Larutan Standar COD vs Theoritical Oxygen Demand (ThOD)

Dalam analisis COD, salah satu bahan kimia yang dibutuhkan adalah larutan baku Kalium Hidrogen Ftalat (KHP) sebagai larutan standar COD, tetapi tahukah anda bagaimana perhitungannya sehingga kalau kita menimbang 425 mg KHP, maka didapatkan larutan standar COD 500 mg O2/L?

Standardisation of Stock Cyanide Solution

1. Principle:

CN- is titrated with standard silver nitrate to form the soluble cyanide complex, Ag(CN)2-. As soon as all CN- has be complexed and a small excess of Ag+ has been added, the excess Ag+ is detected by the silver-sensitive indicator, p-dimethylaminobenzal-rhodanine, which turns from a yellow to a salmon colour end-point.


2. Reagents:

2.1 Potassium cyanide (KCN), AR. Extremely toxic – read MSDS before handling.

2.2 Sodium hydroxide (NaOH), AR

2.3 Stock cyanide solution, ~1000 ppm: Dissolve 1.6 g NaOH and 2.51 g KCN in 1 L reagent grade water.

2.4 p-dimethylaminobenzal-rhodanine

2.5 Acetone, AR

2.6 Indicator solution: Dissolve 20 mg p-dimethylaminobenzal-rhodanine in 100 mL of acetone.

2.7 Standard AgNO3 solution; (see : Standardisation of Silver Nitrate)


3. Procedure:

To one 250 mL Erlenmeyer flask, add 20 mL of stock KCN solution plus approximately 100 mL reagent grade water. Add a couple of drops of rhodanine indicator; titrate with standard silver nitrate titrant to the first change in colour from a ‘canary’ yellow to a salmon hue. A blank must also be established containing the same amount of alkali and water. Record the results. Carry out standardisation in triplicate. Calculate normality of CN- as per section 5.


4. Frequency of Standardisation

Restandardise every week.


5. Calculation:




Where:
T    =    mL AgNO3 titrant
B    =    blank titre (mL)
N    =    Normality of AgNO3
V    =    Volume standard CN


6. Reference:

APHA 20th Edition: 4500 CN-, D. pp. 4-38-39.

Standardisation of Mercuric Nitrate

1. Principle

Chloride can be titrated with mercuric nitrate, because of the formation of soluble, slightly dissolved mercuric chloride. In the pH range 2.3 to 2.8, diphenyl – carbazone indicates the titration end-point by the formation of a purple complex with the excess mercuric ions. Xylene cyanol FF serves as a pH indicator and end-point enhancer. By increasing the titrant strength and modifying the indicator mixtures, the range of measureable chloride concentration can be extended.



2. Reagents

2.1 Standard Sodium Chloride

2.2 Sodium hydrogen carbonate (NaHCO3), AR

2.3 Ethanol, AR

2.4 1-5 diphenylcarbazone, AR

2.5 Nitric acid (HNO3), 70%, AR

2.6 Xylene cyanol FF, AR

2.7 Diphenylcarbazone

2.8 Bromophenol blue, AR

2.9 Indicator – acidifier reagent: Into 100 mL 95% ethanol dissolve in the following order: 0.250 g 1-5 diphenylcarbazone, 4 mL HNO3 and 0.030 g xylene cyanol FF. Mix well, after the addition of each reagent. Store in a dark bottle in the refrigerator.

2.10 Mixed indicator reagent: Dissolve 0.5 g diphenylcarbazone powder and 0.05 g bromophenol blue powder in 75 mL of Ethanol. Dilute to 100 mL with ethanol.

2.11 Mercuric nitrate (Hg(NO3)2.H2O), AR. Extremely toxic – read MSDS before use. Extremely hygroscopic. Keep jar well sealed.

2.12 Standard mercuric nitrate solution, ~0.0141 N: Dissolve 2.5 g Hg(NO3)2.H2O in 100 mL reagent grade water containing 0.25 mL HNO3. Dilute to 1 L. Standardise by procedure

3.1. Store away from light in a dark bottle.

2.13 Strong Standard mercuric nitrate titrant, ~0.141 N: Dissolve 25 g Hg(NO3)2.H2O in 900 mL of reagent grade water containing 5.0 mL of HNO3. Dilute to 1 L. Standardise by procedure 3.2. Store away from light in a dark bottle.

