Determination of Phosphite in Electroless Nickel Plating Bath

Importance of the Topic

Electroless nickel plating is widely used in industries such as electronics, automotive, and aerospace to deposit uniform nickel-phosphorus coatings. Over time, the reducing agent sodium hypophosphite oxidizes to phosphite, affecting plating efficiency and bath longevity. Accurate monitoring of phosphite concentration ensures consistent coating quality, extends bath life, and reduces downtime.

Objectives and Study Overview

This study demonstrates the determination of phosphite in an electroless nickel plating bath using ion chromatography. The primary goal is to quantify phosphite levels accurately and reproducibly. Although hypophosphite determination was not the main focus, the method can also indicate its presence under optimized conditions.

Methodology

Samples from a working nickel plating bath were diluted 1000-fold before analysis. A gradient elution was applied, starting with 12 mM KOH for 0–10 minutes, increasing to 35 mM KOH from 10.1–15 minutes. Chromatographic separation was performed at 30 °C with a flow rate of 1.2 mL/min. Detection was carried out using suppressed conductivity in an external water mode.

Used Instrumentation

• ICS-2100 or equivalent Reagent-Free™ IC system
• IonPac® AS17 analytical column (4 × 250 mm)
• IonPac AG17 guard column (4 × 50 mm)
• EGC II KOH eluent generator
• ASRS® 300 suppressor
• Suppressed conductivity detector

Main Results and Discussion

The chromatogram revealed clear resolution of key anions in the plating bath. Major detected species in the undiluted sample included:

• Chloride: 2885 mg/L
• Phosphite: 14 675 mg/L
• Sulfate: 133 657 mg/L
• Phosphate: 424 mg/L

A peak at approximately 2.2 minutes may correspond to hypophosphite or co-eluting anions such as fluoride. Adjusting eluent strength can enhance hypophosphite quantification.

Benefits and Practical Applications

The described IC method offers:

• High sensitivity and selectivity for phosphite
• Reagent-free operation reducing preparation errors
• Rapid analysis suitable for routine quality control
• Improved bath maintenance through real-time monitoring

Future Trends and Opportunities

Advancements may include on-line process monitoring using automated sampling coupled with IC, development of tailored eluent programs for simultaneous hypophosphite measurement, and integration of data analytics for predictive maintenance. Miniaturized or portable IC systems could enable in-situ bath assessment.

Conclusion

The IonPac AS17 column paired with a Reagent-Free™ IC system provides a robust and precise approach for determining phosphite in electroless nickel plating baths. This methodology enhances process control, optimizes bath life, and supports consistent coating quality.

References

• McDowell MM, Ivey MM, Lee ME, Firpo VVV D, Salmassi TM, Khachikian CS, Foster KL. J Chromatogr A. 2004;1039:105–111.
• Ivey MM, Foster KL. J Chromatogr A. 2005;1098:95–103.