Expert Persona: Top-Tier Senior Analytical Chemist and Certified Laboratory Quality Assurance Manager specializing in Environmental Water Analysis.
Abstract:
This material details the standardized procedure for determining the concentration of dissolved Iron (Fe) in clean water samples utilizing Flame Atomic Absorption Spectrometry (AAS), adhering strictly to the Indonesian National Standard (SNI) No. 6989.84:2019. The methodology encompasses three primary phases: required material and equipment specification, wet acid digestion for sample preparation using concentrated nitric acid (HNO3), and instrument calibration. Critical procedural steps include the preparation of standardized working solutions, optimization of the AAS instrument, and rigorous quality control measures requiring a linear correlation coefficient ($R$) of $\geq 0.995$ for the calibration curve prior to sample measurement. The procedure emphasizes dilution if sample absorbance exceeds the established optimum concentration range.
Standardized Fe Analysis in Clean Water using Flame Atomic Absorption Spectrometry (SNI 6989.84:2019)
0:21 Regulatory Context: The testing method follows the Indonesian National Standard (SNI) 6989.84:2019, which specifies the procedure for analyzing dissolved and total metals via Flame Atomic Absorption Spectrometry (SSA-Nyala, or AAS-Flame).
1:04 Required Materials: Key consumables include concentrated nitric acid (HNO3), a 1000 PPM Iron (Fe) stock standard solution, acetylene gas (for the flame), and compressed air (from a compressor).
1:24 Required Equipment: The core instrumentation is the AAS unit equipped with a burner appropriate for the oxidant gas used, and an Fe Hollow Cathode Lamp. Required calibrated glassware includes volumetric flasks (50 mL, 100 mL, 1000 mL), volumetric pipettes (1 mL, 100 mL), and beakers/Erlenmeyer flasks (250 mL). Auxiliary equipment includes an electric heater, a vacuum filtration system, and a watch glass/funnel.
2:14 Sample Preparation (Wet Digestion): A 100 mL homogenized sample is transferred to a beaker/Erlenmeyer flask. 5 mL of concentrated HNO3 is added, and the sample is heated slowly (not boiling) until the volume is reduced to 10–20 mL. If the solution is not clear (implying incomplete destruction), an additional 5 mL of concentrated HNO3 must be added, and the heating process repeated until the precipitate color is near white or the sample is clear.
3:16 Final Sample Volume: The resulting digested sample is transferred into a 100 mL volumetric flask, filtered if necessary, and diluted to the mark with mineral-free water before homogenization.
3:43 Standard Solution Preparation: Intermediate standards (100 PPM and 10 PPM) are prepared via volumetric dilution from the 1000 PPM stock standard.
4:36 Working Curve Definition: A calibration curve must be constructed using a blank and a minimum of three distinct working standards, ensuring the concentrations are proportional and span the required measurement range.
5:16 Calibration Procedure: The AAS instrument must be optimized and operated according to the manufacturer's instructions. The blank solution is aspirated first to set the instrument's absorbance reading to zero. Working standards are then aspirated sequentially, and their absorbance is measured at the specific wavelength for Fe.
5:53 Quality Control (QC) Metric: A linear calibration curve must be generated from the absorbance data. The coefficient of correlation ($R$) for the curve must be greater than or equal to $0.995$. If this threshold is not met, the instrument condition must be checked, and the calibration steps repeated.
7:18 Sample Measurement: The prepared sample solution is aspirated into the calibrated AAS unit, and the absorbance is measured.
7:30 Dilution Requirement: If the measured absorbance of the sample exceeds the optimal concentration range of the calibration curve, the sample must be diluted and remeasured.
8:24 Analytical Observation: A visible change in the AAS flame color—from bluish to reddish—is observed during the aspiration of the tested solution, indicative of the presence and ionization of the Fe analyte.