Extracted from public literature: DOI-http://dx.doi.org/10.17509/ijost.v4i1.15806
1. INTRODUCTION
Fourier transform infrared (FTIR) is one of the important analytical techniques for researchers. This type of analysis can be used for characterizing samples in the forms of liquids, solutions, pastes, powders, films,fibers, and gases. This analysis is also possible for analyzing material on the surfaces of substrate. Compared to other types of characterization analysis, FTIR is quite popular. This characterization analysis is quite rapid, good in accuracy, and relatively sensitive.
In the FTIR analysis procedure, samples are subjected to contact with infrared (IR) radiation. The IR radiations then have impacts on the atomic vibrations of a molecule in the sample, resulting the specific absorption and/or transmission of energy. This makes the FTIR useful for determining specific molecular vibrations contained in the sample.
Many techniques for explaining in detail regarding the FTIR analysis have been reported. However, most papers did not report in detail about how to read and interpret the FTIR results. In fact, the way to understand in detail for beginner scientists and students are inevitable.
This report was to discuss and explain how to read and interpret FTIR data in the organic material. The analysis was then compared with the literatures. The step-bystep method on how to read the FTIR data was presented, including reviewing simple to the complex organic materials.
2. CURRENT KNOWLEDGE FOR UNDERSTANDING FTIR SPECTRUM
2.1. Spectrum in the FTIR analysis result.
The main idea gained from the FTIR analysis is to understand what the meaning of the FTIR spectrum (see example FTIR spectrum in Figure 1). The spectrum can result “absorption versus wavenumber” or “transmission versus wavenumber” data. In this paper, we discuss only the “absorption
versus wavenumber” curves.
In short, the IR spectrum is divided into three wavenumber regions: far-IR spectrum (<400 cm -1), mid-IR spectrum (400-4000 cm-1), and near-IR spectrum (4000-13000 cm-1).The mid-IR spectrum is the most widely used in the sample analysis, but far- and near-IR spectrum also contribute in providing information about the samples analyzed. This study focused on the analysis of FTIR in the mid-IR spectrum.
The mid-IR spectrum is divided into four regions:
(i) the single bond region (2500-4000 cm-1),
(ii) the triple bond region (2000-2500 cm-1),
(iii) the double bond region (1500-2000 cm-
1), and(iv) the fingerprint region (600-1500 cm-1).
The schematic IR spectrum is available in Figure 1, and the specific frequency of each functional groups is available in Table 1.
Figure 1. Mid-IR spectrum regions
2.2. Step-by-step Analysis Procedure.
There are five steps to interpret FTIR:
Step 1: Identification of number of absorption bands in the entire IR spectrum. If the sample has a simple spectrum (has less than 5 absorption bands, the compounds analyzed are simple organic compounds, small mass molecular weight, or inorganic compounds (such as simple salts). But, if the FTIR spectrum has more than 5 absorption bands, the sample can be a complex molecule.
Step 2: Identifying single bond area (2500-4000 cm-1). There are several peaks in this area:
(1) A broad absorption band in the range of between 3650 and 3250 cm-1, indicating hydrogen bond. This band confirms the existence of hydrate (H2O), hydroxyl (-OH), ammonium, or amino. For hydroxyl compound, it should be followed by the presence of spectra at frequencies of
1600–1300, 1200–1000 and 800–600 cm-1. However, if there is a sharp intensity absorption in the absorption areas of 3670 and 3550 cm-1, it allows the compound to contain an oxygenrelated group, such as alcohol or phenol (illustrates the absence of hydrogen bonding).
(2) A narrow band at above 3000 cm-1,indicating unsaturated compounds or aromatic rings. For example, the presence of absorption in the
wavenumber of between 3010 and 3040 cm-1 confirms the existence of simple unsaturated olefinic compounds.
(3) A narrow band at below 3000 cm-1, showing aliphatic compounds. For example, absorption band for longchain linear aliphatic compounds is
identified at 2935 and 2860 cm-1. The bond will be followed by peaks at between 1470 and 720 cm-1.
(4) Specific peak for Aldehyde at between 2700 and 2800 cm-1.
Step 3: Identifying the triple bond region (2000-2500 cm-1) For example, if there is a peak at 2200 cm-1, it should be absorption band of C≡C. The peak is usually followed by the presence of additional spectra at frequencies of 1600–1300, 1200–1000 and 800–600 cm-1.
Step 4: Identifying the double bond region (1500-2000 cm-1) Double bound can be as carbonyl (C = C),imino (C = N), and azo (N = N) groups.
(1) 1850 - 1650 cm-1for carbonyl compounds
(2) Above 1775 cm-1, informing active carbonyl groups such as anhydrides, halide acids, or halogenated carbonyl, or ring-carbonyl carbons, such as lactone, or organics carbonate.
(3) Range of between 1750 and 1700 cm-1, describing simple carbonyl compounds such as ketones, aldehydes, esters, or carboxyl.
