Naslov
Nitrite and Nitrate in Tobacco – A Case study in IC method development

Autori
Vinković, Kristinka ; Crey Desbiolles, Caroline ; Jensen, Detlef

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, prošireni sažetak, znanstveni

Izvornik
11th International School of Ion Chromatrography / Ukić, Šime ; Bolanča, Tomislav - Zagreb : Fakultet kemijskog inženjerstva i tehnologije Sveučilišta u Zagrebu, 2010, 26-27

ISBN
978-953-6470-51-8

Skup
11th International School of Ion Chromatography

Mjesto i datum
Zagreb, Hrvatska, 08.07.2010. - 09.07.2010

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Tobacco, nitrate, nitrite, ion chromatography

Sažetak
Conductivity detection is very often considered as the standard detection technique in ion chromatography (IC). While most of the IC- applications indeed use suppressed conductivity, other detection techniques like UV and amperometry are commonly used as well. In case of demanding sample matrices the combination of both, improved separation and optimized detection conditions can help to solve the analytical task. The determination of Nitrite and Nitrate in aqueous tobacco extracts was chosen as a real-life example to explore different detection techniques. This matrix and analytes were chosen, as nitrites are precursors in the formation of carcinogenic nitrosamines. Since nitrosamines are found in tobacco smoke, concentration of nitrites should be kept under control. Method development started with nitrite and nitrate separation on IonPac AS19 column with potassium hydroxide eluent and suppressed conductivity detection. As the extracts contained high concentrations of organic acids initially KOH-gradient elution was applied to allow the determination of the target analytes. Since the extracts contained high concentrations of chloride eluting next to nitrite, its trace determination was hampered. The use of parallel UV-detection was considered, but the end user voted for a method allowing the selective determination of nitrite and nitrate in combination with a shorter cycle time of analysis. In a different approach we tested the separation on AS9-HC column applying UV detection. The eluent chosen was 30 mmol L-1 sodium chloride, eluting all interesting components while being UV-transparent. Good correlation coefficients (> 0.999) were achieved for both, nitrites and nitrates, in the range from 0.01 to 1.00 mg L-1. Signal to noise ratio at 0.01 mg L-1 was 18.1 for nitrite and 31.5 for nitrate for aqueous standard solutions. Unfortunately, in real samples organic interferences prevented identification of nitrite at concentrations lower than 0.2 mg L-1. Several sodium chloride gradients were tested in order to achieve better separation between nitrite and interfering compounds. pH value of the eluent was set to 7.5 trying to transfer most organics to neutral molecules. Unfortunately, neither gradients, buffering of the eluent, wavelength changes on the UV-detector or choosing a column of different selectivity (e.g. CarboPac PA100) did improve the chromatographic resolution of nitrite from matrix components. In addition we tested an SPE sample preparation using OnGuard P and RP cartridges. The total amount of UV-absorbing organics was reduced, though the determination of nitrite was difficult. Hence amperometric detection was chosen to solve the issue. As working electrode glassy carbon was chosen being superior to other electrode materials in terms of sensitivity. Applying an isocratic elution with 30 mmol L-1 NaCl on an IonPac AS9-HC all ionic components were eluted in 35 min. Due to the high specificity and sensitivity of the amperometric detection it was possible to reliably quantify nitrite in aqueous tobacco-extracts at concentrations down to 0.01 mg L-1 with excellent reproducibility. The approach chosen uses UV-detection in parallel to detect Nitrate selectively, interference-free and with high specificity at concentration levels from 10 to 800 mg L-1. During method development the chromatographic and the detection conditions, as well as the sample preparation prior to the analytical separation were evaluated to generate a robust and reliable method suited for routine application. Pros and Cons of three detection techniques were examined and evaluated for specific samples. This application might be of interest also for other food samples, if the determination of nitrite is hampered by other matrix components. As limits on the amount of nitrites used in meat products are established in order to decrease cancer risk in the population, the experiments shown could become the basis for wider usage of the same approach or similar methods.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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