Automated Turbidimetric Sulfate Analysis
- High Throughput – Rapid sample analysis up to 100 samples per hour
- Low Cost per Analysis – Less lab tech time needed to operate, very cheap consumables and reagents
- Smaller bench space – The single channel unit occupies less than one foot squared of table space and stands one foot tall
Sulfate, turbidity, EPA 9038, FIA, flow injection, robust
Introduction and Principle
The automated turbidimetric method for determination of sulfate has been in use by commercial agricultural and environmental laboratories for many years. The manual method, EPA 9038, was validated by the EPA in 1986 and since then the method has been automated and refined for high throughput operations. Principally, it operates based on the precipitation of sulfate as barium sulfate. The amount of barium sulfate is proportional to the concentration of sulfate in the sample and is calculated based on the turbidity of the Barium Sulfate solution. The measurement is taken at 420 nm with no reference wavelength .
The turbidimetric analysis method has been employed by laboratories with enthusiasm for many reasons. It has exceptional throughput while remaining robust. It outperforms IC in terms of throughput by a factor of 10 . It is more robust than an ion selective electrode, which has significant phosphate interferences, especially with fertilizer samples. Although the AOAC Official Method for sulfur in fertilizers and plant tissues is the gravimetric barium sulfate method, like the IC, the AOAC method has a very slow throughput and is labor intensive . The turbidimetric method works well at eliminating interferences. For these reasons, the turbidimetric method is the ideal choice for agriculture laboratories.
Experiments were carried out using the FIAlyzer-1000 Flow Injection Analyzer equipped with the Flame T-VIS-NIR SpectrometerExperiments were carried out using the FIAlyzer-1000 Flow Injection Analyzer equipped with the Flame T-VIS-NIR Spectrometer (pictured here).
- Carrier (C): Water
- Reagent 1 (R1): 0.01 M HCl with 10 ppm S-SO4 sulfate seed (1 L)
- Reagent 2 (R2): 0.3M HClO4 (1 L)
- Reagent 3 (R3): 0.2% PVA - 140 g/L BaCl2 x 2H2O solution (1 L)
- Wash Solution: 0.1 M DTPA - 2M KOH solution (1 L)
- C: 0.9 mL/min
- R1: 1.8 mL/min
- R2: 0.5 mL/min
- R3: 0.4 mL/min
- S: 1.6 mL/min
- 280 μL
- Primary Wavelength: 420nm
- Reference Wavelength: 0nm
Figure 1: A schematic view of the instrument setup.
Figure 2: Example calibration run
|Detection Limit||1 mg S/L - 0.03 mmol/L|
|Range Upper Limit||20 mg S/L – 0.6 mmol/L|
|Sample throughput||100 samples/hr|
|Startup Time||5 minutes|
|Shutdown Time||5 minutes|
Table 1: Method Performance Parameters