Extract from manual:
U. S. Environmental Protection Agency. 1983.
Magnesium: Method 242.1 (atomic absorption, direct aspiration). pp.
242.1-1 -- 242.1-2. In Methods for Chemical Analysis of Water and
Wastes, EPA-600/4-79-020. U.S.E.P.A., Cincinnati, Ohio, USA.
Method 242.1 (Atomic Absorption, direct aspiration)
STORET NO. Total 00927
Optimum Concentration Range: 0.02-0.5 mg/1 using a wavelength of 285.2 nm
Sensitivity: 0.007 mg/l
Detection Limit: 0.001 mg/l
Preparation of Standard Solution
1. Stock Solution: Dissolve 0.829 g of magnesium oxide, MgO (analytical
reagent grade), in 10 ml of redistilled HNO3 and dilute to 1 liter with
deionized distilled water. 1 ml = 0.50 mg Mg (500 mg/1).
2. Lanthanum chloride solution: Dissolve 29 g of La203, slowly and in
small portions in 250 ml conc. HCl, (Caution: reaction is violent), and
dilute to 500 ml with deionized distilled water.
3. Prepare dilutions of the stock magnesium solution to be used as
calibration standards at the time of analysis. To each 10 ml volume of
calibration standard and sample alike add 1.0 ml of the lanthanum
chloride solution, i.e., 20 ml of standard or sample + 2 ml LaCl3 = 22
1. For sample handling and preservation, see
[part 4.1] of the Atomic Absorption Methods section of this manual.
1. For the analysis of total magnesium in domestic and industrial
effluents, the procedures for the determination of total metals as
given in [parts 4.1.3 and 4.1.4] of the
Atomic Absorption Methods section of this manual have been found to be
2. For ambient waters, a representative aliquot of a well-mixed sample
may be used directly for analysis. If suspended solids are present in
sufficient amounts to clog the nebulizer, the sample may be allowed to
settle and the supernatant liquid analyzed directly.
3. Samples should be preserved with (1:1) nitric acid to a pH of 2 at
the time of collection.
Instrumental Parameters (General)
1. Magnesium hollow cathode lamp
2. Wavelength: 285.2 nm
3. Fuel: Acetylene
4. Oxidant: Air
5. Type of flame: Oxidizing
1. The interference caused by aluminum at concentrations greater than 2
mg/1 is masked by addition of lanthanum. Sodium, potassium and calcium
cause no interference at concentrations less than 400 mg/1.
2. The following line may also be used: 202.5 nm, Relative Sensitivity 25
3. To cover the range of magnesium values normally observed in surface
waters (0.1-20 mg/1), it is suggested that either the 202.5 nm line be
used or the burner head be rotated. A 90 rotation of the burner head
will produce approximately one-eighth the normal sensitivity.
4. Data to be entered into STORET must be reported as mg/l.
5. The gravimetric method may also be used (Standard Methods, 14th
Edition, p 221).
Precision and Accuracy
1. In a single laboratory (EMSL), using distilled water spiked at
concentrations of 2.1 and 8.2 mg Mg/1 the standard deviations were -0.1
and +0.2, respectively. Recoveries at both of these levels were 100%.