2.14 Nitric acid, 0.1 N: Carefully add 6.4 mL of nitric acid to 800mL of reagent grade water. Make to 1 L with water.



3. Procedure:

3.1 Standardisation of ~0.0141 N Mercury Nitrate

Titrate an aliquot of standard sodium chloride (e.g. 5.0 mL standard NaCl solution and 0.01 g NaHCO3 diluted to 100 mL) with mercuric nitrate titrant, adding 1.0 mL of indicator – acidifier reagent and 1.0 mL of mixed indicator reagent as the indicators. The solution turns from green-blue to blue a few drops before the ‘definite’ purple end-point. Determine a blank by titrating 100 mL reagent grade water containing 0.01 g NaHCO3. Record the results. Carry out standardization in triplicate. Calculate normality of Hg(NO3)2 as per section 5.

3.2 Standardisation of ~0.0141 N Mercuric Nitrate

Aliquot 25 mL of standard sodium chloride and 25 mL of reagent grade water, into a conical flask adding 0.5 mL of mixed indicator reagent and mix well. The colour should be purple. Add 0.1 N HNO3 dropwise until the colour just turns yellow. Titrate with strong mercuric nitrate titrant to the first permanent dark purple. Titrate a reagent grade water blank as well. Record the results. Carry out standardization in triplicate. Calculate normality of strong Hg(NO3)2 as per section 5.



4 Frequency of Standardisation

Restandardise every 6 months.



5. Calculation:



Where
B = Blank Titre (mL)



6. Reference:

APHA 20th Edition; 4500 - Cl – C; pp.-4-68-69.

Standardisation of Silver Nitrate (Indicator End-point Titration method)

1. Principle

AR silver nitrate has a purity of at least 99.9%, so that a standard solution can be prepared by direct weighing. AR sodium chloride has a purity of 99.9 - 100%; the substance is therefore an excellent primary standard. Sodium chloride is very slightly hygroscopic, and for accurate work it is best to dry the solid at 140oC prior to use. In a neutral or slightly alkaline solution, potassium chromate can indicate the end-point of the silver nitrate titration of chloride. Silver chloride is precipitated quantitatively before red silver chromate is formed.





2. Reagents

2.1 Sodium chloride (NaCl), AR – dried at 140 oC.

2.2 Standard sodium chloride, 0.0141 N: Dissolve 0.824 g NaCl in reagent grade water and dilute to 1L.

2.3 Calcium carbonate, AR

2.4 Potassium chromate (K2CrO4), AR

2.5 Silver nitrate (AgNO3), AR

2.6 Standard silver nitrate solution, ~0.141 N: Dissolve 23.95 g AgNO3 in reagent grade water and dilute to 1 L. Store in a dark bottle. Standardise as per Section 3.

2.7 Standard silver nitrate solution, ~0.0141 N: Dissolve 2.395 g AgNO3 in reagent grade water and dilute to 1 L. Store in a dark bottle. Standardise as per Section 3.

2.8 Potassium chromate indicator: Dissolve 50 g K2CrO4 in a small amount of reagent grade water. Add AgNO3 solution until a definite red precipitate is formed. Let stand 12 hours, filter and dilute to 1 L.



3. Procedure

Take a know aliquot of standard NaCl (e.g. 10 mL diluted to 100 mL for standardize ~0.0141 N AgNO3 or 50 mL diluted to 100 mL for ~0.141 N AgNO3). Add 1 spatula of calcium carbonate to solution, add 1.0 mL K2CrO4 indicator solution, and titrate with AgNO3 to a pinkish-yellow end-point. Be consistent in the end-point recognition. A blank must also be established by this titration. Record information on workbook. Carry out standardization in triplicate. Calculate the normality of AgNO3 as per section 5.



4. Frequency of Standardisation

Restandardise every 6 months.



5 Calculation




Where
B = Blank titre (mL)



6. Reference

APHA 20th Edition: 4500 - Cl – B; pp.4-67-68.

