OIL Potentiometric Analysis Collection OIL PAC 6 6040 003 Methods for the titrimetric / potentiometric analysis of petrochemical products Dear User, You have decided to purchase a Metrohm titrator who[.]
OIL Potentiometric Analysis Collection OIL PAC 6.6040.003 Methods for the titrimetric / potentiometric analysis of petrochemical products Dear User, You have decided to purchase a Metrohm titrator whose collection of methods is specially adapted to your particular requirements Metrohm always tries to provide its customers with as comprehensive a range of support as is possible in order to facilitate daily analytical work In this Application binder you will find descriptions of the corresponding analytical methods with comments, explanations and - particularly important - printouts of the instrument parameters and examples of curves All these methods are stored on the Method memory card You only need to insert the card, load the required method into the titrator's working memory and off you go!!! We hope that your work will be both pleasant and successful, Your Metrohm Additional information – These methods have been drawn up taking into account the latest standards In particular, they make use of the newest methods and the newly developed Metrosensors, which have been specially designed for nonaqueous titrations – All methods have been designed so that you can adopt them in your oil laboratory as so-called SOPs (Standard Operating Procedures) – Of course, almost all these methods, at least as far as their titration part is concerned, can be further automated In the Appendix you will find an example of the complete automation of the titrimetric determination of the base number For details please contact your local Metrohm supplier, whose address can be found on the Internet under: www.metrohm.com Distributors – The Method memory card supplied can be used with the 785 and 751 Titrinos (from program version 20) You or your Metrohm supplier can also use the demo version of VESUV 3.0 (VESUV = Verification Support for Validation), which is also supplied, to load the parameter sets into the 716, 736 or 751 Titrinos (751: formula Titer=C00/C01/EP1 RS1 text Titer RS1 decimal places RS1 unit: RS1 limit control: OFF >silo calculations match id: OFF >common variables C30=MN1 >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-13 time 11:31 DET U M1.1 C-fmla C01 20.423 Method 1.2 Page Method – Determination of the base number Recommended accessories • 6.3014.223 Exchange Unit, 20 mL • 6.0229.100 Solvotrode; 6.2312.000 electrolyte diluted 1:1 with ethanol (approx mol/L LiCl in ethanol) • 6.2104.020 electrode cable General Components in oil products that exhibit a basic reaction are determined as a cumulative total under the base number These are chiefly primary organic and inorganic amino compounds, but the salts of weak acids and basic salts of polycarboxylic acids, as well as some heavy metal salts and detergents, are also determined The determination is used to assess relative alterations during the working life of the product Definition The base number is the amount of basic components, expressed as mg KOH, that is contained in g sample Reagents – Titrant: c(HClO4) = 0.1 mol/L in glacial acetic acid – Solvent mixture I: glacial acetic acid/toluene 1:1 – Solvent mixture II: glacial acetic acid/chlorobenzene 1:2** – Buffer solution pH = 4.0 (6.2307.100) and pH = 7.0 (6.2307.110) – Ethanol, dist H2O, hexane ** For environmental reasons the use of this solvent mixture should be avoided Electrode storage, maintenance and checks – When not in use the Solvotrode is stored in electrolyte solution (approx mol/L LiCl in ethanol) – Before use the electrode is placed in dist H2O overnight – After each titration the electrode is rinsed with solvent mixture, then with ethanol and finally with dist H2O It is then immersed for in dist H2O, rinsed with ethanol and the next sample is titrated The ground joint of the diaphragm is loosened from time to time so that electrolyte can flow out The joint is then lightly pressed together again If precipitates are formed on the electrode during the titration (occurs with used oils and with some additives) then these are removed by placing the electrode in a stirred solution of hexane – In order to check the electrode functions (slope, response behavior, etc) please proceed as follows: Rinse the electrode with dist H2O and dab it dry with a soft