Assay of Milk of Magnesia

Assay of Milk of Magnesia

• Milk of magnesia is assayed to determine the percentage present in a sample.
• An acidimetric analysis using residual titration is preformed.
• The USP requires milk of magnesia to contain not less than 7% and not more than 8.5% of Mg(OH)2.

Materials

• Milk of magnesia
• Standard hydrochloric acid solution
• Methyl red or methyl orange
• Standard sodium hydroxide solution

Procedure

• Accurately weigh 5 g of milk of magnesia.
• Accurately measure 25 mL of standard hydrochloric acid and add to the weighed sample.
• Add three drops of either methyl red or methyl orange.
• Titrate the excess acid with standard sodium hydroxide solution until the peach or salmon color disappears.
• Perform a blank determination.

Calculations

• To calculate the percentage of Mg(OH)2, use the formula: [(mLHCl x NHCl) – (mLNaOH x NNaOH)] x meq Mg(OH)2 x 100 / Sample weightMg(OH)2
• A sample calculation is [(25mL x 0.94N) – (8.5mL x1.08N)] x 0.02916 x 100 / 5g = 8.35% Mg (OH)2.
• To determine the blank, use the formula: Nactual x (Vactual - Vblank) x MW/f x 1000 x 100 / Weight of sample (g)
• A sample blank determination is 1.08N x (8.5mL – 12mL) x 0.02916 x 100 / 5g = 2.20%.

Definitions and Reactions

• Milk of magnesia’s Name is Mg (OH)2.
• The alternate name is Magnesium hydroxide.
• The Molecular Weight is 58.3197 g/mol.
• The Factor is 2.
• Use the Std. NaOH Solution and Std. HCl Solution.
• Methyl orange is the Indicator.
• The End Point is the disappearance of peach or salmon color.
• The chemical reactions include: Mg (OH)2 + 2HCl -> MgCl2 + 2H2O and HCl + NaOH -> NaCl + H2O
• Milk of magnesia dissolves in an accurately measured excess of 1N HCl/H2SO4 solution to ensure complete neutralization of all the magnesium hydroxide and the formation of soluble MgSO4.

Principles of the Assay

• This assay follows an acid-base reaction where a standard acid is used.
• Magnesium hydroxide is practically insoluble in water, therefore direct titration is not possible, and back or residual titration is employed.
• Back titration involves dissolving the substance in excess standard solution of known strength, followed by titrating the excess with another standardized solution.
• The computed purity is 8.35% of Mg (OH)2, which conforms to USP standards which require nlt 7 and nmt 8.5% Mg (OH)2.
• A result of 2.20% was obtained in the blank determination, failing to conform to specification because Mg (OH)2 was not present in the analyte solution.

Defining Milk of Magnesia

• Milk of magnesia is an over-the-counter antacid and laxative to neutralize stomach acid and relieve constipation.
• It is a suspension and not a solution because its active ingredient, magnesium hydroxide (Mg(OH)2), is only slightly soluble in water.
• The milky appearance results from undissolved magnesium hydroxide particles.

Methods for Assaying

• Analytical methods exist for determining the percentage of magnesium hydroxide in milk of magnesia.
• Acid-base titration, the most common method, uses an acid (usually HCl) to react with magnesium hydroxide.
• Gravimetric analysis involves precipitating Mg(OH)2 and weighing the dried product.
• Complexometric titration with EDTA determines magnesium ion concentration.
• Spectrophotometry measures absorbance related to magnesium compounds.
• Acid-base titration is preferred due to its accuracy and ease of use.

Acid-Base Titration

• The titration reacts magnesium hydroxide (Mg(OH)2) with a strong acid, typically hydrochloric acid (HCl).
• The reaction is Mg(OH)2+2HCl→MgCl2+2H2O
• Magnesium hydroxide is a weak base, so it reacts with strong acid to form a neutral salt (MgCl2) and water.

Sample Preparation Steps

• Shake the suspension well to ensure uniformity.
• Gradually add a known volume of HCl from a burette.
• Use a suitable pH indicator to observe pH changes to signal the endpoint.
• Calculate the percentage of Mg(OH)2 using the volume of HCl required to neutralize the sample and the mass of Mg(OH)2 in the original sample.

