AAS Method for Sodium

According to Wikipedia...

In analytical chemistry, atomic absorption spectroscopy is a technique for determining the concentration of a particular metal element in a sample.The technique can be used to analyze the concentration of over 70 different metals in a solution.

PRINCIPLE: The technique makes use of absorption spectrometry to assess the concentration of an analyte in a sample. It relies therefore heavily on Beer-Lambert law.

In short, the electrons of the atoms in the atomizer can be promoted to higher orbitals for a short amount of time by absorbing a set quantity of energy. This amount of energy (or wavelength) is specific to a particular electron transition in a particular element, and in general, each wavelength corresponds to only one element. This gives the technique its elemental selectivity.
As the quantity of energy (the power) put into the flame is known, and the quantity remaining at the other side (at the detector) can be measured, it is possible, from Beer-Lambert law, to calculate how many of these transitions took place, and thus get a signal that is proportional to the concentration of the element being measured.

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I) Preparation of Stock Standard
In a 1000 mL volumetric flask, dissolve 2.5420 g sodium chloride (NaCl) to the mark with deionized water. This standard stock solution is 1000 mg Na+/L.

II) Preparation of Reagents

0.5 % Lanthanum Solution
In a 1000 mL volumetric flask, dissolve 13.37 g lanthanum chloride (LaCl3.7H2O) to the mark with deionized water.

III) Analysis Procedure

A) Spike each standard, control and sample 9:10 with 0.5 % Lanthanum Solution (1 part 0.5 % Lanthanum Solution and 9 parts standard, control or sample).

B) Install Na-K hollow cathode lamp. Perkin-Elmer part #N305-0204.

C) Ensure that the correct Default Conditions are entered.
1) Recall Method=2
2) Lamp Current=12
3) Slit=0.2
4) Full Height=Y(Yes)
5) Wavelength(nm)=589.0
6) Int. Time=5.0
7) Replicates=5
8) Cal=1(Nonlinear)
9) Cal=1(Hold)
10) STD1-----
11) Read Delay(sec)=3

D) Use an oxidizing (lean, blue) air-acetylene flame.

E) Calibrate with standards that bracket the sample concentration. Check the calibration curve for drift, accuracy and precision with standards and controls every 20 samples. Correlation coefficient should be greater than or equal to 0.990.


http://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy
http://snobear.colorado.edu/cgi-bin/Kiowa/Kiowa.con.pl?na.doc.html