tissue (e.g Kleenex) Immerse in buffer solution pH = 7.0, stir for and then read off the potential in mV After rinsing with dist H2O and dabbing it dry the same procedure is repeated in buffer solution pH = 4.0 With good electrodes a potential difference of >150 mV is obtained at 20 25 °C If the difference is formula Titer=C00/C01/EP1 RS1 text Titer RS1 decimal places RS1 unit: RS1 limit control: OFF >silo calculations match id: OFF >common variables C36=MN1 >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:38 DET U M21.2 C-fmla C01 5.045 Page Method 21 – Titer determination of EDTA solutions Method parameters & calculations 'pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:41 DET U M21.3 parameters >titration parameters meas.pt.density min.incr 10.0 µl dos.rate max ml/min signal drift 30 mV/min equilibr.time 32 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 20 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: ON mean n= res.tab: original >evaluation EPC EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF -'de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:41 DET U M21.3 def >formula Titer=C00/C01/EP1 RS1 text Titer RS1 decimal places RS1 unit: RS1 limit control: OFF >silo calculations match id: OFF >common variables C36=MN1 >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:41 DET U M21.3 C-fmla C01 10.09 Page Titration curve Method 21.3 Method 22 – Total content of Ba, Ca, Mg, Pb and Zn in unused lubricating oils Recommended accessories • 6.3014.153 Exchange Unit(s), mL, or 6.3014.213, 10 mL • Spectrode 610 nm, 6.5501.01X or General • 6.3014.223 Exchange Unit, 20 mL • 6.0502.140 Cu ISE with 6.2104.020 electrode cable • 6.0726.017 Ag/AgCl reference electrode with 6.2106.020 electrode cable Apart from other additives, lubricating oils also have metal soaps (e.g barium arylsulfonates) added to them Ba, Ca, Mg, Pb and Zn are the metal ions chiefly used The method is only suitable for unused lubricating oils or the corresponding raw materials As already explained in Method 21, in the titration with EDTA it is always the total content of the metal ions listed above that is determined – separation is not possible! Method A describes the determination of the total content of mixtures that may contain Ba, Ca, Mg, Pb and Zn The metals are complexed with EDTA in semiaqueous solution and the excess EDTA is photometrically back-titrated with Mg Method B is used for mixtures that not contain Ba and/or Pb The sample is ashed and Ca, Mg and Zn are titrated potentiometrically with EDTA Indication is by the Cu ISE Definition Total content of the metal ions Ba, Ca, Mg, Pb and Zn in mmol/kg sample Method 22.1 – Photometric titration of Ba, Ca, Mg, Pb and Zn Reagents – c(Na2EDTA) = 0.025 mol/L: preparation and titer determination see Method 21 – Buffer solution pH = 10: preparation see Method 21 – Color indicator Eriochrome black T: preparation see Method 21 – Titrant c(MgCl2) = 0.025 mol/L: 5.083 g MgCl2 x H2O, e.g Merck No 116102 «Fractopur», is dissolved in dist H2O and then made up to liter – Solvents: toluene and isopropanol, analytical grade Sample preparation Table, metal content (abs.) The sample weight depends on the metal ion content It should be selected so that the consumption of c(Na2EDTA) = 0.025 mol/L does not exceed mL See the following table The sample is weighed into a 100 mL volumetric flask, dissolved in and made up to the mark with toluene and mixed Metal Atomic mass Minimum Maximum 137.33 g/mol 30 mg 140 mg Lead 207.2 g/mol 50 mg 200 mg Calcium 40.08 g/mol 10 mg 40 mg 24.305 g/mol mg 25 mg 65.38 g/mol 15 mg 65 mg Barium Magnesium Zinc Page Method 22 – Total content of Ba, Ca, Mg, Pb and Zn in unused lubricating oils The titer of the EDTA solution has already been determined in Method 21 (common variable C36) Analysis 10.0 mL prepared sample solution is pipetted into a beaker and treated with 10 mL toluene and 50 mL isopropanol under stirring Then mL buffer solution pH = 10 and 5.00 mL c(Na2EDTA) = 0.025 mol/L are added If oil droplets are formed then further toluene is added until they have dissolved The Spectrode and buret tip are immersed in the solution, 0.5 mL Eriochrome black T is added and the excess EDTA is back-titrated with c(MgCl2) = 0.025 mol/L (instrument parameters and an example of a curve are given in the appendix) mL c(Na2EDTA) = 0.025 mol/L corresponds to 0.025 mmol Me Calculation mmol Me / kg = (C01 - EP1) x