T O C 1 3 Swab Method for TC – Determination

T O C 1 3 Swab Method for TC – Determination
SCA-130-013E
TOC
13
Swab Method for TC – Determination
of polluted surfaces
Herr Dr Fuchs and Far Dipl-Chem (FH) K. Tillschneider, Relectronic-Remech GmbH & Co. KG
Dipl-Chem. Gabriele Braun, Shimadzu Deutschland GmbH
1. Preface
In some technical application fields – especially in electronics,
in
Food Industry, in precision engineering, in pharmacy, medicine, space technology and semiconductor production –
special demands are made on the purity of the production area
(surfaces, machines, tools) and the product itself.
Surface cleanness, according to the guideline for pollutionfree-room-technology VDI 2083, is defined as the absence of
pollution of all kind, which could influence the process or
the product respectively.
The target of all pollution-free-technological measurements is
the achievement of a permissible, i.e., the process not disturbing residual pollution on workstation surfaces. As there is
no covered sampling method known to us, to determine the
TC-pollution on products or factory surfaces - developing an
appropriate method has been determined to be necessary. In
the following sections the extraction of swab samples is described in detail.
Instrumentation:
Shimadzu Unit:
TOC – 5000 A with SSM – 5000 A
Carrier Gas:
Synthetic Air (or Oxygen)
TC-furnace temperature: 900 °C
short measurement cell.
Fig. 1: Two-point-TC-Calibration curve with a 2000 ppm
C- or 5000 ppm C-Glucose solution.
2. Cleaning of relevant surfaces
In order to determine the rest contamination, according to the
below mentioned cleaning method, glass tops have been
chosen, since those show no evaporation of organic substances. For the cleaning process, powder free gloves were
used, made from natural rubber latex, rinsed carefully with
fully deionized water (Conductivity < 1 µS/cm /VE WATER)
furthermore cellulose which was exhausted with pure water
(VE-WATER). The glass tops were carefully cleaned with 3-4
pieces towelling paper, before swab samples were taken with a
micro filter of quartz fibre. These filter papers have a diameter
of 37 mm, consisting of very pure quartz, which was preheated in order to remove traces of organic pollution and
3. Storage of the swabs
For the TC–value does not increase within the factory-new
pre-heated filters, they are supposed to be stored in sealed
glass containers. Plastic containers are not suitable, because,
evaporating organic components (softeners etc.) can cause
which is heat resistant up to 950°C. Preferentially, the filters
shall be handled only with heated tweezers and powder free
gloves. The investigation of 10 filter papers revealed an average TC-baseline-pollution of 15µg/filter. This rest contamination was subtracted from all other results. If necessary, the
quartz fibre filters, might be heated up together with the ceramic combustion boats, leaving a slight remaining TC–pollution which cannot be determined. Even after this pre-heating
the papers are still supple and suitable for swabbing.
With the swab method, described in section 4, pollution values up to 0,1 µg TC/cm² have been found.
contamination. Moreover, only empty and clean glass containers should be taken to the place of sampling.,
where all filters from the sample surface should immediately be
put
in
one
of
these
glass
containers.
4. Swabbing method
Swab samples are real surface samples. For sampling, new, power free gloves (made of natural rubber latex or pure-room-gloves,
which are rinsed with VE water ) should be worn. Here the gloves of natural rubber-latex, described in section 2 were used. In
any case, each touch of the sampling surface with the hands, has to be avoided.
Implementation of Sampling:
For one sample three swabs were used.
Swab No. 1
was moistened with 0,5 ml VE water and then wiped off the whole glass top with it.
Swab put in a glass container.
Swab No. 2
was moistened with 0,5 ml VE water and then wiped off again the whole glass top with it.
Swab put in a glass container
Swab No. 3
was used for wiping dry the whole glass top
swab put in a glass container .
Close glass container tight and label it accordingly (numbering); note also surface, appearance, kind of wiped off samplesurface.
Just so much sampling-material (swab) should be used on the surfaces until it looks optically clean. It is important, to use a dry
swab at the end, in order to soak up remaining humidity from the sampling-surface.
5. Measurement Method
The quartz fibre filters which were used for the swabbing were
rolled and then separately put into a pre-heated ceramic boat.
Afterwards the catalytic oxidation was done in oxygen atmo sphere at 900°C. The emergence of CO2-gas during oxidation is
6. Calibration
Depending on the CO2-concentration of the samples, three
different measurement ranges can be chosen: Range 1 (most
sensitive measurement range), Range 5 and Range 30 (highest
detected by NDIR method. The TC -concentration, which is
proportional to the peak area is calculated using the calibration
curve.
measurement range). The instrument itself chooses the measurement range automatically. TC calibration is done using two
glucose-standard-solutions.
Fig.1: shows a two-point-TC-calibration curve with a 2000 ppm C- and. 5000 ppm C- glucose-solution.
