FOE ADMINISTRATIVE USE
WATER POLLUTION SURVEILLANCE SYSTEM
APPLICATION AND DEVELOPMENT REPORT
#21
A Comparison of the Use of the Plastic Membrane
the Glass-Fiber Filter in Handling Aqueous Samples:
Speed, Cost, and Data
Donna Lee Barnett
John F. Kopp
Water Quality Activities
Division of Pollution Surveillance
Federal Water Pollution Control Administration
Department of the Interior
1014- Broadway
Cincinnati, Ohio 45202
October 1966

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A Comparison of the Use of the Plastic Membrane
Vs. the Glass-Fiber Filter in Handling Aqueous Samples:
Speed, Cost, and Data
OBJECTIVE:
The purpose of the present study was to investigate
which type of filter—the plastic membrane or the glass-
fiber filter-—is more suitable for the filtration of a
wide variety of aqueous samples. The following dis-
cussion compares the speed, cost, and accuracy of the
two methods of filtration.
INTRODUCTION:
Within the past water year the spectrographs
laboratory analyzed a total of 956 samples. Because
our interest lies mainly with those trace elements in
solution, all suspended matter must be removed before
the actual analysis is performed. This filtration
step is frequently a time consuming operation as well as
an expensive one when several plastic membranes are
required. Thus, an improved method of filtration would
be desirable.
Prior to the completion of this study, the procedure
employed allowed the suspended material to settle before
filtering thru a plastic membrane with a pore size of
0.45 micron. In this way the clear supernatant could be
decanted from the main portion of suspended material.

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With many samples, however, a very fine material remained
in suspension which clogged the membrane pores quite
rapidly. With these samples, it was not uncommon to use
as many as four to six filters, especially if large
volume samples were required "by the spectrographs pro-
cedure. In addition to the cost of the filters, the
man-hours required to process a sample "became significant.
Thus, any improvement that would reduce the time of sample
treatment or analysis was desirable.
Recently, a new type of filter, the glass-fiber
filter, has been introduced on the market. It is reported
that because of its larger pore size, this filter does not
clog as easily. Also, its cost is half that of the membrane.
The glass-fiber filter is now being used by this laboratory
except when suspended solids are to be analyzed.
EXPERIMENTAL AND RESULTS:
During the first phase of the study, duplicate 250 ml
portions of five samples were taken for comparison. The
samples were chosen such that a wide range of turbidities
would be represented. One aliquot of each sample was
filtered thru a single glass-fiber filter, while its 250
ml counterpart was passed thru a single plastic membrane.
The time required for each filtration was recorded.
Comparison of the total times of 66 minutes with plastic
membranes and 49 minutes with glass-fiber filters, as

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derived from Table I, shows a savings in time of approx-
imately 25% when glass-fiber filters are used in place of
plastic membranes. Moreover, many actual samples require
500 ml and often 1 liter for analysis; thus, the times
listed in Table I would be much greater if actual sample
requirements were considered.
Table I also lists the number and cost of filters
required to filter a 250 ml sample. Filters were changed
when the filtrate slowed down to less than several drops
per minute. The total cost of the plastic membrane used
to filter the five aliquots was $2.16 while the cost of
the glass-fiber filters totaled $1.00, The data pre-
sented shows a savings in cost of more than 50% when
glass-fiber filters are substituted for plastic membranes.
Again, it must be remembered that for actual samples two
to four times this volume is actually processed.
While the first two points considered are significant,
the analytical results are by far the most important. If
the analyses do not agree, no amount of savings in cost
would off-set the analysis error. Tables II thru VIII show
the spectrographic results of these analyses for Zn, Fe,
Mn, Ba, Sr, Na, and K. Comparison of these data show
veiy good agreement between the two sets of samples. The
other elements not listed—Cd, As, B, Mo, Al, Be, Ni, Co,
V, and F~also showed excellent agreement. Five elements,