C36 x C02 x C03 / C00 C00 = 1/10 sample weight in g C01 = (volume of Na2EDTA in mL) C02 = 0.025 (titrant concentration in mol/L) C03 = 1000 (for kg) C36 = titer of Na2EDTA Method 22.2 – Potentiometric titration of Ca, Mg and Zn – Titrant: c(Na2EDTA) = 0.1 mol/L Preparation and titer determination see Method 21 Reagents – Buffer solution pH = 10: preparation see Method 21 – Cu complexing solution: c[Cu(NH4)2EDTA] = 0.1 mol/L; Merck No 105217 – Hydrochloric acid: w(HCl) = 30 35%, analytical grade – Sodium hydroxide: c(NaOH) = mol/L The sample weight depends on the metal ion content It should be selected so that the consumption of c(Na2EDTA) = 0.1 mol/L is mL See the following table The sample is weighed into a platinum crucible and completely ashed at 900 °C in a muffle furnace After cooling down the white ash is dissolved in a little HCl and rinsed into a beaker with dist H2O Metal Calcium Magnesium Zinc Atomic mass mg metal / sample 40.08 g/mol 20 24.305 g/mol 12 65.38 g/mol 33 The titer of the EDTA solution has already been determined in Method 21 (common variable C36) The acidic sample solution in the beaker is made up to approx 50 mL with dist H2O and the pH adjusted to with NaOH After the addition of mL buffer solution pH = 10 and mL Cu complexing solution the electrodes (Cu ISE and reference electrode) and the buret tip are immersed in the solution which is then titrated with c(Na2EDTA) = 0.1 mol/L (instrument parameters and an example of a curve are given in the appendix) Page Sample preparation Table, metal content (abs.) Analysis Method 22 – Total content of Ba, Ca, Mg, Pb and Zn in unused lubricating oils Calculation mL c(Na2EDTA) = 0.1 mol/L corresponds to 0.1 mmol Me mmol Me / kg sample = EP1 x C36 x C01 x C02 / C00 C00 = sample weight in g C01 = 0.1 (titrant concentration in mol/L) C02 = 1000 (for kg sample) C36 = titer of titrant Remarks This method is not suitable for the determination of Ba and/or Pb, as insoluble sulfates (from the sulfonates) are formed during the ashing process Page Method 22 – Total content of Ba, Ca, Mg, Pb and Zn in unused lubricating oils Method parameters & calculation Titrations curve Method 22.1 'pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:55 MET U M22.1 parameters >titration parameters V step 0.10 ml dos.rate max ml/min signal drift 30 mV/min equilibr.time 32 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 20 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: OFF >evaluation EPC 30 mV EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF -'de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:55 MET U M22.1 def >formula mmol/kg=(C01-EP1)*C36*C02*C03/C00 RS1 text mmol/kg RS1 decimal places RS1 unit: Me RS1 limit control: OFF >silo calculations match id: OFF >common variables >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:55 MET U M22.1 C-fmla C01 C02 0.025 C03 1000 Page Method 22 – Total content of Ba, Ca, Mg, Pb and Zn in unused lubricating oils Method parameters & calculation ‘pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:59 DET U M22.2 parameters >titration parameters meas.pt.density min.incr 10.0 µl dos.rate max ml/min signal drift 20 mV/min equilibr.time 38 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 10 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: OFF >evaluation EPC EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF —————— ‘de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:59 DET U M22.2 def >formula mmol/kg=EP1*C36*C01*C02/C00 RS1 text mmol/kg RS1 decimal places RS1 unit: Me RS1 limit control: OFF >silo calculations match id: OFF >common variables >report report COM1:full;curve; >mean MN1=RS1 >temporary variables —————— ‘cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 08:59 DET U M22.2 C-fmla C01 0.1 C02 1000 —————— Titration curve Method 22.2 Page Method 23 – Ca and Mg in water (water hardness) Recommended accessories General • 6.3014.223 Exchange Unit, 20 mL • 6.0504.100 Ca ISE with 6.2104.020 electrode cable • 6.0726.107 Ag/AgCl reference electrode with 6.2106.020 electrode cable The determination of the Ca, Mg and total hardness in water is carried out very frequently throughout the world (also in oil industry laboratories) The method described below allows the simultaneous determination of Ca and Mg by a potentiometric titration using the Ca ISE This is made possible by adding an auxiliary complexing agent (acetylacetone) to the