[화학과 수석의 A+ 레포트] 콜라 속 인의 정량 (분석화학실험)

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1. Spectroscopic Determination of Phosphorus in Soft Drink

이번 실험에서는 molybdenum blue method를 통해 콜라 1병(500mL)에 함유된 phosphorus의 양을 정량했다. spectrophotometer로 다양한 농도의 phosphorus standard solution의 absorbance를 측정한 후, 그를 바탕으로 flask 내 P의 양(mu g)를 x축으로 하고 absorbance를 y축으로 한 calibration curve를 얻어 콜라 sample의 absorbance로부터 phosphorus의 양을 구했다. 그 결과 콜라 1병(500mL)에 함유된 phosphorus의 양은 90mg였으며, 이는 문헌값을 통해 계산한 콜라 1병(500mL) 당 phosphorus 함유량인 86mg과 비교했을 때 4mg의 오차와 4.7%의 % error를 보였다.
2. Molybdenum Blue Method

molybdenum blue method는 phosphorus를 정량할 때 사용하는 대표적인 spectrophotometry 중 하나다. 시료 중에 존재하는 phosphate salt를 ammonium molybdate와 산성 조건에서 반응시켜 (NH _{4} ) _{3} PO _{4} BULLET 12MoO _{3}를 생성한 후, 이에 다시 reducing agent를 가해 생성된 진한 청색의 molybdenum blue를 spectrophotometry로 정량해 phosphorus의 양을 얻어내는 방식이었다.
3. Spectrophotometry and Colorimetry

spectrophotometry는 빛을 이용해 화학 물질의 농도를 측정하는 방법으로, 특히 absorbance에 따라서 농도를 측정하는 과정을 colorimetry라 한다. absorbance(A0의 정의는 <식 2>와 같으며, colorimetry로 물질의 농도를 측정하는데 근거를 두는 beer's law는 <식 3>으로 주어진다.
4. Preparation of P Standard Solution

P stock solution 20.00mL를 100mL까지 증류수로 묽혀서 P standard solution을 준비했다. (P stock solution은 KH _{2} PO _{4} 0.4422g을 1L까지 증류수로 묽혀서 만들었다.)
5. Preparation of Sample Solution

김빠진 콜라 10.00mL를 100mL까지 증류수로 묽혀서 sample solution을 준비했다.
6. Sample Processing

100mL volumetric flask 7개를 준비해서 1부터 7까지 label 했다. flask 2 - 5에는 P standard solution을 각각 0.50mL, 1.00mL, 2.00mL, 4.00mL 가했고, flask 6 ? 7에는 sample solution을 2.00 mL씩 가했다. 그다음 flask 7은 증류수로 표선까지 채웠으며, flask 1 - 6에는 ammonium molybdate 수용액을 8mL씩 가하고 2분간 기다렸다. 그리고 flask 1 - 6에 hydroquinone 8mL씩 가한 후, Na2SO3 수용액을 8mL씩 가하고 즉시 증류수로 표선까지 채우고 시간을 기록한 후 실온에 30분간 놔뒀다.
7. Absorbance Measurements

flask 1 ? 7의 용액들과 증류수를 8개의 cuvet에 각각 채운 후, 증류수를 넣은 것을 reference cuvet으로 하여 spectrophotometer를 통해 7종류 cubet의 650nm에서의 absorbance를 측정했다.
8. Calculation of P Content in Samples

flask 1 - 7 내 P의 양을 계산하고, 각 solution의 corrected absorbance를 계산했다. 이를 바탕으로 least square method를 통해 구한 calibration curve에 콜라 sample의 absorbance를 대입하여 콜라 1병(500mL)에 함유된 총 P의 질량을 계산했다.
9. Comparison with Literature Values

실험 결과, 콜라 1병(500mL)에 함유된 P의 양은 90mg이었다. 문헌에 따르면 콜라는 250mL 당 43mg의 P를 함유하고 있으므로 문헌으로부터 계산한 콜라 1병(500mL)에 함유된 P의 양은 86mg이다. 측정값(90mg)은 문헌값(86mg)과 비교했을 때 4mg의 오차와 4.7%의 % error를 보이는 값이다.

