Suggest analytical procedures which can solve the problems described below. You

Question

Suggest analytical procedures which can solve the problems described below. You will need to take into account the required selectivity, sensitivity, accuracy, throughput, portability, and the cost of the analysis. There are no restrictions of what type of techniques you can use (feel free to use those that you studied in Quantitative Analysis too). You will get a full credit if you propose a technique that would do the job, and if you address all the steps named below (when relevant): sampling sample preparation, preconcentration, matrix removal, etc. all chemical reactions, including derivatization. separation (stationary phase., mobile phase, mass-analyzer, etc.) detection (type of detector, light source, monochromator, etc.) calibration: calibration curve, standard addition, internal standard; matrix for standards and sample. You will get bonus points if your answer is the best solution for the particular situation. Be brief. 5-10 sentences should be enough. (Total = 36 points; 4q*9 points each) Imagine that you've got a job with the Center for Disease Control and Prevention and you are assigned to a project aimed to determine the distribution of heavy metals (Pb, Cd, Hg, Cu) in salmon of different provenances (wild Pacific/Atlantic, farm-raised in Oregon/Scotland etc.). How would you do the analysis? The safe concentrations of heavy metals in seafood are in the 0.01 ppm range. You will need to analyze over 200 samples in 1 year.

Explanation / Answer

I am giving a general insight into the approach. You can trim the answer as per your needs.

In order to determine the heavy metal contents in the salmon fish species, we first need to collect the samples from the different specified places. This sampling job is the easiest part as you just need to collect the fishes from freshwaters or other water bodies in the specified locations.

After the sampling has been done, we need to do sample preparation, by which we mean that we need to produce samples which can be tested for the presence of heavy metals in the laboratorty. Thus we need to study salmon tissues to determine their content. Generally it is good to take scale samples from the anterior portion ( front ) of the fish. Two sacles per fish are sufficent for good sampling.

All the acids used for the reaction are either ultra pure HNO3 or ultra pure H2SO4. HNO3 is also employed for preservation purposes. All the water used is also doubly deionized ( MilliQ systems).

Since we need to find the concentration in the range of ppm, so it is advised to go with the use of inductively coupled plasma mass spectroscopy (ICP-MS), or graphite furnace atomic absorption spectroscopy (GFAAS).

ICP-MS is very costly but gives high precisio results as compared to GFAAS instrument. Since we will be sampling 200 samples per year, it is better to go with GFAAS because the instrument cost as well as operation cost of ICP-MS is too high.

A calibration plot is prepared by using solution of known concentration of a heavy metal ( say, lead) and serial dilutions of the sample. A blank(control) is also used and the Absorbance plot equation ( A = e*l*c) is determined. Using this equation, the concentration of lead o can be determined in any unknown sample by checking its absorbance reading.

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