(4) Below 1700 cm-1, replying amides or carboxylates functional group.
(5) If there is a conjugation with another carbonyl group, the peak intensities for double bond or aromatic compound will be reduced.
Therefore, the presence of conjugated functional groups such as aldehydes, ketones, esters, and carboxylic acids can reduce the frequency of carbonyl absorption.
(6) 1670 - 1620 cm-1for unsaturation bond (double and triple bond).Specifically, the peak at 1650 cm-1is for double bond carbon or olefinic
compounds (C = C). Typical conjugations with other double bond structures such as C = C, C = O or aromatic rings will reduce the intensity frequency with intense or strong absorption bands. When diagnosing unsaturated bonds, it is also necessary to check absorption below 3000 cm-1. If the absorption band is identified at 3085 and 3025 cm-1, it is intended for C-H. Normally C-H has absorption above 3000 cm-1.
(7) Strong intensity at between 1650 and 1600 cm-1, informing double bonds or aromatic compounds.
(8) Between 1615 and 1495 cm-1, responding aromatic rings. They appeared as two sets of absorption bands around 1600 and 1500 cm-1.These aromatic rings usually followed by the existence of weak to moderate absorption in the area of between 3150 and 3000 cm-1(for C-H stretching).For the simple aromatic compounds, several bands can be also observed between 2000 and 1700 cm-1in the form of multiple bands with a weak intensity. It is also support the aromatic ring absorption band (at 1600/1500 cm-1absorption frequency), namely C-H bending vibration with the intensity of medium absorption to strong which sometimes has single or multiple absorption bands found in the area between 850 and 670 cm-1.
Step 5: Identifying the fingerprint region (600-1500 cm-1)
This area is typically specific and unique. See detailed information in Table 1. But, several identification can be found:
(1) Between 1000 and 880 cm-1 for multiple band absorption, there are absorption bands at 1650, 3010, and 3040 cm-1.
(2) For C-H (out-of-plane bending), it should be combined with absorption bands at 1650, 3010, and 3040 cm-1 which show characteristics of
compound unsaturation.
(3) Regarding vinyl-related compound, about 900 and 990 cm-1 for identifying vinyl terminals (-CH=CH 2), between 965 and 960 cm-1 for trans unsatrated vinyl (CH=CH), and about 890 cm-1 for double olefinic bonds in single vinyl (C=CH 2).
(4) Regarding aromatic compound, a single and strong absorption band is around 750 cm-1 for orto and 830 cm- 1 for para.
Table 1. Functional group and its quantified frequencies.
Extracted from public literature: DOI-http://dx.doi.org/10.17509/ijost.v4i1.15806
1. INTRODUCTION
Fourier transform infrared (FTIR) is one of the important analytical techniques for researchers. This type of analysis can be used for characterizing samples in the forms of liquids, solutions, pastes, powders, films,fibers, and gases. This analysis is also possible for analyzing material on the surfaces of substrate. Compared to other types of characterization analysis, FTIR is quite popular. This characterization analysis is quite rapid, good in accuracy, and relatively sensitive.
In the FTIR analysis procedure, samples are subjected to contact with infrared (IR) radiation. The IR radiations then have impacts on the atomic vibrations of a molecule in the sample, resulting the specific absorption and/or transmission of energy. This makes the FTIR useful for determining specific molecular vibrations contained in the sample.
Many techniques for explaining in detail regarding the FTIR analysis have been reported. However, most papers did not report in detail about how to read and interpret the FTIR results. In fact, the way to understand in detail for beginner scientists and students are inevitable.
This report was to discuss and explain how to read and interpret FTIR data in the organic material. The analysis was then compared with the literatures. The step-bystep method on how to read the FTIR data was presented, including reviewing simple to the complex organic materials.
2. CURRENT KNOWLEDGE FOR UNDERSTANDING FTIR SPECTRUM
2.1. Spectrum in the FTIR analysis result.
The main idea gained from the FTIR analysis is to understand what the meaning of the FTIR spectrum (see example FTIR spectrum in Figure 1). The spectrum can result “absorption versus wavenumber” or “transmission versus wavenumber” data. In this paper, we discuss only the “absorption versus wavenumber” curves.
In short, the IR spectrum is divided into three wavenumber regions: far-IR spectrum (<400 cm -1), mid-IR spectrum (400-4000 cm-1), and near-IR spectrum (4000-13000 cm-1).The mid-IR spectrum is the most widely used in the sample analysis, but far- and near-IR spectrum also contribute in providing information about the samples analyzed. This study focused on the analysis of FTIR in the mid-IR spectrum.
The mid-IR spectrum is divided into four regions: (i) the single bond region (2500-4000 cm-1), (ii) the triple bond region (2000-2500 cm-1), (iii) the double bond region (1500-2000 cm- 1), and(iv) the fingerprint region (600-1500 cm-1). The schematic IR spectrum is available in Figure 1, and the specific frequency of each functional groups is available in Table 1.
