Volume 35, Issue 3

Nitrate monitoring of environmental samples is essential to safeguard human and environmental health. Various non-enzymatic methods such as Griess reaction-based chemical method; Fourier transform infrared spectroscopy; chromatographic, electrochemical and optical sensors yield reproducible results but suffer from drawbacks such as use of hazardous chemicals, interference from coexistent anions, and bulky and expensive instrumentation and hence are not favored for routine analysis. On the other hand, nitrate reductase (NR)-based methods are simple, sensitive, specific, environment friendly, easy to carry out, and, therefore, suitable for routine analysis. NR in these methods is employed in both free (in commercially available kits) and immobilized form. In comparison to the native NR, immobilized NR shows better activity and stability accompanied by overall reduction in the cost of the method. The review gives a brief account of non-enzymatic nitrate quantification, whereas recent advances in enzyme-based determination have been explored in more detail.

Online enzyme assay based on capillary electrophoresis (CE) offers several advantages for the assay, such as low consumption of samples, easy automation of all steps, and less requirement of sample work-up. As a widely used approach for online enzyme assay, CE-integrated immobilized enzyme microreactor (IMER) has been applied in almost all aspects of enzyme assays during the past two decades, including evaluation of the enzymatic activity and kinetics, screening of inhibitor, investigation of enzyme-mediated metabolic pathways, and proteome analysis. In a CE-integrated IMER, enzyme is bound to the capillary surface or a suitable carrier attached to the capillary and substrates/products of the enzymatic reaction are separated and online detected by CE at downstream of the capillary. Enzymatic reactions can be viewed as interaction between the stationary phase (immobilized enzyme) and the mobile phase (substrate(s)/co-enzyme(s) solution), in analogy to the well-known separation technique, capillary electrochromatography. From this point of view, CE-integrated IMERs can be categorized into open tubular capillary IMER, monolithic IMER, and packed capillary IMER. In this review, we have surveyed, analyzed, and discussed advances on fabrication techniques of the three categories of CE-integrated IMERs for online assays involving various enzymes in the past two decades (1992–2015). Some recent studies using microfluidic-based IMERs for enzyme assays have also been reviewed.

Polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs), heavily used as flame retardant in plastics, are harmful to environment and human health. It is of great importance for method development to determine PBDEs and PBBs in plastics. A review of developments on the analysis of PBDEs and PBBs in plastics is presented in this paper. The analytical procedures including sample pretreatment, extraction, clean-up/fractionation, and detection are carefully discussed. The drawbacks and merits of each method are summarized. The aim of this review is to improve the analytical accuracy, and precision for the determination of PBDEs and PBBs in plastics on the basis of the published papers.