AAS · Calibration procedure
Sensitivity (characteristic concentration)
Checks that the AAS gives enough absorbance for a known standard, expressed as the concentration that would give 1% absorption (absorbance 0.0044).
PURPOSE
Why this is checked
Poor sensitivity means a weak lamp, a dirty or misaligned burner, a blocked nebuliser or wrong gas flows. Comparing the characteristic concentration with the manufacturer's cookbook value shows whether the whole system is working as designed.
Frequency
Typically sensitivity is checked each day of use and the full calibration is done every 6 or 12 months, and after lamp, burner or major repair, as defined in your calibration SOP.
Learn how the AAS worksYOU WILL NEED
Standards & tools
- Certified copper standard solution (traceable), diluted to a known concentration in the linear range, e.g. 2.0 mg/L Cu in dilute nitric acid
- Blank of the same acid
- Copper hollow cathode lamp
BEFORE YOU START
Prerequisites
- Warm up the Cu lamp and set the wavelength to 324.8 nm with the slit from the cookbook
- Light an air–acetylene flame, let it stabilise and optimise burner position with the standard
- Zero the instrument on the blank
PROCEDURE
Step by step
- 1Aspirate the blank and auto-zero.
- 2Aspirate the 2.0 mg/L Cu standard and record the absorbance (use the mean of at least three readings).
- 3Aspirate the blank again and confirm the baseline has returned to zero.
- 4Calculate the characteristic concentration and compare it with the value specified for your instrument and burner.
RECORD
Example observation table
| Solution | Concentration (mg/L) | Absorbance (mean of 3) |
|---|---|---|
| Blank | 0.0 | 0.0000 |
| Cu standard | 2.0 | 0.2150 |
CALCULATION
How to calculate the result
Characteristic concentration (mg/L) = (Standard concentration × 0.0044) ÷ Measured absorbance
- Standard = 2.0 mg/L Cu, measured absorbance = 0.2150
- Characteristic concentration = 2.0 × 0.0044 ÷ 0.2150 = 0.0409 mg/L
- Compare with the instrument specification (for example ≤ 0.05 mg/L for Cu on this model): passes
ACCEPTANCE CRITERIA
Pass if
- Characteristic concentration not more than the manufacturer's specified value for the element, lamp and burner (smaller is more sensitive). Use the limit stated in your SOP.
- Some labs instead specify a minimum absorbance for the check standard (e.g. the cookbook 'sensitivity check' concentration giving about 0.2 A).
IF IT FAILS
What to do
- Label the instrument 'Out of calibration' and stop using it.
- Check lamp energy, burner alignment and height, nebuliser uptake and gas flows; clean the burner and nebuliser.
- Replace the lamp if energy is low and repeat the check.
- Assess the impact on results since the last passing check.
MORE
Other AAS calibrations
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.