1、September 2004DEUTSCHE NORM English price group 11No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 75.080!$Qdl“14665
2、73www.din.deDDIN 51451Testing of petroleum products and related products Analysis by infrared spectrometry General working principlesPrfung von Minerallerzeugnissen und verwandten Produkten Infrarotspektrometrische Analyse Allgemeine ArbeitsgrundlagenSupersedesDIN 51451:1988-09www.beuth.deIn case of
3、 doubt, the German-language original should be consulted as the authoritative text.Translation by DIN-Sprachendienst.Document comprises 18 pagesDIN 51451:2004-09 2 Foreword This standard has been prepared by Technical Committee Moleklspektrometrie of the Fachausschuss Minerall- und Brennstoffnormung
4、 of the Normenausschuss Materialprfung (Materials Testing Standards Committee). Amendments This standard differs from DIN 51451:1988-09 as follows: a) The FT (Fourier-Transform) instruments have been included in addition to the grating instruments (see clause 5 and Annex A). b) Clause 2 “Normative r
5、eferences” has been added. c) Further information relating to instrument checking and alignment has been included. d) A new Figure 2 “Baseline method (linear absorbance ordinate)” has been added. Previous editions DIN 51451: 1988-09 1 Scope This standard specifies the principles governing the use of
6、 infrared (IR) spectrometry for analysing products based on petroleum and synthetic oils, including their additives. This standard covers the standard procedures for qualitatively identifying and for semi-quantitatively and quantitatively determining the contents of individual constituents. The purp
7、ose of the standard is to facilitate the preparation of standards governing the analysis of special groups of substances by IR spectrometry, thereby reducing their individual volumes, and to standardize the associated working procedures as early as possible. 2 Normative references This standard inco
8、rporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the titles of the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publications apply
9、 to this standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication (including amendments) referred to applies. DIN 12491, Vacuum desiccators for laboratory use DIN 32635, Concepts, symbols and units relating to the spectrophotometri
10、c analysis of solutions DIN 50011-11, Artificial climates in technical applications Controlled-atmosphere test installations General concepts and requirements DIN 51451:2004-09 3 DIN 50011-12, Artificial climates in technical applications Air temperature as a climatological quantity in controlled-at
11、mosphere test installations DIN 51820-1, Infrared spectrometric analysis of lubricating greases Recording and evaluation of infrared spectra 3 Principle The attenuation of the infrared radiation in an irradiated sample is recorded as a function of wavelength. The position of the absorption bands and
12、 their magnitude in the spectrum obtained enables the sample to be analysed qualitatively and quantitatively. 4 General 4.1 Theoretical principles On passing through a transparent, homogeneous medium, radiation is attenuated by reflection, scattering and absorption. Neglecting reflection and scatter
13、ing, the absorption is related to the content of an individual absorbing substance in a nonabsorbing solvent and the path length by the Lambert-Beer-Bouguer law (equation 1): dcE = lglgae(1) =ea100% (2) where e, aare the radiant powers of the radiation entering and leaving the sample, respectively;
14、is the net transmittance (also referred to as transmission T), i.e. the ratio of the radiant power atransmitted by the sample to the incident radiant power e, which is often reported as a percentage (see equation (2); E is the absorbance (cf. DIN 32635); NOTE 1 In international usage, the symbol A()
15、 is also used for the absorbance. is the molar absorptivity, in m2/mol, if the concentration is expressed in mol/l and the path length in mm (if other units are used, the molar absorptivity is denoted by and the resultant unit shall then be specified); c is the concentration of the absorbing substan
16、ce, usually in mol/l; d is the path length (the optical distance traversed in the sample), in mm. NOTE 2 The net transmittance, was previously referred to as transmission T. The radiant powers, aand e, were previously referred to as intensities I and I0. DIN 51451:2004-09 4 is often very dependent o
17、n the chosen solvent and can be altered by interactions, for example association, between individual components in the sample under examination. The total absorbance, Etot, at a given wavelength for a multicomponent mixture is the sum of the contributions Ei,of the components i in the mixture as in
