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CHEM 20500

Analytical Measurement Science – Toolkit II: Assignment

As part of a registration submission document it is essential to supply a valid analytical method using the ICH 2QB regulations (available in the same folder as the assignment on Blackboard). These regulations are used to provide an analytical method that is reliable to check the safety and efficacy of the product.

In this assignment you are provided with data for two alternative methods for the assessment of the toxic metal Pb in a product. No knowledge of the techniques is necessary since the assessment will be based solely on the calculations resulting from the data provided.

There is a proforma to submit your work. Please make sure you use the proforma provided to submit your work. This also shows the marks allocated for each part.

The ultimate question is simple:

Which technique would you recommend and why?

You must provide any graphs, calculations or other material that enabled you to arrive at your answer.

Technique 1 – Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)

Technique 2 – Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

The task is to take the data provided below and assess the Linearity, Accuracy, Limit of Detection (LoD), and Limit of Quantification (LoQ).

Note that the data is generated over a wide dynamic range.  It may be easier to visualize this using a log-log plot.

1) Linearity

Use the data below (concentration in µg/mL and response signal is in counts (cts) to assess the linearity and linear range of each of the techniques. Remember to supply any graph(s) that you think are necessary to demonstrate the linearity. Clearly explain how you reached the decision and explain which technique you would select based on linearity and why.

2) Accuracy

In order to assess the accuracy of each technique a sample of a standard reference material NIST SRM 3280 was analysed. The certificate of analysis is available on Blackboard for you to consult. The preparation of the standard is given below. Using the data provided assess the recovery of Pb obtained for both techniques.

A 0.2221 g sample of NIST 3280 was digested in 10 mL of a solution consisting of nitric acid (8 mL) and hydrochloric acid (2 mL). The resulting solution was diluted to 25 mL This solution was then analysed by ICP-OES (calibrated for the range 0-100 ng/mL) and ICP-MS (calibrated for the range 0-50 ng/mL). The resulting solution gave the following data and signals for the solution being analysed in counts (cts).

Using the data provided calculate the % recovery of Pb, and comment on both the results and the variability in the sample reading obtained, particularly in reference to which technique might be most appropriate for this analysis.

3) Limit of Detection (LoD) and Limit of Quantification (LoQ)

The calibration used to generate the equations in question 2 was obtained by using 6 concentrations for each technique. A blank was then analysed 10 times. You are provided with the mean and standard deviation of the blank below. The equation for the calibration line is provided in question 2. Calculate the limit of detection (LoD) and limit of quantification (LoQ) for each technique. Justify the method you use as part of your answer.

ICP-OES

Blank Mean = 3,034

SD = 2282

ICP-MS

Blank Mean = 20.65

SD = 0.94

Comment on the LoD and LoQs obtained for this determination

4) Summary

Finally summarize the important data and conclusions from information you have obtained and suggest either ICP-OES or ICP-MS as your method of choice, explaining your decision.

Answer Proforma

Student ID Number:

Course Number: CHEM 20500

1)  Linearity

Linearity – ICP-OES – Insert a calibration graph to the last points of linearity, and any other graphs you feel are important to show, and include any information necessary to interpret the linearity of the graph               4 Marks

What is the range over which ICP-OES is linear?                 1 Marks

How did you reach this conclusion?                           2 Marks

Linearity – ICP-MS - Insert a calibration graph to the last points of linearity, and any other graphs you feel are important to show, and include the information necessary to interpret the linearity of the graph                    4 Marks

What is the range over which ICP-MS is linear?                      1 Marks

How did you reach this conclusion?                         2 Marks

Which technique is most linear, what overall conclusion can be drawn about the linearity of both techniques?                5 Marks 

2) Accuracy

Calculate the percentage recovery of Pb for each technique clearly showing your calculations. This should be done using the SRM 3280 certificate to obtain the true value of Pb. Please clearly explain your calculation method

ICP-OES Calculation                            4 Marks

ICP-MS Calculation                         4 Marks

Comment on the % recovery obtained, and what this tells you about each technique.                      4 Marks

Comment on the variability (errors) in the results                      3 Marks

3) Limit of Detection (LoD) and Limit of Quantification

a) Calculate the LoD and LoQ for ICP-OES. Show all of your calculations.                     4 Marks

b) Calculate the LoD and LoQ for ICP-MS. Show all of your calculations.                    4 Marks

c) Comment on the LoD and LoQ results obtained for each technique and how they compare.                     3 Marks

4) Selection of the best method.

Considering the information you have generated, under what circumstances would ICP-OES be the best technique, and under what circumstances would ICP-MS be best?                   5 Marks