Giáo Trình Phân Tích Mẫu Thực Phẩm Bằng Chuẩn Độ Điện Thế.pdf

food e buch indb 1 Food Potentiometric Analysis Collection Food PAC 6 6055 003 Methods for the Titrimetric/Potentiometric Analysis of Foodstuffs Dear User, You have decided to purchase a Metrohm Titra[.]

In this Application File you will find descriptions of the analytical methods together with

the necessary comments and explanations and – specially for you – printouts of the ment parameters and examples of curves.

instru-All these methods are loaded on the method memory card instru-All that you need to do is to

«feed» your titrator with the card, load the required method into the working memory and off you go!!!

For Titrando users: a conversion program ensures that you can use Titrino parameters

in the Titrando without any problems This conversion program is contained in the 6.6050.XXX PC Control program.

We wish you lots of pleasure and success in your work,

Your Metrohm

8.110.1911

– The methods described here have been drawn up taking the current state of knowledge into account.

– All the methods are formulated so that you can use them as SOPs (Standard Operating Procedures) in

your laboratory

– Many of the methods described here can be automated even further; see the proposal given in the annex For details please consult your local Metrohm distributor, which can be found on the Internet under:

www.metrohm.com ⇒ Distributors– The method memory card supplied can be used with the 798, 799, 785 and 751 Titrinos (from program

version 20) With the Metrodata VESUV Light 3.0 software (VESUV = Verification Support for Validation),

which is also supplied, you or your local Metrohm distributor can also transfer the sets of parameters to

716, 736, 794 or 751 Titrinos (<program version 20)

– Among other things, the supplied CDs contain:

• The VESUV backup file, which allows you to copy the 96 methods into 716, 736, 751, 785, 794, 798 and

799 Titrinos For further information please consult the section «Restoring methods» in the Instructions for Use supplied or contact your local Metrohm distributor

If the VESUV software is used for data acquisition instead of the printer then the report «curve» must be deleted at the Titrino, which is set instead to «mplist» (VESUV can only process measuring point lists)

• A conversion program for taking over Titrino parameters into the Titrando This conversion program is

contained in the 6.6050.XXX PC Control program

• Acrobat® Reader® for installation on your PC so that you can read PDF files

• Application Bulletins nos 25, 33, 53, 69, 84, 85, 86, 87, 94, 125, 129, 130, 139, 140, 141, 180, 188, 225,

235, 249 and 252

– We recommend that you only load the methods that you require in your instrument

– The method overview can be removed and kept near your instrument together with the Food PAC card

Important symbols used in the methods

c(X) molar concentration of substance X in mol/L

M(X) molar mass of substance X in g/mol

w(X) mass fraction of substance X, e.g w(NaCl) = 10%

σ(X) volume fraction of substance X, e.g σ (EtOH) = 40% (formerly: % V/V, e.g.)

ρ((X) mass concentration of substance X, e.g ρ(NaOH) = 4.0 g/L (β is also used – difference from density)

Literature

The procedures and methods have been drawn up based on the following publications:

– German Standard Methods for the Examination of Water, Waste Water and Sludge

– Official Methods of Analysis of the Association of Official Analytical Chemists (AOAC, USA)

– Swiss Foodstuffs Manual (Schweizerisches Lebensmittelbuch)

– U.S Environmental Protection Agency (EPA)

Remarks

The determination of the water content of foodstuffs and semi-luxuries is not described in Food PAC Please consult the Metrohm monograph «Water determination by Karl Fischer titration», which can be obtained free of charge from your local Metrohm distributor.

