Transcript Slide 1
Chlorine testing with HACH colorimeters Sampling Sample point - tap sampling Why is water not allowed to have sat in the pipework or tap for any period of time when sampling? Click here for the answer. To go to next page, click on Page-12 Chlorine testing with HACH colorimeters Sampling Sample point - tap sampling Why is water not allowed to have sat in the pipe work or tap for any period of time? 1. Must reflect true condition of the water being tested. 2. Need to test water in main pipe and not the off-take pipe. To go to next page, click on Page-12 Chlorine testing with HACH colorimeters Sampling process The following steps will describe the sampling process. Step 1: • Run the tap on full flow for 2 minutes then reduced to a slow steady flow. Note: When the off-take point is a long distance from the main pipe, more time is needed to flush the pipe – 5 minutes or more may be needed. To go to next page, click on Page-13 Chlorine testing with HACH colorimeters Sampling process Step 2: • Sample container and cap rinsed with the sample three (3) times. Step 3: • Fill the sample cell and adjust volume to the line. To go to next page, click on Page-14 Chlorine testing with HACH colorimeters Sampling process Step 4: Cap immediately. Why is the cell capped immediately in step 4? Click here for the answer. To go to next page, click on Page-15 Chlorine testing with HACH colorimeters Sampling process Step 4: Cap immediately. Why is the cell capped immediately in step 4? To prevent loss of chlorine from the sample. To go to next page, click on Page-15 Chlorine testing with HACH colorimeters Sampling When taking a sample, why is it important to run the tap for at least 2 minutes? Click here for answer. To go to next page, click on Page-16 Chlorine testing with HACH colorimeters Sampling When taking a sample, why is it important to run the tap for at least 2 minutes? To ensure that a fresh sample from the main pipe is tested (and not the water that has been sitting in the off-take pipe and tap) To go to next page, click on Page-16 Chlorine testing with HACH colorimeters Sampling When taking a sample, describe how to correctly prepare the sample cells? Click here for answer. To go to next page, click on Page-17 Chlorine testing with HACH colorimeters Sampling Before taking a samples, are the sample cells prepared? The cells and caps are rinsed three (3) times with the sample. Also - check the cells for dirt and staining – clean them if necessary. Replace the dirty cells if they cannot be cleaned. To go to next page, click on Page-17 Chlorine testing with HACH colorimeters Measuring free & total chlorine - residual • DPD method - N,N diethyl-p-phenylenediamine. • Forms reddish pink dye - colour proportional to chlorine concentration (the more chlorine present, the darker the pink colour becomes). • Chlorine concentration is measured using a HACH pocket colorimeter or other HACH models: DR 800 & 2000 series. • Free chlorine – ready to measure within 1 minute. • Total chlorine – ready to measure between 3 - 6 minutes. To go to next page, click on Page-18 Chlorine testing with HACH colorimeters Chlorine reading • Free chlorine = Hypochlorous acid (HOCl ) • Total chlorine = HOCl + Combined chlorine • Combined chlorine is the sum of all chloramines Can Free chlorine be greater than Total chlorine? Click here for the answer. To go to next page, click on Page-19 Chlorine testing with HACH colorimeters Chlorine reading Can Free chlorine be greater than Total chlorine? Free chlorine shouldn’t be greater than Total but it can happen due to instrumental inaccuracies under certain conditions. 80% FREE CHLORINE 20% COMBINED CHLORINE TOTAL CHLORINE To go to next page, click on Page-19 Chlorine testing with HACH colorimeters Sample cell types – Your HACH chlorine colorimeter will take specific size cells. Learn which ones you need to use in both Low and High ranges. To go to next page, click on Page-20 Chlorine testing with HACH colorimeters Sample cell types To go to next page, click on Page-21