Detection of calcium and zinc concentration in water and wine

Transcription

1 Detection of calcium and zinc concentration in water and wine Version 2, Group M 14 Jorge Ferreiro, degree course Chemical engineering, 4 th semester fjorge@student.ethz.ch Natalja Früh, degree course Interdisciplinary sciences, 4 th semester fruehn@student.ethz.ch Arman Nilforoushan, degree course Chemical engineering, 4 th semester armanni@student.ethz.ch Assistent: Tatiana Egorova Abstract: Using Atomic Absorption Spectrometry we have analyzed the concentration of Calcium and Zinc in four different types of water and four different types of wine. The zincconcentration of the water samples could not be determined, as it was under the detection limit. The results for the calcium-concentration of the samples were: San Pellegrino ( ± 1.17) ppm, Swiss Alpina (85.0 ±0.9) ppm, Valser (240.9 ±2.5) ppm and Evian (50.9 ±0.9) ppm. The zinc-concentration of the wine samples were: Vin Blanc (0.290 ± 0.010) ppm, Chardonnay (1.177 ± 0.023) ppm, Beaujolais (0.581 ± 0.014) ppm and Kalterersee ( ±0.008) ppm. The calcium-concentration of the wine samples were: Vin Blanc (67.0 ± 0.5) ppm, Chardonnay (53.3 ± 0.6) ppm, Beaujolais (34.8 ± 0.5) ppm and Kalterersee (56.7 ± 0.6) ppm. Zürich, 25. Mai 2009 Jorge Ferreiro Natalja Früh Arman Nilforoushan 1

2 1. Introduction Atomic Absoprtion Spectrometry (AAS) is an analytical method to determine elemental composition of a sample. Thereby you atomize the sample spraying it into a flame. Each atom will absorb a characteristic wavelength. So, to analyze one atom type it needs a lamp which creates the characteristic energy to excite the specific atom type (ground state first excited state). Basically you will use a lamp containing your atom type; so to analyze Zinc you need a lamp containing Zinc. When the sample is being irradiated with light of the specific wavelength, a detector at the other end registers a drop if intensity with respect to the light s source. This difference in intensity can be used to determine the concentration of the atoms according Lambert-Beer. (1) To determine a sample s concentration one often uses the term A which means absorbance and it s given by (2). (2) One can combine all constant factors of the equation to get a linear relation between the concentration and de absorbance. This factor is called sensitivity S: The detection limit N is defined as follows: (3) (4) To get the specific wavelength you use a hollow-cathode lamp containing the same element which is being analyzed in the sample. So, only specific wavelength is being emitted and only the specific atoms in the sample will be excited. The method is accurate because only the specific atom will be excited; however it s possible to measure only one element. Symbol Explanation Unit I 0 radiant power input cd I radiant power output cd l coat thickness cm κ absorption -1 M -1 cm coefficient c concentration M σ standard deviation - S sensitivity M -1 Tab. 1: used mathematical symbols and its explanation 2

3 2. Experimental part 2.1. Equipment and chemicals Perkin Elmer Insturments Analyst 200 atomic absorption spectrometer Mettler Toledo AB 204 for CaCl 2 2 H 2 O and Zn-solution Mettler Toledo P 1210 for other weightings Chemical Molar weight [g mol -1 ] R-phrases S-phrases CaCl 2 2 H 2 O Ethanol Zn-solution Tab.2: Used chemicals in experiment 2.2. Preparation of standard solutions There were made four standard solutions each for water and wine for the calibration of the spectrometer. With this data you could generate a calibration curve with which the measurements of the water and wine samples were compared. Afterwards you could determine your Zinc and Calcium concentration in water and wine. The calibration solutions contained 1000 ppm of Zinc and a known amount of calciumchloride dihydrate. Chemical Exact weight [g] Exact concentration [ppm] Zn-solution (c = 1012 mg ml -1 ) CaCl 2 2 H 2 O Tab. 3: Exact concentrations of standard solutions of zinc and calcium with water as solvent. Diluted solutions Exact concentration [ppm] Zinc-standard (0.1 ppm) Zinc-standard (0.5 ppm) Zinc-standard (1.0 ppm) Calcium-standard (10 ppm) Calcium-standard (50 ppm) Calcium-standard (100 ppm) Tab. 4: Diluted standard solutions for calibration curve with solvent water Chemical Exact weight [g] Exact concentration [ppm] Zn-solution (c = 1012 mg ml -1 ) CaCl 2 2 H 2 O Tab. 5: Exact concentrations of standard solutions of zinc and calcium with 12% ethanol/water as solvent. Diluted solutions Exact concentration [ppm] Zinc-standard (0.1 ppm) Zinc-standard (0.5 ppm) Zinc-standard (1.0 ppm) Calcium-standard (10 ppm) Calcium-standard (50 ppm) Calcium-standard (100 ppm) Tab. 6: Diluted tandrd solutions for calibration curve with solvent 12% ethanol/water. 3

4 2.3. Measurements First, the measurements were done for Zinc. Before measuring the standard solutions for the calibration you had to measure distilled water as blank. Then we ve checked the blank making a first measurement of the same distilled water. Afterwards we ve started measuring the standard solutions by the lowest concentration. Later, the Zinc-concentration in the four waters was measured. Next, the whole process was repeated for the calibration of the wine solutions. As blank, we ve used a 12% ethanol/water solution. Here the blank was checked, too. Then, the calibration was made starting by the lowest concentration followed by the measurements of the wines. At least the lamp was changed to measure the calcium concentration in water and wine. It was made the same way as for zinc. 3. Results 3.1. Zinc San Pellegrino under detection limit Swiss Alpina under detection limit Valser under detection limit Evian under detection limit Detection limit: ppm Vin Blanc ± Chardonnay ± Beaujolais ± Kalterersee ±0.008 Detection limit: ppm 3.2. Calcium San Pellegrino ± 1.17 Swiss Alpina 85.0 ±0.9 Valser ±2.5 Evian 50.9 ±0.9 Detection limit: 2.65 ppm Vin Blanc 67.0 ± 0.5 Chardonnay 53.3 ± 0.6 Beaujolais 34.8 ± 0.5 Kalterersee 56.7 ± 0.6 Detection limit: 3.00 ppm Tab. 7-10: Measured concentrations for zinc and calcium in different samples 4

5 4. Discussion 4.1. Zinc The concentration of zinc in the water-samples couldn t be detected because the concentrations were below the detection limit. To measure the values the method is too inaccurate. In the wine-samples the concentration could be measured without any problems. The concentrations were above the detection limit. We unfortunately didn t have some literature values to compare our results Calcium The detection limit for the water and the wine samples was below the measured values. The concentration in the water samples was lower as the indicated concentrations on the bottles. One reason could be a different ionization of the calcium atoms because they don t absorb the specific wavelength sent out by the hollow cathode lamp. Adding easier ionisable elements this interference could have been lower. Reference [ppm] San Pellegrino ± Swiss Alpina 85.0 ± Valser ± Evian 50.9 ± Tab. 11: Comparison of reference value and measured concentration of calcium in different water samples For the wine samples there was no reference available. 5. Source [1] Praktikum Physikalische und Analytische Chemie, Anleitung Atom Absorptions Spektrometrie, Frühlingssemester Appendix 6.1. Calculation 6.2. Output Spectrometer 6.3. Lab-Journal 5