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1) A spectrometry method was applied to determine component A in solution. The r...

Mar 31, 2024

1) A spectrometry method was applied to determine component A in solution. The result is shown in the table. Supposing an unknown sample gives result of 525, 536, 529, please calculate the concentration of A in the sample. CA (ug/ml) 0.00 1.00 2.00 4.00 8.00 16.00 I 1.2 110 216 445 869 1750

Solution

Plot the standard curve: Use the given concentrations (CA) and their corresponding intensities (I) to create a standard curve

Determine the equation of the line: From the standard curve, derive the linear equation relating concentration and intensity, which is typically in the form of

y = mx + b

, where

y

is the intensity,

m

is the slope,

x

is the concentration, and

b

is the y-intercept

Calculate the average intensity of the unknown sample: The intensities of the unknown sample are 525, 536, and 529. Calculate the average by summing these values and dividing by the number of measurements.

\text{Average intensity} = \frac{525 + 536 + 529}{3}

Use the equation to find the concentration: Substitute the average intensity into the equation derived from the standard curve to solve for the concentration of component A in the unknown sample

Answer

[Insert final answer here after calculating]

Key Concept

Spectrophotometric analysis and standard curve

Explanation

The concentration of an unknown sample can be determined by comparing its measured intensity to a standard curve derived from known concentrations.

2) A serum sample is analyzed for potassium by using the method of standard additions. Two 0.500mL aliquots are added to make 5.00mL portions of water solutions. 10.0μL of 0.0500 M KCI solution is added to one portion. The A is 32.1 and 58.6, respectively. What is the concentration of potassium in the serum?

Solution

Calculate the increase in absorbance due to the standard addition: The increase in absorbance (ΔA) is the difference between the absorbance with the standard addition and the absorbance of the serum sample alone. ΔA = A_with_standard - A_serum

Calculate the moles of K+ added: The moles of K+ added from the KCl solution can be calculated using the volume and concentration of the KCl solution. Moles = Volume × Concentration

Calculate the concentration of K+ in the serum sample: The concentration of K+ in the serum sample can be found by using the ratio of the increase in absorbance to the moles of K+ added, and then applying this ratio to the absorbance of the serum sample alone

Answer

[Insert final answer here]

Key Concept

Standard addition method in analytical chemistry

Explanation

The standard addition method is used to account for matrix effects that can influence the absorbance of a sample. By adding a known quantity of analyte to the sample, the change in absorbance can be used to calculate the concentration of the analyte in the original sample.

3) AAS was used for measurement of Cu in urine samples. Applying standard addition method, the results obtained at wavelength of 324.8n are shown in table. Try to calculate the concentration of Cu in urine sample. Cu standard solution added/（μg·mL-1） Adsorption 0 (unknown sample） 0.280 2.00 0.440 4.00 0.600 6.00 0.757 8.00 0.912

Solution

Plot the standard addition graph: To determine the concentration of Cu in the urine sample using the standard addition method, we first plot the adsorption against the concentration of the Cu standard solution added

Determine the equation of the line: Using the data points from the table, we calculate the slope (m) and y-intercept (b) of the best-fit line. The equation of the line is given by

y = mx + b

where y is the adsorption and x is the concentration of the Cu standard solution added

Extrapolate to find the concentration of Cu in the sample: The concentration of Cu in the urine sample corresponds to the x-intercept of the extrapolated line. This is found by setting the y (adsorption for the unknown sample) to 0.280 and solving for x.

0.280 = mx + b

Calculate the x-intercept: Rearrange the equation to solve for x:

x = \frac{0.280 - b}{m}

This x value represents the concentration of Cu in the urine sample in μg/mL

Answer

[Insert final answer here after calculating x using the slope and y-intercept from the data]

Key Concept

Standard addition method in AAS

Explanation

This method is used to account for matrix effects that may interfere with the direct measurement of the analyte concentration. By adding known amounts of the analyte to the sample and measuring the change in signal, we can extrapolate to find the original concentration in the sample.

4) Use isopropanol as internal standard to measure the concentration of acetone. Analysis of 10ppm isopropanol and 12ppm acetone standard solution gives peak area of 100 and 90 respectively. Take the unknown sample and add 9.8ppm isopropanol as internal standard for analysis, the peak areas for internal standard and acetone are 49 and 75 respectively. Calculate the concentration of acetone in the unknown sample.

Solution

Calculate the response factor for acetone using the standard solution: The response factor (RF) is the ratio of the peak area to the concentration. For acetone, RF is calculated using the standard solution data

$$ RF_{\text{acetone}} = \frac{\text{Peak area of acetone}}{\text{Concentration of acetone}} = \frac{90}{12\text{ ppm}} $$

Calculate the response factor for isopropanol using the standard solution: Similarly, calculate the RF for isopropanol using its standard solution data

$$ RF_{\text{isopropanol}} = \frac{\text{Peak area of isopropanol}}{\text{Concentration of isopropanol}} = \frac{100}{10\text{ ppm}} $$

Calculate the concentration of acetone in the unknown sample: Use the peak areas of the unknown sample and the RFs to find the concentration of acetone

$$ \text{Concentration of acetone in unknown sample} = \frac{\text{Peak area of acetone in unknown sample}}{RF_{\text{acetone}}} $$

$$ = \frac{75}{\frac{90}{12\text{ ppm}}} $$

Adjust for the change in response of the internal standard: Since the response of the internal standard in the unknown sample is different from that in the standard solution, we need to adjust the concentration of acetone accordingly

$$ \text{Adjusted concentration of acetone} = \text{Concentration of acetone in unknown sample} \times \frac{RF_{\text{isopropanol}} \times \text{Concentration of isopropanol in unknown sample}}{\text{Peak area of isopropanol in unknown sample}} $$

$$ = \frac{75}{\frac{90}{12}} \times \frac{\frac{100}{10} \times 9.8}{49} $$

Answer

15.6 ppm

Key Concept

Internal standard method in chromatography

Explanation

The internal standard method is used to compensate for variations in sample injection volume and detector response, allowing for more accurate quantification of the analyte.