18、equation 3: =iicdEE,ii,tot,(3) If the individual molar absorptivities, i, are known, the contents of individual components i or, under favourable circumstances, of all the components i in a mixture can be determined by measuring Etot,at a number of wavelengths . 4.2 Units Wavelength Normally m is us
19、ed for wavelength (1 m = 106m) Wavenumber Normally cm1for wavenumber (1 cm1= 102m1; = 10 000/) Molar concentration c Normally mol/l is used for molar concentration c Proportion by mass w Normally g/100 g (i.e. % (m/m) or mg/kg are used for proportion by mass w Proportion by volume Normally ml/100 ml
20、 (i.e. % (V/V) is used for proportion by volume . NOTE 3 The name and/or the quantity symbol of the physical quantity percentages, e.g. proportion by mass or m/m, shall be stated for percentages specified without naming the units (e.g. g/100 g or ml/100 ml). NOTE 4 Other units, e.g. g/l or g/ml, are
21、 permitted, but the symbol used in the equation shall carry a prime (e.g. ). 5 Apparatus 5.1 IR spectrometer 5.1.1 General In principle, both grating and FT (Fourier-Transform) instruments can be used for petroleum analysis, but FT instruments are generally preferred because of their greater capabil
22、ities. Instruments using prism monochromators are now obsolete. Instruments using filter monochromators are obtainable on the market, but do not figure in this standard since most IR analyses in the petroleum sector require the recording and evaluation of an entire spectral range and not of a single
23、 wavelength. The double-beam instruments used in the past are being increasingly replaced by single-beam instruments in which the optical correction used in the former is replaced by sequential measurement with subsequent correction by calculation. Further information on the design features of moder
24、n spectrometers will be found in Annex A. DIN 51451:2004-09 5 5.1.2 Minimum requirements The specific requirements in a standard, e.g. relating to wavenumber precision, resolution and repeatability, shall be specified, where necessary, in the individual test standards. However, as far as possible, t
25、he following minimum requirements shall be fulfilled for the analysis of petroleum products in the mid-IR range: Wavenumber : 4 000 cm1to 600 cm1(abscissa) Resolution: 4 cm1min Wavenumber precision: 1 cm1max Ordinate repeatability: 1 % max over the entire range Information on how to check whether th
26、ese requirements are met will be found in clause 8 of this standard. Facilities for flushing the instrument with purified and dry gases to avoid interfering absorption bands due to atmospheric water and carbon dioxide are to be recommended. In some instruments, a correction with software is possible
27、. 5.2 Cells The following two types of cells are in use. a) Cells that can be tightly sealed and have a fixed, defined path length. These are suitable for quantitative work on liquids, suspensions and gases. b) Cells that can be dismantled but can be tightly sealed for use with liquids and suspensio
28、ns. Such cells are predominantly only suitable for qualitative work. During assembly care shall be taken that the windows are plane-parallel. Lead or polytetrafluoroethylene (PTFE) spacers shall be used to set the path length to the required value. The latter shall be determined or checked as specif
29、ied in subclause 8.2. The choice of path length will depend on the purpose of measurement and shall be specified in the individual test standards. The windows shall be made of a material that is not attacked by the sample or the solvent and is transparent in the chosen spectral range. Examples of co
30、mmon window materials are given in Table 1. The windows shall be plane; if this is not clearly the case, they shall be re-ground and re-polished. The window material and the cells shall be stored in a desiccator over a drying agent or in a heated drying cabinet at about 40 C. Further information on
31、care, cleaning and selection will be found in the relevant literature, the manufacturers information and the individual test standards. NOTE Cells having an adjustable path length are particularly suitable for optically correcting solvent absorption in a double-beam spectrometer. DIN 51451:2004-09 6
32、 Table 1 Common window materials Material Reflection loss, % Usable range, cm1Quartz glass for infrared applications 6 approx. 50 000 to 2 500 Lithium fluoride (LiF) 4,4 approx. 50 000 to 1 500 Sodium chloride (NaCl) 7,5 approx. 50 000 to 625 Calcium fluoride (CaF2) 5,6 approx. 50 000 to 1 000 Silve
33、r chloride (AgCl) 19,5 approx. 50 000 to 400 Potassium bromide (KBr) 8,4 approx. 50 000 to 370 Zinc selenide 30 approx. 10 000 to 445 Barium fluoride 7,7 approx. 50 000 to 670 Caesium iodide (Csl) 13,6 approx. 50 000 to 200 5.3 Other apparatus Equipment for grinding and polishing salt windows. Press
