ISO 9289:1991 download free.Oilseed residues – Determination of free residual hexane.
ISO 9289 specifies a method for the determination of the free residual hexane content In oilseed residues after extraction with hydrocarbon-based solvents,
2 NormatIve reference
The following standard contains provisions which, through reference in this text, constitute provisions of ISO 9289 At the time of publication. the edition Indicated was valid All standards are subject to revision, and parties to agreements based on ISO 9289 are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of (EC and ISO maintain registers of currently valid International Standards.
ISO 5500:1986, Oilseed residues — Sampling
3 DefinItion
For the purposes of ISO 9289, the following definition applies.
free residual hexane: Proportion of volatile hydrocarbons, referred to generally as hexane. remaining in oilseed residues after extraction with hydrocarbon-based solvents and which is desorbed directly by heating at 80 °C without the addition of water.
It is expressed as milligrams of n-hexane per kilogram of sample.
4 PrInciple
Desorption of hexane by heating at 80 °C In a closed vessel after addition of an internal standard. Determination of the hexane content in the head-space by gas chromatography using capillary or packed columns.
5 Reagents and materials
All reagents shall be of recognized analytical grade unless otherwise stated.
5.1 Technical hexane or light petroleum, with a composition similar to that used In the industrial extraction of ollseeds or. failing these, n-hexane
NOTE I It is recommended that technical hexane be used for the calibration This reagent usually contains more than 50 % of n’hexane and consists predominantly of C, isomers.
5.2 Internal standards use either 52.1 or 522.
NOTE 2 If the technical hexane used for the extraction or calibration contains appreciable amounts of cyclohex.
ane, n-heptane should be used as the internal standard
5.2.1 Cyclohexane.
5.2.2 n-Heptane.
5.3 CarrIer gas, e.g. hydrogen, nitrogen, helium.
etc.. thoroughly dried and containing less than
10 mg/kg of oxygen
5.4 AuxilIary gases.
5.4.1 Hydrogen, 99,9 % pure, containing no organic’ impurities.
5.4.2 AIr, containing no organic impurities
5.5 Calibration ollseed residues, of the same origin as the sample to be analysed and having a low hexane content. If the hexane content is too high. reduce It by spreading the residue in a thin layer and leaving it to stand in the open air for several hours.
Commercial oilseed residues usually have a moisture content of 12 % (rn/rn) to 14 % (rn/rn). In the case of samples having a different moisture content, it is necessary to carry out the calibration
with oilseed residues having the same moisture content as the sample.
6 Apparatus
Usual laboratory apparatus and, in particular, the following
6.1 Gas chromatograph. with flame ionization detector and an integrator and/or recorder, equipped with either
a) a packed steel column approximately 2 m long and of internal diameter approximately 3,2 mm, packed with an acid-washed diatomaceous earth support of particle size 150 pm to 180 pm (Chromosorb P NAW 60/80 mesh” Is suitable). and coated with 10 % squalane or methylpolysiloxane (SE 30” is suitable), or
b) a capillary column, approximately 30 m long and of 0,3 mm internal diameter, coated with methylpolysiloxane (SE 30’ is suitable) having a film thickness of 0.2 pm.
The injector and detector temperature shall be set at approximately 120 °C and the oven temperature at approximately 40 °C. The carrier gas pressure shall be set at approximately 0,3 bar (30 kPa).
If a capillary column is used, the apparatus shall have a 1/100 split injection system.
NOTE 3 For analyses in series, it is recommended to use a gas chromatograph having an automatic sample injection system, combined with a heating bath.
6.2 Heating bath, fitted with a rack to hold the flasks
(6.4), capable of being set at 80 °C ± 2 °C and of maintaining the set temperature constant to ±0.1 °C.
NOTE 4 For continuous use, glycerol is recommended as the heating liquid.
6.3 Gas syringe, of 1 ml capacity.
6.4 Septum flasks, of 20 ml ± 2 % capacity
6.5 Septa. inert to hexane. of approximately 3 mm thickness, made of a material such as nitrile rubber (e.g. Perbunan”), or butyl rubber with a polytetrafluoroethylene or polychloroprene seam (e.g. Neoprene11).