Standardisation of Sodium Thiosulphate

1. Principle

Sodium thiosulphate is readily obtainable in a state of high purity, but there is always some uncertainty as to the exact water content. The substance is therefore unsuitable as a primary standard. Among the variables affecting the stability of thiosulphate solutions are the pH, the presence of micro-organisms and impurities, the concentration of the solution and the presence of atmospheric oxygen. The reaction between iodine and thiosulphate is described by the equation:




2. Reagents

2.1 Potassium Iodide, AR – free from iodate

2.2 Sulphuric Acid (H2SO4), 98%, AR
OR
2.3 Sulphuric Acid, 6 N: Cautiously add 167 mL of H2SO4 to 800 mL of reagent grade water. Make up to 1 L with reagent grade water.

2.4 Potassium bi-iodate (KH(IO3)2), AR

2.5 Standard potassium bi-iodate, 0.021 M: Dissolve 0.8124 g KH(IO3)2 in reagent grade water and dilute to 1 L.

2.6 Sodium Thiosulphate pentahydrate (Na2S2O3.5H2O), AR

2.7 Sodium Hydroxide (NaOH), AR

2.8 Sodium hydroxide, 6 N: with caution dissolve 240 g NaOH in 1 L of reagent grade water in a glass beaker. Prepare this reagent in a fume cupboard.

2.9 Chloroform (CHCl3), AR

2.10 Standard sodium thiosulphate solution, ~0.025 N: Dissolve 6.205 g Na2S2O3.5H2O in reagent grade water. Add 1.5 mL 6 N NaOH or 0.4 g solid NaOH and dilute to 1 L. Add 2 drops of CHCl3.

2.11 Vitex indicator, laboratory grade



3. Procedure

Dissolve approximately 2 g KI in an Erlenmeyer flask with 100 to 150 mL DI water. Add 1 mL 6 N H2SO4 or a few drops of H2SO4 and 20.0 mL Bi-iodate solution. Dilute to 200 mL and titrate liberated iodine with thiosulphate titrant, adding Vitex indicator toward the end of the titration, when a pale straw colour is reached. The titration is complete when the blue colour is discharged. Record information on the work book. Carry our standardization in triplicate. Calculate normality of Na2S2O3 as per Section 5.


4. Frequency of Standardisation

Restandardise every 6 months.


5. Calculation:




6. Reference

APHA 20th Edition. 4500 – 0 C. pp. 4-131.

Standardisation of Sodium Hydroxide (NaOH)

1.1 Principle:

Potassium hydrogen phthalate (KHP) is an excellent primary standard for the standardization of sodium hydroxide due to its high purity and non-hygroscopic nature. It is a weak organic acid, which requires the use of an indicator, in this case phenolphthalein, with a basic transition range.





1.2 Reagents

1.2.1 CO2 free water: Boil reagent grade water for 15 minutes and cool to room temperature.

1.2.2 Potassium hydrogen phthalate (KHC8H4O4) (KHP), AR: Dry at 120oC for 2 hours and allow to cool in a covered vessel in a desiccator.

1.2.3 Potassium hydrogen phthalate (KHP) primary standard solution, 0.049 N: Accurately weigh 10.0 g of KHP and dissolve in ~800 mL of reagent grade water. Make up to 1000 mL in a volumetric flask.

1.2.4 Phenolphthalein, AR

1.2.5 Ethanol, AR

1.2.6 Phenolphthalein indicator solution: Dissolve 5 g of the reagent in 500 mL of ethanol and add 500 mL of reagent grade water with constant stirring. Filter if a precipitate forms.

1.2.7 Sodium Hydroxide (NaOH), AR

1.2.8 Standard Sodium Hydroxide, ~0.1 N: Dissolve 4.0 g NaOH in 1 L or reagent grade water in a glass beaker and store in a plastic bottle. Standardise against KHC8H4O4 as directed in Section 1.3.

1.2.9 Standard Sodium Hydroxide, ~0.02 N: Dilute 200 mL ~0.1 N NaOH to 1 L and store in a plastic bottle. Standardise against KHC8H4O4 as directed in Section 1.3.


