experimental report subject practice of food analysis

Introduction Determine the deviation/error of mass analytical balance or volumetric instrument burette, pipette, micropipette, volumetric flask, beaker.. Procedure 5.1: Evaluate the erro

TRUONG DAI HOC ;

SU’ PHAM KY THUAT TP HO CHi MINH HCMC University of Technology and Education

Member ID Work efficiency

Phan Thi Thanh Huyén 21116301 60%

Assessment of Accuracy and Precision

1 Introduction

Determine the deviation/error of mass (analytical balance) or volumetric instrument (burette, pipette, micropipette, volumetric flask, beaker) From there determine the error range of the instrument in the experiment, estimate the error of the experimental results Thereby making comments and comparing the deviations between supplies

2 Objective

Assess accuracy and precision of data generated in using balance, mechanical pipettes and volumetric glassware

3 Principle

Using equipment in analytical tests helps ensure more accurate and precise results

4 Supplies and equipments

5 Procedure

5.1: Evaluate the error of the pipette

1.Put the 100mL beaker on the analytical balance

2.Press Tare to not calculate the beaker weight, reduce to the value 0.00g

3.Use a 100mL pipette to accurately draw 100mL of distilled water into the beaker placed on the balance

4 Weigh the volume of water added

Note: It is not necessary to pour the water from the previous measurement out of the cup, just press Tare and then take another mL of water

(Do the same with the ImL Pipette)

Repeat the experiment 6 times

5.2: Evaluate the error of the buret

1.Place the 100mL or 20mL beaker on a precision balance

2.Press Tare to subtract the cup weight, reducing it to a value of 0.00g

3.Using a burette (25/50ml) add 10ml of distilled water (ml) to the beaker

4.Drain 10 mL from the burette in turn until the amount of water in the burette is not enough 10

mL, then add water and adjust to zero

5.Repeat until 6 measurements are obtained

Then repeat the process as above but take 1 mL from the burette

5.3: Evaluate the error of the micropipette

1.Place the 100mL or 20mL beaker on a precision balance

2.Press Tare to subtract the cup weight, reducing it to a value of 0.00g

3.Using a 1000 wL micropipette add Iml of distilled water (ml) to the beaker

4 Weigh the volume of water added

Repeat this process 6 times

Note: It is not necessary to pour the water from the previous measurement out of the cup, just

press Tare and then take another mL of water

5.4:Total amount of water and amount of water taken from the volumetric flask

1.Place the 100ml/Beaker 100ml volumetric flask on the precision balance

2.Press tare to subtract the cup weight, convert to the value 0.00g

3.Fill the flask up to the mark with water and weigh the amount of water in it

4 Then tare a 100 mL beaker and pour water from the upper volumetric flask into the beaker, weighing the amount of water removed from the flask

Repeat this process 6 times

5.5: Accuracy of measurements from balance

1.Press the balance tare to return to the 0.00g value

2.Put weights 50g, 100g, 2009 respectively on a precision balance.Record the result

Note:Do not touch the weight with bare hands to avoid the oils from sweat sticking the weight Work with precision balances and analytical balances Then record the number of the balances

6 Calculation and results

6.1: Evaluation of pipette error

6.3:Evaluation of micropipette error

Mechanical

1 ml Mass(g)

0,98 0,99 0,99 0,98 1,00 1,00

0,9866

0,0058 0,5852 1,34

0,9866%0,01

44

0,99 2

0,0089 0,9035

l 0,99%0.0009

6.4:Total amount of water and amount of water taken from the volumetric flask

Mass(g) Volume Water in volumetric flask 98,98 100ml

Water in beaker 98,92 100ml

balances(g) balances(g) 1- Weight 50g 49.88 49,91

The obtained accuracy is relative, the relative error rate is not too high

Errors may appear due to: Instruments are relative, misaligned, chipped, sweaty hands

When taking water into the cup and weighing it, there may be some water left on the wall of the machine