Ensure that the septa used will produce a hermetic seal after crimping.
NOTE 5 The septa often have a very high mechanical resistance; if It Is thought therefore, that the needle of the gas syringe may be damaged by using it to perforate septa, perforate them with a pin before taking the sample from the head-space. Reuse of sepIa is not recommended
6.6 Metallic foil caps. for example made of aluminium
6.7 CrImping pliers, for closing the septum flasks
6.8 Liquid syringes, of 10 il capacity.
7 Sampung and sample storage
Sampling shall have been carried out in accordance with ISO 5500. It is essential that loss of hexane from the sample be prevenIed
The laboratory sample shall fill a hermetically sealed container (preferably a crimped metal box) and shall be stored at 4 °C. Plastic containers shall not be usecL
The determination of residual hexane shall be carried out as soon as the container has been opened.
8 Procedure
8.1 CalibratIon
8.1.1 Weigh, to the nearest 0.1 g. 5 g of the calibration oilseed residues (5.5) into each of five septum flasks (6.4). Seal each flask with a septum (65). cover with a foil cap (6 6) and crimp using the pliers (67)
8.1.2 Add. using a syringe (6.8). the volume of solvent (5.1) specified in table I to four of the five flasks Do not add solvent to the fifth flask
8.1.3 Allow the flasks to stand at room temperature for 24 h.
NOTE 7 In the case of a shorter period, it Is not certain that the technical hexane has been completely absorbed by the ollseed residue and, furthermore, that the sorption-desorption equilibrium of the technical hexane between the residue and the vapour phase has been reached
8.1.4 At the end of this time add, by means of a syringe (68), 5 jil of the internal standard (5.2.1 or 5.2.2) to each of the five septum flasks through the septum.
8.1.5 At intervals of 15 mm, place one septum flask after the other in the heating bath (6.2), set at 80 °C ± 2 ‘C. The flasks shall be immersed in the heating liquid up to the level of the foil cap.
8.1.6 After heating each of the flasks for exactly
60 mm, take, by means of the gas syringe (6.3) previously heated to between 50 °C and 60 °C, exactly I ml of the gaseous phase from the head-space, without removing the flasks from the heating bath. Quickly Inject into the chromatograph the gaseous phase so removed
8.1.7 From the chromatogram corresponding to the flask to which no technical hexane was added, calculate the hexane content 4, expressed as a percentage of the total peak areas.
8.1.8 From each of the chromatograms corresponding to each of the flasks to which technical hexane was added, calculate the calibration factor F using the formula
9 Do not include peaks due to the oxidation products. some of which may be present in significant amounts.
Wh is the free hexane content of the calibration oilseed residue concerned (see table 1). expressed in milligrams per kilogram;
w is the content of the internal standard in the calibration sample, expressed In mliii. grams per kilogram, ie. 680 for n-heptane or 780 for cyclohexane.
Calculate the mean calibration factor F from the resuits of the four calibration samples.
F shall be equal to 1,0 ± 0.1.
8.2 DeterminatIon
8.2.1 Weigh, to the nearest 0,1 g, 5 g or the laboratory sample into a septum flask (6.4). Seal the flask Immediately with a septum (6.5). cover with a foil cap (6.6) and crimp using the pliers (6.7).
These operations shall be performed rapidly,
8.2.2 inject 5 pi or the internal standard (5.2.1 or
5.2.2) into the septum flask through the septum using a syringe (6.8). and place the flask in the heating bath (6.2). set at 80 °C ± 2 °C, for exactly 60 mm The flasks shall be immersed in the heating liquid up to the level or the foil cap.
8.2.3 Using the gas syringe (6.3). previously heated to between 50 °C and 60 °C, take exactly I ml of the gaseous phase from the head-space, without removing the flask from the heating bath. Quickly inect into the chromatograph the gaseous phase so removed.
8.3 Number of determinations
Carry out two determinations on the same laboratory sample.
9 Expression of results
The free residual hexane content w, in milligrams per kilogram. is given by the formula