A pH value

A 1 Calibrating the pH glass electrode

A 2 Measuring the pH value

B Preparing the most important titrants and

determining their titer

B 1 Alkaline titrants (NaOH, KOH)

C Drinking water and mineral water

C 1 pH value and acid capacity (carbonate

hard-ness)

C 2 Calcium and magnesium (Ca hardness, Mg

hardness and total hardness)

C 3 Chloride

C 4 Sulfate

C 5 Sulfides and hydrogen sulfide

C 6 Total and residual chlorine (free chlorine)

C 7 Permanganate index (oxidizability)

C 8 CO2 content of carbonated water

C 9 Oxygen content according to Winkler

D Milk and dairy products

E Edible fats and oils

E 1 Acid number and free fatty acids (FFA)

F 1 pH value and degree of acidity

F 2 Chloride and cooking salt content

F 3 Kjeldahl nitrogen, total protein

F 4 Calcium and magnesium (in ash)

G Honey, sugar and sweets

G 1 pH value and free acids

G 2 Formol number

G 3 Reducing sugars

H Soft drinks, lemonades

H 1 Citric acid, citrates

H 2 Phosphoric acid (cola drinks)

H 3 Potassium

H 4 Total phosphorus

J Fruit and vegetable juices, fruit nectars and jams

J 1 pH value and titratable total acidity

J 2 Ascorbic acid (vitamin C)

J 3 Sulfurous acid (sulfite)

J 12 Reducing sugars in jams

K Beer, vinegar, spirits and wine

K 1 Beer, pH value

K 2 Beer, CO2 content

K 3 Beer, ascorbic acid (vitamin C)

K 4 Beer, total sulfurous acid

K 5 Vinegar, pH value and total acidity

K 6 Vinegar, volatile acidity

K 7 Vinegar, ascorbic acid (vitamin C)

K 8 Vinegar, free sulfurous acid

K 9 Vinegar, total sulfurous acid

K 10 Vinegar, ash alkalinity

K 11 Vinegar, chloride

K 12 Vinegar, sulfate

K 13 Spirits, pH value and total acidity

K 14 Spirits, volatile acidity

K 15 Spirits, total esters

L Coffee, cocoa and chocolate

L 1 pH value and degree of acidity (green and

roasted coffee, coffee extracts)

L 2 Ash alkalinity (green and roasted coffee,

cof-fee extracts)

L 3 Chloride (green and roasted coffee)

L 4 Directly reducing sugars (roasted coffee,

coffee extracts)

L 5 pH value (cocoa and chocolate powder)

L 6 Ash alkalinity (cocoa and chocolate

pow-der)

L 7 Kjeldahl nitrogen (cocoa and chocolate

powder)

L 8 Free fatty acids in cocoa butter

L 9 Iodine number of cocoa butter

L 10 Saponification number of cocoa butter

M Artificial sweeteners, gelling and thickening agents

M 1 Methoxy and ethoxy groups in gelling and

thickening agents

M 2 Cyclamate in artificial sweeteners

M 3 Saccharin in artificial sweeteners

N Preserved fruits, vegetables and mushrooms

N 1 Oxalic acid in fruits and vegetables

N 2 Total sulfurous acid in dried fruits and

veg-etables

N 3 Cooking salt content of mushroom extracts

and concentrates

O Cooking salt, spices, pickling salt,

seasoning, herbal and flavored salts

O 1 Chloride content

O 2 Total iodine in cooking salt

O 3 Fluoride in cooking salt

O 4 Tricalcium phosphate in cooking salt

O 5 Nitrite in pickling salt

P Meat products, meat extracts, bouillon preparations, aspic, seasonings, soups, sauces

P 1 Chloride (NaCl) in meat products

P 2 Kjeldahl nitrogen and raw protein in meat

products

P 3 Sulfurous acid in meat products

P 4 Chloride (NaCl) in meat extracts, aspic and

General Free protons (H+ ions) occur in solutions just as little as free electrons They

combine with water to form oxonium ions:

H+ + H2O → H3O+The pH value is defined as the negative logarithm of the oxonium ion activity, i.e of the concentration of free, dissociated oxonium ions in mol/L: pH = –log [H3O+]

Strictly speaking, the term pH only applies to purely aqueous solutions

The pH scale ranges from 0 to 14 with the neutral point at pH = 7.0, where the

H3O+ and OH– ions are present in equilibrium pH values below 7 result from

an H3O+ excess, pH values above 7 from an OH– ion excess The more acidic a solution the higher its H3O+ ion concentration and the lower its pH value

