Determination of sugar

TITLE OF EXPERIMENT  Determination of Sugar by Refractometric and Volumetric Methods

INTRODUCTION Sugar (sucrose) is a carbohydrate that occurs naturally in every fruit and vegetable. It is the major product of photosynthesis, the process by which plants transform the sun's energy into food. Sugar occurs in greatest quantities in sugar cane and sugarbeets from which it is separated for commercial use. The white stuff we know as sugar is sucrose, a molecule composed of 12 atoms of carbon, 22 atoms of hydrogen, and 11 atoms of oxygen (C12H22O11). Like all compounds made from these three elements, sugar is a carbohydrate. Sucrose is actually two simpler sugars stuck together: fructose and glucose. In recipes, a little bit of acid (for example, some lemon juice or cream of tartar) will cause sucrose to break down into these two components. If we look closely at dry sugar, you’ll notice it comes in little cubelike shapes. These are sugar crystals, orderly arrangements of sucrose molecules. Refractometric is a method to measuring substances refractive index and brix besides to determine the sucrose level in food sample used. There are two types of refractometer used in this experiment which is abbe refractometer and hand held refractometer. Abbe refractometer are used to determine refractive index while hand held refractometer are used to determine brix. The refractive index of a carbohydrate solution increase with the increases concentration.The percentages sugar, measured in degrees brix. Lane-Eynon’s titration method is an example of a titration method of determining the concentration of reducing sugar in a sample. Sugar that contain aldehyde group that are oxidized to carboxylic acid are classified as reducing sugar. Common test reagent used benedict’s and Fehling’s reagent. High concentration of food sample gives high value of refractive index and brix. High concentration of food sample show high result in high carbohydrate content.

A) REFRACTOMETRIC METHOD OBJECTIVE To determine the total soluble solids of selected food samples using refractometric method PRINCIPLE All chemical compounds have an index of refraction. Refractive index (RI) of material can be determined by measuring the angle of incidence (i) to angle of refraction (r). APPARATUS Abbe refractometer, handheld refractometer and dropper.

PROCEDURE 1. The secondary prism was opened and 2-3 drops of specimen were dropped onto the center of the surface of the main prism. The secondary prism was closed gently. 2. By looking through the eyepiece, the measurement knob was turned slowly until the boundary line appears in the refraction field of vision. 3. Read the Refractive Index and the Brix.

B) LANE-EYNON’S TITRATION METHOD OBJECTIVE To determine the concentration of unknown sugar solution using Lane and Eynon’s titration method. PRINCIPLE Lane-Eynon Method is an example of a titration method based on reaction of reducing sugar with copper sulphate followed by reaction alkaline tartrate. Mixture boiled for specific time, followed by addition of methylene blue. Coloured solution titrated with original sample solution until decoloration of the indicator. APPARATUS Burette 50ml, Erlenmeyer flask 300ml, hot plate, retort stand and dropper. CHEMICALS Fehling’s solution No 1 and No 2 and Methylene blue.

PROCEDURE Preparation of Chemical Reagents 1) Fehling solution A : 69.28g CuSO4.5H2O and 1.0ml of 1M H2SO4 are dissolved in water and make up to 1.0 litre water. 2) Fehling solution B : 346g KnaC4H406.4H2O and 100g NaOH are dissolved in water and make up to 1.0 litre water

3) Mixed Fehling solution : equal volumes of Fehling solution A and B are mixed by pipetting 4) Methylene blue : 1% aqueous solution Preliminary Titration 1) The burette is filled with sugar solution 2) 25ml of mixed Fehling solution are pipette into a conical flask and 10-15ml of sugar solution are added from the burette 3) The flask on hotplate are heated and the liquid were let to boiled briskly 4) 4 drops of 1% methylene blue are added and additions of sugar solution are make further at a rate 1ml per second 5) the liquid was kept boiling throughout, continue add until blue colour is discharged (titre = A ml)

Accurate Titration 1) 25ml of mixed Fehling solution are pipette into a conical flask and (A-2) ml of sugar solution is added from the burette. 2) The flask is swirl, heated on hotplate and boiled liquid moderately for 1.5min-2min and 4 drops of methylene blue solution are added 3) The sugar solution are added about 2-3drops per second and the titration are complete within 3min from the time boiling commences 4) The dextrose table is used to calculate the concentration of sugar in the solution

CALCULATIONS

Sugar Content (mg/100mL solution) = Factor x 100 Titration (mL)

