1. iCAP OES Analysis of Trace Elements in Hair
Dr. Fred Omega Garces
Chemistry 251
Miramar College

2. Objective
In this experiment, ICP-OES will be used to detect Copper (Cu), and iron (Fe) in hair and an unknown solution. The procedure and analysis for these elements will consist of calibration curve and/or standard addition analysis using ICPES technique. be determined by AAS using standard addition and calibration curve techniques. Both method will be evaluated using the comparison of Student-t.

3. Introduction: Trace metal significance
Human hair is approximately 80 % protein and 15 % water, with smaller amounts of lipid and inorganic substances, and its composition also includes copper, zinc, iron and other elements3. Normal values, or intervals of concentration of some metals in hair, expressed in mg/g (ppm) of hair are given in Table 1 below. The shaded column (light yellow) are trace elements to be analyzed in this experiment. .
Ions, vitamins, and minerals are obviously critical for our basic biochemistry and normal physiology, and while a balanced diet usually provides them in ample quantities, many people carefully monitor their intake of these critical elements and compounds to manage disease or improve athletic performance. .

4. Introduction:
The two different techniques of analysis require the dissolution of the the analyte by applying different protocol. Analysis via OES only requires that all the analyte be dissolved, but not necessarily in the same oxidation state. Thus, the procedure involves first dissolving all the analyte in a measured sample, and filtering out any undissolved solids. This solution can then be used directly for determination by OES. In most cases however this stock solution must be diluted to the appropriate concentration range.
The two techniques to be carried out in this experiment requires 1) generating a calibration curve from a concentration range of standards solutions containing all elements to be analyzed, and 2) adding a concentrated known amount of standard solution to the unknown analyte. The results from the calibration curve and the standard addition techniques will be compared by applying the statistical analysis, “Comparison of Means with Student’s t”, Case 2, Comparing Replicate measurements.

5. Introduction: Analysis
Calibration Curve: The series of standard solution can be prepared by dilution of a stock solution. The stock standard is prepared by diluting the primary stock standard analyte and then placing in a volumetric flask and diluting to the mark. The series of standards are then prepared by diluting various volumes from this stock. Diligent measurements must be carried out since a preparation of the diluted samples from the stock will be used to determine the concentration of the trace elements in the unknown solution.
Standard Addition: Calibration curves are usually used to determine the relation between signal and concentration in a chemical analysis. In cases where a calibration curve would be inappropriate and unreliable, standard addition or internal standards is used. In the method of standard addition, a known quantity of concentrated analyte is added to a sample and the increase in signal is measured. The relative increase in signal allows us to infer how much analyte was in the original specimen. The key assumption is that signal is proportional to the concentration of analyte.
Standard addition is used when the sample matrix is complex or unknown. For example, a matrix such as blood has many constituents that you could not incorporate into standard solutions for a calibration curve. We add small volumes of concentrated standard to the unknown so that we do not change the matrix very much.

6. Introduction: Standard Addition
Suppose that a sample with unknown initial concentration [X]i gives a signal Ax where A might be the absorbance intensity, the detector current or voltage of an instrument or the area of a chromatogram signal. Then a known concentration of standard S (a known concentration of analyte) is added to the sample and a signal As+x is observed. Because signal is proportional to analyte concentration, the following equation can be used.   
Where [X]f is the final concentration of unknown analyte after adding the standard, and [S]f is the final concentration of standard after addition to the unknown. Note that concentration in these equations can be expressed in either molarity or ppm (ml / L). Be sure to apply the correct conversion when working with either one of these concentration units.
If we began with an initial volume Vo of unknown and added the volume Vs of standard with initial concentration [S]i the volume is V = Vo + Vs and the concentration from the above standard addition equation are

7. Introduction: Standard Addition
In this experiment, the amount of zinc in a supplemental tablet will be determined by converting dissolving all the analyte. The absorbance of the trace elements in the analyte will be compared to the absorbance of a pre-calculated amount of trace element standard. The analysis is one of constant volume so the standard addition equation from the analysis of vitamin-C via cyclic voltammetry is similar to this experiment.
Where [M]unk is the concentration of trace element in the unknown, and [M]std is the concentration of trace elements in the standard. Iunk is the absorbance of the unknown and I std+unk is the absorbance of the elements in the unknown and standard solution.
Rearranging this equation for [M]unk leads to:
Note that equation above is the concentration of the [M]unk in the cuvette (the sample that is analyzed). Dilution correction must be applied to calculate the true [M] concentration of the original unknown solution, which will lead to the concentration of trace element (in ppm).
The standard addition equation is in the form of y = mx + b
Istd+unk = Iunk + (Iunk / [M]unk) • [M]std
A plot of Istd+unk (vs. [M]std yields an x-intercept of [M]unk

8. Procedure •Prepare of unknown and Hair sample solutons
___ g/ L Solution
ppm

9. Procedure •Prepare solutions for calibration curve
Solutions-Se
Solutions-Mn
Solutions-Cu
Solutions-Mg
Solutions-Zm
* These stock solutions may be prepared for you by the lab tech.

10. Procedure •Prepare solutions for standard addition

11. Procedure •Entire Experiment
Hair Sample Unknown Sample Standards Standard Addition Fe Cu

12. Tip Sheet
Set up for Calculations