TU SMANDA vol.1

Indikator Kisi-kisi UAS Kimia XI/2 SMAN 1 Pandaan

INDIKATOR :

§ Menjelaskan pengertian asam dan basa menurut Arrhenius

§ Menjelaskan pengertian asam dan basa menurut Bronsted dan Lowry

§ Menuliskan persamaan reaksi asam dan basa menurut Bronsted dan Lowry dan menunjukkan pasangan asam dan basa konjugasinya

§ Menjelaskan pengertian asam dan basa menurut Lewis

§ Mengidentifikasi sifat larutan asam dan basa dengan berbagai indikator. 

§ Memperkirakan pH suatu larutan elektrolit yang tidak dikenal berdasarkan hasil pengamatan trayek perubahan warna berbagai indikator asam dan basa.

§ Menjelaskan pengertian kekuatan asam dan menyimpulkan hasil pengukuran pH dari beberapa larutan asam dan larutan basa yang konsentrasinya sama 

§ Menghubungkan kekuatan asam atau basa dengan derajat pengionan ( a ) dan tetapan asam (Ka) atau tetapan basa (Kb)

§ Menghitung pH larutan asam atau basa yang diketahui konsentrasinya. 

§  Menjelaskan penggunaan konsep pH dalam lingkungan.

§ Menentukan konsentrasi asam atau basa dengan titrasi

§ Menentukan kadar zat melalui titrasi.

§ Menentukan indikator yang tepat digunakan untuk titrasi asam dan basa

§ Menentukan kadar zat dari data hasil titrasi ,Membuat grafik titrasi dari data hasil percobaan.

§ Menganalisis larutan penyangga dan bukan penyangga melalui percobaan.

§ Menghitung pH atau pOH larutan penyangga

§ Menghitung  pH larutan penyangga dengan penambahan sedikit asam atau sedikit basa atau dengan pengenceran  ,Menjelaskan fungsi larutan penyangga dalam tubuh makhluk hidup

§ Menentukan ciri-ciri beberapa jenis garam yang dapat terhidrolisis dalam air melalui percobaan

§ Menentukan sifat garam yang terhidrolisis dari persamaan reaksi ionisasi, Menghitung pH larutan garam yang terhidrolisis,Menganalisis grafik hasil titrasi asam kuat dan basa kuat, asam kuat dan basa lemah, asam lemah dan basa kuat untuk menjelaskan larutan penyangga dan hidrolisis.

§ Menjelaskan kesetimbangan dalam larutan jenuh atau larutan garam yang sukar larut

§ Menghubungkan tetapan hasil kali kelarutan dengan tingkat kelarutan atau pengendapannya

§ Menuliskan ungkapan berbagai Ksp elektrolit yang sukar larut dalam air

§ Menghitung kelarutan suatu elektrolit yang sukar larut berdasarkan data harga Ksp atau sebaliknya

§ Menjelaskan pengaruh penambahan ion senama dalam larutan

§ Menentukan pH larutan dari harga Ksp-nya,Memperkirakan terbentuknya endapan berdasarkan harga Ksp

§ Menjelaskan proses pembuatan koloid melalui percobaan.

§ Mengklasifikasikan  suspensi kasar, larutan sejati dan koloid berdasarkan data hasil pengamatan (effek Tyndall, homogen/heterogen, dan penyaringan)

§ Mengelompokkan jenis koloid berdasarkan fase terdispersi dan fase pendispersi

§ Mendeskripsikan sifat-sifat koloid (effek Tyndall, gerak Brown, dialisis, elektroforesis, emulsi, koagulasi)

§ Menjelaskan koloid liofob dan liofil, Mendeskripsikan peranan koloid di industri kosmetik, makanan, dan farmasi

KIMIA ANALITIK

TUGAS

KIMIA ANALITIK

Oleh : Muhammad Ardiansyah (PPs Pend. Kimia)

Contoh-contoh analisis dalam ilmu kimia :

1.    Analisis Kandungan

a.    Menentukan kadar timbal (Pb) pada rambut Polisi Lalulintas

Polisi Lalulintas memiliki resiko yang sangat tinggi terkontaminasi polutan timbal (Pb) yang dihasilkan oleh kendaraan bermotor, kadar timbal yang tinggi berdampak negatif pada kesehatan seorang Polisi Lalulintas. Kadar Pb dapat dianalisis dengan beberapa metode instrument analitik diantaranya menggunakan AAS (Atomic Absorption Spectroscopy), sebelum dianalisis sampel rambut harus dilakukan perlakuan awal yaitu merubah ukuran sampel (menggunakan pelarut) tujuannya yang pertama untuk mengekstrak Pb yang ada pada rambut dan yang kedua untuk mempermudah proses nebulizer pada analisis AAS.

