Analysis of High Solids Solutions by Flame Atomic Absorption

Importance of the topic

Flame atomic absorption spectroscopy (FAAS) is widely employed for elemental analysis in environmental, industrial, and research laboratories. High concentrations of dissolved solids in samples can cause salt deposition within the atomizer, leading to signal drift, reduced precision, and frequent interruptions for cleaning. Understanding and mitigating these effects is essential to maintain analytical reliability and laboratory productivity when handling challenging matrices.

Objectives and study overview

This application note examines the behaviors of high-solids solutions in a flame atomizer and identifies critical factors influencing salt buildup. The study evaluates how salt type, concentration, gas flows, and internal geometry affect performance and proposes practical sample preparation and instrument adjustments to extend operating times between maintenance.

Methodology

Investigations were performed using an air-acetylene flame on a Varian AA-975 atomic absorption spectrometer equipped with a Mark V nitrous oxide-acetylene burner and a fixed-rate nebulizer. Salt solutions of varying composition and concentration were continuously aspirated while absorbance drift and flame appearance were monitored to determine blocking times. Tests included varying hydrochloric acid levels and adjusting the position of the glass impact bead to assess their influence on aerosol formation and salt deposition.

Instrumentation

• Varian AA-975 atomic absorption spectrometer
• Agilent/Varian Mark V burners (air-acetylene and nitrous oxide-acetylene)
• Varian fixed-uptake-rate nebulizer
• Standard spray chamber
• Compressed air for drying

Main results and discussion

Salt deposition occurs chiefly in three regions: the nebulizer, the fuel/auxiliary oxidant inlet, and the burner slot. In the nebulizer, evaporation and cooling can exceed solubility limits, precipitating solids that degrade aerosol formation. Salt accumulation at the fuel inlet and burner slot walls arises from droplets adhering and evaporating, ultimately obstructing gas flow and causing flame irregularities and signal noise.

Figure analyses showed that blocking time is approximately inversely proportional to salt concentration. Sodium chloride solutions blocked the burner much faster than sodium nitrate at equivalent concentrations, highlighting the importance of matrix selection. Increasing HCl concentration reduced solubility of chloride salts and decreased operating time from 6.1 ± 0.7 min (0.1 M HCl) to 4.1 ± 0.3 min (1 M HCl) for a 7.5 % NaCl solution.

Adjusting the glass bead to reduce aerosol density extended blocking times, although at the expense of sensitivity. Operating with the air-acetylene burner rather than the nitrous oxide model further prolonged run times, as the larger slot tolerates higher solids loads before flame loss.

Benefits and practical applications

Implementing these guidelines allows laboratories to analyze high-solids samples with fewer interruptions, improved accuracy, and reduced downtime. Optimizing sample preparation—minimizing total dissolved solids, selecting matrix salts with favorable atomization behavior, and using absorbance expansion—supports routine analysis of challenging matrices such as digestions and fusions.

Future trends and potential applications

Emerging burner designs with antiadhesive coatings and advanced spray chambers may further reduce salt buildup. Integration of inline dilution and matrix removal modules could automate sample conditioning. Coupling FAAS with machine-learning algorithms to predict and adjust for matrix effects in real time presents another promising avenue.

Conclusion

Careful control of sample composition, instrument geometry, and operating conditions is essential for reliable FAAS analysis of high-solids solutions. By selecting appropriate burner types, adjusting aerosol formation, and adhering to simple cleaning and preparation protocols, analysts can significantly extend run times and maintain data quality.

References

1. Nebulizers for Atomic Absorption Spectrophotometers—Operation Manual, Varian Techtron Pty. Limited, Mulgrave, Australia, Publication No. 85-100360-00, March 1980.