VIMS Analytical Service Center for Nutrients
Advantages of Instrumental Methods
Colorimetric Nutrients-Continuous Flow Analysis:
Primary Instrument - SKALAR SAN plus System
Advantages of Instrument/Method:
- Background Correction - Instrument employs simultaneous dual wavelength detection to directly
subtract refractive index effects of saline matrices. Sensitivity of reference
wavelength is normalized to that of measurement wavelength in the presence
of actual matrix.
- Multiple Analytes - Up to four chemistries may be run simultaneously from a single sample
aliquot (approx 1 mL drawn per replicate).
- SKALAR uses standard equilibrium colorimetric chemistries.
- Orthophosphate - Molybdate/Ascorbic, Two Reagent Method.
- Nitrite - Diazotization
- Nitrate - Cadmium reduction, Diazotization
- Ammonia - Modified Berthelot, Phenol
- TDN/TDP - Alkaline Persulfate Digestion
- Flow is standard segmented, no bubble gating.
Carbon - Nitrogen Analysis :
Primary Instrument - Exeter Analytical CE-440 CHN Analyzer
High Temperature Catalyzed Combustion - more complete oxidation than wet chemical digestion,or other methods.
Horizontal combustion chamber ensures consistent carrier flow and extends column lifeSealed Helium sample environment controls moistureComputer Control and Acquisition - Allows efficient continuous unattended operation
Dissolved Organic Carbon :
Primary Instrument - Shimadzu TOC5000
Advantages of Instrument/Method:
- Catalyzed High Temperature Combustion - Comparison studies by Sharp and other experts have found that platinum
catalyzed combustion results in more complete oxidation than wet chemical
or UV based methods, for a number of refractory compounds. Additionally,
method recovery is largely unaffected by saline matrices.
- Non-Dispersive Infrared Detector - Has been found to be more sensitive and stable than conductometric or
flame ionization units. Selectivity is enhanced by the use of CO2 gas as
an absorptive element.
- Multiple Calibration Ranges - Instrument selects optimal calibration series for a wide range of sample
concentrations, preserving sensitivity of lower range samples. Significantly
reduces the need for dilution and/or sample manipulation.
Analytes: DOC (NPOC), TC, TOC, DTC