sample This additive also has the advantage that it masks Al, Fe and Mn ions so that they not interfere The titration is carried out with EDTA in an alkaline sample solution buffered with TRIS Definition Ca and Mg and total hardness in process and drinking water in mmol/L Reagents – Titrant: c(Na2EDTA) = 0.05 mol/L Preparation and titer determination see Method 21.2 – Auxiliary complexing solution: 10 g acetylacetone (e.g Merck No 109600) and 12.1 g tris-(hydroxymethyl)aminomethane (e.g Merck No 108387) are dissolved in dist H2O and then made up to liter Analysis 100 mL water sample is measured out into a beaker and treated with 15 mL auxiliary complexing solution The electrodes and buret tip are immersed and the solution is titrated with c(Na2EDTA) = 0.05 mol/L Two endpoints are obtained EP1 corresponds to Ca, the difference between EP1 and EP2 to Mg (instrument parameters and an example of a curve are given in the appendix) Calculations Ca hardness in mmol/L = EP1 x C01 x C36 x C02 / C00 Mg hardness in mmol/L = (EP2 - EP1) x C01 x C36 x C02 / C00 Total hardness in mmol/L = EP2 x C01 x C36 x C02 / C00 C00 = 100 (sample volume in mL) C01 = 0.05 (concentration Na2EDTA in mol/L) C02 = 1000 (for liter) C36 = titer c(Na2EDTA) = 0.05 mol/L Remarks – Ca ISEs that have been stored dry are conditioned for about 10 in c(CaCl2) = 0.01 mol/L before the determination – The Ca ISE should not be allowed to stand for a long time in a sample that has already been titrated as this shortens its working life – Samples that contain a lot of Ca but only a little Mg produce only one EP for the sum of the two ions In such cases an Mg standard is added to the auxiliary complexing solution, which is then added to the sample This addition must be subtracted again in the calculations Literature – Metrohm Application Bulletin No 125 Page Method 23 – Ca and Mg in water (water hardness) Method parameters & calculation 'pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 10:40 DET U M23 parameters >titration parameters meas.pt.density min.incr 10.0 µl dos.rate max ml/min signal drift 10 mV/min equilibr.time 52 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 10 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: OFF >evaluation EPC EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF -'de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 10:40 DET U M23 def >formula Ca=EP1*C01*C02*C36/C00 RS1 text Ca RS1 decimal places RS1 unit: mmol/L RS1 limit control: OFF Mg=(EP2-EP1)*C01*C02*C36/C00 RS2 text Mg RS2 decimal places RS2 unit: mmol/L RS2 limit control: OFF Total=EP2*C01*C02*C36/C00 RS3 text Total RS3 decimal places RS3 unit: mmol/L RS3 limit control: OFF >silo calculations match id: OFF >common variables >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 10:40 DET U M23 C-fmla C01 0.05 C02 1000 Page Titration curve Method 23 Method 24 – Pb in leaded gasoline Recommended accessories General • 6.3014.223 Exchange Unit, 20 mL • 6.5501.01X Spectrode 610 nm • Separating funnel 250 mL Leaded gasoline is decreasing in importance as a fuel for motor engines as most vehicles are now equipped with catalytic converters It is nevertheless important to be able to determine the lead content of «red» gasolines The Pb content of leaded gasoline is normally 0.026 1.3 g/L The method described is based on the following principle: A known volume of sample is diluted with lead-free «heavy distillate» and the tetraalkyllead converted with iodine monochloride Dialkyllead and the conversion products are extracted with water and any organic constituents in the aqueous extract are oxidized with nitric acid At the same time the lead compounds are converted to Pb(NO3)2 The lead nitrate is then titrated photometrically with EDTA Definition Lead content in g/L Pb at 15 °C (60 °F) Can also be given in g/US gal or g/UK gal Reagents – Titrant: c(Na2EDTA) = 0.005 mol/L 1.865 g Na2EDTA x H2O (e.g Merck No 108418, Titriplex III) is dissolved in dist H 2O, treated with mL c(NaOH) = mol/L and made up to liter with dist H 2O – Lead standard: c(Pb) = 0.005 mol/L 1.656 g Pb(NO3)2 analytical grade (e.g Merck No 107398) is treated with 10 mL conc HNO3, dissolved in dist H2O and then made up to liter – Acetate buffer: 23 g anhydrous sodium acetate is dissolved in dist H2O After the addition of 7.2 mL glacial acetic acid the solution is made up to liter with dist H2O – Color indicator (xylenol orange): 0.2 g xylenol