Electronic Theses and Dissertation

ABSTRAK
Metode Laser-Induced Breakdown Spektroscopy (LIBS) mampu mendeteksi unsur unsur yang terkandung dalam suatu bahan secara presisi hingga unsur unsur dalam jumlah yang kecil. Dalam penelitian ini, metode LIBS digunakan untuk menganalisa kandungan unsur unsur dominan dan unsur unsur minor dalam buah pinang. Pinang merupakan salah satu komoditi pertanian penting yang dihasilkan oleh petani di wilayah Aceh. Sampel pinang diambil dari Desa Kubu, Kecamatan Peusangan Siblah Krueng, Kabupaten Bireuen. Dalam penelitian ini digunakan laser Nd-YAG pada panjang gelombang 1064 nm dengan energi maksimum pulsa laser 480 mJ. Plasma pinang dihasilkan oleh energi laser minimum sebesar 68 mJ. Plasma kemudian difokuskan ke detektor dengan lensa berpanjang fokus f = 120 mm. Dalam operasi laser, ada fluktuasi daya sebesar 3 %. Plasma dibangkitkan dalam lingkungan udara pada tekanan atmosfer 1 atm (760 Torr). Spektrum emisi plasma dideteksi menggunakan sistem detektor optik kanal (optical multichannel analyzer, OMA) dengan waktu tunda 8 ns. Sampel pinang yang diuji yaitu sampel biji pinang segar. Sampel biji pinang dipotong setebal 3 mm dalam bentuk keping berdiameter 20-30 mm sesuai ukuran biji pinang. Intensitas plasma yang dibangkitkan dari biji pinang cukup kuat sehingga semua unsur penting pinang dapat terdeteksi dalam spektrum emisinya. Spektrum emisi yang diperoleh didominasi oleh bahan organik dengan intensitas spektrum dipengaruhi oleh tempat tumbuhnya pinang (C-H-O-N). Unsur organik pinang tampak dominan dalam spektrum yang dihasilkan, sesuai yang diharapkan. Dengan teknik LIBS beberapa unsur yang komposisinya kecil seperti barium (Ba), stronsium (Sr) dan vanadium (V) dapat terdeteksi juga, unsur unsur ini dapat menjadi penciri khas lokasi tumbuhnya pinang. Secara umum dapat disimpulkan bahwa teknik LIBS dapat digunakan untuk mendeteksi kandungan unsur pinang dengan cukup presisi.
Kata kunci : Laser-Induced Breakdown Spectroscopy (LIBS), laser pulsa, plasma, spektrum emisi, waktu tunda, multichannel analyzer.








ABSTRACT

Laser-Induced Breakdown Spektroscopy (LIBS) is a precised method to detect elements in a solid material down to minor elements. In this research we used Laser-Induced Breakdown Spectroscopy (LIBS) to find the elemental composition of betel nut fruit, both the dominants and minor elements. Betel nut is an important farm product among farmers in Aceh Province. The betel nut fruit samples were obtained from Kubu Village, Peusangan Siblah Krueng District, Bireuen Regency. We used Nd-YAG laser with wavelength at 1064 nm and maximum laser energi at 480 mJ. Plasma from the betel nut fruit was emitted when the sample was exposed by pulsed laser at a minimum energi of 68 mJ. The spectral emission from plasma was then focussed to the detector using lens with focal length 120 mm. When the laser was in operation, there is a 3% power fluctuation due to the pulsed characteristic of the laser. The plasma was generated in ambient environment at atmospheric pressure of 1 atm (760 Torr). The plasma emission spektrum was detected using an optical multichannel analyzer (OMA) with 8ns delay time and a measurement duration of 50 ?s. The betel nut samples used in this study were taken from the fresh fruit without any other special treatment. The betel nut samples were cut in form of a disc, 3 mm thick and 20-30 mm in diameter according to the original size of the betel nut. The plasma emission generated from betel nut dics was quite intense and easy to detect by OMA, enabling all important elements in betel nut samples to be detected. The emission spektrum was dominated by its organic contents (C-H-O-N), the variation of which is attributed to the place where the betel nut grow. With LIBS technique, minor elements which present in small composition such as barium (Ba), strontium (Sr) and vanadium (V) can also be detected. Therefore in general we can conclude that the LIBS technique can be used to detect the elemental content of betel nut in high accuracy.
Keywords : Laser-Induced Breakdown Spectroscopy (LIBS), pulsed laser, plasma, emission spektrum, delay time, betel nut, multichannel analyzer.

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