ASTM D7575 Total Oil and Grease in Water Tutorial: How to Perform an MDL Study скачать в хорошем качестве

ASTM D7575 Total Oil and Grease in Water Tutorial: How to Perform an MDL Study

So, you’ve received your order from Orono Spectral Solutions and you’re ready to start analyzing samples from the field to determine total oil and grease in water. Not so fast! Before reporting any data, all first-time users of the method must calibrate the FTIR unit using OSS provided solid-state calibration standard devices, and each analyst who will run the method must perform two studies constituting the Initial Demonstration of Capability: This includes an Initial Precision and Recovery Study and a Method Detection Limit Study. The calibration and initial demonstration of capability studies are to be performed when a new FTIR instrument is to be used, for each new analyst running the method, and when any changes are made to the method. Please see Orono Spectral Solutions’ separate tutorial videos for instrument calibration and the Initial Precision and Recovery study (IPR). This video will show you how to perform the Method Detection Limit study (MDL). First, make sure you’ve watched Orono Spectral Solutions’ previous video showing you how to prepare the 4 mg/mL Heavy Mineral Oil in acetone spike solution. We will use this solution as our spike. The MDL study is required to determine the detection limit of oil concentration as well as the reporting limit. The user will analyze seven replicates of data obtained from a sample containing 4 mg/L total oil and grease. The method detection limit will be calculated as 3.143 times the standard deviation of the seven replicates. The recommended reporting limit is 10 times the standard deviation. The mean measured concentration of the seven replicates must be 1 to 5 times the calculated method detection limit; if this criterion is not met in the detection limit study, it must be repeated. The MDL study should be repeated until the desired method detection limit is achieved, with the lowest possible detection limit being the lowest calibration standard device level in the CSD set provided by OSS. You will perform the MDL by adding the spike solution to a laboratory control sample (LCS). The LCS is composed of reagent water acidified to a pH of 2 with hydrochloric acid. Prior to spiking you must inspect the spike solution for degradation or evaporation. A fresh spike solution should be prepared weekly or biweekly. I will now demonstrate how to perform the spiking and homogenization procedures. First, shake the sample for 30 seconds and place in an ultrasonic bath heated to 40⁰C for 5 minutes. Remove from bath and shake the sample for 10 seconds before spiking. Gather 1 mL of the spike solution with a volumetric pipette. Place the tip of the pipette in the sample so it is submerged at least 1 inch below the surface and quickly inject the spike solution. Here you can see the oil dispersing within the sample as a cloudy volume of solute. Immediately cap the sample and shake vigorously for 30 seconds. It is important to sonicate the sample for a FULL 40 minutes after spiking, rotating and shaking every 5 minutes. You must immediately process the LCS after homogenization. Remember to always shake your sample bottle between draws into each syringe. This is especially important to do when performing an MDL study, since you want each aliquot drawn to be as homogeneous as possible to minimize the standard deviation of all aliquots. Thank you for watching this tutorial video. See you next time!