Weak acids, e.g tartaric acid, do not dissociate completely This means that only a small fraction (approx 2 3%) of their acid ions are released This also means that only on very rare occasions can the pH value be used as a measure

of the concentration of acids or bases

As the pH scale is logarithmic this means that small differences in pH spond to large differences in the concentration of H3O+ ions For example, at pH

corre-= 3.0 there are ten times more H3O+ ions present than at pH = 4.0, and at pH = 3.1 there are twice as many H3O+ ions present than at pH = 3.4

The measuring setup for potentiometric measurements always consists of two electrodes – a measuring or indicator electrode and a reference electrode For practical reasons these two electrodes are usually contained in a single com-bined electrode

The indicator electrode (in this case the pH glass electrode) produces a tial that is dependent on the composition of the sample solution

poten-The reference electrode (usually Ag/AgCl) has the task of providing a potential that is as independent as possible of the sample solution (reference potential).The potential measurement itself takes place virtually current-free by using a

«voltmeter» (in this case a Titrino) with a high-impedance measuring input (this

is necessary to avoid unwanted potential drops) The measured potential U is made up from the individual potentials produced by the indicator and reference electrodes The following illustration shows a schematic diagram with a sepa-rate pH glass electrode (left) and a reference electrode (right):

• Comb pH glass electrode with built-in Pt 1000 temperature sensor, e.g 6.0258.000 Unitrode

• Buffer solutions pH = 4.00, 7.00 and 9.00, e.g 6.2307.100, 6.2307.110 and 6.2307.120

A 1 Calibrating the pH glass electrode

The individual potentials U2, U3 and U4 are determined by the construction of the electrodes and are therefore constant for a given electrode pair The diffu-sion potential U5 should be kept relatively constant and low by taking suitable measures These measures include an optimal and clean diaphragm, constant stirrer speed during the measurements as well as a suitable reference electro-lyte solution whose anions and cations have similar ionic mobilities – e.g KCl

In this way the potential U1 measured between the electrodes depends only on the sample solution In the pH measurement this potential is again dependent

on the activity ai of the measuring ion (H3O+ ion / OH– ion) This relationship is described by the Nernst equation:

U = U0 + * log ai = U0 + UN * log a

where:

The Nernst slope UN describes the theoretical electrode slope and corresponds

to the change in potential produced by altering ai by a factor of ten It depends

on the temperature and charge z of the measuring ion Please note: The ment compensates the effect of temperature on U N but not on the pH value

0 mV

Things are different in practice The electrode zero point should have a value for Uas of ±15 mV (corresponds

to pHas = 6.75 7.25) and the slope should be >0.95 (>56.2 mV / pH at

solu-A 1 Calibrating the pH glass electrode

We recommend the following procedure for calibrating a pH glass electrode:

– Remove the electrode from its storage vessel, attach a cable if necessary and connect it to the instrument

– Open the electrolyte filling opening and, if necessary, top up the electrolyte solution

– Rinse the electrode thoroughly with dist H2O and dab dry with a soft paper tissue (do not rub)

– Fill pH = 7.0 buffer solution into a beaker and add a stirrer bar

– Immerse the electrode into the buffer solution and stir for approx 1 min Measure the temperature of the buffer solution and enter in the Titrino (not necessary if temperature sensor is connected)

– On the Titrino enter the pH value of the buffer solution (at the corresponding temperature) and start the calibration with buffer 1 under stirring

– When the measured value has been accepted, remove the electrode from the solution, rinse it thoroughly with dist H2O and dab dry with a soft paper tissue

– Add pH = 4.0 or 9.0 buffer solution to a second beaker, add a stirrer bar, immerse the electrode and stir for approx 1 min (the second buffer solution must have the same temperature as the first one)

– On the Titrino enter the pH value of the second buffer solution (at the sponding temperature) and continue the calibration under stirring

corre-– After the measured value has been accepted, end the calibration Remove the electrode from the solution, rinse the electrode thoroughly with dist H2O and dab dry with a soft paper tissue

A 1 Calibrating the pH glass electrode

Handling

Laboratory electrodes should have a long lifetime Their characteristics (slope, response behavior, pHas / Uas) must lie within the given criteria In order to en-sure this a few basic rules must be observed:

