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| PREPARATION 1. Charcoal dye receptors are washed under a high-speed jet of tap water to remove as much sediment as possible. 2. A typed label containing the site location name, sample number, and date of collection are stapled to each receptor. 3. The receptors are placed in an oven and dried. 4. A predetermined mass of the charcoal is placed into a disposable plastic container that is labeled with the sample identification number. 5. The remainder of the charcoal is returned to its original zip-lock bag and stored until the dye trace investigation is complete. 6. A measured volume of Smart solution (an eluent consisting of 1-propanol 100% assay, distilled water, and ammonium hydroxide 28-30% assay mixed at a ratio of 5:3:2) is added to the charcoal and the plastic container is capped. 7. After the appropriate time, all of the elutant is transferred into a KIMAX®51 borosilicate glass test tube that is then sealed with a polypropylene cap. 8. The sample trays are then placed in a constant temperature bath, covered to prevent photochemical decay and allowed to equilibrate to the analysis temperature. 9. The test tube is then placed in the Shimadzu Model RF-5301PC Spectrofluorophotometer for analysis by synchronous scanning. ANALYSIS Analysis on a scanning spectrofluorophotometer provides the lowest detection limits and most reliable dye analysis. For a typical analysis for Tinopal CBS-X Direct Yellow 96, Fluorescein, Rhodamine WT, Eosine, FD&C Red 3, D&C Red 28 or Sulphorhodamine B, a synchronous scan is performed. The emission spectra from the synchronous scan is displayed on the monitor and plotted on a laser printer. The printout has the file number, sample identifier, job name, date collected and scanning parameters at the bottom of the page. If the scan indicates positive results for fluorescent dye, a second printout is made utilizing spectrum integration and calibration curves stored in the computer to determine the concentration of the dye in question. If the emission spectra from two or more dyes overlap, then the spectra for each dye is separated by use of a non-linear curve-fitting computer program specifically designed for spectral separation. Spectrum integration and calibration curves stored in the computer are then used to determine the concentration of each individual dye present in the sample. For a sample where the concentration is approaching the quenching threshold, serial dilutions are made until it can be scanned without quenching occurring. |
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