orange tetrasodium salt is dissolved in dist H2O, treated with 0.5 mL c(HCl) = mol/L and made up to 100 mL with dist H2O The solution can be kept for approx week – Nitric acid: w(HNO3) = 65%, analytical grade – Ammonia: w(NH3) = 25%, analytical grade, diluted 1:1 with dist H2O – Iodine monochloride: 111.0 g potassium iodide is dissolved in approx 400 mL dist H2O in a 1000 mL volumetric flask and mixed with 445 mL conc HCl The mixture is allowed to cool down to room temperature and then 75.0 g KIO3 is slowly added under stirring Stirring is continued until a clear orange-red liquid is obtained The solution is made up to the mark with dist H2O – «Heavy Distillate»: Petroleum distillate with a low bromine number (fraction of approx 10% of 205 °C and approx 90% of 240 °C distillates) Page Method 24 – Pb in leaded gasoline 50 mL iodine monochloride and 25 mL «Heavy Distillate» are placed in the separating funnel The temperature of the sample is measured to 0.5 °C and then 25.0 mL sample is added to the separating funnel This is sealed immediately and shaken for 60 s The phases are then allowed to separate for a few minutes The lower aqueous phase is run off into an Erlenmeyer flask and the organic phase extracted a further three times with portions of 20 mL dist H2O (these aqueous extracts are also run off into the Erlenmeyer flask) A few glass boiling beads are added to the Erlenmeyer flask and its contents are heated and boiled off until a volume of 15 20 mL remains mL HNO3 are run into the boiling solution down the inner wall of the flask and heating is continued to virtual dryness The addition of HNO3 and heating to dryness are continued until a white deposit remains Sample preparation The titer of the EDTA solution is determined first 10.00 mL lead standard is added to a beaker and diluted to approx 70 mL with dist H2O 10 mL acetate buffer and drops of xylenol orange are then added and the solution is titrated with c(Na2EDTA) = 0.005 mol/L (instrument parameters and an example of a curve are given in the appendix) Analysis Calculation of the titer: Titer = C00 / EP1 C00 = 10 (added lead standard in mL) The titer is stored in the Titrino as common variable C37 Sample After cooling down, the deposit is dissolved in approx 200 mL dist H2O by heating and swirling it around It is allowed to cool down and the pH is adjusted to with NH3 solution 10 mL acetate buffer and drops of xylenol orange are then added and the solution is titrated with c(Na2EDTA) = 0.005 mol/L mL c(Na2EDTA) = 0.005 mol/L corresponds to 1.036 mg Pb Calculations g/L Pb = EP1 x C01 x C37 / C00 C00 = sample volume in mL*** C01 = 1.036 C37 = titer of titrant *** The sample volume must be converted to 15 °C The coefficient of expansion for gasoline is assumed to be 0.00065 / °C For conversion to a sample volume at 15 °C the result obtained above is multiplied by the following expression: + 0.00065 (t - 15) Example: the sample was measured at 22.5 °C and a content of 1.55 g Pb / L was obtained + 0.00065 (22.5 - 15) = 1.005 1.005 x 1.55 = 1.558 g/L Pb at 15 °C – ASTM D 3341-91 Standard Test Method for Lead in Gasoline – Iodine Monochloride Method Page Literature Method 24 – Pb in leaded gasoline Method parameters & calculation Titration curve Method 24 'pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:02 MET U M24 parameters >titration parameters V step 0.10 ml dos.rate max ml/min signal drift 30 mV/min equilibr.time 32 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 20 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: OFF >evaluation EPC 30 mV EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF -'de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:02 MET U M24 def >formula Pb=EP1*C01*C37/C00 RS1 text Pb RS1 decimal places RS1 unit: g/L RS1 limit control: OFF >silo calculations match id: OFF >common variables >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:02 MET U M24 C-fmla C01 1.036 Page Method 25 – Icing inhibitor additives in motor fuel Recommended accessories General • 6.3014.223 Exchange Unit, 20 mL • 6.0431.100 Pt Titrode with 6.2104.020 electrode cable • Reaction tubes (2.2 x 17.5 cm) • Separating funnel 125 mL Motor fuels have about 0.05 0.2% ethylene glycols added to them as icing inhibitors The following have proven themselves in practice: ethylene glycol monomethylether (EGME) and diethylene glycol monomethylether (DGME) The ethylene glycols are extracted from the