• After use rinse the electrode thoroughly with dist H2O and dab dry with a soft paper tissue Close off the electrolyte filling opening and store the electrode

by immersing it in electrolyte solution – usually c(KCl) = 3 mol/L – to an adequate depth Dry storage leads to delayed and poor response behavior The electrolyte solution may become concentrated and pHas / Uas could alter Storage in dist H2O could result in the diaphragm being blocked by AgCl

• If the electrode responds sluggishly and/or the slope is unsatisfactory then the electrode membrane must be etched This is done by immersing the membrane in a 10% solution of ammonium difluoride (NH4HF2, use plastic beaker) for 1 min, then swirling it for approx 10 s in c(HCl) = 5 mol/L, rins-ing it thoroughly with dist H2O and then wiping off the silicate residue with

a moist tissue In order to build up a new gel layer the electrode is placed in c(KCl) = 3 mol/L for 24 h (or for 5 h in the same solution at 50 °C)

• If the diaphragm becomes blocked please refer to the electrode data sheet that accompanies each electrode Removing such a blockage is complicated and time-consuming – it is better to send the electrode to your local Metrohm distributor for this

• Contamination by fats, oils, lacquers, paints, etc.: remove the contamination with an organic solvent (acetone, petroleum benzine, toluene), rinse thor-oughly with ethanol and dist H2O, dab dry and place in electrolyte solution

• Contamination by proteins: immerse the electrode in a solution of 5% pepsin

in c(HCl) = 0.1 mol/L for a few hours Then rinse thoroughly with dist H2O, dab dry and place in electrolyte solution

What happens in the instrument (in this case Titrino) during calibration can be seen in the following plot:

A 1 Calibrating the pH glass electrode

BUFFER BUFFER BUFFER CALTEMP

SLOPE

@FR



$ATE

A 2 Measuring the pH value

The pH value is extremely important for biological systems It influences the growth of microorganisms, the taste, color, redox potential and many other properties

The pH value of the sample also depends on the temperature This temperature dependency cannot be compensated by the instrument (e.g Titrino), which only adjusts the slope of the electrode This means that information about the

pH value must always include the temperature at which it was measured

Example of a red wine sample:

pH = 3.52 at 18.2 °C

The calibrated electrode is thoroughly rinsed with dist H2O and dabbed dry with a soft paper tissue The electrode is immersed in the sample solution (or pushed into the sample until the diaphragm is covered) and the pH is measured (under stirring for liquid samples) When the drift criterion has been reached, the pH value is displayed by the instrument or printed out (do not forget to mea-sure the sample temperature) When the measurement has been completed the electrode is thoroughly rinsed and dabbed dry with a soft paper tissue

A 2 Measuring the pH value

Instrument parameters and calculation

#

and determining their titer

General Titrants are standard solutions, i.e solutions that contain a defined content of

a reactant This content is given as the molar concentration c in mol/L The

«normality», which was frequently used previously, is no longer valid today and should therefore not be used

Examples:

• 0.1 N HCl ⇒ c(HCl) = 0.1 mol/L

• 0.1 N H2SO4⇒ c(H2SO4) = 0.05 mol/L

• 0.1 N iodine solution ⇒ c(I2) = 0.05 mol/L

• 0.1 N KMnO4⇒ c(KMnO4 ) = 0.02 mol/L [or c(1/5 KMnO4) = 0.1 mol/L]

Not all titrants have a stable titer, i.e their concentration can vary with time

Examples:

• Hydroxides absorb CO2 from the atmosphere to form carbonates

• Iodine solutions release iodine

• Thiosulfate solutions can decompose and deposit sulfur

• In the presence of organic substances, e.g dust particles, permanganate solutions deposit manganese dioxide (MnO2)

• The solvent may evaporate from non-aqueous titrants

This all means that the titer of the titrant may alter as time passes In order to know the true titer concentration the titer must be determined at regular inter-vals