Indicators

• Methyl orange or phenolphthalein are typically used, depending on the titration type.
• Phenolphthalein is preferred when titrating with strong acids; its color changes from pink (basic pH) to colorless (neutral or acidic pH) at an endpoint of pH ≈ 8.2–10.
• Methyl orange changes from yellow (basic) to red (acidic) at pH ≈ 3.1–4.4, useful in excess acid titration methods.
• Phenolphthalein is chosen because milk of magnesia is a weak base, which causes a clear color change.

Importance of Assay Preparation

• Magnesium hydroxide is a suspension, and it settles.
• If improperly mixed, the assay may measure only the liquid phase, causing inaccurate results.
• A uniform distribution of Mg(OH)2 in the sample improves titration precision.
• Carefully control any dilution, as excess water alters concentration calculations.

Potential Errors

• Incomplete mixing of the suspension may result in non-uniform sampling.
• Over or under-titration causes incorrect endpoint determination.
• Sample loss due to spillage or evaporation affects the final concentration.
• Contaminants in reagents can alter reaction stoichiometry.

Minimization Strategies

• Thoroughly shake or stir the milk of magnesia before sampling.
• Use a consistent drop rate when adding acid.
• Perform replicate titrations to ensure accuracy.
• Use properly calibrated burettes and glassware.

Implications of Inaccurate Assay

• If the assay underestimates Mg(OH)2 content, the dose may be too low, reducing its effectiveness as an antacid or laxative.
• If the assay overestimates Mg(OH)2 content, patients could receive excessive doses, leading to hypermagnesemia, diarrhea, or electrolyte imbalances.
• Regulatory bodies like USP and FDA set strict quality control standards; failure to meet standards can lead to recalls or safety warnings.

Interfering Substances

• Flavoring agents, sweeteners, or stabilizers added to commercial formulations can interfere.
• Other magnesium compounds, like magnesium carbonate, can react differently with acids.
• Insoluble impurities won't participate in the titration reaction.

Manufacture Methods

• Blank titrations account for non-reactive components.
• Purity tests are used on raw materials before manufacturing.
• Standardizing titration conditions ensures reproducibility.

Endpoint pH Significance

• The endpoint pH determines when all Mg(OH)2 has reacted with the acid.
• With phenolphthalein, expect an endpoint pH around 8.2–10 for complete neutralization of magnesium hydroxide.
• A lower pH (around 4) with methyl orange may indicate excess acid.
• Monitoring pH ensures precise calculation of the Mg(OH)2 content.

Safety Precautions

• Wear a lab coat, gloves, and safety goggles.
• Hydrochloric acid (HCl) can cause burns and irritation; use pipettes or burettes to measure precisely.
• Even though it may be a pharmaceutical product, do not swallow .
• Work in a well-ventilated area due to strong acids fumes.
• Neutralize excess acid or base before disposal.

Assay of Aspirin Tablets

• Aspirin tablets (C6H4OCOCH3COOH) are assayed to determine the percentage.
• An alkalimetric analysis using residual titration is preformed.
• USP standards state that Aspirin tablets needs to contain not less than 95% and not more than 105% of the labeled amount.

Materials

• 10 Aspirin tablets
• Standard Sulfuric acid solution
• Standard Sodium hydroxide

Procedure

• Weigh 1.0g of previously pulverized aspirin accurately in a filed Erlenmeyer flask.
• Run down 50mL of standard sodium hydroxide solution to the filed sample of aspirin.
• Cover with an inverted beaker and boil for 10 minutes.
• Let it cool.
• Add 1 pipette-full (10mL) of phenolphthalein TS.
• Titrate the excess sodium hydroxide with standard sulfuric acid solution until the pink color disappears.
• Perform a blank determination.

Calculations

• To calculate the ASA/Tab, use the formula: (mLNaOH - mLH2SO4) x NH2SO4 x meqwtASA x 100 / Wt (g)ASA
• To determine the blank, use the formula: NactualH2SO4 x (VactualH2SO4 - VblankH2SO4) x MW/f x 1000 x 100 / Weight of sample (g)

Definitions and Reactions

• The name of the sample is Acetyl salicylic acid – HC9H7O4 or C9H8O4.
• The Other Names are 2-acetoxybenzoic acid acetylsalicylate, acetylsalicylic acid O-acetylsalicylic acid, Aspirin.
• The Molecular Weight is 180.158 g/mole.
• The Factor is 1.
• The Standard solution is Standard NaOH solution and H2SO4.
• The Indicator is phenolphthalein TS.
• The End Point is the disappearance of the pink color.
• The Chemical Reactions are C6H4OCOCH3COOH + H2O -> C6H4OHCOOH + CH3COOH and C6H4OCOCH3COOH + NAOH -> C6H4OCOCH3COONa + H2O
• To neutralize hydrolysis products of acetylsalicylic acid, this should be carried out at room temperature or slightly below.