Gambar 1. Skema Analisis AAS

Sumber : http://www.chemistry.nmsu.edu/Instrumentation/AAS_Cham_Body.jpg

Gambar 2. Bagian-bagian AAS

Sumber : http://www.chemistry.nmsu.edu/Instrumentation/AAS_Cham_Body.jpg

Untuk menganalisis sampel timbal, maka lampu (HCL) pada AAS harus disesuaikan dengan sampel yang dianalisis, serapan atom pada proses nebulizer akan diterjemahkan oleh detector yang nantinya kadar Pb dalam sampel dapat diketahui

b.    Analisis Kandungan Fosfat Pada Air Danau Limboto Secara Spektrofotometri UV-VIS

Danau Limboto merupakan salah satu sumber daya alam yang ada di Kabupaten Gorontalo. Danau ini memiliki fungsi ekologis dan ekonomis pada wilayah dan masyarakat di sekitar. Fakta yang ada sekarang menunjukan bahwa ekosistem danau Limboto telah rusak. Kerusakan ekosistem danau tersebut dapat diamati dari keadaan fisik dan biologis danau. Keadaan fisik menunjukan bahwa setiap tahun telah terjadi sedimentasi 46,66 cm dan peneyempitan danau yang berkisar antara 66,66 ha per tahun. Sedangkan keadaan biologis dapat dilihat dengan adanya pertumbuhan ganggang, eceng gondok serta tumbuhan air berukuran mikro yang berkembang biak dengan pesat (blooming) akibat berlebihnya fosfat.

Analisis kandungan fosfat menggunakan spketro UV-vis dengan cara membuat larutan standart terlebih dahulu, hasil pengukuran berupa nilai absorbansi dimana nilai absorbansi di buat grafik yang nantinya konsentrasi sampel dapat dicari dari persamaan grafik larutan standart. Adapun diagram spektrofotometer UV-vis sebagai berikut.

Gambar 3. Diagram Spektrofotometer

Sumber : http://eckhochems.blogspot.com/2010/04/analisis-kandungan-fosfat-pada-air.html

2.    Analisis Struktur

a.    Analisa senyawa organic dari buah mengkudu

Mengkudu (Morinda citrifolia L) atau di Jawa Barat lebuh dikenal dengan sebutan “cangkudu” merupakan pohon yang banyak tumbuh di daerah tropis, terutama di kawasan Asia Tenggara termasuk Indonesia. Sejalan dengan peningkatan kesadaran konsumen dan volume permintaan terhadap penggunaan obat alami, maka penelitian terhadap pohon mengkudu juga difokuskan untuk penggunaan sebagai bahan obat. Penggunaan khusus pohon mengkudu sebagai obat antara lain buah mengkudu berkhasiat untuk melancarkan urin, menurunkan kadar gula dan kolesterol darah. Sedangkan daun dan akarnya berkhasiat untuk obat sakit perut, disentri, serta eksim. Beberapa khasiat lain dari mengkudu dalam bentuk sediaan jus, kapsul, lulur antara lain sebagai antibiotik, antibakteri, aterioskerosis, artrisis, sakit punggung, beri – beri, kosmetik, dan antikanker. Daging buah mengkudu juga dapat diolah menjadi bahan makanan berserat tinggi (dietary fiber).

Pengujian kandungan komponen asam lemak dalam minyak mengkudu bertujuan untuk mengetahui jenis asam lemak yang ada dan dilakukan dengan menggunakan alat kromatografi gas. Data analisis data kualitatif berdasarkan perbandingan waktu retensi beberapa puncak kromatogram contoh terhadap standar asam lemak, maka diamati minyak mengkudu mengandung beberapa asam lemak yaitu asam palmitat, asam linolenat, asam oleat dan asam linoleat.

Kromatografi adalah suatu prosedur pemisahan zat terlarut oleh suatu proses migrasi, diperensial dinamis dalam sistem yang terdiri dari dua fase atau lebih salah satunya bergerak secara berkesinambungan dalam arah tertentu dan didalamnya zat-zat itu menunjukkan perbedaan mobilitas disebabkan adanya perbedaan dalam absorbsi, partisi, kelarutan, tekanan uap, ukuran molekul atau kerapatan muatan ion.

