Study On The Applications Of Luminol-Co²⁺ System In Food Analysis

The catalysis of transition Co2+ on luminol chemiluminescence(CL)has been well studied since 20th century.The thesis focused on the applications of luminol-Co2+ CL system in the fields of food safety testing,evaluation of polyphenol antioxidant activity and real-time monitoring of urine uric acid excretion with flow injection(FI)CL method.The content included two parts,as follows:Chapter 1 IntroductionBased on the total 146 references from 1975 to 2014,the nature of CL and FI-CL were given,the current applications of luminol CL system in different fields of environmental monitoring,food safety testing,biological sample analysis and pharmaceutical analysis were summarized.Chapter 2 The optimization of luminol-Co2+ CL system The effects of luminol concentration(5.0 × 10-7-5.0 × 10-5 mol L-1)and Co2+concentration(7.0 × 10-10-7.0 × 10-8 mol L-1)on the CL intensity were investigated.Considering the stable and strong CL intensity,5.0 × 10-6 mol L-1 luminol and 1.0 × 10-8 mol L-1 Co2+ were chosen for the CL system.The optimum conditions of this proposed CL systemwere as follows:pH of Co2+ solution was 6.0 ± 0.5,flow rate was 2.0 mL min-1,high voltage was-700 V and the length of mixing tubing was 10.0 cm,etc.The operational stability and reproducibility of the FI-CL system was tested with the FI system regularly worked over 8 h per day for 5 days,results of relative standard deviations(RSDs)lower than 3.5%(n = 5)showed that the system exerted good stability.The possible mechanism of luminol-Co2+ CL reaction was discussed by FI-CL.Chapter 3 Application of luminol-Co2+ CL system/Ultrasensitive determination of cadmium in rice by flow injection chemiluminescence analysis Based on the enhancive effect of Cd2+ on luminol-Co2+ CL system,a sensitive FI-CL method for the determination of Cd2+ in rice was developed,giving the the linear equation of?I=38.1CCd + 34.5(R = 0.9989),with the linear range from 7.0 pmol L-1 to 5.0 nmol L-1 and the limit of detection(LOD)2.0 pmol L-1(3?).The relative standard deviations(RSDs)were 3.3%,3.0%and 2.5%(n = 5)for 10.0,1.0 × 102 and 1.0 × 103 pmol L-1 Cd2+(n = 7),respectively.The content of Cd2+ in rice were found to be 0.07-0.1 mg kg-1,which met the standard regulated by GB2762-2012.The proposed FI-CL method was also successfullyapplied to determining Cd2+ in spiked human serum samples with recoveries from 96.9%to 105.5%and RSDs<4.0%.This work has been published in the journal of Food Analytical Methods(2014,doi:10.1007/s12161-014-9804-z).Chapter 4 Application of luminol-Co2+ CL system/Evaluation of the antioxidant ability for phenolic acids and flavonoidsIt was found that the CL intensity from luminol-Co2+ system could be quenched by the investigated phenolic acids(caffeic acid,gallic acid,ferulic acid,protocatechuic acid,vanillic acid)and flavonoids(myricetin,quercetin,luteolin,kaempferol,apigenin).The CL intensity decrements were logarithm over their concentrations,yielding a general calibration equation of ?I = AlnC + B(R>0.99,C:1.0-1.0 × 102 ng mL-1).According to the curves of quenching proportionalities vs concentration,IC50(concentration of sample needed to reduce in 50%CL intensity from luminol-Co2+ system)was obtained.A comparison of IC50 showed that the antioxidant ability of the investigated polyphenol followed the monotonic decreasing order of myricetin>caffeic acid>quercetin>gallic acid>luteolin>ferulic acid>protocatechuic acid>vanillic acid>kaempferol>apigenin,well agreeing with the sequence of minimum O-H bond dissociation enthalpy of their structure.Further study revealed that sensitivity factor A and quenching efficiency factor B decreased with increasing IC50 with good correlation,thus it can be concluded that A and B in FI-CL method can also be used for evaluating the antioxidant ability of polyphenol.Discussion of possible CL mechanism of luminol-Co2+-phenolic acids(flavonoids)system and the structure-antioxidant relationship were also given.Chapter 5 Application of luminol-Co2+ CL system/monitoring of human urine uric acid excretion under different food intakeBased on that uric acid remarkably inhibited the CL intensity from luminol-Co2+ system,uric acid excretion in human 24 h urine with different diets was determined,showing that porridge,vegetables and meats intake caused differential uric acid excretions of 741.6,797.7 and 878.4 mg,respectively,and uric acid concentrations under the three kinds of food intake simultaneously reached maximum at 2 h after meals.The results were found to be consistent with that obtained by repetitive experiment with luminol-KIO4 CL system.Luminol-Co2+ CL system was also successfully applied to the determination of uric acid in human serum with contents found to be 38.0 ± 1.5-51.4 ± 0.6 ?g mL-1.This work has been published in the journal of Journal of Analytical Methods in Chemistry(2013,V2013,Article ID:854041,7 pages).