When completing the Quality Control Sample and the five RSD samples.
How much of water/stock volume.
Could you also provide me with a brief explanation as to what the QC and RSD are and what they are used for so I can better understand.Analytical Methods -
Part A
Calibration Curve preparation (prior calculations required!)
Scenario
You have been asked by a senior analytical chemist to provide proof that your scientific analytical method for paracetamol is reliable and robust before they instruct you to perform an analysis on their behalf. To this end they have asked you to:
- Create a calibration curve covering the expected blood therapeutic to fatal levels of paracetamol, with an associated quality control and RSD samples as well.
You will have to find out some more information about this drug: find out the therapeutic and fatal blood drug concentrations of paracetamol, usually expressed in mg/L (or possibly μg/ml, which is the same) - note where a mass of drug is indicated this refers to a dose and not a blood drug concentration - do not confuse the two!
Instructions
For this lab session you ONLY have to prepare a calibration curve based on the information above, but you will have to do your calculations PRIOR to attending this session. Your samples will be racked and stacked in the trays provided and these will be run for you. It is essential that you have performed appropriate initial reading on the drug in question (to determine appropriate concentrations) and are careful with the preparation of your curve (pipetting skills, quality etc) as the appropriateness of the curve and its linearity will form the basis of this assessment.
You will need to construct a calibration curve covering this concentration range using a pure drug stock solution that has been prepared for you at the following concentration - paracetamol (2000mg/L) and will be available in the lab on arrival. To do so you will need to do your calculations PRIOR to attending this lab (time is limited and you will not have enough time to calculate and prepare your curve, so don't forget to bring your calculations with you!)
You will have to prepare your standards from this stock solution. It is likely that you will need to consider an intermediary stock solution in order to obtain an accurate calibration curve.
You should prepare FIVE standards you want to use for your calibration curve using GILSON pipettes only (Note you will NOT be using 10 ml volumetric flasks) - and don't forget about your blank!
Calculate what you intend the final concentration of each standard is to be and what volumes you need to take from the stock solution and water to dilute to achieve this concentration but bear in mind that you will prepare your calibration solutions directly into an autosampler vial (minimum volume 0.5ml, maximum capacity volume 1.8 ml) so you will have to think carefully about your volumes that you need to pipette and ensure they will fit in the vial!
Use this table to provide the following information:
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Calibrant number
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Concentration (mg/L)
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Volume of stock (ml)
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Calculation:
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Blank
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0
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0
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1
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|
|
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2
|
|
|
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3
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|
|
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4
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|
|
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5
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|
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You will also need to include your full calculation of at least 1 concentration to illustrate that you understand the principles behind this calculation.
1) Using your notes, prepare your set of calibration standards that cover the appropriate concentration range using the apparatus provided - make sure you have labelled your glassware appropriately.
2) Make sure the vials have your name and your concentrations written on them. Rack these samples into the tray provided as well as documenting the appropriate details on the log sheet provided next to the tray.
3) Leave a copy of your calculations and table of concentrations with your name clearly printed on it.
Analytical Methods - Part B
QC & RSD Preparation
Quality Control:
Prepare 1 quality control (QC) sample in duplicate at a concentration of 50mg/L. You will have to calculate how to prepare this sample from the stock solution of 2000mg/L.
RSD:
Prepare 5 samples at a concentration of 100mg/L. You will have to calculate how to prepare these samples from the stock solution of 2000mg/L.
Rack these samples into the tray provided as well as documenting the appropriate details on the logsheet provided next to the tray.
Accuracy:
Take note, this QC has already been analysed and your results will be compared against this analysis. If your calculated analytical result deviates <3% from the previously analysed QC, then you will score 100% for this part of the assessment ie 10 marks out of 10. If however your calculated result indicates a 10% deviation then you will score 6 marks out of 10 for this part of the assignment and so on according to the accuracy of your data.
Precision:
The preparation of your 5 samples will be used to calculate the RSD. This calculation will measure how precise you are in repetition of a single sample concentration preparation. It also gives an indication of the performance of the HPLC system (which is known to be 0.5%). As with the accuracy, the RSD data will be compiled and assessed as indicated by the tables below:
Assessment marking:
The Quality Control data will automatically be inputted against your prepared calibration curve. Marks will be awarded according to closeness to target as indicated below:
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Expected vs actual: criteria for error:
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Error
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Mark awarded
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Mark awarded
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<3%
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10
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Marks
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20.1-30%
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3
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Marks
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3.1-5%
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8
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Marks
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30.1-40%
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2
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Marks
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5.1-10%
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6
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Marks
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40.1+%
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1
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Marks
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10.1-20%
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4
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Marks
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|
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Quality Control = 10 marks available
The RSD data will automatically be calculated for you. Marks will be awarded on a sliding scale according to how precise (small % RSD) your data is as indicated below:
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Expected RSD <1%:
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Error
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Mark awarded
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Mark awarded
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<0.5%
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10
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Marks
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2.1+%
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1
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Marks
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0.51-1%
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8
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Marks
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|
|
|
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1.1-1.5%
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4
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Marks
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|
|
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1.51-2%
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2
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Marks
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|
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RSD = 10 marks available