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- 4 -
Cu, Ag, Pb, Cr, and P, showed some lack of reproducibility,
but these inconsistencies are believed to be within the
range of experimental error and not great enough to
prevent the adoption of the glass-fiber filter for routine
use.
DISCUSSION:
Table I shows that the glass-fiber requires less time
and fewer filters to process equal volumes of a particular
composite as with the plastic membrane. Since most of our
samples contain large amounts of suspended matter, filtra-
tion can be a veiy time consuming operation. This is a
very important consideration since a savings in time means
a savings in money also. On the basis of $3.61/hour or
approximately $.06/minute the savings in time amounts to
16 minutes on this series of five 250 ml filtrations, or
approximately $1.00. On the basis of this study, the
following savings can be extrapolated. On an annual basis,
assuming 800 ml volumes on the average for approximately
700 samples, about $450.00 could be saved.
In addition, millipore membranes cost $.18 each while
glass-fiber filters cost $.10 each. During the past water
year, approximately 700 of the 956 samples needed filtering.
This required 1400 plastic membranes at $.18 each for a
total of $252.00. Had glass-fiber filters been used only
750-800 would have been required at $.10 each for a total

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of $75•00-80.00. Thus, $175*00 could have been saved in
materials in addition to $450.00 salary—wise for a total
of $625.00.
Spectrographic results showed very good agreement
between the two sets of samples for the majority of
elements. While five elements did show some lack of
reproducibility, these inconsistencies were small and
considered to be within the range of experimental error.
CONCLUSION:
From the data presented, it can be concluded that the
glass-fiber filter is as efficient in our work as the
plastic membrane. Because the glass-fiber filter is
faster, less expensive and just as accurate, it is
recommended that for all future samples, the glass-fiber
filter be used in place of the plastic membrane except
in those instances where suspended solids are to be
analyzed.

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Table I
Station
Turbidity in
Jackson Units
A

p4
M
0)
0)
O
0
O
h>
h

ft
•
•H
-p

03
02
470
255
at
S
o
Hi
180

«d

•H

A

Pi

H

©

'd
O
aS
U
rl
•H
•H
ctf
A
O
P4
98
25
vQ
Time (in Minutes) to
Filter 250 ml of a
Sample Without Changing
the Filter; Plastic/G.F,
Number of Filters Used
to Filter 250 ml of a
Sample: Plastic/G.F.
23/21
V3
17/13 17/11
3/2
2/2
8/4
2/2
1/.2
1/1
Cost to Filter 250 ml
of a Sample: Plastic/G.F. $.72/.30
.5V.20 .36/.20 .36/.20 .18/.10

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Table II
Zinc
PPB
Station No,	Plastic Membrane Glass-Fiber
15	18	12
20	30	<30
21	<15	<13
31	<46	60
35	30	46
40	<16	<15
57	4	7
66	14	14
97	16	30
116	7	6
127	<30	<30
130	<14	16

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Table III
Iron
PPB
Station Ho.	Plastic Membrane Glass-Fiber
15
5
<4
20
8
8
21
<8
9
31
<12
14
35
<7
12
40
<8
<8
57
5
6
66
2
2
97
21
17
116
5
7
127
<8
24
130
<7
<7

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Table IV
Manganese
FPB
Station No,	Plastic Membrane Glass-Fiber
15 4.3	<4.0
20	<4.5	<4.5
21	<7.5	<6.5
31 <6.9	9.2
35 <5.9	5.2
40 <4.8	<7.5
57 <1.7	<1*7
66 <1.5	<1.5
97 <1.3	<1.3
116 <2.3	2.5
127 <^«5	<4.5
130 <7.0	<7.0

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Table V
Barium
PPB
Station No.	Plastic Membrane Glass-Fiber
15	18	17
20	75	62
21	59	63
31	67	81
35	44	61
40	34	48
57	11	19
66	8	11
97	14	15
116	17	23
127	32	39
130	36	44

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Table VI
Strontium
PPB
Station No.	Plastic Membrane Glass-Fiber
15	81	67
20	140	150
21	141	143
31	334	391
35	143	169
40	165	177
57	12	19
66	15	13
97	36	28
116	46	44
127	255	255
130	150	172

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Table VII
Sodium
PFB
Station No.	Plastic Membrane Glass-Fiber
15
6.0
6.0
20
24
24
21
20
20
31
63
64
35
20
20
40
25
25
57
5.0
5.0
66
1.0
1.0
97
2.0
2.0
116
7.0
7.0
127
19
19
130
20
20

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13
Table VIII
Potassium
PPB
Station No.	Plastic Membrane Glass-Fiber
15	0.8	0.8
20	4.1	4.1
21	4.0	3.8
31	5.6	5.6
35	3.5	3.3
40	3.8	3.6
57	1.0	1.0
66	0.2	0.2
97	0.6	0.7
116	0.9	1.1
127	4.7	4.7
130	3.2	3.1

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