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Troubleshooting
6.4 Peak shapes interpretation and troubleshooting
6.4.1 Refractive index
A refractive index usually shows up as a negative peak before the analyte peak. There
may be a small positive peak after the analyte peak. A refractive index is the difference in
density between the carrier and sample matrices (Figure 55).
6.4.1.1 Common causes of refractive index
• Overacidified samples: Some standard procedures recommend acidifying samples
to a pH of less than 2 for preservation. When working with flow injection analysis, this
can be interpreted as adjusting the pH just below 2 (e.g., 1.95). Most QuikChem
methods include recommendations for sample preservation.
• Wrong carrier: Check the QuikChem method for the correct carrier for the analysis.
Make sure that the method used is intended for the matrix of the samples under
analysis. Verify the QuikChem method number in the methods list. Water methods
start with number 10, soil-extract methods start with number 12, etc.
Figure 55 Refractive index
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