Determination of chemical oxygen demand in fresh waters using flow injection with on-line UV-photocatalytic oxidation and spectrophotometric detection

Abstract

A flow injection manifold incorporating UV-photocatalytic oxidation for the determination of chemical oxygen demand (COD) in freshwater is reported. The method utilises the UV-photocatalytic oxidation of organic compounds instead of conventional heating (used in the standard method), with acidified potassium permanganate as the oxidant. Sodium oxalate, d-glucose and potassium hydrogen phthalate were used as COD standards. A 100 microL sample solution was injected into a 0.3 mol L(-1) H2SO4 carrier stream containing 0.1 mol L(-1) (NH4)2SO4, merged with a permanganate solution (8 x 10(-4) mol L(-1)) and passed through a 250 cm FEP (fluoroethylene polymer) photo-reaction coil wound around a 15 W UV lamp. The sample throughput was 30 h(-1), with an LOD (blank plus 3sigma) of 0.5 mg COD L(-1) and a linear range of 0.5-50 mg COD L(-1) (D-glucose, r2 = 0.9966). The method had good precision with relative standard deviations of 2.7% at 5 mg COD L(-1) and 1.2% at 20 mg COD L(-1) (n = 12) for glucose. Results for a COD certified reference material (QC Demand Quality Control Standard) were in good agreement with the certified COD value. Recovery from Tamar River water samples for all three COD standards was 83.0-111.0% and the COD values determined were in good agreement with those of a permanganate index reference method.

TiO2 nanofibers fixed in a microfluidic device for rapid determination of chemical oxygen demand via photoelectrocatalysis

“…It also requires the use of expensive (Ag 2 SO 4 ), highly corrosive (H 2 SO 4 ), and toxic (Cr 2 O 2− 7 and HgSO 4 ) reagents [1]. Other alternative assays have been developed based on either electrocatalytic [2][3][4][5] or photocatalytic [6][7][8] and photoelectrocatalytic principles [9][10][11][12]. Although many advantages over traditional methods, such as the great speed and directness in determination, could be realised through electrocatalytic oxidation method [2][3][4][5], the reliability of electrocatalysis for practical application is still unsatisfied due to the low oxidation ability and the potential risk of toxic metal ion leaching (e.g.…”

“…lead). Photocatalytic oxidation approach, which utilizes TiO 2 as photocatalyst to replace the conventional oxidizing agent, is the most effective degradation method for COD determination due to the superior oxidation ability of illuminated TiO 2 [6][7][8]. The main drawback of photocatalysis is the low photocatalytic efficiency resulted from the easy recombination of the photogenerated electrons and holes in discrete TiO 2 particles and coated nanofilms [13].…”

Rapid Determination of the Chemical Oxygen Demand of Water Using a Thermal Biosensor

“…A number of alternative methods based on photocatalytic [13–15] or electrochemical [7,16–22] principles have been proposed and investigated. Although these methods have been shown to have a number of advantages over the traditional COD determination methods, they are far from perfect.…”

Repetitive Determination of Chemical Oxygen Demand by Cyclic Flow Injection Analysis Using On-line Regeneration of Consumed Permanganate

“…[6][7][8][9][10] These methodologies could be applicable in this cyclic FIA, and actual applications are in progress.…”

“…[2][3][4][5][6] When D-glucose was used in this cyclic FIA at 70˚C digestion, very small responses were obtained. This was due to the slow reactivity of D-glucose being analyzed, and because the proposed method requires a very high temperature digestion.…”