The person conducting the experiment did not perform the operation correctly

Due to laboratory conditions such as when the balance meets the wind, it will affect the weighing results

Because there are computational differences between the data, it is necessary to perform many times to obtain a set of values around the true value, minimizing errors

In addition, it is necessary to limit some human factors and surrounding factors when

In general, the standard deviation, coefficient variation, mean, relative error, and 95%

confidence interval will be less than or equal to when the experiment is repeated many times, thereby reducing the difference between the samples calculated value This is also shown by the data obtained during the experiment when calculating the values with n = 3 and n=6

2.Why should relative error and coefficient variation be used to compare the accuracy and

precision of the 1 mL and 10 mL volumes obtained from the pipette and burette in sections

2 and 3, instead of just taking the average value? and standard deviation?

Instead of just the mean and standard deviation, we use the relative error and the coefficient of variation to compare the accuracy and precision of the ImL and 10mL volumes taken from the pipette and the burette for the coefficient of variation, which is more reliable, in addition to showing more clearly the range of errors between the values, the coefficient of variation also helps to gather data in a region and the acceptability of the obtained value

4 If the accuracy and/or precision of the micropipette is lower than expected, what can be done to improve these characteristics?

Pre-wash the tip: Pre-wash the tip to ensure that all internal components are in contact with the

solution Aspirate the sample into the tip and then back-flush or flush the waste cup to rinse the tip, increasing the accuracy of the pipetting process

Reverse pipetting technique: This technique is used when aspirating viscous solutions (blood samples, ) or volatile solvents This technique also allows aspiration of microscopic volumes such as 0.5 ul or less The reverse pipetting technique begins with pressing the plunger down to the stop position 2nd, thus including an additional volume remaining during sample aspiration, not included in the final discharge

Consider ambient temperature: People or companies often align pipettes at room temperature,

so if you use a pipette at a different temperature (e.g in a cold room), you may not get the correct volume corpse

Consider sample temperature: When continuously aspirating samples at cold temperatures, the volume of solution at the first flush is always greater than the volume aspirated, but not on subsequent aspiration with the same tip for exact volume Therefore, it is recommended to rinse the first aspiration into the solution tube and start aspirating from the second time

Use volume-matched micropipettes: Micropipette accuracy will decrease when the discharge volume is close to the smallest volume the pipette can handle

Install the pipette:

Adjust more than 1/3 of the turn to the desired volume Then adjust back to the required volume

Do the same with different volumes, with different times

5 In a titration experiment with a burette, should the stopping volume be too much less than 10 mL? Is it better to use 10 mL burette or 50 mL burette for accuracy and precision?

Why?

The stop-point volume should not be too much less than 10mL because the opening of the shut- off valve is unstable, which can lead to errors in titration or reading Using a 10 mL burette offers greater accuracy and precision Because the smaller the error of the device, the higher the accuracy and precision Where the 10 mL burette has an error of +0.02 (mL), while the 50 mL burette has an error of 0.05(mL)

6 Is the volume indicated on the volumetric flask a “take in” or “take out” volume? What

does the volume on the pipette indicate?

The volume of each volumetric flask is the volume contained to exactly a given volume The volume indicated on the pipette is the volume aspirated to an exact volume within a given

Errors due to people and tools

To eliminate and minimize errors:

Repeat the measurement several times

Test and calibrate measuring devices and instruments

Determination of Moisture & Ash Content

obtain accurate and precise data There are several application areas, benefits, and drawbacks for various analytical techniques Due to its ease of use and low cost, the gravimetric approach is most frequently utilized

And if the ash content also is to be determined, it is often convenient to combine the moisture and ash determinations

Dry the petri dish Cool ina Weigh plate then Place sample on -

with lid in the desiccator (room weigh the sample the plate and Drying at 105°C ovenat105°Cfor |—>} temperature) [| >) byanalytical | >| weighwiththelid [> sae

