Presentation on theme: "Review of Analytical Methods for Nutrient Parameters focusing on Nitrates An Overview By Michael Jackman Chemistry Expert."— Presentation transcript:
Review of Analytical Methods for Nutrient Parameters focusing on Nitrates An Overview By Michael Jackman Chemistry Expert
Manual Colorimetric Methods. This technique can be used to analyse up to 50 different parameters in water. The analysis of nitrates the method is slightly more complicated by requiring the reduction of the Nitrate ion to Nitrite ion, normally by passing the water sample through a reduction column of powdered cadmium.
Automatic Colorimetric Methods The manual colorimetric methods can be automated by three types of equipment: 1) Continuous Flow Analysis (CFA) - the solutions are pumped with peristaltic pumps, mixed and flow in tubing about 2mm wide. To avoid longitudinal cross contamination air gaps or bubbles are introduced. These systems are normally set up and dedicated to one parameter, e.g. Nitrate, with other similar systems set up in parallel to analyse other parameters, e.g. Nitrite using different reagents and tubes etc.
Continuous Flow Analysis Once these systems are set up, they can produce reliable results with excellent precision and accuracy. However these systems are not very flexible and can be difficult to reconfigure for other parameters, so they are ideal where there are a many samples submitted for the same parameters, e.g., Central Reference Laboratory
Flow Injection Analysis (FIA) – Developed from continuous flow systems but to avoid longitudinal contamination very fine capillary tubing is used ~ 0.5mm. Also the sample is injected for a short but accurate periods of time into the reagent carried flow to obtain a fine peak of colorimetric absorption. As this injection time is the exactly the same for the standards and samples the reaction does not need to go the completion, The analysis is quick and the equipment can easily be modified to analyse different parameters.
Flow Injection Analysis Equipment The analysis is quick and the equipment can easily be modified to analyse different parameters
Ion Chromatography This is a specialised high performance liquid chromatographic (HPLC) technique using dedicated columns for anion and cation parameters. Anions: F−, Cl−, NO2−, HPO4−2, Br−, NO3−, SO4−2, CO3 -2, HCO3−
Ion Chromatography An excellent technique providing excellent accuracy and provision and is best applied when a number of other parameters are also required with the nitrate and nitrite results. Equipment is expensive, but has the benefit of producing excellent results for a number of parameters in one injection.
Discrete Auto Analyser (DAA) These are robotic systems which use programmable syringes to copy the manual method, which are often used in clinical laboratories. These can be very effective by processing and analysing one parameter at a time. Therefore they are ideal where there are a many samples submitted for the same parameters, e.g., Central Reference Laboratory.
Discrete Auto Analyser (DAA) These can be very effective by processing and analysing one parameter at a time. Therefore they are ideal where there are a many samples submitted for the same parameters, e.g., Central Reference Laboratory.
Total Kjeldahl Nitrogen Total Kjeldahl Nitrogen is an important parameter to assess the total nitrogen in the sample. It requires an aggressive digestion procedure to break up the complex biological matter which will require dedicated glassware etc It is time consuming and requires optimum chemical skills.
The method consists of heating a substance with sulphuric acid, which decomposes the organic substance by oxidation to liberate the reduced nitrogen as ammonium sulphate.sulphuric acidammonium sulphate In this step potassium sulphate is added to increase the boiling point of the medium (from 337°C to 373°C). potassium sulphateboiling point It is time consuming and requires optimum chemical skills.
Total Kjeldahl Nitrogen Distillation unit It is recommended that ideally at least one central laboratory in each province has one of these combined units as these semi- automatic methods are often the more precise, and it is easier to apply than the manual TKN methods
Ion Specific Electrodes ISE However these methods can be affected by certain pollutants and in serious cases can poison the electrode so de-activating it. Therefore unless all the constituents in the water are known, it is recommended to use the other methods, but could be used as a screening method
Ultra Violet (UV) Spectrophotometer Screening Method for Nitrates If there are any doubts concerning the analysis of the nitrate concentrations, or if there is a need to obtain some initial results quickly, especially if there a large number of samples, a simple screening method can be applied as an initial check. It must be stressed that this method should not
Ultra Violet (UV) Spectrophotometer Screening Method for Nitrates The basis of this spectrophotometric method is to measure absorbance by the NO3- ion directly at the UV wavelength of 220 nm and also measuring at 275 nm to asses the interference from organic compounds The net absorbance for NO3- = (Abs 220) - 2x(Abs 275 The concentration is then calculated by applying a prepared calibration curve to convert the Net absorbance to the concentration in mg/l NO3.
Ion Specific Electrodes ISE The ISE methods apply a potentiometric technique that can be relatively easy by simply using specific electrodes that are sensitive to certain ions such as nitrates. Normally there is no need to filter the samples but often require the addition of specific buffer solutions the electrode must be calibrated using semi-logarithmic
Harmonisation of Methods If all the laboratories use the same method, and an unexpected problem is occurs with this method, then it could result in the disastrous situation of affecting all the results and not being identified until it is too late To harmonise results all the laboratories should apply optimum Quality Assurance and Analytical Quality Control systems Thank you for your attention
Harmonisation of Methods Many of these methods are used by MOFAL and other Turkish government departments. It is essential that the results are comparable from all laboratories. It is not feasible and not recommended that all laboratories use exactly the same method. In fact by using a diverse set of methods one can identify problems or inaccuracies that may occur with one method.