A common problem labs have is that the filter housing (bowl) gets tightened too much when the Ion-Ex or 1 Micron filters are changed and the next time they need to be replaced it seems like it is impossible to loosen it.
When doing up the bowl make sure the O-ring is in place and has not fallen out, without the O-ring the filter housing can seize as there is little give in the head and it plastic on plastic.
Bowls should only be done up by hand. The seal is provided by the O-ring, so it should be replaced if it does not seal when don up hand tight. The black spanner is intended for for loosening the housings.
IMPORTANT: If the bowl is over tightened they can crack as the styrene material it is made from can be quite brittle.
Any organic molecule you break down you will find carbon in. Total organic carbons (TOC) is the amount of carbon found in an organic compound and can be used a indicator of water purity.
Water also has inorganic carbon (IC) but IC is not included in the TOC measurement. (TOC = TC – IC)
How does does TOC affect me as a pathologist?
This is where the importance of consistently pure water becomes essential. In pathology impure water can give false readings of samples, incorrect analysis and diagnosis of medical conditions and contaminate your analyser.
As a guide the following levels of TOC are what are acceptable in type 1,2 and 3 water as according to the American society for Testing and Materials (ASTM)
Type 1 2: <50 ppb of TOCs
Type 3 : <200 ppb of TOCs
Water quality parameters for ISO grades.
Perameter
Grade 1
Grade 2
Grade 3
pH value at 25oC
—
—
5.0-7.0
Conductivity (μS/cm) at 25oC, max
0.1
1.0
5.0
Oxidisable matter Oxygen content (mg/l), max
—
0.008
0.4
Absorbance at 254 nm and 1 cm optical path length, absorbance units, max
0.001
0.01
—
Residue after evaporation on heating at 110oC (mg/kg), max
—
1
2
Silica (SiO2) content (mg/l), max
0.01
0.02
—
American Society for Testing and Materials (ASTM) The ASTM uses D1193-06 and has four grades of water (see table below).
Water quality parameters for ASTM types.
Perameter
Type I*
Type II**
Type III***
Type IV
Conductivity (μS/cm) at 25oC, max
0.056
1.0
0.25
5.0
Resistivity (MΩ-cm) at 25oC, max
18.0
1.0
4.0
0.2
pH at 25oC
—
—
—
5.0–8.0
TOC (μg/l), max
50
50
200
No limit
Sodium (μg/l), max
1
5
10
50
Sodium (μg/l), max
3
3
500
No limit
Chloride (μg/l), max
1
5
10
50
*Requires use of 0.2 μm membrane filter; **Prepared by distillation; ***Requires the use of 0.45 μm membrane filter.
*Requires use of 0.2 μm membrane filter; **Prepared by distillation; ***Requires the use of 0.45 μm membrane filter.
Clinical and Laboratory Standards Institute (CLSI) – formerly NCCLS
As of 2006, the CLSI has moved away from the typical Type I, II and III designations, instead preferring to suggest that water be simply ‘fit for purpose’, and only describes one grade in significant detail: Clinical Reagent Laboratory Water. The CLSI has also briefly outlined other grades in less detail, such Special Reagent Water (SRW) and instrument feed water.
Parameter
CLSI-CLRW
Resistivity (MΩ·cm at 25°C)
≥10.0
Conductivity (µS/cm at 25°C)
≤0.1
TOC (ppb)
≤500
Bacteria (CFU/mL)
≤10
Endotoxins (EU/mL)
≤0.25
Silica (mg/L)
≤0.05
Particulates
0.22 µm filtration recommended
pH
Not specified
International Organization for Standardization (ISO)
The ISO based its specification on ISO 3696:1987, and specifies three grades of water: Grade 1, Grade 2 and Grade 3, where Grade 1 is the most pure (see below):
