Flow Injection Analysis: Flow injection analysis, or FIA, is a continuous flow method for rapidly processing samples. A peristaltic pump draws sample from the sampler into the injection valve. Simultaneously, reagents are continuously pumped through the system. The sample is loaded into the sample loop of one or more injection valves. The injection valve is then switched to connect the sample loop in line with the carrier stream. This sweeps the sample out of the sample loop and onto the manifold. The sample and reagents then merge in the manifold (reaction module) where the sample can be diluted, dialyzed, extracted, incubated and derivatized. Mixing occurs in the narrow bore tubing under laminar flow conditions. For each method, the operating parameters are optimized to address high sample throughput, high precision and high accuracy. The samples are passed over a spectrophotometer that is set to specific wavelengths for reading N or P.
Lachat Quickchem 8500 Total Phosphorous Method:
Use samples that have been digested using the EPA 3051 for microwave digestion.
Make calibration standards using a 20% nitric acid solution. Then standards range in concentration from 10 mg P/L to 0 mg P/L. Made form a stock solution of 1000 mg P/L. Weigh 4.396 g of dry Potassium phosphate and add to 1 liter volumetric flask. Dissolve in water. Use this to make a liter of 10 mg P/L solution. This second solution is then used to make a series of diluted standards. (10, 4, 2, 1, 0.4, 0.2, 0.1, 0).
Load calibration standards and samples into test tubes to put in sample holder for the auto sampler. Use the placement chart to keep track of sample location. A total sixty tubes may be run at one time (7 calibration standards and 53 unknowns).
Run 3 samples for each digestion in duplicate. These are labeled on the results sheet with an R.
Turn on the computer, the quickchem 8500, the autosampler, the pump and the heater. Start running distilled water through the system at set speed 35. Set the heater temperature to 125o C. Liquid must be running through the tubes when the temperature is above 80o C (the tubes will melt if there is no liquid).
Once the temperature has reached 125, put the tubes in the proper reagent bottles. The reagents are as follow: Digestion regent 1 (a dilute sulfuric acid solution), Digestion reagent 2 (a potassium persulfate solution), an ascorbic acid solution, the carrier (distilled water for this method) and the molybdate color reagent. Run all these solutions through the lines for at least 15 minutes to guarantee that the solutions are completely through and there is no extra water remaining in the tubes.
Open the Omnion program on the computer. Open the file Total P starting point2.omn. Use this file as the template for your samples. Type in the calibration standards and samples that you have written on the placement chart.
Check to make sure that the reagents have run through all the lines, by using the preview button when the file is open. The baseline for all the reagents should between .6 and .75. If it is higher than this, the lines need to be cleaned. Use a sodium hydroxide solution to clean the lines. Run the cleaner solution for at least 20 minutes through the lines. Then rinse the lines in distilled water and the start the reagent solutions again. Run the cleaner solution as many times as it takes to get the baseline low enough.
Once you have ascertained that the baseline is low enough, start the omnion application by pressing the green arrow button.
The autosampler will start automatically and draw the first calibration standard. It will take about 3 minutes for a peak to appear on the computer. Verify that a peak does appear. Once you have made sure that the peaks have appeared and that your calibration coefficient is above .996, you may let the application run by itself and do other things around the lab. About two hours later (depending on the number of samples) the application will be finished.
Once you check the data to make sure that you have everything you need, save this run under a new name (usually Total P followed by the date.omn). Then print the data, using the report function. Use the ten per page format found under the tools/report heading.
Once you have the data, enter it into the excel spreadsheet that contains all the ICP data that has been collected. The spreadsheet will make the necessary calculations to turn the data from mg/L to ppm.
Run distilled water through the lines to clean them and lower the temperature on the heater. Run the water for at least 15 minutes or until the temperature drops below 80o, depending on which one is longer.
Once the heater is cool enough, run air through the lines to keep them dry. Once air is through the lines, turn off all of the machines.
Repeat as necessary.
The waste products from this method are considered hazardous and must be collected and disposed of properly.