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Analytica Chimica Acta (v.651, #1)
Recent trends in microdialysis sampling integrated with conventional and microanalytical systems for monitoring biological events: A review by Pradyot Nandi; Susan M. Lunte (pp. 1-14).
Microdialysis (MD) is a sampling technique that can be employed to monitor biological events both in vivo and in vitro. When it is coupled to an analytical system, microdialysis can provide near real-time information on the time-dependent concentration changes of analytes in the extracellular space or other aqueous environments. Online systems for the analysis of microdialysis samples enable fast, selective and sensitive analysis while preserving the temporal information. Analytical methods employed for online analysis include liquid chromatography (LC), capillary (CE) and microchip electrophoresis and flow-through biosensor devices. This review article provides an overview of microdialysis sampling and online analysis systems with emphasis on in vivo analysis. Factors that affect the frequency of analysis and, hence, the temporal resolution of these systems are also discussed.
Keywords: Microdialysis; Microchip; Microfluidics; Sensors; In vivo; monitoring; Electrophoresis
Swarm intelligence based wavelet coefficient feature selection for mass spectral classification: An application to proteomics data by Weixiang Zhao; Cristina E. Davis (pp. 15-23).
This paper introduces the ant colony algorithm, a novel swarm intelligence based optimization method, to select appropriate wavelet coefficients from mass spectral data as a new feature selection method for ovarian cancer diagnostics. By determining the proper parameters for the ant colony algorithm (ACA) based searching algorithm, we perform the feature searching process for 100 times with the number of selected features fixed at 5. The results of this study show: (1) the classification accuracy based on the five selected wavelet coefficients can reach up to 100% for all the training, validating and independent testing sets; (2) the eight most popular selected wavelet coefficients of the 100 runs can provide 100% accuracy for the training set, 100% accuracy for the validating set, and 98.8% accuracy for the independent testing set, which suggests the robustness and accuracy of the proposed feature selection method; and (3) the mass spectral data corresponding to the eight popular wavelet coefficients can be located by reverse wavelet transformation and these located mass spectral data still maintain high classification accuracies (100% for the training set, 97.6% for the validating set, and 98.8% for the testing set) and also provide sufficient physical and medical meaning for future ovarian cancer mechanism studies. Furthermore, the corresponding mass spectral data (potential biomarkers) are in good agreement with other studies which have used the same sample set. Together these results suggest this feature extraction strategy will benefit the development of intelligent and real-time spectroscopy instrumentation based diagnosis and monitoring systems.
Keywords: Wavelet; Swarm intelligence; Ant colony algorithm; Mass spectrometry; Feature selection; Support vector machine
Chemometric analysis of multiple species of Bacillus bacterial endospores using infrared spectroscopy: Discrimination to the strain level by Joel B. Forrester; Nancy B. Valentine; Yin-Fong Su; Timothy J. Johnson (pp. 24-30).
Previous work using infrared spectroscopy has shown potential for rapid discrimination between bacteria in either their sporulated or vegetative states, as well as between bacteria and other common interferents. For species within one physiological state, however, distinction is far more challenging, and requires chemometrics. In the current study, we have narrowed the field of study by eliminating the confounding issues of vegetative cells as well as growth media and focused on using IR spectra to distinguish only between different species all in the sporulated state. Using principal component analysis (PCA) and a classification method based upon similarity measurements, we demonstrate a successful identification rate to the species level of 85% for Bacillus spores grown and sporulated in a glucose broth medium.
Keywords: Chemometrics; Discrimination; Bacillus; Endospores; Infrared spectroscopy; FTIR
Determination of propranolol enantiomers in plasma and urine by spectrofluorimetry and second-order standard addition method by Patrícia Valderrama; Ronei Jesus Poppi (pp. 31-35).
The determination of propranolol enantiomers in human plasma and urine by spectrofluorimetry and a second-order standard addition method is described. The methodology is based on chiral recognition of propranolol by formation of an inclusion complex with β-cyclodextrin, a chiral auxiliary, in the presence of 1-butanol. The adopted strategy combines the use of PARAFAC, for extraction of the pure analyte signal, with the standard addition method, for determinations in the presence of an individual matrix effect caused by the quenching action of the proteins present in the plasma and urine. A specific PARAFAC model was built for each sample, in triplicate, and the scores were related to (R)-propranolol mole fraction using a linear regression in the standard addition method. Using a propranolol with concentration of 260ngmL−1, good results were obtained for determinations in the mole fraction range from 50 to 80% of (R)-propranolol, providing absolute errors between 0.4 and 3.6% for plasma and between 0.9 and 6.0% for urine.