Gambar 4. Diagram kromatografi gas

Sumber : http://www.makanan.us/lain-lain/minyak-dari-biji-mengkudu

b.    Senyawa Baru Organologam Kalium 18-Mahkota-6 yang Mengandung Turunan Fluorenil sebagai Karbanion

Sintesis 9-(2-metoksietil)-9H-fluorena dan 9-(2-metoksietil)-9H-fluorenil kalium bebas basa telah  dilakukan.  Reaksi  senyawa  terakhir  dengan  suatu  basa  Lewis  heksadentat  18-mahkota-6 menghasilkan  suatu  kompleks  baru  jenis  [MR(18-mahkota-6)]  (R= FluCH₂CH₂OMe).  Kedua senyawa dikarakterisasi dengan spektroskopi IR, NMR dan analisis struktur dengan sinar X. Struktur kristal K(18-mahkota-6)FluCH₂CH₂OMe memperlihatkan  bahwa ion  kalium tidak hanya berdekatan dengan ke enam atom oksigen dari eter mahkota, tetapi juga dengan gugus -OCH₃ . Selain itu teramati pula suatu interaksi dihapto antara kation dan karbanion.

Gambar 5. Diagram NMR Spectroscopy

Gambar 6. Diagram Infra Red Spectroscopy

Sumber : http://www.kimiawan.org/journal/index.php/jki/article/view/8

3.    Analisis Distribusi

a.    Peningkatan Mutu Membran Komposit Nanopori Selulosa Asetat-Polistirena Menggunakan Poli(Etilena Glikol)-2000

Penggunaan  membran  dalam  proses  desalinasi  telah  banyak  dilaporkan.  Salah satunya adalah membran selulosa asetat (CA). CA mudah terurai secara hayati sehingga berdampak   pada   kekuatannya.   Pencampurannya   dengan   polimer   sintetik,   seperti polistirena  (PS),  dapat  meningkatkan  kekuatan  membran  yang  terbentuk.  Akan  tetapi, pori-porinya tidak selalu seragam. Pengaruh penambahan porogen dan aplikasi membrane dalam  proses   desalinasi    dipelajari   dalam  penelitian  ini.  Membran dibentuk  dengan  mencetak campuran menjadi lapisan tipis.  Selanjutnya membran ditentukan nilai  fluks air dan indeks  rejeksi NaCl  menggunakan  modul  alat  saring  cross  flow  dan  dilakukan  analisis  terhadap morfologi permukaannya dengan mikroskop elektron susuran (SEM).

Hasil analisis SEM memperlihatkan  bahwa  PEG  berpengaruh  pada  jumlah  dan  ukuran  pori,  serta  tekstur permukaan  membran.  Hasil  SEM  menunjukkan  bahwa  membran  tergolong  nanofiltrasi dengan  kisaran  ukuran  pori  120-240  nm  dan  tergolong  asimetrik  dari  pembuatannya secara pembalikan  fase. Selain itu,  Nilai fluks  air semakin tinggi  dan nilai  rejeksi NaCl semakin rendah dengan bertambahnya jumlah PEG. Nilai fluks air tertinggi terjadi pada membran  90:10:5,  yaitu  291.2271  L/(jam.m 2 ),  sedangkan  nilai  indeks  rejeksi  NaCl tertinggi  terjadi  pada  membran  90:10:1,  yaitu  55.97  %.  Hasil  ini  menunjukkan  bahwa membran yang dihasilkan dapat berfungsi dalam proses desalinasi.

Gambar 7. Diagram SEM

Gambar 8. Hasil SEM membrane

Sumber : http://repository.ipb.ac.id/bitstream/handle/123456789/18005/G08rus_abstract.pdf?sequence=1

b.    Persiapan Nanopartikel silver dan Karakterisasi

Sintesis Nano Partikel dan studi tentang ukuran dan sifat sangat penting fundamental dalam kemajuan penelitian baru-baru ini. Hal ini ditemukan bahwa sifat optik, elektronik, magnetik, dan katalitik dari partikel nano logam tergantung pada ukuran, bentuk dan sekitarnya kimia.

