739 Hastings Street
Traverse City, MI 49686
Phone: (231) 941-2230
Fax: (231) 941-2240
1295 King Avenue
Columbus, Ohio 43212
Phone: (614) 487-1040

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Calibration Standards. For tests in which calibration curves are applicable, a set of five standards, representing the analytical range of the method is prepared and run each day before the surface water samples are analyzed. The standards are made from a purchased stock of known concentration. The correlation coefficient of these standards must be 0.995 or higher to prove that a linear relationship exists between concentration and absorbance. If the correlation coefficient is unacceptable, the calibration standards are prepared again and rerun before any samples are analyzed.



Calculation Standards for Chlorophyll a: An intermediate standard is prepared by mixing chlorophyll a powder, purchased from the manufacturer, with acetone to obtain the proper concentration. This intermediate is transferred in 5 mL portions to ampules that are flame sealed and kept in the freezer for future use. Three working standards of 10, 25 and 50 ug/L are prepared from the intermediate standard and these are read prior to the samples of interest. These three standard concentrations are averaged as part of the sample calculations.



Performance Check for Chlorophyll a and TOC: A prepared standard of 19.1 ug/L is purchased as a reference to validate chlorophyll a calculation standards. For TOC, performance is checked with periodic analyses of the QC check sample that should result in a value of 28.334% +/- 1.261%.



Quality Control Samples for Phosphorus and Nitrate + Nitrite. Each day three dilutions of a quality control sample are run as a check of the digestion procedure. The dilutions are prepared from a purchased stock that contains a known amount of the analyte of interest, in addition to a variety of other analytes. In the analysis of phosphorus a complete digestion must occur to convert all of the phosphorus in the samples to dissolved orthophosphate; the form that reacts with reagents to produce the blue color read by the colorimeter. The quality control samples are used to confirm that the phosphorus digestion process was complete and, for both phosphorus and nitrate, to confirm that the automated chemistry is accounting for any interferences attributable to the other analytes in the quality control samples. Recovery must be within 15% of the true value to be considered acceptable.



Laboratory Reagent Blank (LRB) for Phosphorus, Nitrate+Nitrite, Chorophyll a, and Solids Analysis. One laboratory reagent blank is prepared with every analytical batch. It consists of de-ionized water that has been processed in the same way as the samples. If the concentration of analyte in this sample is greater than the absolute value of the limit of detection the analytical batch requires re-analysis.



Laboratory Fortified Blank (LFB) for Phosphorus, Nitrate+Nitrite and TOC. For phosphorus and nitrate + nitrite one laboratory fortified blank is prepared with every analytical batch. It consists of de-ionized water that has been spiked with a known concentration of analyte. If it deviates from the known value by more than 10% , the analytical batch requires re-analysis. This is used as a confirmation that the reagents are mixing properly during automated analysis. With every 10 TOC samples a standard ring is run through the same process as the samples and results should be within the tolerances stated on the standard ring container.



Replicate Samples . For all analysis a number of replicates are processed for every batch of investigative samples. Every group of ten or less samples (20 or less for TKN and 15 or less for COD) includes one sample which is prepared and analyzed in triplicate for most analyses and in duplicate for solids, alkalinity, TOC and COD. The result for each individual replicate must be within 15% (10% for COD and TOC) of the mean result for the replicates. This comprises a check of the precision of the analysis; any sample not meeting the criteria is processed and rerun.



Matrix Spike Samples (MS) for Phosphorus, Nitrate+Nitrite, TKN, COD and TOC. One sample in ten or less (fifteen or less for COD) is duplicated and spiked with a known concentration of standard spiking solution. The recovery of the spiked concentration must be between 80% and 120% (90 and 110% for COD and TOC) to be considered acceptable. The purpose of the matrix spike is to check for matrix interference. If the matrix spike recovery is low a post-processing spike or analytical spike is done. If this confirms the matrix spike result, the method of standard additions is used to determine the concentration of the anlalyte present in each of the samples from the matrix in question.



Instrument Performance Checks for Phosphorus, Nitrate+Nitrite and TKN. Instrument performance is checked with periodic analyses of calibration standards and blank samples. The mid-level calibration standard is analyzed after every 10 samples. This verification is performed to monitor instrument conditions over the time period of the analytical run. Recovery for these calibration check samples must be within 10% of the true value. If recovery is outside the acceptable range, the samples between the failed calibration check sample and the preceding one must be re-analyzed. In addition, blank samples are run after every sample to assure that there is no background interference. A blank consists of de-ionized water in the same acid matrix as the samples and standards.



Method Detection. A method detection limit (MDL) study has been performed to determine the minimum concentration that can be identified, measured, and reported with 99% confidence that the analyte concentration is greater than zero. In the MDL study, seven aliquots of a standard solution of a concentration 3-5 times the expected MDL were digested and analyzed, and the standard deviation of the results was determined. The MDL was determined by multiplying the standard deviation by 3.14 to obtain an MDL value (EPA Methods and Guidance For Analysis of Water, Method 365.1).