The so-called standard titrimetric substances are used for determining the titer Their content hardly changes, they are available with a defined degree of purity, can be dried and can be traced back directly to standard reference materials (e.g National Institute of Standards and Technology – NIST, USA)

Such standard titrimetric substances /secondary standards are:

• For bases potassium hydrogen phthalate, M = 204.23 g/mol

• For acids tris(hydroxymethyl)-aminomethane, M = 121.14 g/mol

• For iodine arsenic trioxide, M = 197.841 g/mol

• For thiosulfate potassium iodate, M = 214.001 g/mol

• For permanganate disodium oxalate, M = 133.999 g/mol

• For AgNO3 sodium chloride, M = 58.443 g/mol

• For Na2EDTA calcium carbonate, M = 100.09 g/molMost standard solutions/titrants are commercially available as ready-to-use solutions with a titer adjusted by the manufacturer at 20 °C to 1.000 We recom-mend that you purchase such ready-to-use solutions and do not prepare them yourselves

In principle titer determinations should always be carried out at the same perature at which the analyses are later to be carried out Please note that solu-tions expand as their temperature increases

and determining their titer

For aqueous solutions a temperature difference of 5 °C for a theoretical sumption of 10.00 mL results in a difference in volume of 12.5 μL This means that a titer of 1.0000 at 20 °C becomes a titer of 0.9988 at 25 °C – and for non-aqueous solutions this difference is even larger In such a case a titer of 1.0000

con-at 20 °C becomes a titer of 0.9950 con-at 25 °C (possible error 0.5%)!

Normally the titer determination is carried out three times and the mean value is used The mean value of the titer** is best saved as a «Common Variable» (e.g C30) in the Titrino

** In Europe a dimensionless factor, with at least 4 decimal places (e.g 1.0015).

In the USA already multiplied by c, with at least 4 decimal places (e.g 1.0015 mol/L).

• c(NaOH) = 0.1 mol/L

If possible this titrant should be bought ready for use Otherwise dissolve 4.0 g NaOH in CO2-free dist H2O, make up to 1 liter and mix

• c(KOH) = 0.1 mol/L in ethanol or isopropanol (IPA)

If possible this titrant should be bought ready for use Otherwise dissolve 5.6 g KOH in approx 25 mL CO2-free dist H2O, allow to cool down and then make up to 1 liter with ethanol or IPA and mix

• Comb pH glass electrode for aqueous titrations and 6.0229.100 Solvotrode (electrolyte solution 6.2320.000) for non-aqueous titrations, with 6.2104.100 electrode cable

is then immediately titrated to after the first endpoint with c(base) = 0.1 mol/L.

1 mL c(base) = 0.1 mol/L corresponds to 20.423 mg KH-phthalate (C01)

Titer = C00 / C01 / EP1

EP1 = mL base up to endpoint C00 = weight of KH-phthalate in mg C01 = 20.423

%0 4ITER

STOP

• Exchange Unit 6.3026.220

Tris(hydroxymethyl)-aminomethane (TRIS) is dried overnight in a drying oven

at 105 °C and allowed to cool down in a desiccator for at least 1 h Approx 100

mg TRIS is weighed out into the titration beaker with an accuracy of 0.1 mg and dissolved in approx 50 mL dist H2O It is then immediately titrated with HCl or H2SO4 to after the first endpoint

1 mL c(HCl) = 0.1 mol/L or 1 mL c(H2SO4) = 0.05 mol/L corresponds to

12.114 mg TRIS (C01)

Titer = C00 / C01 / EP1

EP1 = mL acid up to endpoint C00 = weight of TRIS in mg C01 = 12.114

%0 4ITER

STOP

Titration curve

If possible this titrant should be bought ready for use Otherwise weigh out

25 g pure, iodate-free potassium iodide into a 1000 mL volumetric flask and dissolve in 40 mL dist H2O Add 12.8 g iodine, seal the flask and shake it until the iodine has dissolved completely Make up to the mark with dist H2O and mix