Dalam sintesis nanopartikel sangat penting untuk mengendalikan tidak hanya ukuran partikel, tetapi juga bentuk partikel dan morfologi juga. Dalam penyelidikan saat ini sintesis nanopartikel perak dengan rute kimia [4,5] dibahas, yang merupakan rute yang mudah, sederhana dan mudah untuk menyiapkan partikel logam dalam rentang nanometer. Partikel nano disusun perak telah tersebar di kloroform dan kemudian diuji menggunakan difraksi sinar-X (XRD), Mikroskop Elektron Transmisi (TEM) dan UV / Vis spektroskopi penyerapan. Studi ini mengungkapkan bahwa nanoprticles dipersiapkan dari ukuran rata-rata 16 nm, yang menunjukkan pentingnya pekerjaan ini.

Gambar 9. Diagram TEM

Gambar 10. Hasil TEM citra Ag partikel nano

Sumber  : http://www.azonano.com/article.aspx?ArticleID=2318&lang=id

4.    Analisis Proses

a.    Efektivitas Katalis Zeolit Cr/Zeolit Alam Pada Perengkahan Tir Batubara Menjadi Fraksi Bensin

Penelitian tir batubara telah banyak dilakukan Hasil perengkaban tir batubara berpotensi sebagai bahan  bakar  pengganti  minyak  bumi.  Pemilihan  katalis  sangat  menentukan  hasil   reaksi  perengkahan tersebut. Penelitian  ini  meninjau   efektivitas  katalis  kromium-zeolit alam  dalam  proses  perengkahan tir batubara.  Katalis  kromium-zeolit  alam  dibuat  melalui:  aktivasi  zeolit  dam,  pertukaran  ion,  kalsinasi, oksidasi dan reduksi.

Gambar 11. Pengaruh Jenis Katalis Terhadap Selektivitas Fraksi Bensin

Gambar 12. Pengaruh Katalsi Terhadap Prosentase Produk

Sumber : http://isjd.pdii.lipi.go.id/admin/jurnal/22034351.pdf

b.    Kajian Kinetika Untuk Menunjukkan Peran katalis KI Dalam Reaksi dekomposisi H₂O₂ Berdasarkan Penurunan Energi Aktivasi Secara Non-isotermal

Kinetika  reaksi  dekomposisi H₂0₂ dengan KI pada pH sekitar <5,3 berlaku mekanisme asam dengan produk berupa I₂, pada pH sekitar 7,3 berlaku mekanisme basa dengan produk O₂ dan pada pH antara  5.5-7,2  berlaku  mekanisme  campuran.  Peran  KI  pada  pH  basa  sebagai  katalis  dalam  reaksi dekomposisi H₂0₂ secara non-isotermal menggunakan   Persamaan Arrhenius dibuktikan berdasarkan  perolehan  harga  E,  sekitar  13.863kkal/mol  sedangkan reaksi  non-katalis  sekitar 563 kkal/mol.

MICELLAR LIQUID CHROMATOGRAPHY

MICELLAR LIQUID CHROMATOGRAPHY

Micellar liquid chromatography (MLC) is a reversed-phase liquid chromatography (RPLC) mode with a solution of surfactant, containing either ionic or non-ionic head groups at concentrations exceeding the critical micellar concentration (cmc), as the mobile phase.^1–4 The mobile phase contains, therefore, micelles in addition to surfactant monomers, whereas the stationary phase is coated by adsorption of surfactant monomers, forming a surface similar to the exterior of micelles. The existence of micelles in the mobile phase and the modification of the stationary phase surface affects retention, selectivity and efficiency.

Figure 1

Non-polar solutes eluted with mobile phases of either non-ionic or ionic surfactants and ionizable solutes eluted with mobile phases of non-ionic surfactants will only experience non-polar, dipole–dipole and proton donor-acceptor interactions with micelles and stationary phase.⁵ Ionizable solutes will also interact electrostatically with the charged outer-layer of ionic micelles and the charged surfactant layer on the stationary phase. In any instance, the steric factor can also be important. Solutes are separated on the basis of their differential partitioning between bulk aqueous phase and micelles in the mobile phase, and between bulk aqueous phase and surfactant-coated stationary phase.