1.3 Procedure

1.3.1 Standardisation of 0.1 N NaOH

Weigh approximately 0.2 g (to the nearest 0.1 mg) KHP into a conical flask and add a 20 mL aliquot of CO2 free water, cover flask and dissolve KHP. Or alternatively pipette 20.0 mL of 0.049 N KHP into a conical flask. Titrate each solution with NaOH using phenolphthalein as the indicator to the first permanent pink tinge. Record the information on the work book. Carry out standardization in triplicate. Calculate normality of NaOH as per 1.5.

1.3.2 Stantardisation of 0.02 N NaOH

Weigh approximately 0.1 g (to the nearest 0.1 mg) KHP into a conical flask and add a 20 mL aliquot of CO2 free water, cover flask and dissolve KHP. Titrate each solution with NaOH using phenolphthalein as the indicator to the first permanent pink tinge. Record the information on the work book. Carry out standardization in triplicate. Calculate normality of NaOH as per 1.5.

1.4 Frequency of Standardisation

Sodium hydroxide solutions must be standardized prior to use. Due to the nature of these solutions, the absorb CO2 from the atmosphere.

1.5 Calculations




1.6 Reference:

Vogel’s, ‘Textbook of Quantitative Inorganic Analysis’, 4th Edition; pp. 242, 301-305.

Air Suling (Reagent Grade Water)

Penggunaan air kemurnian tinggi (air suling) untuk persiapan sampel, blanko dan standar adalah penting untuk mendapatkan hasil yang akurat, karena semua reagen dan pelarut yang digunakan untuk beberapa analisis, terutama trace metal, harus bebas dari unsur-unsur yang diukur dan dari setiap elemen atau senyawa yang berpotensi mengganggu pengujian tersebut.

Standar internasional yang sering dijadikan acuan untuk kualitas air adalah ASTM yang mendefinisikan berbagai jenis kualitas air dimulai dengan Tipe I sampai IV.

Berikut adalah Tabel ASTM unuk kualitas air;

Pengukuran (Unit)	Tipe I	Tipe II	Tipe III	Tipe IV
Resistivity (MΩ-cm)	> 18	> 1	> 4	> 0.2 (200KΩ)
Conductivity (µS/cm)	< 0.056	< 1	< 0.25	< 5
pH pada 25˚C	N/A	N/A	N/A	5.0 - 8.0
Total Organic Carbon (TOC) ppb atau µg/L	< 50	< 50	< 200	N/A
Sodium (ppb atau µg/L)	< 1	< 5	< 10	< 50
Chloride (ppb atau µg/L)	< 1	< 5	< 10	< 50
Silica (ppb atau µg/L)	< 3	< 3	< 500	N/A

Mencapai kualitas air yang benar tergantung pada memilih teknologi pemurnian yang benar dan desain sistem yang secara akurat mengukur dan memonitor kontaminan.

Berbagai tingkat kualitas yang diperlukan untuk berbagai macam aplikasi, oleh karena itu nilai yang berbeda dari air harus dimurnikan dan digunakan untuk mencocokkan prosedur atau peralatan yang diperlukan.

Grade Air	Resisi-tivity (M-cm)	TOC (ppb)	Bakteri (CFU/ml)	*Endo- toxin (EU/ml)	Aplikasi
Tipe 1+	18.2	<5	<1	<0.03	Trace metal menggunakan alat GF-AAS, ICP-MS,
Tipe 1	>18	<10	<10	<0.03	HPLC,, GC, AAS, immunocytochemistry, mammalian cell culture, plant tissue culture
Tipe 2+	>10	<50	<10	NA	Aplikasi umum laboratorium yang memerlukan kemurnian inorganik yang lebih tinggi
Tipe 2	>1	<50	<100	NA	Umpan sistem ultra pure tipe 1, Umpan untuk clinical analyzers, electrochemistry, Dilusi sample, preparasi media, radioimmunoassay
Tipe 3	>0.05	<200	<1000	NA	Umpan untuk sistem ultra pure water tipe 1, Umpan untuk washing machines, dishwashers, autoclave

Membuat Air Suling di Lab

Ketika di lab hanya tersedia air keran (tap water), maka beberapa alat harus disiapkan supaya anda bisa menghasilkan air suling yang sesuai persyaratan.