• 6.0431.100 Pt Titrode with 6.2104.020 electrode cable

• 6.3026.220 Exchange Unit

Approx 200 250 mg Na2S2O3 x 5 H2O is weighed out into the titration beaker

with an accuracy of 0.1 mg, treated with 5 mL c(CH3COOH) = 2 mol/L and luted with dist H2O to approx 80 mL The solution is then titrated with c(I2) = 0.05 mol/L to after the first endpoint

di-1 mL c(I2) = 0.05 mol/L corresponds to 24.817 mg Na2S2O3 x 5 H2O (C01)

Titer = C00 / C01 / EP1

EP1 = mL iodine solution to endpoint

C01 = 24.817

%0 4ITER

STOP

If possible this titrant should be bought ready for use Otherwise weigh out

25 g Na2S2O3 x 5 H2O into a 1000 mL volumetric flask, dissolve in CO2-free dist H2O, use this to make it up to the mark and mix

• 6.0431.100 Pt Titrode with 6.2104.020 electrode cable

iodide and 10 mL w(H2SO4) = 25% and titrate immediately with c(Na2S2O3) =

0.1 mol/L to after the first endpoint

1 mL c(Na2S2O3) = 0.1 mol/L corresponds to 3.567 mg KIO3 (C01)

Titer = C00 / C01 / EP1

EP1 = mL thiosulfate solution up to endpoint

C01 = 3.567

%0 4ITER

STOP

ad-• 6.0431.100 Pt Titrode with 6.2104.020 electrode cable

accu-w(H2SO4) = 25%, warmed to 50 60 °C and titrated with c(KMnO4) = 0.02 mol/L

to after the first endpoint The titration is also possible at room temperature if approx 0.5 g MnSO4 is added to the solution as catalyst before the titration

1 mL c(KMnO4) = 0.02 mol/L corresponds to 6.70 mg Na2C2O4 (C01)

Titer = C00 / C01 / EP1

EP1 = mL permanganate solution up to endpoint

C01 = 6.7

%0 4ITER

STOP

of 0.1 mg and dissolved in approx 50 mL dist H2O After the addition of 1 mL

%0 4ITER

STOP

• c(Na2EDTA) = 0.1 mol/L

If possible this titrant should be bought ready for use Otherwise weigh out 37.224 g Na2EDTA x 2 H2O into a 1000 mL volumetric flask, dissolve in dist

H2O, make up to the mark and mix

• 6.0508.110 or 6.0504.100 Ca ISE with 6.2104.020 electrode cable and 6.0726.107 Ag/AgCl reference electrode with 6.2106.020 electrode cable

• 6.3026.220 Exchange Unit

Calcium carbonate is dried overnight in a drying oven at 140 °C and allowed to cool down in a desiccator for at least 2 h

Approx 100 mg CaCO3 is weighed out into the titration beaker with an accuracy

of 0.1 mg and suspended in approx 20 mL dist H2O Under stirring c(HCl) =

5 mol/L is added drop by drop until everything has dissolved completely After the addition of 30 mL dist H2O and 5 mL buffer solution pH = 10** the solution

is titrated with c(Na2EDTA) = 0.1 mol/L to after the first endpoint

%0 4ITER

STOP

General Drinking water is the foodstuff par excellence, which is why the methods used

for examining it are placed at the start of this collection Nine titrimetric analyses – Food PAC covers only these – are described in subsections Of course, these methods can also be used for other types of water

Other determinations that can be carried out in water with Metrohm instruments are:

• Bromate, bromide, chloride, fluoride, nitrate, nitrite, phosphate, ammonium, potassium, sodium, strontium, etc by ion chromatography (IC)

• Aluminum, arsenic, lead, cadmium, chromium, iron, copper, manganese, mercury, zinc, etc by voltamperometry/polarography (VA)

• Electrical conductivity (and pH value)Assessment of the analytical results has been deliberately ignored in Food PAC Please consult the relevant literature for assessment criteria

C 1 pH value and acid capacity (carbonate hardness)

For the acid capacity up to pH 8.2 (KA 8.2 , previously p value) HCl is used to titrate to pH = 8.2; for the acid capacity up to pH 4.3 (KA 4.3 , previously m value) the titration is to pH = 4.3

• 6.0253.100 Aquatrode Plus with 6.2104.020 electrode cable

• 6.3026.220 Exchange Unit

• Titrant: c(HCl) = 0.1 mol/L (Method 4) For very soft water possibly use

c(HCl) = 0.02 mol/L.