Keywords: Propranolol; Anantiomers; Human plasma; Urine; Second-order standard addition method
High dielectric constant PrY xO y sensing films electrolyte-insulator-semiconductor pH-sensor for the detection of urea by Min-Hsien Wu; Cheng-Da Lee; Tung-Ming Pan (pp. 36-41).
In this paper, we describe the structural and sensing properties of high- k PrY xO y sensing films deposited on Si substrates through reactive co-sputtering. Secondary ion mass spectrometry and atomic force microscopy were employed to analyze the compositional and morphological features of these films after annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device incorporating a PrY xO y sensing membrane that had been annealed at 800°C exhibited good sensing characteristics, including a high sensitivity (59.07mVpH−1 in solutions from pH 2 to 12), a low hysteresis voltage (2.4mV in the pH loop 7→4→7→10→7), and a small drift rate (0.62mVh−1 in the buffer solution at pH 7). The PrY xO y EIS device also showed a high selective response towards H+. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based urea biosensor incorporating a high- k PrY xO y sensing film annealed at 800°C allowed the potentiometric analysis of urea, at concentrations ranging from 1 to 16mM, with a sensitivity of 9.59mVmM−1.
Keywords: Electrolyte-insulator-semiconductor; PrY; x; O; y; pH sensitivity; Urea
Sensitive DNA biosensor improved by Luteolin copper(II) as indicator based on silver nanoparticles and carbon nanotubes modified electrode by Shuyan Niu; Bin Han; Wei Cao; Shusheng Zhang (pp. 42-47).
A novel and sensitive electrochemical DNA biosensor has been developed for the detection of DNA hybridization. The biosensor was proposed by using copper(II) complex of Luteolin C30H18CuO12 (CuL2) as an electroactive indicator based on silver nanoparticles and multi-walled carbon nanotubes (Ag/MWCNTs) modified glassy carbon electrode (GCE). In this method, the 4-aminobenzoic acid (4-ABA) and Ag nanoparticles were covalently grafted on MWCNTs to form Ag/4-ABA/MWCNTs. The proposed method dramatically increased DNA attachment quantity and complementary ssDNA detection sensitivity for its large surface area and good charge-transport characteristics. DNA hybridization detection was performed using CuL2 as an electroactive indicator. The CuL2 was synthesized and characterized using elemental analysis (EA) and IR spectroscopy. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction between CuL2 and ds-oligonucleotides (dsDNA). It was revealed that CuL2 presented high electrochemical activity on GCE, and it could be intercalated into the double helices of dsDNA. The target ssDNA of the human hepatitis B virus (HBV) was quantified in a linear range from 3.23×10−12 to 5.31×10−9M ( r=0.9983). A detection limit of 6.46×10−13M (3 σ, n=11) was achieved.
Keywords: Abbreviations; 4-ABA; 4-aminobenzoic acid; B–R buffer; Britton–Robinson buffer; CV; cyclic voltammetry; DPV; differential pulse voltammetry; EA; elemental analysis; EIS; electrochemical impedance spectroscopy; GCE; glassy carbon electrode; HBV; human hepatitis B virus; MWCNTs; multi-walled carbon nanotubesLuteolin copper; Carbon nanotube; 4-Aminobenzoic acid; Silver nanoparticles; Electrochemical DNA biosensor
Optimisation of supercritical fluid extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives adsorbed on highly sorptive diesel particulate matter by F. Portet-Koltalo; K. Oukebdane; F. Dionnet; P.L. Desbène (pp. 48-56).
