Analysis of Iron and Manganese in Tap Water by Flameless Atomic Absorption Method

Importance of the Topic

Atomic absorption spectrometry with a graphite furnace plays a crucial role in monitoring trace metals such as iron and manganese in tap water due to its high sensitivity, minimal sample preparation and compliance with regulatory standards for water safety.

Objectives and Study Overview

This study aimed to evaluate the validity of a flameless atomic absorption method for quantifying iron (Fe) and manganese (Mn) in tap water according to Japan’s Water Supply Act. Measurements were conducted with both high- and low-sensitivity modes and performance was assessed using calibration curves and spiked samples.

Applied Methodology and Instrumentation

Sample Preparation:

• 10 mL of nitric acid added to 100 mL tap water and heated to reduce volume to ≤ 90 mL.
• After cooling, solution diluted to 100 mL for analysis. Spiked samples were prepared by adding known Fe and Mn standards.

Used Instrumentation:

• Shimadzu AA-7000 atomic absorption spectrophotometer
• GFA-7000 graphite furnace atomizer

Measurement Conditions (key parameters):

• Analytical wavelengths: Fe 248.3 nm; Mn 279.5 nm.
• Slit width: 0.2 nm; background correction: deuterium lamp.
• Ashing/atomization temperatures: Fe 900 °C/2400 °C; Mn 800 °C/2300 °C.
• Calibration ranges: Fe 10–40 µg/L; Mn high sensitivity 1–5 µg/L; Mn low sensitivity 5–50 µg/L.
• Sensitivity adjustment via argon gas flow (0–0.04 L/min) during atomization.

Main Results and Discussion

Calibration curves for Fe and both Mn modes met precision and accuracy targets defined in the Validity Evaluation Guidelines. Recoveries ranged from 98 % to 111 % with repeatability (RSD) below 5 %. High-sensitivity Mn measurement achieved optimal sensitivity with zero argon flow; gradual gas flow reduced sensitivity by up to one-twentieth. Automated dilution and re-analysis successfully measured elevated Mn levels (spiked at 200 µg/L) by reducing injection volume from 10 to 2 µL.

Benefits and Practical Applications

• No need for sample concentration when measuring low-level elements, reducing preparation time.
• Low operational cost due to minimal argon consumption compared to ICP.
• Wide dynamic range handled through argon flow control and auto-dilution functions, suitable for routine water quality monitoring in laboratories and industry.

Future Trends and Potential Applications

• Integration of precise gas flow controllers to further optimize sensitivity adjustments.
• Expansion of automated methods for multi-element screening in environmental and beverage analyses.
• Coupling with data analytics and remote monitoring platforms for real-time water quality assessment.
• Development of portable flameless AA units for field testing.

Conclusion

The flameless atomic absorption method using Shimadzu AA-7000/GFA-7000 reliably quantifies Fe and Mn in tap water, meeting regulatory requirements. Sensitivity tuning via argon flow and automated dilution extends the measurable concentration range while ensuring accuracy and cost-efficiency.

Reference

1. Ministry of Health, Labour and Welfare. Ministerial Ordinance Concerning Water Quality Standards (Ordinance No. 101, 2003; revised 2020, No. 38).
2. Ministry of Health, Labour and Welfare. Methods for Water Quality Inspection (Notification No. 261, 2003; revised 2020, No. 95).
3. Ministry of Health, Labour and Welfare. Validity Evaluation Guidelines for Tap Water Quality Inspection Procedures (Kensui 0906, 2008; revised Yakuseisui 1018, No. 1).