Analysis of Iron Experiments 3, 19 & 20

Experiment 3- Gravimetric Determination of Iron as Fe2O3 Gravimetric analysis is the quantitative measurement of analyte by weighing a pure, solid form of the analyte. Since gravimetric analysis is an absolute measurement, it is the principal method for analyzing and preparing primary standards.

Advantages & Disadvantages of Gravimetric Analysis Provides precise analysis, this process was used to determine the atomic masses of many elements to six figure accuracy. Provides little room for instrumental error and does not require a series of standards for calculation of an unknown. Doesn’t require expensive equipment Also used to calibrate other instruments Disadvantages: Provides for analysis of a single element This method is often complicated and the slightest error in procedure will mean disaster in analysis

Experiment 19- Spectrophotometric Determination of Iron in Vitamin Tablets The Beer-Lambert Law states that for monochromatic light (one wavelength) absorbance is proportional to length and concentration of the species. This means that if concentration doubles, absorbance will also double. If length triples then absorbance triples. If concentration is cut by half then absorbance will be cut by half. We are using the Beer-Lambert Law in a quantitative way, to determine the amount of iron in our vitamin supplement.

Spectrophotometric Accuracy and Advantage Most accurate at intermediate levels of absorbance, A≈0.4-0.9 If too little light gets through the sample (high absorbance), the intensity is hard to measure. If too much light gets through the sample (low absorbance), it is hard to distinguish the difference between the sample and the reference. The advantage: with the Spectrophotometric a much more efficient method.

Experiment 20- Microscale Spectrophotometric Determination of Iron in Foods by Standard Addition The experiment was similar to experiment 19 except that this experiment dealt with smaller volumes. Standard addition is used in instrumental analysis to determine concentration of an analyte in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve.

Spectrophotometric by Standard Addition Advantages Applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem. (The matrix effect problem occurs when an unknown contains many impurities)

Summary of all 3 Methods Gravimetric Spectrophotometric Microscale Spectro. by Standard Addition Methods Filtering precipitate & obtaining accurate mass Dilution of iron & determining the absorbance & concentration then determining the mass Dilution of iron, find absorbance & using standard addition to determine concentration Used For Determining primary standards Determining the concentration of an analyte Determining the concentration of analyte in unknown Accuracy Will give an absolute measurement (complete measurement) For Absorbance, A≈0.4-0.9 & depends on amount of light Will do the same as spectrophotometric accuracy, but will remove matrix effect error