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1. Spectroscopic Determination of Phosphorus in Soft Drink

The spectroscopic determination of phosphorus in soft drinks is an important analytical technique that provides valuable information about the composition and quality of these beverages. This method allows for the accurate quantification of phosphorus levels, which is crucial for regulatory compliance, nutritional labeling, and ensuring product consistency. The ability to reliably measure phosphorus content is particularly relevant for soft drinks, as phosphoric acid is commonly used as an acidulant and preservative in these products. By employing spectroscopic techniques, researchers and manufacturers can gain a deeper understanding of the phosphorus content in soft drinks, which can inform product formulation, quality control, and consumer health considerations. Overall, the spectroscopic determination of phosphorus in soft drinks is a valuable analytical tool that supports the production of safe, high-quality, and well-characterized beverage products.
2. Molybdenum Blue Method

The molybdenum blue method is a widely used spectrophotometric technique for the determination of phosphorus in various sample matrices, including soft drinks. This method relies on the formation of a blue-colored complex between phosphate ions and molybdate ions, which can be quantified by measuring the absorbance of the solution at a specific wavelength. The molybdenum blue method is advantageous due to its sensitivity, selectivity, and relatively simple experimental procedure. By optimizing the reaction conditions, such as pH, reagent concentrations, and reaction time, researchers can obtain accurate and reproducible results for the determination of phosphorus content. Additionally, the molybdenum blue method can be adapted to different sample types and instrumentation, making it a versatile analytical tool for the analysis of phosphorus in a wide range of applications, including the quality control of soft drinks and other food and beverage products.
3. Spectrophotometry and Colorimetry

Spectrophotometry and colorimetry are essential analytical techniques for the determination of phosphorus in soft drinks and other sample matrices. These methods rely on the measurement of the absorbance or transmittance of light by a colored complex formed between the analyte (phosphorus) and a specific reagent. Spectrophotometry, in particular, provides a quantitative approach to phosphorus analysis, allowing for the accurate determination of concentration based on the Beer-Lambert law. Colorimetry, on the other hand, can offer a more qualitative or semi-quantitative assessment of phosphorus content, often through visual comparison to standard color charts or scales. Both techniques are widely used in the analysis of soft drinks and other food and beverage products, as they offer reliable, sensitive, and cost-effective means of determining phosphorus levels. The choice between spectrophotometry and colorimetry may depend on the specific requirements of the analysis, such as the desired level of accuracy, the availability of instrumentation, and the complexity of the sample matrix.
4. Preparation of P Standard Solution

The preparation of a phosphorus (P) standard solution is a crucial step in the spectroscopic determination of phosphorus in soft drinks. The standard solution serves as a reference for the quantification of phosphorus content in the sample, allowing for the construction of a calibration curve and the accurate determination of phosphorus concentrations. The preparation of the P standard solution involves the dissolution of a known mass of a pure phosphorus compound, such as potassium dihydrogen phosphate (KH2PO4), in a suitable solvent, typically deionized water. The concentration of the standard solution must be precisely determined and verified to ensure the accuracy of the subsequent analyses. The use of high-purity reagents and careful volumetric measurements are essential to minimize errors and ensure the reliability of the P standard solution. This step lays the foundation for the accurate and precise determination of phosphorus in soft drinks and other sample matrices using spectroscopic techniques.
5. Preparation of Sample Solution

The preparation of the sample solution is a critical step in the spectroscopic determination of phosphorus in soft drinks. This process involves the appropriate dilution and/or digestion of the soft drink sample to ensure that the phosphorus content falls within the linear range of the analytical method. Depending on the matrix complexity and the expected phosphorus concentration, the sample may require various pretreatment steps, such as filtration, centrifugation, or acid digestion, to remove interfering substances and release the phosphorus from any organic or inorganic complexes. The careful and consistent preparation of the sample solution is essential to obtain accurate and reproducible results, as any errors or inconsistencies in this step can significantly impact the final phosphorus determination. Additionally, the use of appropriate quality control measures, such as the analysis of blank samples and spiked samples, can help to validate the sample preparation procedure and ensure the reliability of the analytical results.
6. Sample Processing

