wtw photolab S12 User manual

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Operating Instructions
Part 1:
Part 2:
General Information
Functional Description
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Contents
1 Photometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Photometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 The Photometers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Photometric Test Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1 Basic Principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Spectroquant®Cell Tests . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Spectroquant®Reagent Tests . . . . . . . . . . . . . . . . . 4
2.2 Notes for Practical Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Measuring Range . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Influence of pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 Influence of Temperature . . . . . . . . . . . . . . . . . . . . 7
2.2.4 Time Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.5 Influence of Foreign Substances. . . . . . . . . . . . . . . 8
2.2.6 Dosing of Reagents . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.7 Shelf-life of the Reagents . . . . . . . . . . . . . . . . . . . . 9
3 Sample Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Taking Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Preliminary Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Dilution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4 Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Homogenization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.6 Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Pipetting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5 Analytical Quality Assurance (AQA) . . . . . . . . . . . . . . . 15
5.1 Quality Control at the Manufacturer . . . . . . . . . . . . . . . . . . 15
5.2 Quality Control for the User. . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2.1 Checking the Photometer . . . . . . . . . . . . . . . . . . . . 17
5.2.2 Checking the Overall System . . . . . . . . . . . . . . . . . 17
5.2.3 Checking the Pipettes . . . . . . . . . . . . . . . . . . . . . . . 18
5.2.4 Checking Thermoreactors. . . . . . . . . . . . . . . . . . . . 18
5.2.5 Testing for Handling Errors . . . . . . . . . . . . . . . . . . . 19
5.3 Determination of Sample Influences . . . . . . . . . . . . . . . . . . 19
5.4 Definition of Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
photoLab®Series
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photoLab®Series
1 Photometers
When a beam of light is transmitted through a colored solution, then this
beam loses its intensity, in other words a part of the light is absorbed by
the solution. Depending on the substance in question, this absorption
occurs at specific wavelengths.
Monochromators (e.g. narrow-band interference filters, lattices) are used
to select the wavelength from the total spectrum of a tungsten-halogen
lamp (VIS spectrum), a deuterium lamp (UV spectrum) or, respectively, a
xenon lamp.
The intensity of the absorption can be characterized using the transmit-
tance T (or, respectively, T in percent).
T = I/I0
I0 = Initial intensity of the light
I = Intensity of the transmitted light
If the light is not absorbed at all by a solution, then this solution has a
transmittance of 100 %; a complete absorption of the light in the solution
means 0 % transmittance.
The measure generally used for the absorption of light is the absorbance
(A), since this correlates directly with the concentration of the absorbing
substance. The following connection exists between absorbance and
transmittance:
A = – log T
Experiments by BOUGUER (1698–1758) and LAMBERT (1728–1777)
showed that the absorbance is dependent on the thickness of the ab-
sorbing layer of the cell used. The relationship between the absorbance
and the concentration of the analyte in ques tion was discovered by BEER
(1825–1863). The com bination of these two natural laws led to the deriva-
tion of Lambert-Beer’s law, which can be described in the form of the fol-
lowing equation:
A = · c · d

=
Molar absorptivity, in l/mol xcm
d = Path length of the cell, in cm
c = Concentration of the analyte, in mol/l
1.1 Photometry
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The photometers that belong to the Spectroquant®Analysis System differ
from conventional photometers in the following important aspects:
•The calibration functions of all test kits are electronically stored.
•The measurement value can be immediately read off from the display
in the desired form.
•
The method for the test kits (Cell Tests and reagent tests) belonging to
the Spectroquant®analysis system is automatically selected via the
scanning of the bar code .
•
All cells formats used are automatically identified and the correct meas-
uring range is selected automatically .
•Instrument-supported AQA ensures that measurement results can be
used as secure, reproducible, and recognized analytical results.
•New methods can be downloaded from the internet site
www.merck-chemicals.com/photometry and permanently stored in the
instrument.
For technical data and instructions for use please refer to the section
“Function description” or can also be found on the internet.
1.2 The Photometers
2 Photometric Test Kits
By means of reagents, the component of a sample to be analyzed is con-
verted into a colored compound in a specific reaction. The reagents or
reagent mixtures contain – in addition to the reagent selective for a para-
meter to be determined – a number of auxiliary substances that are
essential for the course of the reaction. These include, for example, buffers
for adjusting the pH to the optimal value for the reaction, and masking
agents that suppress or minimize the influence of interfering ions.
The color reactions are in most cases based on standardized analytical
methods specifically optimized in terms of ease of use, a low working
effort, and shorter reaction times. Furthermore, methods cited in the litera-
ture or developed by ourselves are also used . Details on the respective ref-
erence procedures are stated in the package insert or else in the para-
meter overview.
