Determination of conductivity of Pharmaceutical Purified Water (PW) and Water for Injection (WFI)

Pharmaceutical manufacturing requires many raw materials to produce drugs. Water is probably the largest raw material used by the bio/pharmaceutical manufacturing industry. The quality of the water used in manufacturing is defined by the global Pharmacopoeias who have harmonized the parameters and requirements for Purified Water (PW) and Water for Injection (WFI).

 

USP/Ph Eur/JP sets the standard for conductivity measurement to determine Purified Water (PW) and Water for Injection (WFI) final quality.

1. Standard Reference

 

Purified water is used in most pharmaceutical manufacturing processes all around the world. Therefore, international and national authorities have established water quality standards for purified and other regulated grades of water. Key authorities include:

The United States Pharmacopoeia (USP)

The European Pharmacopoeia (Ph Eur)

The Japanese Pharmacopoeia (JP)

 

 

2.The Principle

 

2.1Purified Water (PW)

 

PHARMACOPOEIA REQUIREMENTS FOR PURIFIED WATER

CONDUCTIVITY	Ph Eur	USP
PURIFIED WATER	<4.3 µS/cm at 20°C	<1.3 µS/cm at 25°C*
INJECTION AND HIGHLY PURIFIED WATER	<1.1 µS/cm at 20°C	<1.3 µS/cm at 25°C

TEMPERATURE/CONDUCTIVITY REQUIREMENTS (FOR PH EUR)

(for non-temperature compensated conductivity measurements)

TEMPERATURE °C	CONDUCTIVITY µS/cm	TEMPERATURE °C	CONDUCTIVITY µS/cm
0	2.4	50	8.1
10	3.6	60	9.1
20	4.3	70	9.7
25	5.1	80	9.7
30	5.4	90	9.7
40	6.5	100	10.3

 

2.2 Water for Injection (WFI)

 

PHARMACOPOEIA REQUIREMENTS FOR WATER FOR INJECTION AND HIGHLY PURIFIED WATER

CONDUCTIVITY	Ph Eur	USP
INJECTION AND HIGHLY PURIFIED WATER	<1.1 µS/cm at 20°C	<1.3 µS/cm at 25°C

 

Three Stage Philosophy

Stage 1

• Temperature not less than 25°C and conductivity not greater than 1.3 μS/cm
•  SAMPLE PASSES TEST

If measured on-line the conductivity meter must be calibrated and non temperature compensated, the temperature must be measured independently by an adjacently installed calibrated temperature meter. If the temperature is less than 25°C or the conductivity greater than 1.3 μS/cm then the conductivity measured must be checked against the Temperature/Conductivity chart table 1.

 

TABLE 1

STAGE 1: TEMPERATURE/CONDUCTIVITY REQUIREMENTS (FOR USP)

(for non-temperature compensated conductivity measurements)

TEMPERATURE °C	CONDUCTIVITY µS/cm	TEMPERATURE °C	CONDUCTIVITY µS/cm
0	0.6	55	2.1
5	0.8	60	2.2
10	0.9	65	2.4
15	1.0	70	2.5
20	1.1	75	2.7
25	1.3	80	2.7
30	1.4	85	2.7
35	1.5	90	2.7
40	1.7	95	2.9
45	1.8	100	3.1
50	1.9

 

 

Stage 2

 The temperature adjusted to 25°C when change in conductivity is less than a net 0.1 μS/cm per five minutes take a conductivity reading:

• If it is not greater than 2.1 μS/cm then it meets the requirements
• If it is greater than 2.1 μS/cm then go to stage 3

 

Stage 3

• Temperature at 25°C
• Determine pH

If conductivity reading in stage 2 is not greater than conductivity reference for given pH (table 2) it meets the requirements. If the pH is outside the range 5.0 – 7.0 the water does not meet requirements.

 

TABLE 2

STAGE 3: CONDUCTIVITY REQUIREMENTS (FOR USP) AS A FUNCTION OF PH

pH	CONDUCTIVITY µS/cm	pH	CONDUCTIVITY µS/cm
5.0	4.7	6.1	2.4
5.1	4.1	6.2	2.5
5.2	3.6	6.3	2.4
5.3	3.3	6.4	2.3
5.4	3.0	6.5	2.2
5.5	2.8	6.6	2.1
5.6	2.6	6.7	2.6
5.7	2.5	6.8	3.1
5.8	2.4	6.9	3.8
5.9	2.4	7.0	4.6
6.0	2.4

 

3. The Measurement

a. Set the Electrode type as 0.01.

b. Set the EC Cell constant as 0.01.

c. Set the EC compensation as Non-comp type. Non compensation is usually used to obtain the true conductivity value at the measured temperature.

d. Connect the pipeline with the flow cell interface. The water flow into the flow cell through the lower interface, and flow out from the upper interface.

e. Turn on the pump so that the sample to be tested is completely filled into the flow cell and pipeline.

f. Adjust the flow rate of solution until the measured value is stable and does not change with the increase of flow rate.

g. After the data is stable, read the measurement results.

 

 

4. Recommended Configuration

EC500T Conductivity Meter

• Conductivity Range: 0.000 μS/cm～2000mS/cm
• Conductivity Resolution: 0.001 μS/cm, automatic switching according to the range
• Conductivity Accuracy: ±0.5% (FS)

Electrodes

1.  

• DJS-0.01VT Conductivity Electrode.

Model	DJS-0.01VT
Name	Conductivity Electrode（k=0.01, ATC, with removable flow cell）
Measurement Range	0～20 μS/cm
Sensor material	Titanium alloy
Working Temp.	0~60 ℃
Dimensions	Φ18×50 mm
Connector	5-pin aviation

 

PH500T pH Meter

• pH Range: -2.000 to 20.000 pH
• pH  Resolution: 0.1, 0.01, 0.001pH
• pH Accuracy: ±0.002 pH

Electrodes

1.  

• 962221 pH composite electrode (Ultrapure water)

Model	962221
Name	pH composite electrode (Ultrapure water)
pH Range	0～11
Fill Solution	3 M KCl
Sensor material	Glass
Working Temp.	0~80 ℃
Junction material	Unmovable glass grinding mouth
Reference Type	Longlife Ref.
Dimensions	Φ12×185mm
Connector Type	S7