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Resistivity vs. Purity
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| ASTM International |
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"The method of preparing Type I reagent water may add organic contaminants to the water by contact with the ion-exchange materials." – Standard Specification for Reagent Water (D1193), Annual Book of ASTM Standards, American Society of Testing Materials, 11.01(1), 2001 |
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| High-Q |
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". . . deionized, 18 megohm-cm water, often referred to as ultrapure water, is likely to be so impure that it smells – Reagent Water, High-Q position Paper, High-Q, Inc., 2000 |
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| Millipore |
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"Measuring Resistivity Is Not Enough – Water at the theoretically pure limit of 18.2 megohms-cm may still contain high concentrations of neutral organic contaminants which may adversely affect your analytical methods and cause analyses to fail. Most water purification systems exhaust their capacity to remove dissolved organics before they lose their capacity to remove ions." – A10 Brochure, Millipore, Corporation 1996
"What You Can't See Can Hurt You! – When it comes to ultrapure water, what you can't see can often hurt you. Your system's resistivity meter may indicate that your product water is at the theoretically "pure" limit of 18.2 megohm-cm, but don't be fooled! In spite of high resistivity levels, your water can still contain high concentrations of organic contaminants which cannot be detected by resistivity measurements alone." – Waterline, Millipore, Corporation 1995
"Millipore' Corp's Jon DiVincenzo explains that simply dissolving sugar in 18 megohm-cm water can raise the TOC values to 1000 parts per billion (ppb) without reducing the specific resistance of the water." – Brush M. Water, water, everywhere. The Scientist 1998; 12(12):18-20.
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| Intel |
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“We all ‘know’ that a good high-purity water system can meet 18+ megohm-cm, 1 to 2 ppb of TOC and silica, very low oxygen levels, and less than 10 particles per liter (p/L) at 0.05 micron optical size. The agony is that most of these measurements are completely in error. Not only are we not getting real analytical data, we don't know that we are not getting real analytical data. Everything looks OK, and the instruments are behaving like they always have - so there is nothing to indicate that the numbers are entirely bogus.”– Carr G. Instruments - Evaluating the limitations of current technologies and improvements in future analytical methods. Ultrapure Water 2001; 18(2):24-32) |
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That's Interesting
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"Our reagent water is contaminated with complacency."– Anon.
"The big tank is changed once a month, so we have not had to service the polishing system since we bought it." – Anon.
"Not approved for consumption" – The hazard sign attached to a laboratory water purification system.
"As long as that little light on top is green, it's ultra pure." – Anon.
"I suppose it is not wise to leave the end of the hose in the sink, but it drips." – Anon.
"We cannot change purification systems, because our results would change." – Anon.
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Laboratory Water Standards
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| ASTM International D1193 (Reagent Water) |
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"Probably 99% of all supposed Type-I systems have never been tested adequately, if at all, by either the manufacturer or the user, unless you consider measuring resistivity with an uncalibrated, inexpensive meter to be sufficient proof that water is acceptable for reagent purposes. This situation undoubtedly stems from the fact that this standard [Standard Specification for Reagent Water (D1193)] does not require any testing" – Erich Gibbs, President of High-Q, Inc., commenting at the American Society of Testing Materials (ASTM) June 14-16, 1999 Meeting, Louisville, KY.
"The method of preparing Type I reagent water may add organic contaminants to the water by contact with the ion-exchange materials." – Standard Specification for Reagent Water (D1193), Annual Book of ASTM Standards, American Society of Testing Materials, 11.01(1), 2002
"In Committee D-19 [ASTM International Water Committee], Type I reagent water is the required matrix when performing a round robin to determine the precision and bias of a test method. Why? Because Type I is so pure. In other words, because Type I has virtually nothing in it . . . Without it [Type I water] the vast majority of Committee D19 test methods [thousands] would be little better than ‘cookbook’ chemistry.” – ASTM D19 (Water) Comittee Chairperson defending D1193 for the ASTM International Committee on Technical Committee Operations in a letter dated, August 28, 2001.
"Note - Because distillation is a process commonly relied upon to produce high purity water, the levels specified for Type II [distilled] reagent water were selected to represent the minimum [minimum ?] quality of water that a distillation process should produce." – Standard Specification for Reagent Water (D1193), Annual Book of ASTM Standards, American Society of Testing Materials, 11.01(1), 2002
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| ASTM International D5196 (Biomedical Water) |
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"The method of preparation of water described in Appendix X1 [vague pretreatment, followed by 'distillation and suitable storage'] is designed to remove organic, inorganic, volatile, particulate, and biological impurities to provide water that should meet the concentration limits in Table 1 [29 voluntary limits, many without suggested methods]. These are suggested limits, since the actual maxima of the individual impurities will depend upon the required end use of the biomedical grade water. The limits in the guide in most cases are dictated not by the desired maximum concentration of the impurities, but by the methods of analysis." – Standard Guide for Biomedical Grade Water (D5196), Annual Book of ASTM Standards, American Society of Testing Materials, 11.01(1), 2001 |
| NCCLS C3-A3 (Clinical Lab Reagent Water) |
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The widely cited Table 1 ranks carbon adsorption/absorption as "Excellent/Good", more effective than distillation or reverse osmosis; however, Appendix A.4 offers a different view. ". . . carbon beds are viable locations for microbial growth, the adsorptive [actually chemical] affinity for chlorine can greatly increase the growth of these organisms in downstream sections of the purification system. The limitations of carbon use are as follows: Carbon is mechanically degraded to produce fines that must be captured downsteam; Leaches ash minerals in the water stream; Only weakly adsorbs other contaminants as a function of contact time." – Preparation and Testing of reagent Water in the Clinical Laboratory; Approved Guideline -- Third Edition, C3-A3,Vol 17, No. 18, National Committee for Clinical Laboratory Standards (NCCLS), 1997 |
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| USP 24 |
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Activated carbon beds – "The chief operating concerns regarding activated carbon beds include the propensity to support bacterial growth, the potential for hydraulic channeling, the inability to be regenerated in situ, and the shedding of bacteria, endotoxins, organic chemicals, and fine carbon particles."
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General Interest
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| Science |
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"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." – Galileo |
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| Computing |
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"The danger from computers is not that they will eventually get as smart as men, but that we will meanwhile agree to meet them halfway." – Bernard Avishai |
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