The determination of urea is important in a wide range of fields, including clinical diagnostics, environmental monitoring and food science. Numerous analytical techniques have been developed for the determination of urea, with no single technique dominant in all areas because of the diversity of applications. An overview of the existing analytical methodologies for urea is presented, and some new approaches are discussed, particularly those based on chemiluminescence detection to improve the sensitivity and the selectivity for the determination of this important analyte.

Analytical methodology for the determination of urea: current practice and future trends

Highly selective electrogenerated chemiluminescence (ECL) for sulfide ion determination at multi-wall carbon nanotubes-modified graphite electrode

Kinetic spectrophotometric method for rapid determination of trace formaldehyde in foods.

In this work, we report novel amperometric urea biosensor based on immobilization of Urease enzyme onto self-assembled polyamidoamine grafted multiwalled carbon nanotube (MWCNT-PAMAM) dendrimers (from G1, first generation up to G5) on Au electrode. Bio-sensing electrode’s performance parameters such as optimum pH, temperature, and applied potential together with reproducibility were investigated. The electrode based on fifth generation of MWCNT-PAMAM and urease enzyme showed excellent performance in urea detection at an applied potential of 0.45 V with short response time of 3 s, wide linear range of 1–20 mM, detection limit of 0.4 mM, and sensitivity of 6.6 nA/mM. No significant response was detected in the presence of possible interferon molecules. Non-diluted human blood plasma has been used for real sample application where electrode showed excellent performance in urea detection.

Design of amperometric urea biosensor based on self-assembled monolayer of cystamine/PAMAM-grafted MWCNT/Urease

The aim of the present work is the modification of the standard indophenol blue method in order to be feasible the determination of ammonium in geothermal water samples with high mineral content. Several pretreatment techniques were studied and evaluated in order to neutralise the pH of all solutions (blank, sample, standards) and minimise the interferences from salts. The Ultrasonic bath followed by mechanical stirring and vacuum filtration seems to be the most efficient pretreatment technique with almost 100% recovery of . Also there was an optimisation in the main procedure of the method in order to gain in sensitivity. The proposed method was compared with the standard ion chromatography and spectrophotometric indophenol blue methods and a t-test was performed. The RSD% values (n = 4) of the proposed spectrophotometric method were below 3.5% and the LOD of was 0.026 mg L−1. The proposed method was applied to several geothermal water samples from regions of Greece.

A new approach to indophenol blue method for determination of ammonium in geothermal waters with high mineral content

Reaction between urea and hypobromite in alkaline solution was found to produce chemiluminescence with a maximum wavelength at 510 nm. A simple chemiluminescence detection method was used for the determination of urea in human urine and natural aqueous samples, which combined this chemiluminescence reaction with a flow injection analysis system. The relative standard deviation for 5 × 10–7 mol dm–3 urea is 1.9%(n= 6), and the detection limit is 9.0 × 10–8 mol dm–3(3 sr). As this chemiluminescence reaction is very fast, a double concentric tube mixer connected directly to the chemiluminescence cell was used to mix urea solution and hypobromite solution. Alkylamines, carboxylic acids and most amino acids do not interfere in the determination. Ammonium ion interferes, but the sensitivity for ammonium ion is only 1% of that for urea. The interference from ammonium ion was removed sufficiently by using an on-line cation-exchange column.

Determination of trace amounts of urea by using flow injection with chemiluminescence detection

Reaction between ammonia and hypobromite in alkaline solution was found to give chemiluminescence. The maximum wavelength of the chemiluminescence is ∼710 nm. This chemiluminescence reaction has been used for the determination of ammonium ion concentration in rainwater and fogwater with a flow injection analysis system. The detection limit of ammonium ion was 6.1×10 -6 mol/dm 3 (3 RSD). The dominant components in rainwater such as NO 3 - , SO 4 2- and Cl - , do not interfere with the determination, but humic acid and urea do

Determination of ammonium ion in rainwater and fogwater by flow injection analysis with chemiluminescence detection

A continuous flow method for the determination of formaldehyde in urban air has been developed based on the chemiluminescence reaction between hydrogen peroxide solution and gaseous formaldehyde in the presence of 3,4,5-trihydroxybenzonic acid (gallic acid) in alkaline solution. The emission produced by the chemiluminescence reaction is proportionate to the formaldehyde concentration from 10 ppb (109) v/v to 50 ppm v/v. The limit of detection [signal-to-noise (S/N)= 3] for gaseous formaldehyde is 10 ppb. The relative standard deviation for six measurements of 25 ppb v/v of formaldehyde is 7.1%. Hydrocarbon, sulfur dioxide, carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, ozone, acrolein and benzaldehyde do not interfere; however, propinaldehyde and acetaldehyde interfere slightly. Generally, the concentrations of propinaldehyde and acetaldehyde in urban air are less than formaldehyde, therefore their interferences can be considered negligible.

Continuous determination of gaseous formaldehyde by a chemiluminescence method

The reaction kinetics, the chemiluminescence spectra, the products, and the lifetimes of emission species for the chemiluminescence reaction between hypobromite and ammonia or urea in an alkaline aqueous solution were investigated. Results show that the reaction mechanism for ammonia chemiluminescence is different from that for urea. The reaction of ammonia and hypobromite produces NO2 in the gaseous phase and NO2− in solution; however, the reaction of urea and hypobromite does not. For the reaction of ammonia and hypobromite, chemiluminescence intensity obeys 1.5 order kinetics for hypobromite concentration when ammonia is in excess, but the reaction of urea and hypobromite obeys second order kinetics for hypobromite when urea is in excess. The spectrum of the chemiluminescence from the ammonia and urea with hypobromite shows a maximum intensity at 710, and at 510 nm, respectively. The chemiluminescence lifetimes of the emission species were 0.056 and 0.092 s for the reaction of ammonia and the reaction ...

Xincheng Hu

Papers

Determination of trace amounts of urea by using flow injection with chemiluminescence detection

Determination of ammonium ion in rainwater and fogwater by flow injection analysis with chemiluminescence detection

Continuous determination of gaseous formaldehyde by a chemiluminescence method

Mechanism of Chemiluminescence Reaction between Hypobromite and Ammonia or Urea.