5.1.Block diagram how to determine moisture content of a sample

Notes:

- Remember to write the serial number on both plate and lid after drying (Step 1)

- Place a sample on a plate, spread the dough evenly, and weigh with the lid (Step 4)

- Drying at 105 °C for 3h Do not cover the lid, but just keep it next to it or rest it loosely

on the plate so as not to prevent the water from evaporating (Step 5)

- When opening the lid of the desiccator, open it slowly to the side, do not lift the lid 5.2 Determination of ash of soy four sample

at550-600°Cto |—>) temperature) and [| >) porcelaincupand [| > raise the F>'! = ook WEG

constant weight weigh on an weigh temperature _

analytical balance slowly until 550 -

Notes:

- Heat until white ash, which means all organic matter has been removed (step 5)

- In case there is still black ash, take it out to cool, add a few drops of concentrated H202

or HNO3 and reheat to white ash (After step 5)

6 Data and calculation

© % Moisture of soy flour

Ist:

Ash of soy flour:

Crucible(g) Crucible + sample(g) crucible+ashed sample(g)

65.1206 62.2125

“Ash

7 Discussion

1.Comments

- The results achieved are consistent with the original goal

- In general, solid food (soybean flour ) has a lower moisture content than liquid food (milk)

-Moisture and ash calculated close to reality

- Leaving samples and instruments in the air for too long

- Due to inaccurate measuring instrument

- Drying is not long enough to evaporate all the water in the food sample, distorting the measurement results from reality

- When doing the experiment, a small amount of sample is lost or dropped

- The desiccator is not sealed

4 Some methods to reduce errors

- Correct manipulation of experimental techniques

- Drying at the right temperature, at the right time with food samples

Determination of total nitrous by the KJELDAHL

method

1 Introduction

Proteins along with carbohydrates and lipids are the three most important nutritional components found in all foods Therefore, protein is used as a single nutritional standard indispensable to determine the nutritional value of food The higher the protein content, the higher the food value

Nitrogen in food is mostly in protein molecules (protein nitrogen), but there is also a small amount of nitrogen in other components called non-protein nitrogen The sum of these two types of nitrogen is called total nitrogen Total nitrogen = Protein nitrogen + Non-protein nitrogen

Nitrogen found in foods usually exists at a steady rate between 15 and 18 percent of the protein content For the vast majority of foods, the average rate

is 16% In biological materials, because the non-protein nitrogen content is small and the separation is very complicated, the protein content is conventionally calculated according to the total nitrogen content and is called crude protein or total protein Currently, the total nitrogen content is usually determined by the Kjeldahl or Dumas method

2 Objective

Analysis of total nitrogen content in food samples by Kjeldahl method Then, the total protein content will be calculated indirectly through a conversion factor of 15 - 18%

Step 2: Distillation

2NH3 + Na2S04 + 2H20 (NH4)2SO4 + 2NaOH

NH3 + H3BO3 NH4+ + H2BO3-

Step 3: Titration

H2BO3- + H+ H3BO3

Step 4: Calculation %N

Use HCl instead of H3BO3 in the distillation and titration in this experiment

When heating the food to be analyzed with concentrated H2S04 (this process is called sample tnorganization), organic compounds are oxidized Carbon and hydrogen join to form CO2 and H20 And nitrogen after being released in the form of NH3 will combine with H2S04 to form (NH4)2S04 which is soluble in solution

Remove NH3 from the solution with a large, concentrated NaOH, and at the same time, distill and collect NH3 with a condenser tube system

At the outlet of the condenser tube, we install a vessel containing a known volume of 0.1N HCl residual; Condensed NH3 will react with HCl to form

NH4CI

Quantify excess 0IN HCI with standard 0.IN NaOH solution, thereby calculating the amount of nitrogen present in the raw material sample to be analyzed