Supercritical fluid extraction (SFE) was performed to extract complex mixtures of polycyclic aromatic hydrocarbons (PAHs), nitrated derivatives (nitroPAHs) and heavy n-alkanes from spiked soot particulates that resulted from the incomplete combustion of diesel oils. This polluted material, resulting from combustion in a light diesel engine and collected at high temperature inside the particulate filter placed just after the engine, was particularly resistant to conventional extraction techniques, such as soxhlet extraction, and had an extraction behaviour that differed markedly from certified reference materials (SRM 1650). A factorial experimental design was performed, simultaneously modelling the influence of four SFE experimental factors on the recovery yields, i.e.: the temperature and the pressure of the supercritical fluid, the nature and the percentage of the organic modifier added to CO2 (chloroform, tetrahydrofuran, methylene chloride), as a means to reach the optimal extraction yields for all the studied target pollutants. The results of modelling showed that the supercritical fluid pressure had to be kept at its maximum level (30MPa) and the temperature had to be kept relatively low (75°C). Under these operating conditions, adding 15% of methylene chloride to the CO2 permitted quantitative extraction of not only light PAHs and their nitrated derivatives, but also heavy n-alkanes from the spiked soots. However, heavy polyaromatics were not quantitatively extracted from the refractory carbonaceous solid surface. As such, original organic modifiers were tested, including pyridine, which, as a strong electron donor cosolvent (15% into CO2), was the most successful. The addition of diethylamine to pyridine, which enhanced the electron donor character of the cosolvent, even increased the extraction yields of the heaviest PAHs, leading to a quantitative extraction of all PAHs (more than 79%) from the diesel particulate matter, with detection limits ranging from 0.5 to 7.8ng for 100mg of spiked material. Concerning the nitrated PAHs, a small addition of acetic acid into pyridine, as cosolvents, gave the best results, leading to fair extraction yields (approximately 60%), with detection limits ranging from 18 to 420ng.
Keywords: Polycyclic aromatic hydrocarbons; Nitrated polycyclic aromatic hydrocarbons; Highly sorptive diesel particulates; Supercritical fluid extraction; Factorial design
Optimization of cloud point extraction and solid phase extraction methods for speciation of arsenic in natural water using multivariate technique by Jameel A. Baig; Tasneem G. Kazi; Abdul Q. Shah; Mohammad B. Arain; Hassan I. Afridi; Ghulam A. Kandhro; Sumaira Khan (pp. 57-63).
The simple and rapid pre-concentration techniques viz. cloud point extraction (CPE) and solid phase extraction (SPE) were applied for the determination of As3+ and total inorganic arsenic (iAs) in surface and ground water samples. The As3+ was formed complex with ammonium pyrrolidinedithiocarbamate (APDC) and extracted by surfactant-rich phases in the non-ionic surfactant Triton X-114, after centrifugation the surfactant-rich phase was diluted with 0.1molL−1 HNO3 in methanol. While total iAs in water samples was adsorbed on titanium dioxide (TiO2); after centrifugation, the solid phase was prepared to be slurry for determination. The extracted As species were determined by electrothermal atomic absorption spectrometry. The multivariate strategy was applied to estimate the optimum values of experimental factors for the recovery of As3+ and total iAs by CPE and SPE. The standard addition method was used to validate the optimized methods. The obtained result showed sufficient recoveries for As3+ and iAs (>98.0%). The concentration factor in both cases was found to be 40.
Keywords: Arsenic speciation; Cloud point extraction; Solid phase extraction methods; Multivariate technique; Electrothermal atomic absorption spectrometry
Enrichment and sensitive determination of dichlorodiphenyltrichloroethane and its metabolites with temperature controlled ionic liquid dispersive liquid phase microextraction prior to high performance liquid phase chromatography by Huahua Bai; Qingxiang Zhou; Guohong Xie; Junping Xiao (pp. 64-68).
Dichlorodiphenyltrichloroethane (DDT) and its main metabolites are important environmental pollutants and have been in the focusing center. It is of great value to develop simple, rapid, sensitive and easy to operate method for monitoring them. Present work established a novel temperature controlled ionic liquid dispersive liquid phase microextraction method in combination with high performance liquid chromatography for the enrichment and determination of DDT and its metabolites. Proposed method used only ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) for the enrichment and overcame the demerits of conventional single drop liquid phase microextraction and dispersive liquid–liquid microextraction. Temperature has two functions here, one is to promote the dispersing of ionic liquid into the solution and forming infinitesimal micro-drop and increasing the chance of the analytes extracted into ionic liquid phase, and the other one is to perform phase-separation. A series of factors that would affect the extraction performance was systematically investigated and optimized. The experimental results indicated that the detection limits obtained for p, p′-DDD, p, p′-DDT, o, p′-DDT and p, p′-DDE were 0.24, 0.24, 0.45, 0.24ngmL−1, respectively. The linear ranges for them were from 1.0 to 100ngmL−1, and the precisions were between 3.8% and 6.7% ( n=6). The proposed method was validated with four real-world samples and excellent results were achieved.