The measurements were done in Range 1, since the TC-value of the samples is expected within this area.
7. Measurements and Results
7.1 Samples of defined contaminated surfaces
To prove the swab method (described in section 4) several
glass tops of a 980 cm² area were cleaned by the method
described in section 2 . Afterwards these glass tops were
contaminated moreover with a standard solution of 100 µl
each of a 5000 ppm C – Glucose- or potassium hydrogen
phthalat standard solution. The solution used for contamination was equally spread over the glass tops with a pipette’s
point and then dried at room temperature. The swabbing was
done with three quartz fiber. The use of a fourth swab was
proved
to
be
unnecessary
because
TC – measurements showed that, no further contamination
can be absorbed. The entire applied contamination was able
to be captured with three swabs in these experiments. If it is
a persistent contamination we are dealing with, then, more
than three swabs are necessary, in order to achieve an optimal
cleaning of the surfaces. Furthermore, with slighter pollution,
sampling surfaces of approx. 1000 cm² or bigger are being
preferred. Also, measuring the correct surface area is very
important in order to obtain correct experimental values.
The measurement results are shown in table 1.
The theoretical area pollution with TC- after the defined contamination method - was calculated to be 0,51 µg/cm² TC.
Table 1:
No.
Contamination
on glass
Absolute pollution with TC
[µg]
sw 1
sw 2
sw 3
Sum pollution
with TC [µg]
Area
[cm²]
Measured Area
pollution with TC
[µg/cm²]
1.
500 µg Glucose
500 µg Glucose
500 µg Glucose
500 µg Glucose
500 µg
PHP
500 µg
PHP
443,4
82,1
24,1
549,5
980
0,56
422,7
84,5
0,0
507,2
980
0,52
460,2
95,6
3,1
558,9
980
0,57
453,3
104,3
5,1
562,7
980
0,57
447,2
85,2
3,7
536,1
980
0,55
433,0
97,9
5,6
536,5
980
0,55
2.
3.
4.
5.
6.
Short cuts: sw = Swab ; PHP = potassium hydrogen phthalate
7.2 Samples of real surface contamination
In order to get an idea of surface determination in offices,
samples of vertical glass areas and horizontal plastic surfaces
(desk) have been taken. The glass areas have been treated by
the normal dust-pollution for approx. one year and the desksurfaces for about. 2 month.
The measurement-results are shown in chart 2.
The given specifications serve purely as technical information for the user. No guarantee is given on technical specifications of
the described products and/or procedures
Chart 2:
No.
Surface
1.
2.
3.
4.
Glass
( vertical )
Glass
( horizontal))
Desk
Plastic
(horizontal)
Desk
Plastic
(horizontal)
Absolute pollution with TC Sum pollution
[µg]
with TC [µg]
sw 1
sw 2
sw 3
Area
[cm²]
Measured area
pollution with TC
[µg/cm²]
273,1
134,4
53,1
460,6
980
0,47
433,2
122,6
37,8
593,6
980
0,61
591,9
276,4
159,2
1027,5
270
3,81
712,1
190,7
72,4
975,2
270
3,61
Short cut: sw = Swab
Discussion
As shown in table 1, the measured average area pollution
deviates from the theoretically expected pollution of 0,51
µg/cm² TC, with 8,49% . For the measured pollution is higher
than the applied pollution, it can be said that the entire
contamination of the analysed surfaces was captured. At
the same time, it has to be mentioned, that the detection limit
of the used instrument is at 100 µg TC. The experiments
ACC. to table 1 show values from 500 – 565 µg TC. Taking
into account that the measurement concentration level was
at the determination limit an analysis error of < 10% is tolerable. Therefore the swab method, which is described in
section 4, can be used also with similar surface concentrations of water-soluble organic contamination higher than
0,1 µg/cm².
The fact, that the deviation from the defined surface pollution was traced only in the positive direction, it might be
assumed, that in spite of careful sampling, certain contamination have been imported. These contamination can be put
down to the use of deionized water (TC up to 2 ppm), to the
dust-import from the atmosphere and to possible existing
contamination from the gloves. If these guidelines can be
improved, more specific result-data could be obtained. ACC.
to chart 2, the plastic-surfaces (desk) show a 7 times higher
contamination than the glass-surfaces, despite the desksurfaces had to withstand the normal dust-pollution for a
shorter time. The reason for this, is the position of the sampled surface and the type of the surface (plastic, glass) Information , which have to be registered during sampling,
in order to be able interpreting the results properly. On a
further refining of the here introduced sampling- and examination-method it is being worked currently.
Literature:
VDI 2083, Guideline for pure-room-technology (Surface purity), Page 4, February 1996
0.2/E/10/00/GBB/SV
Shimadzu Deutschland GmbH
Albert-Hahn-Str. 6 – 10, D-47269 Duisburg
Tel. 0203-7687-0
Fax: 0203-766625
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