4, Chemical and equipment

Chemicals & food sample

e Soy flour

e Concentrated H2S04

e HC10.1N, NaOH 40%

5g K2SO4 0.15g CuSO4 0.15g TIO2

Digestion Weigh sample Kjeldahl tube

and inorganic sample until completely clear

Step 2: Place the sample solution after Put in 20mL of HCl Carry out nitrogen

from the sample

Titrate with NaOH 0.IN Record & Calculation the

result

method

Notes:

Step 1

- This process is usually carried out in a hood or a well-ventilated place

- First, the sample will be accurately weighed (measured) by mass or volume and then placed into a Kjeldahl tube

- Depending on the type of material with more or less protein content, we will choose an appropriate sample volume or volume: solid samples weigh 2 to 5g, liquid samples take from 2 to 5mL

- Slowly add 10 — 15 mL of concentrated H2S04 (specific gravity 1.84) slowly added to the Kjeldahl tube

- To accelerate the process of mineralization (combustion) it is necessary to add a catalyst

e K2S04 has the effect of increasing the boiling point

e CuS0O4 and TiO2 catalyze the reaction

e Concentrated H2S04 oxidizes organic samples to inorganic samples Step 2:

- Plug in the power, turn on the machine, open the cooling tap, wait until the screen appears, the machine is ready to work Add 20mL of HCl solution to erlen, install it in the machine Pay attention to submerging the outlet of the condenser tube into the HCI solution Install the program for the machine according to the instructions of the teacher/laboratory staff or the user manual of the machine (aeration rate: 50%, volume of NaOH 40%: 5—-l0mL, storage time: 15-30 minutes)

- Pay attention not to install misalignment, the gas will escape, causing errors

6 Calculation

Content (“) of total nitrogen in the sample:

In there:

N: Nitrogen content in mass percent

a: number of mL of 0.1N H2S04 standard solution to absorb NH3

b: number of mL of 0.1N NaOH solution used for titration

m: mass of sample to be inorganic, g

V: total volume of the inorganic solution (100 mL)

v: volume of inorganic distillation solution (10 mL)

0.0014: amount of Nitrogen (grams) corresponding to | mL H2S04 0.1N

K: 0.1N NaOH concentration correction factor (titration factor is considered equal to

1 if we use a standard tube)

- Suitable for all kinds of food

- Relatively low cost for manual method

- Trusted and recognized by AOACs

- The operator's actions are incorrect

Disadvantage:

- Only total Nitrogen can be measured, not directly measured protein content

- Takes a lot of time to analyze

- Use of corrosive chemicals such as sulfuric acid (H2SO04)

- Has less precision than the Buret method

The cause of the error

- Incorrect technical operations such as incorrect weighing of samples

- The process of sample inorganization is not technically correct, there are still black stains of the test sample remaining on the walls of the flask, the solution is not clear, the heating has been stopped

- The identification process is wrong

- Chemicals are mixed with impurities

Methods of minimizing errors

- Before performing the experiment, check the equipment and wash the test equipment thoroughly with distilled water

- For buret, it is recommended to rinse with a titration solution and release air

bubbles before titration

- When the concentrated H2SO4 is put into the Kjeldahl tube, it should be put down from the wall of the tube to rinse the sample and the catalyst adheres to the wall to avoid the wall of the flask being blackened when the sample is inactivated

Determination of total carbohydrates by phenol-

sulfuric acid method

1 Introduction

The phenol-sulfuric acid method 1s a fast and simple colorimetric method used for the determination of the total carbohydrates present in a sample This method detects nearly all types of carbohydrates, including mono-, di-, oligo- and polysaccharides However, the absorption of different carbohydrates is not the same

In this method, concentrated sulfuric acid hydrolysis all polysaccharides, oligosaccharides and disaccharides into monosaccharides The pentoses (5- carbon carbohydrates) are then dehydrated to furfural, and the hexoses (6- carbon carbohydrates) to hydroxymethyl furfural These compounds will then react with phenol to a yellow product