BS ISO 23381:2020 pdf download – Determination of salt out (crystallization) temperature of liquid fertilizers
This document specifies the test procedure for the determination of the salt out temperature (SOT), also known as the crystallization temperature (CT) of liquid (fluid) fertilizers, using an inexpensive and simple technique. This method might not be applicable to the binary and ternary fertilizers, especially with regards to the last crystal to disappear (LCTD). Some of these exceptions are discussed in the procedure (Clause 8).
2 Normative references
The following referenced documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 3696:1987, Water for analytical laboratory use —Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.
lSO and lEC maintain terminological databases for use in standardization at the following addresses:—IEC Electropedia: available at
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4 Principles
Liquid fertilizers have been defined in ISO 8157:2015.
An aliquot of the original liquid fertilizer sample is placed into a glass test tube and is then immersedinto an alcohol-dry ice bath until it crystallizes. The alcohol could be chosen from methanol, ethanol,or isopropanol (IPA). Acetone could also be used instead of alcohols; however, IPA (rubbing alcohol)is preferred due to its higher boiling point. If dry ice is not available,other lowering temperaturemixtures such as salt-ice could be used to achieve the proper cooling and crystallization of the fertilizertest sample.
Once the precipitation (formation of salt crystals) is complete, the cooling source is removed and theglass test tube and its contents are allowed to warm up to room temperature. The SOT in most casesis defined when the last crystal to dissolve (LCTD) dissolves (i.e. is no longer visible in the solution).Exceptions to the LCTD rule are covered below and in 8.11.
The underlying principal of the technique can be illustrated with the following cooling curvel9l shownin Figure 1.
5.1 Use only water conforming to grade 3 of ISO 3696:1987.
5.2 Dry ice snow maker (cone, clamp, ring, and thermal bag), or supply of dry ice.
5.3 CO 2 cylinder with a dip tube for making dry ice (or supply of dry ice).
5.4 IPA or other appropriate solvents such as methanol, ethanol, or acetone.
5.5 If dry ice is not available, other cooling systems such as an ice-salt bath could be used. However,
care must be taken to achieve a proper low temperature.
6 Equipment
6.1 1 × stir motor apparatus 1) .
6.2 3-Jaw Keyless Chuck with Arbor 2) .
6.3 1 × 2-foot steel rod with attachable base 3) .
6.4 1 × three-prong clamp.
6.5 2 × Silver-lined Dewar Vacuum Flask with cap 4) .
6.6 50 cm 3 glass test tubes (several, Pyrex or similar quality).
6.7 Thin Stainless steel wire (several inches, such as 40 AWG, 0,079 9 mm, or 30 gauges, 0,010 inch, or
24 gauges, 0,58 mm).
6.8 Thin walled latex rubber tubing (several inches).
6.9 1 × thermometer (−40 °C to a least +30 °C), red liquor preferred for ease of reading. Alcohol filled thermometers are preferred over mercury-in-glass thermometers due to safety concerns with mercury.
It is recommended that several alcohol thermometers with different temperature ranges be available.
7 Set Up
7.1 Attach a steel rod to its frim base (lab stand).
7.2Attach the stir motor apparatus to the lab stand.
7.3 Remove the stir blade and associate metal shaft from the stir motor.These shall be replaced by theglass thermometer.
7.4Take a thermometer that reads at least -40 °C and add 1 inch of the thin walled latex rubber tubingto the top (non-bulb) of the thermometer.
7.5To the bottom 3 inches (bulb end) of the thermometer, coil some stainless steel wire.Ensure thatthe added wire fits within the glass test tube and does not contact (scratch) sides or bottom of the glasstest tube when rotated by stir motor.
7.6 Place the thermometer into where the stir blade rod was before and carefully tighten it around thethermometer.
NOTE lf the stir blade rod is tightened too much, the thermometer might break.7.7 Examples of equipment and set up are shown in Annex A.
8.1 Pour approximately 250 ml of lPA into the silver-lined Dewar vacuum flask (methanol, ethanol, oracetone can be used as well).
8.2 Pour dry ice snow gently (from dry ice supply or the thermal bag) to the Dewar flask.As the dry icedissipate, add more. Do not add large pieces of dry ice (crush the dry ice, if large pieces exist).
CAUTION -Dry ice will cause freeze burn. Do not handle with bare hands (use insulatedgloves). Dry ice added to IPA (or other aforementioned solvents) creates a bubbly reaction.Addthe dry ice slowly.
8.3Stir the lPA/dry ice mixture with a spatula.Use a variable transformer (variac) connected to thestirrer.Adjust the variac setting in order to provide adequate stirring of about 50-60RPM(the setting onvariac is about 30-40).
8.4Add 15 ml of the test sample (liquid fertilizer) to the test tube.
8.5 Affix the test tube containing the test sample with a three-pronged clamp and position such thatthe thermometer end containing the stainless steel wire is placed inside and centred on the test tube.Make sure the thermometer is almost to the bottom of the test tube, but not touching it; this is done toensure that almost all the forming crystal will mix and not settle on the test tube bottom.BS ISO 23381 pdf download.