sample with water The extracts are made strongly acidic and oxidized with potassium dichromate The excess dichromate is back-titrated iodometrically The oxidation of the ethylene glycols depends primarily upon the strength of the acid and is normally non-stoichiometric For this reason a so-called calibration factor is determined by using standard solutions (Φ = 0.1%; «volume %») and used in calculating the content Oxidation (theoretical): Cr2O72– + n H+ + C2H6O2 → CO2 + H2O + Cr3+ And for the titration: Cr 6+ + KI → Cr3+ + I2 I2 + Na2S2O3 + H2O → Na2S4O6 + HI Definition Φ(EGME) or Φ(DGME); «volume %» Reagents – Reaction solution: c(K2Cr2O7) = 0.0333 mol/L («0.2 N») 9.8064 g K2Cr2O7 analytical grade (e.g Merck No 104865) is dissolved in dist H2O, treated with mL conc H2SO4 and made up to liter with dist H2O – Titrant: c(Na2S2O3) = 0.1 mol/L (0.1 N), e.g Merck No 109147 – Ethylene glycol standards: These are unstable and must be freshly prepared before the determination by making 10.0 mL EGME* or DGME* up to liter with dist H2O and mixing thoroughly 10.0 mL of this mixture is pipetted into a 100 mL volumetric flask, made up to the mark with dist H2O and thoroughly mixed This mixture contains F(ethylene glycol) = 0.1% of the corresponding compound * Ethylene glycol monomethylether, e.g Merck No 100859 Diethylene glycol monomethylether, e.g Merck No 103617 – Potassium iodide: KI, reagent grade, e.g Merck No 105043 – Sulfuric acid: w(H2SO4) = 96%, e.g Merck «Suprapur» No 100714 Page Method 25 – Icing inhibitor additives in motor fuel 5.00 mL standard solution is pipetted into a reaction tube and treated with 10.0 mL potassium dichromate reaction solution The mixture is cooled in an ice bath and mL H2SO4 is slowly added while the tube is swirled about well It is very important that the mixture does not overheat! After cooling down again the reaction tube is placed in a boiling water bath for 10 After cooling down the reaction tube contents are rinsed quantitatively into a beaker with dist H2O The solution is treated with approx g KI and the released iodine is back-titrated with c(Na2S2O3) = 0.1 mol/L (instrument parameters and an example of a curve are given in the appendix) Pretitration for determining the calibration factor The calibration factor is determined three times and the average value stored in the Titrino as common variable C31 Calculation Calibration factor F = 0.005 (VD × ND) – (VT × NT) 0.005 = standard solution aliquot VD ND VT NT = 10 = volume of dichromate solution, in mL = 0.2 = x c(K2Cr2O7) = «normality» of dichromate solution, in mol/L = consumption of thiosulfate solution, in mL (EP1) = 0.1 = x c(Na2S2O3) = «normality» of thiosulfate solution, in mol/L 25.0 mL each of the sample and dist H2O are pipetted into a dry separating funnel The funnel is sealed and thoroughly shaken for After separation the lower aqueous phase is run off into a beaker 5.00 mL of the aqueous extract is pipetted into a reaction tube, treated like the standard solution and titrated in the same way See above «Pretitration for determining the calibration factor» RS1 = EP1 x C01 RS2 = Φ(ethylene glycols) in % = C31 x C02 x (C03 – RS1) C01 = 0.1 = x c(Na2S2O3) = «normality» of thiosulfate solution, in mol/L C02 = 20 (conversion factor) C03 = (VT x NT) C31 = calibration factor Page Sample analysis Calculations Method 25 – Icing inhibitor additives in motor fuel Method parameters & calculation 'pa 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:17 DET U M25 parameters >titration parameters meas.pt.density min.incr 10.0 µl dos.rate max ml/min signal drift 30 mV/min equilibr.time 32 s start V: OFF pause s meas.input: temperature 25.0 °C >stop conditions stop V: abs stop V 20 ml stop U OFF mV stop EP filling rate max ml/min >statistics status: OFF >evaluation EPC EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF >preselections req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF -'de 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:17 DET U M25 def >formula RS1=EP1*C01 RS1 text RS1 RS1 decimal places RS1 unit: RS1 limit control: OFF EG=(C31*C02)*(C03-RS1) RS2 text EG RS2 decimal places RS2 unit: % RS2 limit control: OFF >silo calculations match id: OFF >common variables >report report COM1:full;curve; >mean MN1=RS1 >temporary variables -'cf 785 DMP Titrino 02287 785.0010 date 2000-11-24 time 11:17 DET U M25 C-fmla C01 0.1 C02 20 C03 Titration curve Method 25 Page