2.1 Basic Principle
1 Photometers
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2 Photometric Test Kits
The principle behind the reagent tests is that the reagents necessary for the
color reaction are combined in the form of liquid concentrates or solid-sub-
stance mixtures . A few drops of the reagent concentrate are added to the
sample. This means that there is no need to dilute the sample, which in turn
enhances the sensitivity of the detection . The procedure generally used in
classical photometry by which the sample is made up to a defined volume
in a volumetric flask is dispensed with.
The method is selected automatically by means of the scanning of the bar
code by the AutoSelector.
All cells formats used are automatically identified and the correct measur-
ing range is selected automatically.
Subsequently the result is automatically shown on the display .
2.1.2 Spectroquant®Reagent Tests
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Identification mark for the
correct insertion into the cell
compartment of the photo-
meter
Cat. No. of test kit
Designation of test kit
Details regarding contents
Special cell in
optical quality
2.1.1 Spectroquant®Cell Tests
Leakproof cap
Bar code for identification
in the photometer
Risk phrases
Highly precise dosage of
the reagent
14560
CSB/COD
Quecksilber(II)-sulfat,
Schwefelsäure
Mercury(II) sulfate,
sulfuric acid
Mercure(II) sulfate,
acide sulfurique
Mercurio(II) sulfato,
ácido sulfúrico
7.91145.608x-XXXXXX
Merck KGaA,
64271 Darmstadt, Germany
Additional reagent(s)
Certain cell tests, e.g. COD or nitrite, already contain all necessary rea-
gents in the cells, and the sample must merely be added with a pipette.
In other tests, however for reasons of chemical compatibility it is neces-
sary to separate the test into two or three different reagent mixtures. In
such cases, besides the sample a metered reagent must also be added.

The intensity of the color of a solution, measured as the absorbance, is
proportional to the concentration of the respective analyte only within a
specific range. This measuring range (effective range) is electronically
stored in the photometers for each individual test kit .
Below the specified measuring range, either a different cell or else another
procedure must be used. The lower limit of the measuring range either
takes the form of nonlinearity of the calibration curve, as shown in the
figure, or else is given by the method detection limit. The method detec-
tion limit of an analytical method is the lowest concentration of the ana-
lyte in question that can be measured quantitatively with a defined degree
of probability (e.g. 99 %).
The upper limit of the measuring range is the point at which the linear
correlation between the concentration and the absorbance ends. In such a
case the sample must be diluted accordingly so that it lies ideally in the
middle of the effective range (least-error measurement).
In photometry it is conventional practice to measure against the reagent
blank value. Here the analysis is carried out “blind”, i.e. without any ana-
lyte added. Instead of the sample volume, the corresponding quantity of
distilled or DI water is used. This reagent blank value is prestored in the
photometers belonging to the Spectroquant®analysis system, which
means that - due to the high batch reproducibility - it is possible to dis-
pense with a separate measurement of the reagent blank. At the lower
limit of the measuring range, the accuracy of the determination can be
enhanced by performing the measurement against a separately prepared
reagent blank.
2 Photometric Test Kits
2.2 Notes for Practicle Use
2.2.1 Measuring range
Concentration
Absorbance
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Cat. No. Method Correct indi- Color change
cation of
result up to
sample conc.
114739 Ammonium CT 100 mg/l turquoise instead of green
114558 Ammonium CT 500 mg/l turquoise instead of green
114544 Ammonium CT 1000 mg/l turquoise instead of green
114559 Ammonium CT 5000 mg/l turquoise instead of green
114752 Ammonium Test 100 mg/l turquoise instead of green
100683 Ammonium Test 2500 mg/l turquoise instead of green
100605 Bromine Test 50 mg/l yellow instead of red
100595 Chlorine CT 25 mg/l yellow instead of red
100597 Chlorine CT 25 mg/l yellow instead of red
100598 Chlorine Test 25 mg/l yellow instead of red
100602 Chlorine Test 25 mg/l yellow instead of red
100599 Chlorine Test 25 mg/l yellow instead of red
100086/ Chlorine Test 300 mg/l yellow instead of red
87/88
100608 Chlorine Dioxide Test 15 mg/l yellow instead of red
114553 Copper CT 50 mg/l turquoise instead of blue
114767 Copper Test 50 mg/l turquoise instead of blue
114557 Fluoride CT 5 mg/l brown instead of violet
100809 Fluoride CT 5 mg/l brown instead of violet
114598 Fluoride Test 5 (50) mg/l brown instead of violet
100606 Iodine Test 50 mg/l yellow instead of red
101632 Monochloramine Test 300 mg/l turquoise instead of green
100607 Ozone Test 15 mg/l yellow instead of red
114551 Phenol CT 100 mg/l weakening of color
114831 Silver Test 5 mg/l no change (flocculation)
In some cases the intensity of the color of the solution and thus the ab-
sorbance can drop again when very high concentrations of the analyte
are present. The examples are listed in the following table. The values indi-
cated in the display are correct up to the concentrations specified in the
third column, and false measuring values are obtained above these con-
centrations. In such a case it is necessary to conduct a plausibility check
by running preliminary tests using test strips or dilution.
