Applications of Flow Injection Analysis with Chemiluminescence Detection
As an ultrasensitive analytical technique, chemiluminescence has attracted increasing attention in analytical chemistry. It is shown how chemiluminescence technique in combination with flow injection analysis can be used to obtain sensitive, rapid, simple and efficient analytical methods. The work tries to develop an understanding of the chemical processes involved in FI-CL. The major contributions of this work are as follows:
(1) Ultrasensitive FIA-CL Protocol for Cr(VI) determination
This work proposes a new chemiluminescence (CL) method combined with continuous flow injection analysis for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalyzed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimized experimental conditions, the relationship between the logarithm of concentration (logC) of Cr(VI) and the logarithm of intensity (logI) is linear over the range of 2×10-11―5×10-4 mol L-1, with the detection limit (3σ) of 4×10-12 mol L-1. Relative standard deviation of ten measurements of 1×10-9 mol L-1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyze up to 40 samples h-1. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values.
(2) Modified Trautz–Schorigin reaction based FIA-CL detection of carbonyl compounds
an investigation is made based on modified Trautz–Schorigin reaction, by using tannic acid-H2O2 system for the oxidation and determination of two kinds of carbonyl compounds. It was found that formaldehyde and acetaldehyde effectively enhanced the chemiluminescence signals of tannic acid–H2O2 system in alkaline medium. Effects of reagent concentrations, temperature, pH, flow rates and mixing coil length on the chemiluminescence intensity were studied in detail. The proposed method is simple, rapid, convenient and sensitive, has a linear range of 7×10-9-1×10-4 mol L-1 for formaldehyde and 1×10-8-1×10-4 mol L-1 for acetaldehyde with detection limits of 9×10-11 and 3×10-10 mol L-1 respectively. The relative standard deviations for 15 repeated measurements of 1×10?6 mol L?1 HCHO and CH3CHO are 1.13% and 1.65%, respectively. Analysis time per sample is 35 seconds. The method was applied to the determination of carbonyl compounds in wine samples successfully.
(3) Determination of Pyrogallol compounds
Proposed method is based on the enhanced effect of pyrogallol compounds on the chemiluminescence signals of KMnO4–H2O2 system in slightly alkaline medium. Three important pyrogallol compounds, pyrogallic acid, gallic acid and tannic acid, have been detected by this method, and the possible mechanism of the CL reaction is also discussed. The proposed method is simple, convenient, rapid (60 samples h-1), and sensitive, has a linear range of 8x10-10-1x10-5 mol L-1, for pyrogallic acid, with a detection limits of 6x10-11 mol L-1, 4x10-8-5x10-3 mol L-1 for gallic acid with a detection limits of 9x10-10 mol L-1, and 8x10-8-5x10-2 mol L-1 for tannic acid, with a detection limits of 2x10-9 mol L-1, respectively. The relative standard deviation (RSD, n=15) was 0.8, 1.1 and 1.3% for 5x10-6 mol L-1 pyrogallic acid, gallic acid and tannic acid, respectively. The proposed method was successfully applied to the determination of pyrogallol compounds in tea and coffee samples.
(4) CdTe QDs based CL system for detection of Chromium(III)
Water-soluble CdTe quantum-dots (CdTe-QDs) of different sizes and capped with mercaptosuccinic acid were prepared by the microwave irradiation method. The CdTe-QDs significantly enhanced the chemiluminescence (CL) of the pyrogallol-H2O2 system. Those with a diameter of 3.8 nm produced the most intensive CL. UV-vis, photoluminescence (PL) spectra and CL spectra were acquired in order to explore the effect. The results showed that the Cr3+ in the concentration range of 20 pM– 30μM enhances CL, and this is exploited for its trace determination. Limit of detection (3σ) was 6 pM, with relative standard deviation (n=11) of 1.7%. A continuous flow injection CL method was developed and applied to the determination of Cr3+ in tap water and lake water samples with satisfactory results.
(5) Luminol-H2O2 CL signal enhancement by CdTe Quantum Dots-IgG bioconjugates (A CRET phenomenon)
In this method we developed an entirely new and highly sensitive luminol-H2O2 flow injection chemiluminescence system using the enhancement effect of CdTe quantum dots-IgG bioconjugates. Immunoglobulin G (IgG) as a kind of bio-molecule was conjugated to different sized CdTe semiconductor quantum dots (QDs). Using PL spectra and CL intensity profiles, it was found that chemiluminescence resonance energy transfer (CRET) was possibly occurring between CdTe-IgG bioconjugate and luminol. Under optimum conditions, increase of IgG concentration in CdTe-IgG bioconjugate produced enhancing effect on CL intensity of luminol-H2O2 system. Moreover quenching effects on CL intensity by addition of different proteases can construct turn off kind of biosensor for these proteases, along with low detection limits and wide linear range. Furthermore, the effects of various organic and inorganic species on CdTe-IgG biocojugates enhanced luminol-H2O2 CL system were also studied in this work.
(6) Doubly coded CdTe QDs based sandwich FI-CL immunoassay
In this work we propose a specific sandwich immunoassay method for human-immunoglobulin G (HIgG). This immunoassay protocol takes advantage of sandwich binding of primary and secondary antibodies for increased specificity. Polystyrene microspheres (PS) served as immobilizing support, site for sandwich immunoassay and subsequently used for chemiluminescence (CL) detections. In this sandwich immunoassay, PS was modified with the primary anti-HIgG (Ab1) via electrostatic interaction, while CdTe nanoparticles (CdTeNPs) were modified with horseradish peroxidase labeled anti-HIgG (Ab2) via covalent binding. Antigen HIgG (Ag) could be specifically captured by the first and secondary antibody and form sandwich immunoassay format. The combination of the remarkable sensitivity of CL method and the use of CdTe NPs as an anti-HIgG–HRP carrier for the enzymatic signal amplification, provided a linear response range of HIgG from 0.01 to 300 ngmL?1 with an extremely low detection limit of 0.3 pgmL?1. This immunoassay system has many desirable merits including sensitivity, accuracy, and little required instrumentation. The assay results were compared with an enzyme-linked immunosorbent assay (ELISA), and showed relatively good reliability. Significantly, the new protocol may become quite promising technique for protein immune-detection as well as DNA analysis and other biological analyses.