The Aquatrode has already been calibrated as per Method 1

100 mL water sample is added to the titration beaker The pH value is first

mea-sured under stirring The sample is then titrated with c(HCl) = 0.1 mol/L using

pH = 3.5 as the stop criterion

KA 8.2 = EP1* x C01 x C02 x C30

KA 4.3 = EP2** x C01 x C02 x C30EP1* = mL HCl until first endpoint is reached or a fixed EP at pH = 8.2

(e.g C51)EP2** = mL HCl until second endpoint is reached or a fixed EP at pH = 4.3

(e.g C52)C01 = concentration of HCl in mol/L (0.1 or 0.02)C02 = 10 (conversion factor for mmol/L if 100 mL sample is used)C30 = titer of HCl used (Method 4)

• Many waters have an initial pH value below 8.2 – KA 8.2 is not found and fore cannot be calculated (only EP1 at pH = 4.3)

there-• For calculating the carbonate hardness please refer to table under C 2

• If the CO2 content is to be determined in carbonated waters (Method 17) then

KA 4.3 is saved in the Titrino as a Common Variable (e.g C35)

Calculations

(Results given to two

decimal places)

C 1 pH value and acid capacity

(carbonate hardness)

Instrument parameters and calculation

Result Titration curve

tFR



$ATE P(CINIT SMPL

+S +S STOP

.O

$%4

 DATE

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

C 1 pH value and acid capacity (carbonate hardness)

#

Result – pH Instrument parameters and calculation – pH

Titration curve – pH

C 1 pH value and acid capacity

C 2 Calcium and magnesium

As Al, Ba, Fe, Mn and Sr ions only occur in drinking water in small amounts (if

at all) in drinking and mineral water, the titrimetric determination is limited to calcium and magnesium

• 6.0508.110 or 6.0504.100 Ca ISE with 6.2104.020 electrode cable, and

• 6.0726.107 LL Ag/AgCl reference electrode with 6.2106.020 electrode cable

• Exchange Unit 6.3026.220

• Titrant: c(Na2EDTA) = 0.1 mol/L (Method 9)

• Auxiliary complexing solution: c(acetylacetone) = 0.1 mol/L plus c(TRIS) =

0.2 mol/L 20.4 g tris(hydroxymethyl)-aminomethane is weighed out into a

1000 mL volumetric flask and dissolved in approx 500 mL dist H2O 12 mL acetylacetone is added and the solution is made up to the mark with dist H2O and mixed

100 mL water sample is pipetted into the titration beaker 15 mL auxiliary

com-plexing solution is added and titrated with c(Na2EDTA) = 0.1 mol/L to after the

C00 = sample volume in mL (100) C01 = 4.008

C02 = 1000 (for 1 liter) C03 = 2.431

The following table provides information about the different «degrees of ness»:

hard-Calculations

(The results are given to

two decimal places.)

C 2 Calcium and magnesium (Ca, Mg and total hardness)

Total hardness comparison table

17.92

>9.50

17.22 moderately hard3.2 4.2 320 420 >32 42 >17.92

C 2 Calcium and magnesium

%0

%0

#A -G 4OTAL STOP

$%4

 DATE

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

100 mL water sample is pipetted into the titration beaker After adding 5 mL

ni-tric acid titrate with c(AgNO3) = 0.01 mol/L to after the first endpoint

1 mL c(AgNO3) = 0.01 mol/L corresponds to 0.3545 mg chloride

mg/L chloride = EP1 x C01 x C02 x C30 / C00

C00 = sample volume in mL C01 = 0.3545

C02 = 1000 (for 1 liter)

• The Ag2S coating on the Ag Titrode provides short response times and creases the long-term stability of this electrode

in-• If a sample contains sulfides or hydrogen sulfide then these are comprised

in the first, very distinct endpoint Chloride is then calculated from the ence EP2 – EP1

#HLORIDE STOP