Annex I
3. Procedure
a. Instrument operation: Because of differences between makes and models of atomic
absorption spectrophotometers, it is not possible to formulate instructions applicable to
every instrument. See manufacturer's operating manual. In general, proceed according
to the following: install a hollow cathode
lamp for the desired metal in the instrument
and roughly set the wavelength dial according to Table 303:1. Set slit width according to manufacturer's suggested setting for
the element being measured. Turn on instrument, apply to the hollow cathode lamp the
current suggested by the manufacturer and
let instrument warm up until energy source
stabilizes, generally about 10 to 20 min. Readjust current as necessary after warm-up.
Optimize wavelength by adjusting wavelength dial until optimum energy gain is
obtained. Align lamp in accordance with
manufacturer's instructions.
Install suitable burner head and adjust
burner head position. Turn on air and adjust
flow-rate to that specified by manufacturer to
give maximum sensitivity for the metal being
measured. Turn on acetylene, adjust flowrate to value specified and ignite flame.
Aspirate a standard solution and adjust
aspiration rate of the nebulizer to obtain
maximum sensitivity. Atomize a standard
(usually one near the middle of the linear
working range) and adjust burner both up
and down, and sideways, to obtain maximum
response. Record absorbance of this standard
when freshly prepared and with a new hollow
cathode lamp. Refer to these data on subsequent determinations of the same element
to check consistency of instrument set-up
and aging of hollow cathode lamp and standard.
The instrument now is ready to operate.
When analyses are finished, extinguish flame
by turning off first acetylene and then air.
b. Standardization: Select at least three
concentrations of each standard metal solution (prepared as in above) to bracket the
expected metal concentration of a sample.
Aspirate each in turn into flame and record
absorbance. For calcium and magnesium
calibration, mix 100 mL of standard with
10 mL lanthanum solution (see above) before
aspirating. For chromium calibration mix
179
1 mL 30% H20 2 with each 100 mL chromium
solution before aspirating. For iron and
manganese calibration, mix 100 mL of
standard with 25 mL calcium solution before
aspirating.
Prepare a calibration curve by plotting on
linear graph paper absorbance of standards
versus their concentrations. For instruments
equipped with direct concentration readout,
this step is unnecessary. With some instruments it may be necessary to convert
percent absorption to absorbance by using a
table generally provided by the manufacturer. Plot calibration curves for calcium
and magnesium based on original concentration of standards before dilution with
lanthanum solution. Plot calibration curves
for iron and manganese based on original
concentration of standards before dilution
with calcium solution. Plot calibration curve
for chromium based on original concentration of standard before addition of H20 2 •
Check standards periodically during a
run. Recheck calibration curve by aspirating
at least one standard after completing analysis of a group of samples. For instruments
with built-in memory, enter one to three
standards to register a calibration curve for
use in subsequent sample analyses.
c. Analysis of samples: Rinse nebulizer by
aspirating water containing 1.5 mL conc
HN03 /L. Atomize blank and zero instrument. Atomize sample and determine its
absorbance.
When determining calcium or magnesium,
dilute and mix 100 mL sample with 10 mL
lanthanum solution before atomization. When
determining iron or manganese, mix 100 mL
with 25 mL of calcium solution before aspirating. When determining chromium, mix
1 mL 30% H20 2 with each 100 mL sample before aspirating.
Analyse standards at the beginning and
end of a run, and at intervals during longer
runs. Run a blank or solvent between each
sample or standard to verify baseline stability. Determine metal concentration from
calibration curve.
4. Calculations
Calculate concentration of each metal ion, in
micrograms per litre, by referring to the
appropriate calibration curve.
3. Procedure
a. Instrument operation: Because of differences between makes and models of atomic
absorption spectrophotometers, it is not possible to formulate instructions applicable to
every instrument. See manufacturer's operating manual. In general, proceed according
to the following: install a hollow cathode
lamp for the desired metal in the instrument
and roughly set the wavelength dial according to Table 303:1. Set slit width according to manufacturer's suggested setting for
the element being measured. Turn on instrument, apply to the hollow cathode lamp the
current suggested by the manufacturer and
let instrument warm up until energy source
stabilizes, generally about 10 to 20 min. Readjust current as necessary after warm-up.
Optimize wavelength by adjusting wavelength dial until optimum energy gain is
obtained. Align lamp in accordance with
manufacturer's instructions.
Install suitable burner head and adjust
burner head position. Turn on air and adjust
flow-rate to that specified by manufacturer to
give maximum sensitivity for the metal being
measured. Turn on acetylene, adjust flowrate to value specified and ignite flame.
Aspirate a standard solution and adjust
aspiration rate of the nebulizer to obtain
maximum sensitivity. Atomize a standard
(usually one near the middle of the linear
working range) and adjust burner both up
and down, and sideways, to obtain maximum
response. Record absorbance of this standard
when freshly prepared and with a new hollow
cathode lamp. Refer to these data on subsequent determinations of the same element
to check consistency of instrument set-up
and aging of hollow cathode lamp and standard.
The instrument now is ready to operate.
When analyses are finished, extinguish flame
by turning off first acetylene and then air.
b. Standardization: Select at least three
concentrations of each standard metal solution (prepared as in above) to bracket the
expected metal concentration of a sample.
Aspirate each in turn into flame and record
absorbance. For calcium and magnesium
calibration, mix 100 mL of standard with
10 mL lanthanum solution (see above) before
aspirating. For chromium calibration mix
179
1 mL 30% H20 2 with each 100 mL chromium
solution before aspirating. For iron and
manganese calibration, mix 100 mL of
standard with 25 mL calcium solution before
aspirating.
Prepare a calibration curve by plotting on
linear graph paper absorbance of standards
versus their concentrations. For instruments
equipped with direct concentration readout,
this step is unnecessary. With some instruments it may be necessary to convert
percent absorption to absorbance by using a
table generally provided by the manufacturer. Plot calibration curves for calcium
and magnesium based on original concentration of standards before dilution with
lanthanum solution. Plot calibration curves
for iron and manganese based on original
concentration of standards before dilution
with calcium solution. Plot calibration curve
for chromium based on original concentration of standard before addition of H20 2 •
Check standards periodically during a
run. Recheck calibration curve by aspirating
at least one standard after completing analysis of a group of samples. For instruments
with built-in memory, enter one to three
standards to register a calibration curve for
use in subsequent sample analyses.
c. Analysis of samples: Rinse nebulizer by
aspirating water containing 1.5 mL conc
HN03 /L. Atomize blank and zero instrument. Atomize sample and determine its
absorbance.
When determining calcium or magnesium,
dilute and mix 100 mL sample with 10 mL
lanthanum solution before atomization. When
determining iron or manganese, mix 100 mL
with 25 mL of calcium solution before aspirating. When determining chromium, mix
1 mL 30% H20 2 with each 100 mL sample before aspirating.
Analyse standards at the beginning and
end of a run, and at intervals during longer
runs. Run a blank or solvent between each
sample or standard to verify baseline stability. Determine metal concentration from
calibration curve.
4. Calculations
Calculate concentration of each metal ion, in
micrograms per litre, by referring to the
appropriate calibration curve.