CHM 343 Separations Lab Report - CHM 343 Separations Lab...

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CHM 343 Separations Lab Report # 1 Ion Chromatographic Separation and Determination of Chloride, Nitrate, Nitrite, and Sulfate Name: Choon Liang Tan Bronco ID: 007156760 Class Session: CHM343L Lecturer: Dr. Gutnikov & Dr. Dr. Hossein Ahmadzadeh Date: 01.30.08 1
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Abstract: Four standard solutions of various ions, chloride, nitrite, nitrate and sulfate, were created at 100ppm each, as well as a mixture of 25ppm of each. A sample with unknown concentration of any of the four ions was provided and the concentrations had to be determined experimentally through ion chromatography. It resulted in some fairly unconvincing data with 56.112ppm of nitrite ions (NO 2 ), 30.572ppm of nitrate ions (NO 3 ), and an overwhelming 971.496ppm of sulfate ions (SO 4 2- ). All samples were run a 3.5mM p-hydroxybenzoic acid eluent to create a gradient for the ions to be detected by the column. There were many experimental flaws such as long periods of experimental trials, three weeks, machine errors that couldn’t be avoided or fixed, and nitrite and nitrate ions being so similar in their retention times that good resolution wasn’t possible. Introduction: Ion chromatography can be used to analyze both anions and cations but it is more popular for its ability to analyze anions more rapidly and more conveniently than any other technique. It applies the theory of ion-exchange separations. Although the technology of ion-exchange was already invented, it wasn’t used with ion-exchange chromatography until the mid-1970s. In 1970’s anions and cations mixtures can be resolved on HPLC columns packed with anion-exchange or cations-exchange. During this period the way they detected was by conductivity measurements. They weren’t ideal because most of the electrolytes were in mobile phase. Thus, they created low-exchange capacity columns. These new columns used low-ionic strength mobile phases that could be de-ionized further. De-ionizing it further would allow high sensitivity conductivity detection. The theory of ion-exchange processes is based on exchange equilibriums between ions in solutions and ions of like sign on surface of an insoluble, high molecular mass solid. The most common active sites for cation-exchange resins are the sulfuric acid group, a strong acid and the carboxylic acid group, and a weak acid. The ones for anionic exchangers contain strongly basic tertiary amine groups or weakly basic primary amine groups. Detection in this experiment is done by indirect photometric detection. This focuses on the anions. Anions are transparent in UV and visible wavelength. Thus, a UV- active eluent is needed. With it the anions can be detected by a decrease in absorbance.
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