實驗室用水的種類和區(qū)別

1、水是實驗室內(nèi)一個常常被忽視但至關(guān)重要的試劑。實驗室用水有那些種類能達到什么級別不同實驗對水的要求有那些 實驗室常見的水的種類： 1、蒸餾水（Distilled Water ）： 實驗室最常用的一種純水，雖設(shè)備便宜，但極其耗能和費水且速度慢，應(yīng)用會逐漸減少。蒸餾水能去除自來水內(nèi)大部分的污染物，但揮發(fā)性的雜質(zhì)無法去除，如二氧化碳、氨、二氧化硅以及一些有機物。新鮮的蒸餾水是無菌的，但儲存后細菌易繁殖；此外，儲存的容器也很 講究，若是非惰性的物質(zhì)，離子和容器的塑形物質(zhì)會析出造成二次污染。 2、去離子水（Deionized Water ）： 應(yīng)用離子交換樹脂去除水中的陰離子和陽離子，但水中仍然存在可溶性

2、的有機物，可以污染離子交換柱從而降低其功效，去離子水存放后也容易引起細菌的繁殖。 3、反滲水（Reverse osmosis Water）： 其生成的原理是水分子在壓力的作用下，通過反滲透膜成為純水，水中的雜質(zhì)被反滲透膜截留排出。反滲水克服了蒸餾水和去離子水的許多缺點，利用反滲透技術(shù)可以有效的去除水中的溶解鹽、膠體，細菌、病毒、細菌內(nèi)毒素和大部分有機物等雜質(zhì)，但不同廠家生產(chǎn)的反滲 透膜對反滲水的質(zhì)量影響很大。 4、超純水（Ultra-pure grade water）： 其標(biāo)準(zhǔn)是水電阻率為-cm。但超純水在TOC、細菌、內(nèi)毒素等指標(biāo)方面并不相同，要根據(jù) 實驗的要求來確定，如細胞培養(yǎng)則對細菌和內(nèi)

3、毒素有要求，而HPLC則要求TOC低。 評價水質(zhì)的常用指標(biāo)： 1、電阻率（electrical resistivity）： 衡量實驗室用水導(dǎo)電性能的指標(biāo)，單位為M-cm，隨著水內(nèi)無機離子的減少電阻加大則數(shù)值逐漸變大，實驗室超純水的標(biāo)準(zhǔn):電阻率為-cm。 2、總有機碳（Total Organic Carbon ，TOC）： 水中碳的的濃度，反映水中氧化的有機化合物的含量，單位為ppm 或 ppb。 3、內(nèi)毒素（Endotoxin）： 革蘭氏陰性細菌的脂多糖細胞壁碎片，又稱之為“熱原”，單位cuf/ml。 1Tapwater ）、自來水（Tap water is usually of uncont

4、rolled quality, may have seasonal variations suchas level of suspended sediment depending on the source (municipal reservoir,river, well), may contain other chem-icals purposely added to drinking water(chlorine, uoride), and is generally unsuitable for use in important is ne for washing glassware bu

5、t should always be followed by a rinsewith a higher-grade water (distilled, deionized, etc.). 2DistilledWater ）、蒸餾水（Distillation generally eliminates much of the inorganic con-tamination andparticularly sediments present in tap water feedstock. Itwill also help reduce the level of some organic con-t

6、aminants in the distilling simply gives a slightly higher grade distilled water, butcannot eliminate either inorganic or organic contaminants. Distilled water is often produced in large stills that serve an entiredepartment, or building. The quality of the water is dependent on how well theequipment

7、 is maintained. A signicant stir occurred within a large universitysbiochemistry department when the rst mention of a problem with the housedistilled water was a memo that came out from the maintenance department would like to inform you that the repairs have been made to thestill serving the thatst

8、ated: “We department. There is no longer any radium in the water.” Thenext day, a follow-up memo was issued that stated:“Correctionthere is nolonger any sodium in the dis-tilled water.” 3DeionizedWater ）、去離子水（Deionized water can vary greatly in quality depending on the type and efciencyof the deioni

9、zing cartridges used. Ion exchange beds used in home systems, forinstance, are used primarily to reduce the “hardness” of the water usually dueto high levels of divalent cations such as magnesium and calcium. The resin bedconsists of a cation exchanger, usually in the sodium form, which releasessodi

10、um into the water in exchange for removing the diva-lent ions. (Rememberthat when you attempt to reduce your sodium intake!) These beds therefore donot reduce the ionic content of the water but rather exchange one type of ionfor another. Laboratory deionizing cartridges are usually mixed-bed cartrid

11、ges designed toeliminate both anions and cations from the water. This is accomplished bypreparing the anion-exchange bed in the hydroxide (OH-) form and thecation-exchange resin in the acid (H+) form. Anions or cations in the water(including monovalent) are exchanged for OH-or H+, respectively, whic

12、h combineto form neutral water. Any imbalance in the removal of the ions can result in apH change of the water from deion-izingbeds is slightly acidic, often between pH to . The deionizing resins can themselves increase the organiccon-taminant level in the water by leaching of resin contaminants, mo

13、nomer, andso on, and should always be followed by a bed of activated carbon to eliminatethe organics so introduced. 418M (ReverseOsmosis/MilliQTM) 水、The highest grade of water available is generally referred to as 18MW is because when the inorganic ions are completely removed, the ability ofthe wate