Untuk sistem penyulinagn air yang diperlukan biasanya membutuhkan alat sebagai berikut;

1. Water distillation (misal Water Distillation apparatus dari Schott Instruments GmbH)
2 Ultra pure water purifier system (misal Milli-Q)



Gambar water distillation apparatus (courtesy of Schott Instruments GmbH)

Kadangkala, apabila menggunakan Water distillation yang spesifikasi rendah, biasanya diperlukan alat RO water purifier dengan double filter (1 dan 0,1 um).

Standardization of Hydrochloric Acid and Sulphuric Acid

1.1 Principle

Sodium Carbonate is frequently used to standardize acid solutions. Analytical grade sodium carbonate of 99% purity contains a little moisture and must be dehydrated at 250 oC. The titration of sodium carbonate involves two end-points. The first, corresponding to the conversion of carbonate to bicarbonate at a pH of about 8.3. The second, involving the formation of carbonic acid is observed at a pH of 3.8. It is this second end-point which is used for standardization.






1.2 Reagents

1.2.1 Sodium carbonate (Na2CO3), AR dried at 250 oC for 4 hours.

1.2.2 Sodium carbonate, 0.05 N: Weigh 2.5 ± 0.2 g (to nearest 0.1 mg) Na2CO3 and record this weight. Transfer to 1 L volumetric flask and make up to the mark with reagent grade water. Store in polyethylene bottle in fridge. Remake weekly. Calculate normality of Na2CO3 (to 3 significant figures) as per 1.5 formula 2.

1.2.3 Methyl orange, AR

1.2.4 Indigo Carmine, AR

1.2.5 Methyl orange – indigo carmine indicator: dissolve 0.25 g methyl orange and 0.625 g indigo carmine in 250 mL of DI water. Store in glass bottle in refrigerator. Indicator will turn brown with shelf life has expired.

1.2.6 Hydrochloric acid (HCl), 32% AR or Sulphuric Acid (H2SO4), 98%, AR.

1.2.7 Standard hydrochloric acid or Sulphuric acid, ~0.1 N: Dilute 9.3 mL of conc. HCl or 2.8 mL conc. H2SO4 in 500 mL reagent grade water, transfer to a 1 L volumetric flask and make up to the mark with water. Standardise as per 1.3.1.

1.2.8 Standard hydrochloric acid or Sulphuric acid, ~0.02 N: Dilute 200 mL ~ 0.1 N standard acid to 1 L with reagent grade of water. Standardise as per 1.3.2.


1.3 Procedure:

1.3.1 Standardisation of ~0.1 N Hydrochloric Acid or Sulphuric Acid.

Accurately weigh about 0.1 g sodium carbonate (to the nearest 0.1 mg) into a conical flask and dissolve in 50 mL reagent grade water. Record this weight on the work book. Or alternatively pipette 25.0 mL of ~0.05 N Na2CO3 into a conical flask and dilute with 50 mL reagent grade water. Add 2 drops methyl orange – indigo carmine indicator and titrate with ~0.1 N HCl or H2SO4 until the colour changes from green to magenta with a blue-gray colour at approximately pH 4. Carry out standardization in triplicate. Calculate normality of HCl or H2SO4 as per 1.5 formula (1) or (3).

1.3.2 Standardisation of ~0.02 N Hydrochloric Acid or Sulphuric Acid.

Pipette 5.0 mL of 0.05 N Na2CO3 into a conical flask and dilute with 50 mL reagent grade water. Add 2 drops methyl orange – indigo carmine indicator and titrate with ~0.02 N HCl or H2SO4 until the colour changes from green to magenta with a blue-gray colour at approximately pH 4. Carry out standardization in triplicate. Calculate normality of HCl or H2SO4 as per 1.5 formula (3).

1.4 Frequency of Standardisation

Standardise hydrochloric acid and Sulphuric solutions on preparation. Solutions of hydrochloric acid and Sulphuric acid are stable and may be stored and used over a lengthy period of time without restandardising, provided that the contents of the storage vessel are thoroughly mixed before each use.


1.5 Calculations




1.6 Reference:

Vogel’s ‘Textbook of Quantitative Inorganic Analysis’; 4th Edition pp. 242, 301-305.