Table 2-1. Sample Dilutions

Table 2-2. Sample Sizes for Low Concentrations

TM-5-6630-215-12 Alarm-Monitor Group (AMG) OA-9431/F88-9(V) CAGEC 97403 Manual
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TM 5-6630-215-12 (3) As an aid, the following sample dilution table 2-1 shows the amount of water sample taken, the amount demineralized water used to bring the volume up to 25 ml, and the multiplication factor. Table 2-1. Sample Dilutions Demineralized Water Used Multiplication Water sample to bring the volume to 25 ml factor 25.0 ml 0.0 ml 1 12.5 ml 12.5 ml 2 *10.0 ml 15.0 ml 2.5 * 5.0 ml 20.0 ml 5 * 2.5 ml 22.5 ml 10 * 1.0 ml 24.0 ml 25 * 0.250 ml 24.75 ml 100 *Note: For sample sizes of 10 ml or less, a pipet should be used to measure the sample into the graduated cylinder or volumetric flask. b. Titrimetric Test. In conducting some tests the color change takes place after using only a few drops of titrant indicating a smaller amount of the substance being tested for. It is then desir- able touse a larger sample and additional titrant to obtain more accurate results. The number of indicator powder pillows (and amount of liquid buffer, if any) must be increased by the same factor as the sample size. The result, also, must be divided by this factor. For example, if it is desired to titrate with 4 measuring tubes in the determination of total hardness, four indicator powder pillows and a 4 ml of buffer solution, are required and the result is divided by four (table 2-2). Dilution is recommended when a sample contains unusually large quantities of the substance to be determined and, consequently, requires many burettes full of titrant. In this case, a procedure similar to the one described previously (para 2-10) is recommended. If the sample size for titration is less than 25 ml, use only that portion of the dilution necessary to run the test. The multiplication factor will remain the same. For example, if it is desired to dilute to 1/5 of the original sample concentration for the determination of hardness, 5 ml of sample would be added to a graduated cylinder then add demineralized water to fill to 25 ml. The titration would then be performed with one measuring tube full of this dilution. The results would then be multiplied by 5. c. Standard Additions is a widely accepted technique whereby an analyst can check the validity of his test results. Also known as “Spiking” and “Known Additions” the technique can also be used to check the performance of the reagents, the instruments and apparatus, and the procedure itself. 2-8

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