How to Read and Interpret FTIR Spectroscope of Organic Material

Article History: Submitted/Received 10 Nov 2018 First revised 20 Jan 2019 Accepted 06 Mar 2019 First available online 09 Mar 2019 Publication date 01 Apr 2019 A.B.D. Nandiyanto, et al. Title – How to Read and Interpret FTIR Spectroscope of Organic...| 98 DOI:http://dx.doi.org/10.17509/ijost.v4i1.15806 | pISSN 2528-1410 eISSN 2527-8045 | Many techniques for explaining in detail regarding the FTIR analysis have been reported (Coates, 2000; Jaggi and Vij, 2006; Kirk and Othmer, 1953). 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. As a model of complex organic materials, Lumbricus rubellus (LR) was used. LR has quite high protein (64-76%), fat (7-10%), calcium (0.55%), phosphorus (1%), and crude fiber (1.08%) (Istiqomah et al., 1958). LR also has at least 9 types of essential amino acids and 4 types of non-essential amino acids (Desi, 2016; Istiqomah et al., 1958). As a consequence, LR is classified as one of the most complex organic materials. To ensure the effectiveness in the step-by-step reading procedure, various samples of LR that were heated at specific temperatures were also analyzed since LR is vulnerable against heat. We believe that this paper can be used as a basic knowledge for students and beginner scientists in comprehending and interpreting FTIR data. 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 cm1), and near-IR spectrum (4000-13000 cm-1). The mid-IR spectrum is the most widely used in the sample analysis, but farand 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 cm1), 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. 99| Indonesian Journal of Science & Technology,Volume 4 Issue 1, April 2019 Page 97-118 | DOI: http://dx.doi.org/10.17509/ijost.v4i1.15806 | pISSN 2528-1410 eISSN 2527-8045 Functional group/assignment Wavenumber (cm) 1. Saturated Aliphatic (alkene/alkyl) a) Methyl (−CH3) Methyl C-H asym./sym. Stretch 2970–2950/2880–2860 Methyl C-H asym./sym. Bend 1470–1430/1380–1370 gem-Dimethyl or ‘‘iso’’(doublet) 1385–1380/1370–1365 Trimethyl or ‘‘tert-butyl’’ (multiplet) 1395–1385/1365 b) Methylene (>CH2) Methylene C-H asym./sym. Stretch 2935–2915/2865–2845 Methylene C-H bend 1485–1445 Methylene ―(CH2)n― rocking (n ≥ 3) 750–720 Cyclohexane ring vibrations 1055–1000/1005–925


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 (Fan et al., 2012). Compared to other types of characterization analysis, FTIR is quite popular. This characterization analysis is quite rapid, good in accuracy, and relatively sensitive (Jaggi and Vij, 2006).
As a model of complex organic materials, Lumbricus rubellus (LR) was used. LR has quite high protein (64-76%), fat (7-10%), calcium (0.55%), phosphorus (1%), and crude fiber (1.08%) (Istiqomah et al., 1958). LR also has at least 9 types of essential amino acids and 4 types of non-essential amino acids (Desi, 2016;Istiqomah et al., 1958). As a consequence, LR is classified as one of the most complex organic materials. To ensure the effectiveness in the step-by-step reading procedure, various samples of LR that were heated at specific temperatures were also analyzed since LR is vulnerable against heat. We believe that this paper can be used as a basic knowledge for students and beginner scientists in comprehending and interpreting FTIR data.

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 schematic IR spectrum is available in Figure 1, and the specific frequency of each functional groups is available in
Step-by-step Analysis Procedure.
There are five steps to interpret FTIR: 1.
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.

2.
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 .

3.
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 .
(1) 1850 -1650 cm -1 for 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 -1 for unsaturation bond (double and triple bond). Specifically, the peak at 1650 cm -1 is 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 -1 in the form of multiple bands with a weak intensity. It is also support the aromatic ring absorption band (at 1600/1500 cm -1 absorption 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 .

