Nitrite amperometric detection

To date, electrochemical (amperometric) detection of NO is the only available technique sensitive enough to detect relevant concentrations of NO in real time and in vivo and suffers minimally from potential interfering species such as nitrite, nitrate, dopamine, ascorbate, and L-arginine. Also, because electrodes can be made on the micro- and nano-scale these techniques also have the benefit of being able to measure NO concentrations in living systems without any significant effects from electrode insertion. 

Amperometric detection is a very sensitive technique. In principle, voltammetric detectors can be used for all compounds which have functional groups which are easily reduced or oxidized. Apart from a few cations (Fe , Co ), it is chiefly anions such as cyanide, sulfide and nitrite which can be determined in the ion analysis sector. The most important applications lie however in the analysis of sugars by anion chromatography and in clinical analysis using a form of amperometric detection know as Pulsed Amperometric Detection (PAD). 

Alawi [319] has discussed an indirect method for the determination of nitrite and nitrate in surface, ground and rain water by reaction with excess phenol (nitrite ions first being oxidised to nitrate) and extraction of the o-nitrophenol produced, followed by separation on a reversed phase high performance liquid chromatography column with amperometric detection in the reduction mode. Recoveries were 82% for nitrate and 77% for nitrite in the concentration range 10-lOOOpg L 1. The method is claimed to be free of interferences from other ions. 

J. A. Cox and K. R. Kulkami, Flow Injection Determination of Nitrite by Amperometric Detection at a Modified Electrode. Analyst, 111 (1986) 1219. 

Gaetano da Rocha, J.R., L. Angnes, M. Bertotti, K. Araki, and H.E.Toma (2002). Amperometric detection of nitrite and nitrate at tetraruthenated porphyrin-modified electrodes in a continuous-flow assembly. Anal. Chim. Acta 452, 23-28. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

Strehlitz, B. Gruendig, B. Schumacher, W. Kroneck, P. M. H. Kotte, H. A nitrite sensor based on a highly sensitive nitrite reductase mediator-coupled amperometric detection. AnaZ. Chem. 1996,68, 807-816. 

Hypochlorite, ascorbate, hydrazine, arsenite, thiosulfate, nitrite, nitrate, cobalt and iron are a partial list of the ions that have been detected using amperometric detection [55]. The most common ions determined by amperometric detection in 1C include inorganic anions forming complexes with cyanide, sulfide, and iodide at a silver electrode [56]. The relevant chemical reaction is shovra below. 

Figure 8.8 Amperometric detection of nitrite, thiosulfate, and iodide on a carbon paste electrode. Separator column Supersep Anion eluent 3.3 mmol/L phthalic acid/MeCN (90 ...

Figure 10.17 Amperometric detection of nitrite at trace level. Separator column Metrosep Anion Dual 2 eluent 2mmol/L...

Salimi, A. Noorbakhash, A. Karonian, F. S. Amperometric detection of nitrite, iodate and periodate on glassy carbon electrode modihed with... 

In method (c), the NOC after HPLC separation was photolyzed by a UV lamp (254 10 nm), and the charged nitrite species was determined amperometrically (79). The denitrosation reaction was found to be dependent on the wavelength of the UV light, lamp intensity, exposure time, and pH of the solution. The effluent from the HPLC column was passed through a capillary PTFE tubing coiled around a 40-W mercury lamp. The electrochemical detector used permitted either single- or dual-mode detection corresponding, respectively, to detection limits of 60 pg and 20 pg for NDMA. The method was applied to the determination of NDMA in beer and of... 

Amperometric nitrite detection at 0 V was conducted with a PANl-MWCNT-Au electrode [52]. The electrode showed a large electrocatalytic activity towards reduction of nitrite compared to the bare Au, MWCNT-Au and PANl-Au electrodes on which the nitrite reduction response was almost undetectable. Na", K", Ca ", Mg2", AP", CP, NO3, CIO3, H2PO , HPO , C0 , S0 (50-fold excess to nitrite) and Zn ", Cd ", Ba ", and Br (10-fold excess), UA and AP did not interfere with the nitrite detection, whereas Fe ", Cu ", P, BrOj, IO3, and AA were interfering. 

Apart from UV detection, there are two other alternative detection methods for trace analysis of nitrite. A very sensitive detection method for nitrite is DC amperometry at +1.1 V on a carbon paste electrode. In this case, amperometry and suppressed conductivity detection can be applied simultaneously by directing the conductivity cell effluent through the amperometric celL Figiu-e 10.17 exemplifies this with a surfiice water sample that was injected imdiluted [26]. As can be seen firom this chromatogram, nitrite concentrations in the lowest micro-gram/Liter range can be detected without any problem. 

The oxidation of NO to nitrite and the subsequent oxidation of nitrite to nitrate cannot be clearly discriminated due to their similar oxidation potentials (8). To detect NO electrochemically, the complete three-electron oxidation of NO to nitrate (at ca. 0.9 V vs. Ag/AgCl) at the surface of a working electrode is accomplished (9,10) amperometrically... 

Conductivity detection and DC amperometry can be used simultaneously. In a non-suppressed system the conductivity cell effluent is directed to the amperometric cell in a suppressed system the positioning of the amperometric cell depends on the electrode material. The carbon paste electrode, for example, is positioned between the suppressor and the conductivity cell, so that electroactive anions can be detected together with standard anions [14]. An example of applications involving a carbon paste electrode is shown in Fig. 7-8. The separation of nitrite, thiosulfate, and iodide is performed in an acidic medium with a... 

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