Method for Quantitative Analysis
1) Select Method
-  Flame Atomic absorption spectroscopy of contaminated water.

2) Obtain a representative sample
-  Obtain contaminated water.

3) Prepare a lab sample
- Water is filtered through a 0.45 um membrane filter.

4) Define replicate samples
- Three 5ml water samples are used.

5) Dissolving samples
- Acidify the filtrate with 1:1 redistilled HNO3 to a pH of less than 2
- Discolouration in solution may indicate presence of metals (dilute if colour is too strong)

6) Eliminating Interferences
- Increase heat of flame to eliminate interferences.

7) Measuring amount of analyte
- Measure concentration of metal in solution using FAAS
- Calibration graph

8) Calculating results
- Using the calibration graph and lead standards, determine whether the water has been contaminated with lead.

9) Estimating the Reliability of Results
- Average of replicate samples

http://www.caslab.com/Test-Methods-Search/PDF/USGS-Method-I-2403.pdf
http://www.ffcr.or.jp/zaidan/FFCRHOME.nsf/7bd44c20b0dc562649256502001b65e9/146fd852cd5e269049256f32001a133e/$FILE/B20.pdf
http://www.ifrj.upm.edu.my/19%20%2803%29%202012/%2822%29%20IFRJ%2019%20%2803%29%202012%20Eka.pdf
http://sisbl.uga.edu/epaman4.html#partition

Why use FAAS?
Metals in their ground state absorb light at specific wavelengths. Metal ions in a solution are converted to atomic state by means of a flame. Light of the appropriate wavelength is supplied and the atoms will absorb them and be promoted to their excited state. This state does not last long and gets reverted soon, emitting back the photon that was absorbed. The amount of light absorbed can then be measured against a standard curve.

However, the disadvantage of using this technique is that when absorbance becomes higher than 0.5-1, the calibration line becomes a little non-linear. And some elements like B, Br and C cannot be detected at all using this technique.

http://faculty.sdmiramar.edu/fgarces/LabMatters/Instruments/AA/AAS_Theory/AASTheory.htm