Sugar Content of Accurate Titration in trial 1, 2 and 3: 49.5 x 100 21.2

= 233.49

49.7 x 100 23.2

= 214.22

49.8 x 100 24.2

= 205.79

Mean of sugar content: 233.49+ 214.22 + 205.79 3

= 217.83

RESULT  As in table 4.1 and table 4.2

DISCUSSION In this experiment, we have learned how to determine the total soluble solids of selected food samples using refractometric method. Refractrometer measuring the refractive indexes of solid, liquid, and gaseous media in various regions of the optical-radiation, or light, spectrum. If the refractive index n and its dispersion (dependence on the wavelength of the light) D are known, it is possible to determine other quantities dependent on n and D. The following types of refractometric methods can be distinguished: (1) methods of direct measurement of the angles of refraction when the light crosses the interface of two media; (2) methods based on the phenomenon of total internal reflection; (3) interference methods ; (4) photometric methods, which make use of the Fresnel equations and are based on the dependence of the reflection coefficient or transmission coefficient of light at the interface of two media on the ratio of the refractive indexes of the media; and (5) other methods, such as measurement of the focal length of a lens and the curvature of its surfaces in order to determine the refractive index of the material of which the lens is made, measurement of the lateral displacement of a beam by a plane-parallel plate made of the material under study, and the immersion method. Based on the experiment (A) which is refractometric method, we had discussed about the soluble solid in sugar sample. As the material, we had used cordial and honey to determine their refractive index. The refractive index is correlated with the amount of soluble solids (express as sucrose concentration) using tables, or by direct reading on the refractometer of the mass fraction of soluble solids. Value of refractive index of honey is 1.4889 while for cordial is 1.3403. As for the brix reading are for honey is 75.7 and for cordial is 3.0. Honey have higher value of refractive index and higher Brix reading compare to cordial .Honey and corn syrup are include as a reducing sugar .

For this experiment we take refractive index for honey value that is 1.4889 not 1.3349 because the value for first trial is not same with second and third trial. Maybe have the error at refractive apparatus that’s why the first trial value does not same with second and third. For the cordial we also take second and third value that is 1.3403. We does not take the first value.

In this experiment, we have learned how to determine the concentration of unknown sugar solution using Lane and Eynon’s titration method. This method involves the determination of reducing sugars by titration with Fehling’s solution using the redox indicator, methylene blue. This is an empirical method and standardized experimental conditions andmethods must be rigidly adhered to for satisfactory results.The classical method uses tables indicating the amounts of invert sugar (mixture of fructose and glucose),dextrose (glucose), fructose, maltose

or

lactose

equivalent

to

volumes

of

reduced

Fehling’s

solution.The now accepted and official method (AOAC Method 923.09, 920.183b; 1995) is a constant volume technique where the conditions for reduction are standardized by the addition of water to give a constantfinal volume of 75 ml in the titration flask, and the volume of Fehling’s solution used is calibrated against astandard reducing sugar solution. This standard solution must be specific for a particular reducing sugar.The Lane and Eynon method involves the titration of a boiling solution of the Fehling’s solution with adilute solution of the sugar sample.

As for experiment (B) which is determination of total reducing sugar by using Lane-Eynon’s Titration Method is shown in the data . The preliminary titration sample that we used is 20.2mL, and the mean for the sample is 22.87ml, while for the preliminary sample factor is 49.5 and the mean value is 49.67. Based on the calculation above, we can find the volume of dextrose per 100cm by using the formula :

Sugar Content (mg/100mL solution) = Factor x 100 Titration (mL) After we calculate using the above formula, the mean sugar content we get are 217.83.

CONCLUSION The objective this experiment is to determine the total soluble solids of selected food samples using refractometric method and to determine the concentration of unknown sugar solution using Lane and Eynon’s titration method. For the experiment (A) which is refractometric method the refractive index we get for honey is 1.4889. Meanwhile, for cordial the value we get is 1.3403. Based on result, honey have higher amount of carbohydrate because it have higher concentration compare to cordial. High concentration of food sample show high result in carbohydrate content. For experiment (B), the value of sugar content we get are 217.83 and the concentration also effect the carbohydrate content . The objective is achieved.

QUESTIONS 1) What are reducing sugar? Reducing sugar is sugars that possess free aldehydes or ketone group in their structure react with reducing agent. Examples are Fehling’s solutions or Benedict’s reagent.

2) What is refractive index? Refractive index of a substance is the ratio of light velocity in a vacuum to its velocity of a substance. Refractive index measurement is to measure the content of dissolved solids in sugar solutions.

3) Write the principle reaction (chemical reaction) that occurs in the Lane-Eynon’s determination of reducing sugar. Principle are based on the reaction of reducing sugar with a solution of copper sulfate followed by reaction with alkaline titrate. Mixture is boiled for a specific time, followed by addition of methylene blue (as an indicator).

4) Why is the sample boiled during the titration? Sample boiled during the titration because for air excluded from reaction mixture.

REFERENCES 1) http://www.scribd.com/doc/39341176/Food-Analysis 2) http://www.exploratorium.edu/cooking/candy/sugar.html 3) http://www.crystalsugar.com/coopprofile/sfacts.aspx 4) J.W Stevens W. E Baier,Ind. Eng. Chem. Anal. Ed.Refractometric Determination of Soluble Solids in Citrus Juices,pg 447-449, 1939 .