Figure 2

MLC makes use of the same hardware (pumps, injectors, tubing, detectors, etc.) as classical RPLC with organic solvent–water mixtures. The most interesting characteristics offered by MLC with regard to classical RPLC are its large versatility produced by the different kinds of solute-micelle and solute-modified stationary phase interactions, the change in selectivity, the suppression of peak tailing for basic drugs chromatographed with conventional columns, the analysis of samples containing compounds in a wide range of polarities using isocratic elution, and the direct injection of physiological fluids, avoiding the tedious sample pre-treatment required in classical RPLC (see Figures 1–3). The application field of MLC is summarized in Table 1.

Figure 3

Despite these advantages and others that will be commented on in this report, the applicability of the technique in the analytical laboratories has been limited. This could partially be attributed to the main drawbacks described in the early reports of this technique: the weak eluting power and reduced efficiency of pure micellar mobile phases. Some of the solutions proposed along the years to overcome these limitations, such as the addition of small amounts of alcohol,¹¹ and more recently, the use of large pore stationary phases,¹² have improved the potential of the technique, but have not extended its use. The only real limitation of this chromatographic mode up to-date is related to the use of mass spectrometric detection, because direct on-line coupling to MLC is hindered by the presence of high concentrations of surfactant in the mobile phase.

Table 1: Application field of MLC: reported procedures.a

After almost three decades of MLC experience with a great volume of scientific production, mainly related to the analysis of drugs in pharmaceuticals and physiological fluids (Table 1), the descriptions on the protocols to follow in the MLC routine are insufficient or unclear. In this report, we explain practical steps that a chromatographer involved in the MLC work should consider when developing an analytical procedure. The importance of column conditioning and cleaning is highlighted.

Mobile Phase Preparation

Although pure micellar mobile phases are sometimes used, most separations in MLC are performed with hybrid micellar mobile phases in a buffered medium, that is, micellar solutions containing a small amount of an organic solvent, mainly a short-chain alcohol, with propanol being the most common. The proper stability of the micellar mobile phase is essential.

Table 2: Characteristics of the most common surfactants in MLCa

Critical micellar concentration: A suitable surfactant for MLC should have a low cmc. A high cmc would imply operating at high surfactant concentration, which would result in viscous solutions, giving undesirable high system pressure and background noise in UV detectors. The selection is often limited to the following surfactants: the anionic sodium dodecyl sulphate (SDS), the cationic cetyltrimethylammonium bromide (CTAB) and the non ionic Brij-35, whose main characteristics are summarized in Table 2. The cmc values of these surfactants in pure water are low enough for MLC. It should also be taken into account that the cmc is strongly affected by the presence of an organic solvent (Figure 4). The changes are related to the modification of the structure of the micelle, which also induces, at least partially, the reduced retention in MLC.¹⁵

Figure 4

Krafft point: The Krafft point is defined for ionic surfactants as the temperature at which the solubility of a surfactant monomer becomes equal to the cmc.¹⁶ Below the Krafft point temperature, the solubility is quite low and the solution appears to contain no micelles. Chromatographic work in MLC should be conducted above this temperature to avoid surfactant precipitation. This means that the Krafft point should be well below room temperature. Furthermore, to avoid ruining the column, laboratory temperature should always be above this value. This is especially critical in cold-climate regions where working in an air-conditioned laboratory will be mandatory. The Krafft point for SDS and CTAB is around 15 °C and 20–25 °C, respectively,^17,18 but this is affected by the presence of salts. Thus, for SDS, it increases up to 18 °C in 0.1 M NaCl.¹⁸

Non-ionic surfactants also have a specific temperature, that if exceeded phase separation occurs, which is called the cloud point.^14,19 Chromatographic work with these surfactants should be conducted below this temperature. This doesn't seem to be a problem, because the cloud point for the most common non-ionic surfactant in MLC, Brij-35, is ca. 100 °C for aqueous 1–6% solutions, whereas for Triton X–100 this value is 64 °C.¹⁴

Mobile phase pH: MLC employs the same packing materials as classical RPLC, which for conventional columns have a limited working pH range of 2.5–7.5. Appropriate pH values depend on the nature of the analytes and the surfactant selected. For instance, the separation of weak acids, using the anionic SDS, often requires pH fixed at 2.5–3, where the more retained protonated neutral species dominates.²⁰ In these conditions, the separation space is wider and favours resolution. The pH of the micellar mobile phase is commonly fixed with phosphoric or citric acid buffers.^1,4 For mobile phases containing SDS, potassium salts are not recommended as potassium dodecyl sulphate presents a high Krafft point and precipitates from aqueous solutions at room temperature.¹ In any instance, the column should be equilibrated by purging with the mobile phase until the pH before and after the column is identical.

