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Quality standards for purified water



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Several organizations have set quality standards for purified water based on intended use. Several organizations have set quality standards for purified water based on intended use. Among them are the following:

ASTM (American Society for Testing and Materials)
NCCLS (National Committee for Clinical Laboratory Standards)
ISO International Organization for Standarization
EP y USP (Pharmacopea Europea y Pharmacopea Americana)

(ASTM) D1193-91American Society for Testing and Materials
Standard Specification for Reagent Water

Parameter

Type I

Type II

Type III

Type IV

Electrical Conductivity Max. (µS/cm @ 25ºC)

0,056

1,0

4,0

5,0

Electrical Resistivity (MΩ-cm @ 25ºC

18,2

1,0

0,25

0,2

pH at 25ºC

-

-

-

5,0 - 8,0

TOC máx. (µg/L)

10

50

200

n/a

Sodium máx. (µg/L)

1

5

10

50

Total Silica max. (µg/L) 

3

3

500

n/a

Chlorides max. (µg/L) 

1

5

10

50

Endotoxins IU/ml

< 0.03

< 0.25

-

-


National Committee for Clinical Laboratory Standards (NCCLS)


Parameter

Type I

Type I I

Type III

Bacteria (CFU/ml)

< 10

< 1000

NA

pH

NA

NA

5,0 - 8,0

Resistivity (MΩ.cm @ 25ºC)

> 10*

> 1

> 0,1

SIlica (mg/L)

< 0,05

< 0,1

< 1

Total Solids (mg/L)

0,1

1

5

Total Oxidisable Organic Carbon (mg/L)

< 0,05

< 0,2

< 1

Particulate matter

< 0.2 µm

* Type I resistivity is measured in line 



ISO International Organization for Standardization. ISO 3696.
Water for analytical laboratory use - Specification and test methods 



Parameter

Degree 1

Degree 2

Degree 3

pH at 25ºC

N/A

N/A

5,0 a 7,5

Electrical conductivity (µS/cm 25ºC, máx).

0,1

1,0

5,0

Oxidizable matter. Oxigen (O) (content mg/L. máx)  

N/A

0,08

0,4

Absorbance at 254 nm and 1 cm optical path lenght. Absorbance units, máx.

0,001

0,01

Not specified

Residue after evaporation at 110ºC mg/kg, máx

N/A

1

2

Silica content (SiO2) (mg/L., máx ) 

0,01

0,02

Not specified



Pharmacopoeia 

Some Pharmacopoeias have set requirements for water. Among the best known are the USP (United States Pharmacopoeia.) and EP (European Pharmacopoeia). Pharmacopoeias also establish purity criteria (microbiological and pyrogen content) for  sterile water and water for injection. 

Parameter

EP

USP

Nitrates

<0,2 ppm

-

Heavy Metals

<0,1 ppm

-

TOC

<500 µg/L C

<500 µg/L C

Conductivity

<1,1 µS/cm a 20ºC

<1.3 µS/cm a 25ºC

Bacteria

<100 CFU/ml

<100 CFU/ml



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