33ndnd Meeting MeetingChemical Analysis Chemical Analysis

Steps and issuesSteps and issues

STEPS IN CHEMICAL ANALYSIS

1. Sampling

2. Preparation

3. Testing/Measurement

4. Data analysis

2. Error in chemical analysis

3. Statistics for chemistry

SAMPLING

Prerequisite: sample should be representative

Example: Main sample

A B C Primary sample

1

43

2

2 + 3 1 + 4

dc

ba a b

c d

Bulk sample

Sub-bulk sample

Lab sample

Preparation for Solid Sample

1.Wet Digesting

• Direct solvation with water

• Solvation with: oxydator acids (HNO3, H2SO4, HCl, HClO4, its mixtures) and base.

• Destruction with aqua regia: HNO3 : HCl = 1 : 3.

2. Dry digesting

Ashing (Furnace) in certain temperature (+“ashing aid”. if necessary), solving in acids, and diluting quantitatively

TESTING/MEASUREMENT

Purpose : Qualitative and quantitative

analysisQualitative Analysis: Spot test Analysis

Quantitative Analysis:

Conventional Methods: Volumetri dan Gravimetri

Physico-chemical methods (modern) :

Elektrokimia, Spektrofotometri

Calculatioan and Data Interpretation

DATA CAN BE ACHIEVED (quantitative analysis):

volume, (volumetric),mass, (Gravimetric)Absorption (Spectrometric)Potential Cell (Electrochem)

Should be changed in to

Concentration, (M, ppm)

content (% mass/mass, % vol/mass)

Every steps in analysis steps

always face error.

Need Statistic calculation to help in

decision making

Error in data interpretation

Error in chemical analysis1. Indeterminate Error error can be exactly defined

Examples:

- Noise and deviation in electronic circuits

- Vibration of building

- environment change

2. Determinate Error/Systematical error

- Error in methods: Interfere agents ( can be + or -)

3. Operational Error: Operators/Analysts

4. Instrumental Error: Uncalibated/ un-standardized instruments

Relative Error

True value – measurement value% Error = x 100% True value

Simple Statistics in chemical analysis

1. Mean (harga rata-rata, x ),

x1 + x2 + x3 + ... + xn

X = n

2. Standard Deviation (S), Variability of analysis result

( x – x )2

S =

n – 1

JK

S =

n - 1

3. Relative Standard Deviation (R.S.D) s R.S.D = x

4. Coefficient of Variation (C.V.) s x 100 C.V. = x

Example :

Analysis of iron ores produce % mass of Iron:

7,08 ; 7,21 ; 7,12 ; 7,09 ; 7,16 ; 7,14 ; 7,07 ; 7,14 ; 7,18 ; 7,11.

Calculate: means, Standard of deviation, and coefficient of variation !

Jawab :

X = 7,13 % ; s = 0,045 % ; C.V. = 0,63%

5. Batas Kepercayaan, merupakan daerah di sekitar harga yang sesungguhnya

= x + t (sx)

s

sx = n

Nilai t diperoleh dari Tabel t pada derajat kebebasan (D.B.) = n - 1

Contoh:

Hasil analisis massa nikel (mg) yang terkandung dalam 1 g suatu bahan galian adalah : 5,0 ; 5,3 ; 5,7 ; 4,8 ; 5,2

Hitung batas kepercayaan pada tingkat kepercayaan 95%

ANSWERANSWER

• x = 5,2 ; s = 0,3 ; sx = 5,2 ; s = 0,3 ; sxx = 0,134 = 0,134

= 5,20 = 5,20 ++ 0,37 0,37 So So 95% 95% believe that % mass of Iron is believe that % mass of Iron is between : between : 4,83 – 5,57.4,83 – 5,57.

8.Presision

The similarity of value/data in one set of data, shown by standard of deviation

9. Acuration

The nearness of data measurement to the true value

x x xx x

x x xx x

X

XX

XX

X

X

XX

X

AB C D

x x xx x

x x xx x

X

XX

XX

X

X

XX

X

AB C D

Keterangan:

A : Presisi baik, akurasi baik

B : Presisi baik, akurasi tidak baik

C : Presisi tidak baik, akurasi baik (rata-rata)

D : Presisi tidak baik, akurasi tidak baik

SEKIAN DULUSEKIAN DULU

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