Type and concentration of organic solvent modifier: The selection of the appropriate organic solvent modifier in MLC should consider the polarities of the analytes. For polar compounds, sufficiently short retention times (below 20 min) are obtained with 1-propanol, 2-propanol or acetonitrile. For non-polar compounds or compounds with high affinity for the surfactant adsorbed on the stationary phase, stronger solvents as 1-butanol or 1-pentanol are needed.⁷ However, it should be noted that the two latter alcohols give rise to microemulsion formation at sufficiently high concentration.²¹

In practice, the amount of organic solvent that can be added is limited by its solubility. Additives that would normally not be considered in classical hydro-organic RPLC because of insufficient solubility can give rise to stable mobile phases with micelles. Thus, for instance, in 0.285 M SDS at 25 °C, the molar concentrations of 2-methyl-1-butanol, 1-pentanol, 1-hexanol and pentane were found to be 0.46, 0.92, 0.79 and 0.095, respectively, whereas their molar solubilities in water are only 6.1×10^–3, 4.5×10^–3, 1.2×10^–3, and 9.5×10^–6, respectively.²²

Whereas, at high organic solvent concentration, the micelles disaggregate and the mobile phase contains only free surfactant molecules. The organic solvent contents that preserve the integrity of micelles are below 15% for propanol and acetonitrile, 10% for butanol and 6% for pentanol.²² These contents are low in comparison with those needed in classical reversed-phase liquid chromatography (RPLC). The lower organic solvent consumption results in reduced cost and toxicity, which may become prominent for "green chemistry". Also, the stabilization of the organic solvent in the micellar media decreases the risk of evaporation. This means that micellar mobile phases can be preserved in the laboratory for a long time without significant changes in their composition.

Surfactant Column Coating

The alkyl-bonded C₁₈ is the stationary phase most widely used in MLC, but other columns can be selected (e.g., C₈ and cyanopropyl). Alkyl-bonded phase columns are strongly modified when SDS, CTAB or Brij-35 are incorporated into the mobile phase. Adsorption isotherms of stationary phases of different nature in contact with mobile phases containing these three surfactants have been extensively studied, together with the effect of mobile phase additives on surfactant adsorption.^13,23 The results provided information about column conditioning in MLC, which is useful to achieve reproducible results.

Mobile phase saturation: Pure and hybrid micellar solutions contain high amounts of water (usually more than 90% v/v) and are able to dissolve small amounts of silica, which could produce serious column damage. This is especially critical at >30 °C and/or pH > 6. For this reason, a saturating short column packed with 10 μm bare silica, or alternatively, the same packing as the analytical column, should be placed after the pump and before the injection valve to reduce pressure build-up.

Column conditioning: A column for MLC is generally stored in 100% methanol. Before starting column conditioning, the solvent should be replaced by 100% water. For this operation, a low

flow-rate (≤0.5 mL/min) should be selected at the beginning because of the high viscosity of the methanol–water mixture. Once the pressure decreases, the flow-rate may be raised. At least 30 column volumes of water are required to assure complete organic solvent removing. Now, the system is ready to be flushed with the micellar mobile phase. Different studies of column coating through surfactant breakthrough patterns have revealed that most surfactant adsorbs in less than one hour on the bonded-stationary phase.^13,23 However, some additional surfactant continues to adsorb onto the column, especially in the instance of the non-ionic Brij-35.¹⁴

Mobile phase flushing: The micellar mobile phase should be continuously flushed through the system. If the chromatographic system is stopped during several hours, the micellar solution should not stay in contact with the bonded-silica based stationary phase to avoid surfactant precipitation. A static micellar mobile phase can also produce crystals around the pump plungers and seals. Such crystals may obstruct the system producing plugged connecting tubing and frits, seal failure, or scratched pistons.

A micellar mobile phase can be kept inside the chromatographic system overnight if the pump is not off. This avoids daily cleaning and re-equilibration. To reduce the cost, the mobile phase can be recycled, reducing the flow-rate to a minimal value (often 0.1–0.25 mL/min). However, it should be noted that in case of energy supply failure, column damage can occur. Mobile phase recycling is possible because of the low evaporation risk of organic solvents in hybrid micellar eluents. For the same reason, the micellar mobile phase can be recycled during the analysis, as long as a low number of injections is made.