Purpose of Assay

• The assay involves checking for purity, ensuring compliance with standards (USP, BP, or FDA), and assessing stability.
• Degradation products such as salicylic acid caused by hydrolysis are identified.
• Dosage accuracy is tested for distribution.
• These results ensures safety for customers.

Methods

• An acid-base titration is performed to hydrolyze aspirin with NaOH and back-titrate the excess NaOH with HCl.
• The UV-Visible Spectrophotometry measures absorbance to determine aspirin concentration.
• High-Performance Liquid Chromatography (HPLC) is primarily used for quantity.
• Thin-Layer Chromatography (TLC) is used for quality identification.

Titration for Aspirin

• Aspirin is a weak acid, so A back titration method is used.
• A known excess amount of NaOH is added to dissolve and hydrolyze aspirin.
• The reaction for this is C9H8O4+NaOH→C7H5O3Na+CH3COONa.
• Since excess NaOH remains, it is back-titrated with HCl to determine the exact amount of NaOH that reacted with aspirin.
• The difference in NaOH to helps calculate the amount of aspirin in the tablet.

Chemical Equations

• The hydrolysis of aspirin in the presence of NaOH to form sodium salicylate and sodium acetate is denoted with the equation: C9H8O4+2NaOH→C7H5O3Na+CH3COONa+H2O.
• Two mole of NaOH can fully react and hydrolyze one mole of aspirin.

Aspirin Solution

• Accurately weigh a sample of crushed aspirin tablet.
• Dissolve in a volume of NaOH.
• Heat the mixture gently until aspirin turns into sodium salicylate.
• Cool the solution down.
• Titrate the excess NaOH using HCI.

Error Sources

• One error sources is incomplete hydrolysis of the aspirin.
• To solve this ensure adequate heating and complete dissolution.
• Another error source is evaporation of NaOH solution, perform titration immediately after hydrolysis.
• With endpoint detection, add a suitable indicator (phenolphthalein) for a clear endpoint.
• With contamination, use only freshly prepared standard solutions.
• Viewing the meniscus at eye level can avoid Parallax errors in burette readings.
• Handling errors can be minimized with proper glassware and multiple titration trials.

Fresh Solution Importance

• It's important to use these fresh to avoid degradation of NaOH and HCI which can alter concentration.
• Aspirin is less stable and can lead to the breakdown of salicylic acid.
• By using new solutions this affect your accuracy.

Role of Blank Titration

• A blank titration helps correct for any impurities outside of hydrolysis.
• It involves Performing the same titration procedure without aspirin and Measuring how much HCl is required to neutralize NaOH in the absence of aspirin.
• Subtracting the amount, ensures results are from only the NaOH reacting.

How to Prepare Sample

• Use dry tools to avoid excess water calculations.
• Grind tablets down to fine powder.
• Avoid air contact to dissolve aspirin.
• Make sure no other substances intefere.
• Store away to keep moisture out.

Factors Affecting the Assay

• There are factors that affect the accuracy of measuring the amount of aspirin.
• One factor may be high temperatures accelerate hydrolysis, but overheating can cause errors.
• If solutions are dilute, this can lead to high error chance, but if its too high, they may be rapid, making the endpoint detection difficult.
• An indicator such as Phenolphthalein is commonly used, because it provides a sharp color change in weak acid–strong base titrations.
• Mixing issues may lead to concentration issues, so standardized titrant concentrations, proper heating, and precise endpoint detection should be used.

Preparation and Standardization of Silver Nitrate Solution

• To prepare and standardize silver nitrate solution, or AgNO3 to comply.
• The method being used of analysis is Precipitation.
• A reaction is involved with AgNO3 + H2O -> AgOH + HNO3 and AgOH + HCI -> AgCl + H2O.
• A standard needs to be between 99.8% - 100.5%.

To properly prepare

• Weigh accurately 17.5g of silver nitrate crystals
• Dissolve the silver nitrate crystals, with distilled water to make one (1) L solution.
• Pour the solution into a amber stock bottle

To standardize

• Measure out around 40 mL and mix it with water of 100 ml.
• Add small amounts of acid water
• Boil for for around 5 mins
• Make sure the mixture is in the dark, then let it sit unitl the liquid is clean.
• Move to a tared crucible with a cover
• Wash is soaks into the paper
• Dry the mixture to 110 until its dried up.

