1. A Ca2+ selective electrode was used to determine the Ca2+ concentration in samples. By setting up a cell containing a Ca2+ solution, the potential difference (ΔE) between the Ca2+ selective electrode and a reference electrode (both placed in the Ca2+ solution) is related to the Ca2+ concentration ([Ca2+]) in a solution by the Nernst equation:
ΔE = constant + Log 10 [Ca2+]
(i) Suggest what you would plot to construct an appropriate calibration graph. Give a reason for your answer.
(ii) The analyst started the experiment by measuring ΔE in the presence of series of Ca2+solutions of different concentration. The results obtained are tabulated below
Determine if the calibration plot suggested in (i), using these data, is linear. If it is linear, report the linear equation including the 95% confidence interval for both the slope and the ordinate intercept. Does this electrode obey the above equation?
(iii) Show how you would estimate the limit of detection of the above technique
2.In an experiment, the effects of different catalysts in the results of Kjelkdhl method for determining the protein content of a meat product were studied. It is hoped that commonly used catalysts HgO and SeO2,which leave to xci residues that are difficult to dispose of,can be replaced by the copper-containing catalysts that do not have a similar problem. In the experiment, a single analyst repeated the determination ten times with each catalyst, keeping all of the conditions as similar as possible. The results are shown below.
Appropriately analyse the results to determine if there is a significant difference in the mean results of the four types of catalysts used at the 95% confidence level.
3.Very often, the following measures are used in quality control work. For each of them, write brief notes on how they would aid in quality control.
(ii) Quality control samples
(iii) Repeat samples
(iv) Blind samples
4.Analyst conducted a 239 Pu calibration experiment using ICP-MS. The following table tabulates the triplicate results obtained in the analysis of each standard solution.
(i) Perform both an unweighted regression and a weighted regression to the data.
Clearly explain all workings involved. You must include the two plots in your submission. Test for the significance of the respective correlation coefficient obtained.
(ii) Report the respective regression equation obtained including the 95% confidence intervals for both the slope and the ordinate intercept.What are your comments after comparing the results obtained?
(iii) Estimate the limit of detection based on both unweighted regression and weighted regression.
5.In a laboratory, a method for the routine analysis of Ni in industrial wastewater is to be introduced. For this purpose, the atomic absorption spectroscopy method was chosen. It is known that Fe at various concentration levels can be present in the wastewater. In this respect, three types of test solutions were prepared:
i)A test solution that does not contain Fe (i.e. a blank) was used.
ii)AtestsolutioncontainingalowconcentrationofFeat10mgL-1 (denoted as “low”) was used.
iii)Atestsolutioncontainingthehighestpossibleconcentrationof50mgL-1 Fe (denoted as “high”) was used.
The concentration of Ni remains the same at 30 mg L-1in all test solutions.
The instrumental conditions,as shown below,in the atomic absorption spectrometer were also studied.
|Condition 1||Flame: N2O/ C2H2||λ= 232 nm|
|Condition 2||Flame: Air / C2H2||λ= 342 nm|
The results of the atomic absorption spectroscopic determinations of Ni with five replicates are summarised in the table below:
(i) Determine if the Fe concentration have an influence on the Ni determination.
(ii)Which experimental conditions are appropriate for the atomic absorption spectroscopic determination?
(iii)Is there an interaction between Fe concentration (in (i)) and experimental conditions (in (ii))