Thermal lens studies of the reaction of iron(II) with 1,10-phenanthroline at the nanogram level

Abstract

The determination of iron(II) with 1,10-phenanthroline in aqueous solutions was carried out exemplarily by thermal lens spectrometry. The peculiarities of analytical reactions at the nanogram level of reactants can be studied using this method. Under the conditions of the competing reaction of ligand protonation, the overall stability constant for iron(II) chelate with 1,10-phenanthroline was determined at a level of n x 10(-7) mol L(-1), logbeta3 = 21.3+/-0.1. The rates of formation and dissociation of iron(II) tris-(1,10-phenanthrolinate) at a level of n x 10(-8) mol L(-1) were found to be (2.05+/-0.05) x 10(-2) min(-1) and (3.0+/-0.1) x 10(-3) min(-1), respectively. The conditions for the determination of iron(II) with 1,10-phenanthroline by thermal lensing were reconsidered, and ascorbic acid was shown to be the best reducing agent, which provided minimum and reproducible sample pretreatment. Changes in the conditions at the nanogram level improved both the selectivity and sensitivity of determination. The optimum measurement conditions for thermal lensing were determined not only by the absorption of the analyte and reagents, but also by the background absorption of the solvent. The limits of detection and quantification of iron(II) at 488.0 nm (excitation beam power 140 mW) are 1 x 10(-9) and 6 x 10(-9) mol L(-1), respectively; the reproducibility RSD for the range n x 10(-8)-n x 10(-6) mol L(-1) is 2-5%.

The use of thermal lensing for the determination of pyrogens

“…(1) The ratio of limits of detection, 11.4, is also close to the theoretical value of 12 predicted using the approach in Ref. [30], which shows that an increase in the background fluctuations of thermal lens signal are relatively low compared to spectrophotometry.…”

Sensitivity Enhancement of Thermal-Lens Spectrometry Using Laser-Induced Precipitation

“…9,14,17 The setup comprises an excitation Ar + laser (Innova 90-6, Coherent, Palo Alto, CA) operated at 488.0 nm (170 mW in the sample, the beam waist 61.3 mm) and a HeNe probe laser (SP 106-1, Spectra-Physics, Eugene, OR; 632.8 nm, 5 mW in the sample; the beam size in the sample, 108.8 mm). The chopping frequency was low (4 Hz) to ensure the complete dissipation of the thermal-lens at the end of each steadystate excitation-cooling cycle.…”

“…7,8 In this connection, the primary trend in developing thermooptical spectroscopy lies in its capabilities of facilitating the basic understanding of the processes following laser irradiation in media and their effects on photochemical and optical parameters of analytes and samples. 4,[9][10][11][12][13][14] This area combines the applications of thermooptical spectroscopy that highlight its unique properties as a method of analytical chemistry.…”

“…Laser irradiation in thermooptical spectroscopy could not only provide a local increase in the temperature as a result of laser energy conversion into heat, but could also result in additional effects such as an increase in the reaction rate 9,[14][15][16] or a change in the energy balance of the kinetically controlled reactions, 13 emerging of laser-induced reactions, 11,12 photoinduced decomposition or isomerization, 17,18 or coagulation of metal nanoparticles. 19 On the other hand, products of light-induced or light-enhanced reactions affect the formation of thermal-lens element due to scattering or reabsorption of the radiation.…”

Complexation kinetics of Fe2+ with 1,10‐phenanthroline forming ferroin in acidic solutions

“…The formation of ferroin is utilized in the determination of Fe 2+ by various techniques. Chernysh et al [4] have determined Fe 2+ at the nanogram level by thermal lens spectroscopy. The reduction of ferriin to ferroin by Fe 2+ [5], hexacyanoferrate [6], and by hexakis(N,N-dimethylformamide) Fe 2+ [2] was also studied.…”