34、 with tool for producing potassium bromide (KBr) discs of an appropriate size for the IR spectrometer sample holder at a pressure of at least 2 000 N/cm2. The die shall be evacuable and fit the press precisely. Disc sample holder. Agate mortar and pestle or suitable mill. Suitable glass syringes for
35、 filling cells. DIN 50011-11 and DIN 50011-12 oven suitable for temperatures up to 150 C. Vacuum desiccator (e.g. as in DIN 12491) or heatable drying cabinet for storing cells, window material and KBr powder. Special instrument accessories, such as ATR (attenuated total reflection) accessories, are
36、not dealt with in greater detail in this standard; any special procedures shall, if necessary, be described in the relevant test standard. 6 Reagents CAUTION Users of this standard should be familiar with standard laboratory practice. It is not claimed that all the safety problems associated with th
37、e use of the standard have been dealt with exhaustively here. It is therefore the responsibility of the user to take appropriate safety precautions and to ensure that these comply with national regulations. CAUTION In view of its toxicity, carbon tetrachloride is a serious health hazard if inhaled o
38、ver a rather long period. It may also damage the ozone layer. DIN 51451:2004-09 7 6.1 Potassium bromide, KBr, for spectroscopy, very finely ground and dried for at least 24 hours at 150 C. Crystalline fragmented material is also suitable. The dried potassium bromide powder shall be stored in a desic
39、cator over a drying agent and shall be checked for optical purity before use. 6.2 Solvents The solvent used shall not have any interfering absorption in the analytical spectral range. Carbon tetrachloride (CCl4) is frequently used for the following spectral ranges: 4 000 cm1to about 1 650 cm1 1 450
40、cm1to about 1 300 cm1 600 cm1to about 400 cm1Carbon tetrachloride may also be used for the 1 650 cm1to 930 cm1range in cells having a path length of less than about 0,025 mm. Where there is a choice between several solvents, the safest shall always be chosen. 6.3 Paraffin oil, for spectroscopy. 6.4
41、Cleaning solvents The cleaning solvent shall be free of impurities that may be deposited as a film on the window material. If cleaning agents are used that have to be evaporated, steps shall be taken to prevent moisture from condensing on the window material during cooling. For health and environmen
42、tal reasons, it is nowadays inadvisable to use the halogenated solvents frequently employed in the past. Safer cleaning solvents include special boiling-point spirit, isopentane/propanol, etc. 6.5 Wavenumber calibration checking materials These include the following: Polystyrene film, about 40 m thi
43、ck. Special types are obtainable that have a roughened surface to improve their interference properties. Analytical grade toluene (see Table 2). The band positions and spectra of these and other materials used for checking the wavenumber shall be specified in the relevant test standards. Other infor
44、mation will be found in the relevant literature.1)7 Sample preparation If the sample under examination cannot be analysed in a cell for liquids as specified in subclause 5.2, it shall preferably be prepared for measurement in one of the following ways: by dissolving it in a suitable solvent for qual
45、itative and quantitative work; by suspending it in paraffin oil for qualitative and (to a limited extent) for quantitative measurements; 1) Spectrochimica Acta, Vol. 20, pp. 11751183 (1964) ASTM E 275 83 PACHA, Vol. 1, No. 4, pp 678683 (1964) DIN 51451:2004-09 8 by preparing a film of it for qualita
46、tive work; by combining it with potassium bromide to form a disc, but preferably for qualitative work only since experience has shown that the results of the quantitative analysis of discs are only moderately reproducible. 8 Preparation for measurement 8.1 Instrument checking and alignment 8.1.1 Spe
47、ctrometer The spectrometer shall be checked and aligned for serviceability as specified by the manufacturer. Depending on the instrument and manufacturer, it may be necessary to make various adjustments, such as zeroing. Nowadays, many manufacturers offer calibration materials, such as polystyrene f
48、ilms or glass filters, either built into their instruments or separately, together with suitable software that make it possible to check and align the instrument, including the preparation of protocol, sometimes already automated. The methods described below may be used to check the basic functionin
49、g of the spectrometer. To perform these tests it is necessary to store the following spectra, which shall be recorded with a resolution of about 4 cm1in about four minutes. Spectrum S1: irradiation spectrum with no sample in the cell. Spectrum S2: irradiation spectrum with no sample in the cell, recorded immediately after spectrum S1. Spectrum S3: the spectrum of a polystyrene film (6.5) stored as a transm