Regeneration of surfactant coated reversed-phase columns: There is some concern about surfactant desorption from the column. Some reports claim that removing the surfactant-adsorbed layer for further use of a mobile phase of different nature (i.e., hydro-organic or containing another surfactant) is not possible. Thus, a small amount of SDS was reported to remain adsorbed on a Hypersil ODS column after cleaning,²⁴ but other authors found that the surfactant layer was completely removed.^13,25–27 This is the reason of the recommendation of keeping a column for the exclusive use of a given surfactant.

In general, regeneration can be appropriately performed with methanol, where most surfactants are highly soluble.²⁷ The cleaning protocol comprises a two step procedure that takes about half an hour:

(i) First, the micellar mobile phase should be replaced by 100% pure water, by rinsing the chromatographic system with 10 to 20 column volumes of pure water. This step is necessary to avoid salt crystallization provoked by a brutal change from a buffered micellar mobile phase to 100% methanol.

(ii) Next, water will be replaced by 100% methanol to remove the adsorbed surfactant on the stationary phase. The same caution commented under "column conditioning" about the initial use of a low flow-rate should be followed. To assure complete surfactant desorption, at least 10 column volumes of methanol should be passed through the column.

A third final step can be included to assure complete recovery of the initial stationary phase surface. This consists in checking the retention times of a solute mixture (selected arbitrarily) with a hydro-organic mobile phase before and after using the micellar mobile phase. This step is not needed if the rules about column conditioning and cleaning are respected. A reduction in the lifetime of the columns used in MLC with respect to RPLC has not been observed. In fact, from our experience, column performance can be maintained for more than two years of intensive MLC use. Eventually, a small decrease in column efficiency may be attributed to column ageing.

Method Development

Table 3: Analysis of drugs by MLC in therapeutic and doping control

Therapeutic and doping control of drugs is one of the most important applications in MLC.⁹ Table 3 shows some examples on the use of MLC in this field. Hydrophobic interactions are scarcely affected by changes in the composition of micellar eluents. This implies that solutes of different hydrophobicity can be eluted in retention time windows narrower than in classical RPLC under isocratic elution (Figures 1 and 2). In case gradient elution is needed, equilibration times are also shorter in MLC.^37,38

Interestingly, micellar media have been demonstrated to slow down the photochemical degradation of diverse drugs under the influence of UV radiation. The conditions that favour photodegradation processes can also be different in both aqueous organic and micellar media. For example, photochemical degradation of the diuretic furosemide at acidic pH is faster in hydro-organic media, but slower in a micellar solution of SDS.³⁹ Stability conditions in micellar solutions should be, thus, checked before applying any MLC procedure to avoid undetected compounds.

One of the most interesting features of MLC is the possibility of direct injection of physiological fluids (e.g., urine, plasma, serum and milk) without any other pre-treatment than filtration, with no increase in system pressure or no noticeable damage after repetitive serial injections.¹⁰ The proteins, rather than precipitating on the column, are swept away harmlessly, eluting with or shortly after the solvent front. This could affect the detection of low retained compounds. However, it should be noted that SDS is the only surfactant usually used in MLC that efficiently solubilizes proteins in physiological matrices. Also, it is a good practice to prevent any possible column contamination by diluting or filtering the samples before injection. Some samples, such as serum, need centrifugation before chromatographic analysis. This little pre-treatment minimizes column exposure to undesirable compounds.

Acknowledgments

This work was supported by Projects CTQ2004-02760/BQU and CTQ2007-61828/BQU (Ministerio de Educación y Ciencia of Spain, MEC) and FEDER funds. M.J.R.A. thanks the MEC for a Ramón y Cajal contract.

María José Ruiz-Ángel obtained her PhD from the University of Valencia in 2003 under the direction of Dr M.C. García-Álvarez-Coque. Between 2004 and 2006, she was granted with a post-doctorate fellowship at the Laboratoire des Sciences Analytiques of the University Claude Bernard in Lyon (France) under the supervision of Dr A. Berthod, Since January 2007, she has been a senior researcher (Ramón y Cajal position) in the University of Valencia (Spain).

María Celia García-Álvarez-Coque has been a full professor in analytical chemistry at the University of Valencia (Spain) since 1997. She has written 200 research articles, focusing on HPLC in the last 15 years, particularly on fundamental studies and the development of chemometrical methods to extract the potential information contained in chromatographic signals. She is a coauthor of the books Micellar Liquid Chromatography and Chemometrics.