the performance parameters of new and previously reported analytical procedures in TLM.…”