The sample processing step in the spectroscopic determination of phosphorus in soft drinks is crucial for ensuring the accuracy and reliability of the analytical results. This step typically involves the appropriate dilution, filtration, or other pretreatment of the soft drink sample to prepare it for the subsequent spectroscopic analysis. Proper sample processing is essential to remove any interfering substances, such as suspended particles, colored compounds, or organic matter, that could potentially affect the formation of the phosphorus-molybdenum blue complex or the absorbance measurements. Additionally, the sample processing step may involve the use of appropriate preservation techniques, such as refrigeration or the addition of stabilizing agents, to maintain the integrity of the phosphorus content during storage and transportation. By carefully controlling the sample processing procedures, researchers and analysts can ensure the accuracy, precision, and reproducibility of the phosphorus determination in soft drinks, which is crucial for quality control, regulatory compliance, and product development purposes.
7. Absorbance Measurements

The absorbance measurements are a critical step in the spectroscopic determination of phosphorus in soft drinks. This step involves the quantification of the intensity of the blue-colored complex formed between the phosphate ions and the molybdate reagent, which is directly proportional to the phosphorus concentration in the sample. The absorbance measurements are typically performed using a spectrophotometer, which measures the amount of light absorbed by the sample at a specific wavelength. The accuracy and precision of these measurements are essential for the reliable quantification of phosphorus content in soft drinks. Factors such as the selection of the appropriate wavelength, the optimization of the reaction conditions, the use of appropriate blank and standard solutions, and the proper calibration of the spectrophotometer can all influence the quality of the absorbance measurements. By carefully controlling these parameters and following established analytical protocols, researchers and analysts can obtain accurate and reproducible results for the determination of phosphorus in soft drinks, which is crucial for product quality control, regulatory compliance, and consumer safety.
8. Calculation of P Content in Samples

The calculation of the phosphorus (P) content in soft drink samples is the final step in the spectroscopic determination of phosphorus. This step involves the use of the measured absorbance values, the calibration curve, and appropriate conversion factors to determine the concentration of phosphorus in the original sample. The accuracy of these calculations is essential for the reliable quantification of phosphorus levels, which is crucial for various applications, such as quality control, nutritional labeling, and regulatory compliance. The calculation process typically involves the use of the Beer-Lambert law, which relates the absorbance of the sample to the concentration of the analyte. Additionally, the calculations may require the consideration of sample dilution factors, the molar absorptivity of the phosphorus-molybdenum blue complex, and the molecular weight of phosphorus to arrive at the final phosphorus content in the soft drink samples. By following established calculation protocols and ensuring the accuracy of the input data, researchers and analysts can obtain reliable and reproducible results for the determination of phosphorus in soft drinks, which supports the production of high-quality and well-characterized beverage products.
9. Comparison with Literature Values

The comparison of the determined phosphorus (P) content in soft drink samples with literature values is an important step in the spectroscopic analysis of phosphorus. This comparison serves to validate the accuracy and reliability of the analytical method, as well as to provide context for the obtained results. By comparing the measured phosphorus levels in the soft drink samples to published or reference values, researchers and analysts can assess the performance of their analytical procedure and identify any potential discrepancies or deviations. This comparison can also help to identify any matrix effects, interferences, or other factors that may have influenced the phosphorus determination. Additionally, the comparison with literature values can provide insights into the typical phosphorus content in different types of soft drinks, which can be useful for product development, quality control, and regulatory compliance purposes. Overall, the comparison with literature values is a crucial step in the spectroscopic determination of phosphorus in soft drinks, as it helps to ensure the accuracy and reliability of the analytical results and supports the production of high-quality, well-characterized beverage products.