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Chemical reactions follow an optimal course only within a certain pH
range. The reagents contained in the test kits produce an adequate buf-
fering of the sample solutions and ensure that the pH optimal for the reac-
tion in question is obtained.
Strongly acidic (pH < 2) and strongly alkaline (pH >12) sample solutions
can prevent the pH from being adjusted to an optimal range, since under
certain circumstances the buffering capacity of the test-kit reagents may
not be sufficient. Any necessary correction is made by the dropwise addi-
tion of diluted acid (reduces the pH) or diluted lye (raises the pH), testing
the pH with suitable indicator strips after each drop is added. The addition
of the acid or lye results in a dilution of the test solution. When up to five
drops are added to 10 ml of sample, the change in the volume can be
neglected, since the resultant error is lower than 2 %. The addition of larg-
er quantities should be duly considered by adjusting the sample volume
accordingly.
The specified pH values for the sample solution and, wherever applicable,
for the measurement solution are defined in the respective package
inserts and in the analysis instructions in chapter 3 of the manual.
2 Photometric Test Kits
2.2.2 Influence of pH
The temperature of the sample solution and the reagents may have an
effect on the color reaction and thus on the measurement result . The typi-
cal temperature course is illustrated in the figure.
If the sample temperature is lower than 15 °C, false-low results must be
reckoned with. Temperatures exceeding 30°C generally influence the sta-
bility of the compound that is formed in the reaction. The optimal tem-
perature for the color reaction is stated in the package inserts of the
respective Spectroquant®test kits.
Attention! After thermic decomposition procedures, the determina-
tion of COD or total contents of nitrogen, phosphorus, or metal, a
sufficient waiting time must be allowed for to permit the solution
cool to room temperature.
2.2.3 Influence of Temperature
Temperature (°C)
Absorbance
20 40 10 30
Most of the color reactions require a certain time to reach the maximum
color intensity. The solid curve in the figure at the right gives a schematic
impression of a typical time course. The behavior of relatively instable col-
or reactions with time is shown by the dotted curve.
The reaction time specified in the working instructions refers to the period
of time from the addition of the last reagent until the actual measurement.
In addition, the package inserts for the individual test kits also state the
time interval in which the measurement value does not change. The maxi-
mum time interval is 60 minutes; this time should not be exceeded, even in
the case of stable color reactions.
2.2.4 Time Stability
Reaction time (minutes)
Absorbance
30 60
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Foreign substances in the sample solution can
•raise the measurement value as a result of an amplification of the
reaction
•lower the measurement value as a result of a prevention of the reaction.
A quantification of this effects is stated in tabular form in the respective
package inserts for the most important foreign ions. The tolerance limits
have been determined for the individual ions; they may not be evaluated
cumulatively.
Suitability for use in seawater
A tabular survey (see appendix 1) provides information on the suitability of
the tests in connection with seawater and also on the tolerances for salt
concentrations.
2 Photometric Test Kits
2.2.5 Influence of Foreign Substances
2.2.6 Dosing the Reagents
Small amounts of liquids are dosed by counting the number of drops from
a leakproof bottle .
When using dropper bottles it is extremely important that the
bottle be held vertically and that the drops be added slowly
(approx. 1 drop per second). If this is not observed, the cor-
mrect drop size and thus the correct amount of reagent are not
achieved.
A positive-displacement pipette should be used for larger quantities of liq-
uid or for the exact dosage of smaller reagent quantities. In these cases
the reagent bottles are not fitted with a dropper insert.
Solid substances are dosed either with the dose-metering cap or with
microspoons that are integrated into the screw cap of the respective rea-
gent bottle. The dose-metering cap is used for solid reagents or reagent
mixtures that are free-flowing.
In all other cases the substances are dosed with the microspoon.
In this case it is necessary to add only level microspoonfuls. To this end
the spoon must be drawn over the brim of the reagent bottle .
At the first use replace the black screw cap of the reagent bottle by the
dose-metering cap.
Hold the reagent bottle vertically and, at each dosage, press the slide all
the way into the dose-metering cap. Before each dosage ensure that the
slide is completely retracted.
Reclose the reagent bottle with the black screw cap at the
end of the measurement series, since the function of the rea-
mgent is impaired by the absorption of atmospheric moisture.