5.
Step 5: Identifying the fingerprint region (600-1500 cm -1 ) This area is typically specific and unique. See detailed information in

EXPERIMENTAL METHOD
To understand how to read and interpret the FTIR analysis, the present study used several FTIR patterns. Two FTIR patterns were obtained from reference (Coates, 2000) (as a standard comparison) and the others are from LR microparticles.
In short of the experimental procedure for the preparation of LR microparticles, LR was obtained and purchased from CV Bengkel dan Agrobisnis, Indonesia. Prior to using, LR was washed in warm water (temperature of 40°C) for several hours. The washed LR was then dried at 70°C for about 15 minutes in the electrical drier. The dried LR was then put into a batch-typed sawmilling apparatus, in which the saw-milling process was explained in our previous study (Nandiyanto et al., 2018a). Then, for evaluating the formation of carbon particles from LR, 0.360 g of saw-milled LR was put into an electrical furnace and heated in the atmospheric condition under a fixed condition: a heating rate of 50°C/min and a holding time at a specific temperature for 30 min. To obtain the clear evaluation in the transformation of LR into carbon particles, heating temperatures were varied from 80 to 250°C in a small step of almost every 10°C. The heated material was subsequently cooled to room temperature with a cooling rate of 50°C/min. To support the FTIR p-ISSN 2528-1410 e-ISSN 2527-8045 | analysis, FTIR (FTIR-4600, Jasco Corp., Japan) was utilized. Figure 2 shows the analysis of 2propanone. To understand the appearance peaks in the FTIR below, step-by-step process can be used. The results can be concluded as follows:

RESULTS AND DISCUSSION 4.1. FTIR analysis of sample gained from literature
(1) Regarding the number of peaks, there are more than five peaks, informing that the analyzed chemical is not a simple chemical.
-No broad absorption band was found, informing there is no hydrogen bond in the material. -There is a sharp bond at about 3500 cm -1 , replying the existence of oxygen-related bonding. -No other peaks between 3000 and 3200 cm -1 was found, informing there is no aromatic structure -Narrow bond at less than 3000 cm -1 responded to the C-C bond. -No specific peak for aldehyde has been found at between 2700 and 2800 cm -1 .
(3) No triple bond region (2000-2500 cm -1 ) was detected, informing no C≡C bond in the material. (4) Regarding the double bond region (1500-2000 cm -1 ), there is a huge and sharp peak was detected at about 1700 cm -1 . This informs some carbonyl double bond, which can be from ketones, aldehydes, esters, or carboxyl. Since there is no specific peak for aldehyde at between 2700 and 2800 cm -1 (as desribed in the previous step), the prospective peak for carbonyl should be from ketone. No peak at about 1600 cm -1 , informing there is no C=C bonding in the material.
(5) Based on above interpretation, several conclusions can be obtained, including the analyzed material has no hydrate component. This material has ketones-related component, no double or triple bond in the material. Since the peaks were only about 10 peaks, the material should be a small organic compound.   (7) The result showed that a lot of numbers of peaks were detected, informing the complex structure material (8) In the single bond area (2500-4000 cm -1 ), several peaks were detected.
-No broad absorption band in the range of between 3650 and 3250 cm -1 , indicating no hydrogen bond. -Peaks at between 3000 and 3200 cm -1 , replying the aromatic ring. -Peaks at below 3000 cm -1 , responding the single bond of carbon. -No aldehyde peak was detected at between 2700 and 2800 cm -1 . (9) Regarding the triple bond region (2000-2500 cm -1 ), no peak was detected, informing no C≡C bonding. (10) In the double bond region (1500-2000 cm -1 ), several peaks were detected: -Above 1775 cm -1 , informing active carbonyl groups, in which this should be from ring-carbonyl carbons. -Range of between 1750 and 1700 cm -1 , describing simple carbonyl compounds, in which this is due to the bonding between methyl (CH3) to the benzene ring.
Based on the above analysis, the analysis showed that the material has aromatic ring, and simple functional bonding (methyl). This is in a good agreement with the chemical compound of toluene.

CONCLUSION
The present study demonstrated the simplest ways for understanding FTIR analysis results. The step-by-step method on how to read the FTIR data was presented in detail, including reviewing simple to the complex organic materials. This study also tested to the analysis of LR microparticles since this material has quite complicated organic structure.
To ensure the effectiveness in the step-by-step reading procedure, various samples of LR that were heated at specific temperatures were also analyzed, since LR is vulnerable against heat.
We believe that this paper can be used as a basic knowledge for students and beginner scientists in comprehending and interpreting FTIR data.

ACKNOWLEDGEMENTS
This work was supported by RISTEK DIKTI.

AUTHORS' NOTE
The author(s) declare(s) that there is no conflict of interest regarding the publication of this article. Authors confirmed that the data and the paper are free of plagiaris.