Figure 1. Mid-IR spectrum regions
2.2. Step-by-step Analysis Procedure.
There are five steps to interpret FTIR:
Step 1: Identification of number of absorption bands in the entire IR spectrum. If the sample has a simple spectrum (has less than 5 absorption bands, the compounds analyzed are simple organic compounds, small mass molecular weight, or inorganic compounds (such as simple salts). But, if the FTIR spectrum has more than 5 absorption bands, the sample can be a complex molecule.
Step 2: Identifying single bond area (2500-4000 cm-1). There are several peaks in this area:
(1) A broad absorption band in the range of between 3650 and 3250 cm-1, indicating hydrogen bond. This band confirms the existence of hydrate (H2O), hydroxyl (-OH), ammonium, or amino. For hydroxyl compound, it should be followed by the presence of spectra at frequencies of 1600–1300, 1200–1000 and 800–600 cm-1. However, if there is a sharp intensity absorption in the absorption areas of 3670 and 3550 cm-1, it allows the compound to contain an oxygenrelated group, such as alcohol or phenol (illustrates the absence of hydrogen bonding).
(2) A narrow band at above 3000 cm-1,indicating unsaturated compounds or aromatic rings. For example, the presence of absorption in the wavenumber of between 3010 and 3040 cm-1 confirms the existence of simple unsaturated olefinic compounds.
(3) A narrow band at below 3000 cm-1, showing aliphatic compounds. For example, absorption band for longchain linear aliphatic compounds is identified at 2935 and 2860 cm-1. The bond will be followed by peaks at between 1470 and 720 cm-1.
(4) Specific peak for Aldehyde at between 2700 and 2800 cm-1.
Step 3: Identifying the triple bond region (2000-2500 cm-1) For example, if there is a peak at 2200 cm-1, it should be absorption band of C≡C. The peak is usually followed by the presence of additional spectra at frequencies of 1600–1300, 1200–1000 and 800–600 cm-1.
Step 4: Identifying the double bond region (1500-2000 cm-1) Double bound can be as carbonyl (C = C),imino (C = N), and azo (N = N) groups.
(1) 1850 - 1650 cm-1for carbonyl compounds
(2) Above 1775 cm-1, informing active carbonyl groups such as anhydrides, halide acids, or halogenated carbonyl, or ring-carbonyl carbons, such as lactone, or organics carbonate.
(3) Range of between 1750 and 1700 cm-1, describing simple carbonyl compounds such as ketones, aldehydes, esters, or carboxyl.
(4) Below 1700 cm-1, replying amides or carboxylates functional group.
(5) If there is a conjugation with another carbonyl group, the peak intensities for double bond or aromatic compound will be reduced. Therefore, the presence of conjugated functional groups such as aldehydes, ketones, esters, and carboxylic acids can reduce the frequency of carbonyl absorption.
(6) 1670 - 1620 cm-1for unsaturation bond (double and triple bond).Specifically, the peak at 1650 cm-1is for double bond carbon or olefinic compounds (C = C). Typical conjugations with other double bond structures such as C = C, C = O or aromatic rings will reduce the intensity frequency with intense or strong absorption bands. When diagnosing unsaturated bonds, it is also necessary to check absorption below 3000 cm-1. If the absorption band is identified at 3085 and 3025 cm-1, it is intended for C-H. Normally C-H has absorption above 3000 cm-1.
(7) Strong intensity at between 1650 and 1600 cm-1, informing double bonds or aromatic compounds.
(8) Between 1615 and 1495 cm-1, responding aromatic rings. They appeared as two sets of absorption bands around 1600 and 1500 cm-1.These aromatic rings usually followed by the existence of weak to moderate absorption in the area of between 3150 and 3000 cm-1(for C-H stretching).For the simple aromatic compounds, several bands can be also observed between 2000 and 1700 cm-1in the form of multiple bands with a weak intensity. It is also support the aromatic ring absorption band (at 1600/1500 cm-1absorption frequency), namely C-H bending vibration with the intensity of medium absorption to strong which sometimes has single or multiple absorption bands found in the area between 850 and 670 cm-1.
Step 5: Identifying the fingerprint region (600-1500 cm-1)
This area is typically specific and unique. See detailed information in Table 1. But, several identification can be found:
(1) Between 1000 and 880 cm-1 for multiple band absorption, there are absorption bands at 1650, 3010, and 3040 cm-1.
(2) For C-H (out-of-plane bending), it should be combined with absorption bands at 1650, 3010, and 3040 cm-1 which show characteristics of compound unsaturation.
(3) Regarding vinyl-related compound, about 900 and 990 cm-1 for identifying vinyl terminals (-CH=CH 2), between 965 and 960 cm-1 for trans unsatrated vinyl (CH=CH), and about 890 cm-1 for double olefinic bonds in single vinyl (C=CH 2).
(4) Regarding aromatic compound, a single and strong absorption band is around 750 cm-1 for orto and 830 cm- 1 for para.
Table 1. Functional group and its quantified frequencies.