Techniques for Establishing Purity of Laboratory use Water
Water grades for laboratory usehave been discussed earlier.ASTM 1193 Laboratory grade specifications have been laid down for TypesI, II and III and are outlined below:
| Parameter | Type-1 | Type-II | Type-III |
| Resistivity,min | |||
| （250c的megohm-cm） | 18.0 | >1.0 | >0.05 |
| TOC，最大（μg/L） | <10 | 50 | 200 |
| Na, max(μg/l) | 1 | 5 | 10 |
| 氯化物，最大（μg/L | 1 | 5 | 10 |
| Total silica, (μg/l) | 3 | 3 | 500 |
| Bacteria(CFU/ml) | <10 | 100 | <1000 |
| 内毒素（欧盟/ML | 0.03 | NA | NA |
Similar specifications have been laid down by other global and national standardization bodies such as ISO,CLSI, BS, BIS, Japanese, EU, etc.
It is important to know what test procedures are carried out to measure the specified values.In this article methods adopted to test such parameters are briefly discussed.
电性能
Resistivity and conductivity are important control parameters . Resistivity is expressed as megohmcentimeter (mΩ-cm) at 25 deg C.It is the resistance offered by the water sample to flow of current. Theoretically it lies around 18.2 mΩ-cm at 25 degC, which is the maximum value for water sample free from conducting species. The greater the presence of ions the lower is the resistivity.
Conductivity is the tendency of water to conduct electricity. The unit for conductivity is microsiemens/cm or micromho/cm. Conductivity value is higher the higher the ionic strength of the water sample.The instrument for measuring the conductivity or resistivity is a conductivity meter. Commercial ultrapure purity water generators have online conductivity measurement and dispalay facility.
无机盐
水的无机组成取决于其来源。它包括CA或MG的盐，可导致水硬度，地下沉积物和生锈管道的亚铁和铁离子，Al给药化学药品，来自洗涤剂，硝酸盐，硅酸盐等的磷酸盐等。通常用于检测和估计的技术是离子色谱，是离子色谱法，电感耦合的质谱和石墨炉原子吸收光谱。可以在PPM，PPB甚至子PPB水平中检测到无机物种。
Organic Contaminants
Individual compound identification is not necessary for water classification. Presence of total organics is sufficient and for this purpose Total Organic Analyser (TOC) is recommended.As an examplewater for HPLC analysisshould have TOC values in the range of 1-5ppb.
Bacteria
常见的细菌污染源是革兰氏阴性细菌，真菌，藻类和内毒素。
Methods like microscopic examination or plate count method are commonly employed. Some bacteria are not free floating but exist in biofilms. Plate count methods in such cases under-report microbial activity so require complimentary endotoxin testing.
Endotoxin testing proves useful for gram negative bacteria as well as fungi and algae. The Limus Amebocyte lysate(LAL) test is commonly adopted.
A subsequent article will discuss the suitability of different grades of water for different analytical applications.
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