AgNO3 Properties

• Silver nitrate is known as AgNO3.
• Other Name/s Nitric acid silver(1+) salt; Lunar caustic, Nitrate d'argent; Nitric acid silver(I) salt, Silver mononitrate; Silver(I) nitrate
• The wieght is around 169.8731 g/mol.
• The indicator is none.
• Reaction is Formation of precipitate (AgCl) and has properties of AgNO3 + H2O -> AgOH + ΗΝΟ3.

Handeling Precautions

• Be careful when handling silver nitrates because its a oxidizing ingredient.
• This stains things due to the light
• It is often corrosive.
• Spills can cause issues when contaminating.
• To prevent a accident from occuring, wear gloves and eye protectors.

Concentrations Used

• If doing precipitation.
• If measuring chloride
• If measuring small parts of chloride.
• Often 0.1 silver nitrate is used.
• To store it, amber bottles is reccomended.

Safety

• Wear protective gear and clothes
• Don't breath it in.
• Have disinfected water.
• Follow dissposal guidence
• Dont contacct with metal utensils.

Standardiziation

• You process need to be clean and exact
• Avoid commercial issues
• Concentrate on preciipitation
• Don't consistenly concentrate the solutions.
• Check your work to be quanity.

Sodium Cloride Info

• Most primary standard for silver nitrate
• Often pure and stable.
• It reacts well and often

Silver Nitrate Contamination

• There may be effects if Silver Nitrate is in the pressence of impurities.
• They can alter, react, or affect stability.
• To minmise this use analytical items and filters.

Assay of Povidone - iodine

• To measure iodine content
• The Method being used is Oxidation – reduction lodometry
• USP standasrds state it must be between 9 and 12 percent calculated on the dry formula

Preperations

• With materials such as povidone iodine, distiller water, sodium thiosutlfate, and stratch
• To properly preform start with small amounts of povidone etc. and add the water of around 200 ml. Stir and seal unitl fully dissolved. Test for stratch if the end is aproached
• Preform determation and correction.

The formula used

• Use the formula or the lodine amount

Reactants

• Reaction invovles water and chemicals such as the 2 – Pyrollindonie
• It also creates homo compounds. The iodidde needs ot be in the compounds

Questions Involvued

• What the the points of it? To ensure its correct
• If too low, its not effective but if is too high, it can cause issues.

Iodine Determinate

• Add sulfuric acids and water
• Liberate fodine and make standards
• Add starch
• Test solution with sodium.

Distilled iodine

• UUse dry gloves.
• Stop air exposure.
• Avooid waste.

Redox Reaction

• Redox helps idodine in poviodin

Other parts

• Stratch is commonly used.
• Sodium is the best to minimize errors.
• Need the solutions in the right order and make sure its clean
• Perform it safe..

Assay of Hydrogen Peroxide

• Hydrogen peroxide is measure for the present amount.
• It is a redox measure
• Solution needs to be between 2.5 and 3.5 to be within standards.

The Preperation

• Needs hydrogen liquid, sterilized water and sulfuric acids
• Have potassium until pink.
• Have other tools and solutions.
• To measure use: (Volume K N)/(Measure of H2o)*100
• There are other items like Oxygenada

Disinfectants Questions

• Needs to be a disinfectant, oxidant, and chemical reagent .
• It may also be perservative due to medical uses
• There are a few steps to breakdown, release free actions and a few others, .
• Has many properties but at high and low concentartions.

How safe is it?

• It need to be a small, medium but not high concentraionate formula

Sodium Hypochloride

• Has sodium hypochloride. And distilled water for the substance
• The solution needs to be around 4 to 6 grams.

Steps to preapre

• There are several steps. A liquid needs to go into liquid then the substance.
• Then test by disapeerance
• When testing, to make sure the solution is well, make sure to keep it in check
• Must add the acids and indicator.

Chemicals Questions

• What are the questions?
• Well they can be made with things like potatos but they are normally recuded or combined.
• Acids also can be used to make liquids
• The solvents helps reduce things.

Final Steps

• During the testing is reduced.
• Distilled water is a big usage
• Can calculate chlorine in lime.

The questions

• What is iodine testing?
• This is done with other test and more.
• The data is calculated and compared with the same testing as iodine to test chlorine.