09-09-2016, 03:24 PM
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Aim
To determine the moisture in all spices by co- distillation with toluene with the exception of capsicums and dehydrated vegetables.
Apparatus required
1: One glass distillation apparatus with ground glass joints constructed and assembled
2:500 ml or 1000ml flat bottom short neck flask with a t.s 24/ 40 joint
3:.Wet condenser with drip tip, 400 mm length with a t.s 24/40 joint
4: Bidwell- sterling trap, t.s 24/40 joined, 500 capacities graduated in 0.1 ml intervals
5: Two heat source capable of refluxing solvent in apparatus above.
6: An electric heating mantle supported by available speed stirring plate and an egg shaped Teflon covered stir bar is recommended. If not using stirring plate add boiling chips.
7: Three nylon bristle burette brush, ½ inch diameter or a wire loop. It should be long enough to extend through the conductor
8: Four analytical balance, sensitivity 0.01g
Reagents
1 toluene ACS grade
Introduction
Moisture content analysis is a critical component of material quality and essentially a function of quality control in most production and laboratory facilities, from biological research organization, pharmaceutical manufacturers to food producers and packer, moisture content control greatly influences the physical properties and product quality of nearly all substances and materials at all stages of processing and final product existence [Richardson, 1996].Currently, many moisture analysis methods are available for commercial purposes. The primary method of water content determination include, spectroscopic, chemical, conductively and thermo gravimetric analysis and the use of halogen heating as the source of thermal radiation. To understand the thermo-gravimetric moisture analysis principle, it is important to understand what moistures is the definition of moisture content and the effects of moisture on material processing and formulating
Dean-Stark apparatus
Dean-Stark apparatus or Dean-Stark receiver or distilling trap or Dean-Stark Head is a piece of laboratory glassware used in synthetic chemistry to collect water (or occasionally other liquid) from a reactor. It is used in combination with a reflux condenser and a batch reactor for continuous removal of the water that is produced during a chemical reaction performed at reflux temperature. It was invented by E. W. Dean and D. D. Stark in 1920 for determination of the water content in petroleum.
Two types of Dean-Stark traps exist – one for use with solvents with a density less than water and one for use with solvents with a density greater than water.
More rarely encountered is the model for solvents with a density greater than water. This type has a tube at the bottom of the side-arm to allow the organic solvent at the bottom to flow back into the reaction vessel. The water generated during the reaction floats on top of the organic phase.
This piece of equipment is usually used in azeotropic distillations. A common example is the removal of water generated during a reaction in boiling toluene. An azeotropic mixture of toluene and water distills out of the reaction, but only the toluene (density=0.865 g/ml) returns, since it floats on top of the water (density=0.998 g/cm3), which collects in the trap. The Dean-Stark method is commonly used to measure moisture content of items such as bread in the food industry.
Procedure
1: Weigh sample to the nearest of 0.01g sufficient to yield 2 to 4 ml of water above 40 gm
2: Quantitatively transfer to a distillation flask, add sufficient toluene to cover the sample completely and to middle of distillation flask. Add a stir bar or boiling chips.
3: Assemble the apparatus to heating mantle as shown in the figure fill trap with toluene by pouring through condenser until it just fills the trap and begins to flow into the flask
4: Bring to a boil and reflex at a rate of about 2 drops per sec until most of the water has been collected in the trap then increase the reflex rate to about 4 drops per sec
5: Continue refluxing until 2 consecutive readings 15 min apart show no change (about 2 hrs). Turn off heat and allow it to cool to ambient temperature. Dislodge any water held up in the condenser with a brush or wire loop. Rinse carefully with about 5 ml toluene.
6: Read volume of water in trap
Calculation
1: Moisture percentage = volume of water (ml)/ correction factor x 100/ weight of the sample (g)
2: Correction factor = ml distilled/ml added
Precautions
1: Sugar decomposes and produce water under prolonged heating on toluene or other solvents with boiling point over 100 degree c or near it because boiling point of water is 100 degree Celsius
2: Do not boil too long and boiling point shouldn’t be greater than 100 degree c because as chili is a fruit it contains fats and carbohydrates. Also it will get hydrolyzed as the byproduct is water. This will mislead accuracy of moisture content.
3: The apparatus should be dried.