14、r to conduct electric current decreases dramatically, giving aresistance of 18 systems that produce this grade of waterusually apply a multiple-step cleanup process including reverse osmosis,mixed-bed ion exchangers, carbon beds, and lter disks for particulates. Somemay include lters that exclude mi

15、croorganisms, resulting in a sterile waterstream. High-grade 18 MW water tends to be fairly acidicnear pH pH adjustments of dilute buffer solutions preparedusing 18 MW water could cause discrep-ancies in the nal ionic concentration ofthe buffer salts relative to buffers prepared using other water so

16、urces. 5WhenIs 18M Water Not 18MWater 、Suppose that your research requires 18 MW water, and you pur-chased the systemthat produces 500ml/min instead of the 2L/min version. If your research doesntrequire a constant ow of water, you can connect a 20L carboy to your system tostore your pris-tine water.

17、 Bad Move. 18MW is not the most inert solvent; in practice, it is very aggres-sive. Waterprefers the presence of some ions so as your 18 mW water enters the plasticcarboy, it starts leaching anything it can out of the plastic,contaminating thequality of the same thing happens if you try to store the

18、 water inglass. 18mW water loves to attack glass, leaching silicates and other ionsfrom the con-tainer. If you need the highest purity water, its best not tostore large quantities, but rather prepare it fresh. For the same reason, the tubing used to transfer your high-grade water shouldalways be the

19、 most inert available, typically TeonTM or similar use highly plasticized exible plastic tubing. Absolutely avoid metalssuch as copper or stainless steel, as these almost always guarantee some . levelof contaminants in your water 6pH 值是多少、水的初始As mentioned above, the initial pH of typical laboratory-

20、gradedistilled and deionized water is often between and your water supply from time to time, particularly when deionizing bedsare changed to ensure that no major change in pH has occurred because ofseasonal variation or improperly conditioned resin beds. Although the initial pH of laboratory water m

21、ay be slightly acidic, the goodnews is deionized water should have little or no buffer capacity, so yournormal pH adjustment procedures should not be affected much. Payparticular attention if your buffer concentrations are very low (10mM)resulting in low buffer capacity. 7 、水中有哪些有機物質(zhì)：The answer to t

22、his important question depends on the upstream processing of thewater and the initial water source. Municipal water drawn from lakes or streamscan have a whole host of organics in them to start with, ranging from petroleumproducts to pesticides to humic substances from decaying plant material tochlo

23、rinated species like chloroform resulting from the chlorina-tion water may have lower levels of these contami-nants (since the water hasbeen ltered through lots of soil and rock, but even groundwater may containpesticides and chlori-nated species like trichloroethylene depending on landuse near the

24、aquifer. Municipal processing will remove many organic contaminants from the tap water,but your in-lab water purier is responsible for polishing the water to a gradet for experimental use. Most commercial systems do a good job of that, but asmentioned pre-viously, care must be taken to not introduce

25、 contaminants afterthe water has been polished. Plasticizers from tubing or plastic storage tanks,monomer or resin components from deionizer beds, and surfactants or lubricantson lters or other system compo-nents are the most common type of organic to befound in a newly installed system. Another com

26、mon, yet often overlooked source, is microbialcontamination. In one case, a high-grade water puriermounted on a wall near a window suddenly started showing evidence of organicbackground. Changing the carbon cartridge did not help the situation. Closeinspection of the system showed the translu-cent p

27、lastic tubing connecting thereverse osmosis holding tank to the deionizer beds, and ultimately the linesthat delivered the polished water to the spigot, had been contaminated bymicrobial growth. It was surmised that the intense sunlight during part of theday was providing a more hospitable environme

28、nt for microorganisms to gain afoothold in the system. The clear tubing was replaced with opaque tubing andthe problem disappeared. In a second instance, a facility changed its water source from wells to a riverdraw-off. This drastically changed the stability of the incoming water periods of heavy r

29、ain, silt levels in the incoming water increaseddramatically, quickly destroying expensive reverse osmosis cartridges in thewater puri-er system. The solution was to install two pre-lters ofdecreas-ing porosity in line ahead of the reverse osmosis unit. The rst lterneeded replacing monthly, but the

30、second lter was good for three to six system functioned properly for a while, but then problems reappeared in thereverse osmosis unit. Inspec-tion showed heavy microbial contamination in thesecond pre-lter which had a clear housing, admitting sunlight. After cleaningand sterilizing the lter unit, th

31、e outside of the housing was covered withblack electrical tape, and the microbial contamina-tion problem never returned. As discussed in Chapter 12, dispensing hoses from water reservoirs resting insinks can also lead to microbial contamination. 8 、在水的使用中還有哪些問題 Leaks Leaks are sometimes one of the m

32、ost serious problems that can occur with in-labwater purication systems. Leaks come in three kinds, typically. Leaks of therst kind start as slow drips, and can be spotted and corrected beforedeveloping into big unfriendly leaks. Leaks of the second kind are generally caused by a catastrophic failur

33、e of asystem component (tubing, valve, automatic shutoff switch, or backush drain).Although highly uncommon, they usually occur around midnight on Fridays so asto maximize the amount of water that can escape from the system, thereforemax-imizing the resulting ooding in the lab. The likelihood of a leak of thesecond kind seems to increase exponentially with the cost of instrumentation inlaboratories on oors directly below the lab with the water purier system. Leaks of the third kind result when a person places a relatively large vesselbeneath the water system,