Keywords: 1-Hexyl-3-methylimidazolium hexafluorophosphate; Dichlorodiphenyltrichloroethane; Temperature controlled ionic liquid dispersive liquid phase microextraction; High performance liquid chromatography
Discovery of neurosteroid glucuronides in mouse brain by Sirkku E. Kallonen; Anne Tammimäki; Petteri Piepponen; Helena Raattamaa; Raimo A. Ketola; Risto Kostiainen (pp. 69-74).
Neurosteroid glucuronides were found for the first time in brain samples. The intact glucuronides were extracted from the cortex, hippocampus, hypothalamus, and mid-brain tissues of nicotine- and water-treated mice, and detected with capillary liquid chromatography–electrospray-tandem mass spectrometry (CapLC–ESI-MS/MS). The glucuronides of estradiol, cortisol, corticosterone, tetrahydrodeoxycorticosterone, pregnenolone, and isopregnanolone were identified by comparing retention times in selected reaction monitoring (SRM) chromatograms and the relative abundances of two SRM transitions of each neurosteroid glucuronide between the reference and authentic samples, thus providing reliable identification. In vitro experiments, carried out by using S9 fractions from mouse and rat brains, showed a formation of glucuronides with selected test compounds (corticosterone, pregnenolone, and dehydroepiandrosterone), suggesting that biosynthesis of neurosteroid glucuronides is possible in rodent brain.
Keywords: Neuroactive steroid; Neurosteroid; Glucuronidation; Glucuronide; Liquid chromatography–mass spectrometry
Combating matrix effects in LC/ESI/MS: The extrapolative dilution approach by Anneli Kruve; Ivo Leito; Koit Herodes (pp. 75-80).
Liquid chromatography electrospray mass spectrometry – LC/ESI/MS—a primary tool for analysis of low volatility compounds in difficult matrices – suffers from the matrix effects in the ESI ionization. It is well known that matrix effects can be reduced by sample dilution. However, the efficiency of simple sample dilution is often limited, in particular by the limit of detection of the method, and can strongly vary from sample to sample.In this study matrix effect is investigated as the function of dilution. It is demonstrated that in some cases dilution can eliminate matrix effect, but often it is just reduced. Based on these findings we propose a new quantitation method based on consecutive dilutions of the sample and extrapolation of the analyte content to the infinite dilution, i.e. to matrix-free solution.The method was validated for LC/ESI/MS analysis of five pesticides (methomyl, thiabendazole, aldicarb, imazalil, methiocarb) in five matrices (tomato, cucumber, apple, rye and garlic) at two concentration levels (0.5 and 5.0mgkg−1). Agreement between the analyzed and spiked concentrations was found for all samples. It was demonstrated that in terms of accuracy of the obtained results the proposed extrapolative dilution approach works distinctly better than simple sample dilution.The main use of this approach is envisaged for (a) method development/validation to determine the extent of matrix effects and the ways of overcoming them and (b) as a second step of analysis in the case of samples having analyte contents near the maximum residue limits (MRL).
Keywords: Liquid chromatography mass spectrometry; Electrospray interface; Pesticides; Dilution; Matrix effect
Determination of cyanide, in urine and gastric content, by electrospray ionization tandem mass spectrometry after direct flow injection of dicyanogold by Kayoko Minakata; Hideki Nozawa; Kunio Gonmori; Masako Suzuki; Osamu Suzuki (pp. 81-84).
A rapid and sensitive electrospray ionization tandem mass spectrometric (ESI–MS–MS) procedure was developed for the determination of cyanide (CN−). CN− in biological fluids was reacted with NaAuCl4 to produce dicyanogold, Au(CN)2−, which was extracted with methyl isobutyl ketone (MIBK). One microliter of the extract was injected directly into an ESI–MS–MS instrument. Quantification of CN− was performed by selected reaction monitoring of the product ion CN− at m/ z 26 that derived from precursor ion Au(CN)2− at m/ z 249. CN− could be measured in the quantification range of 10−7 to 5×10−5M with the limit of detection at 4×10−8M using 10μL of urine within 10min. A victim's urine and gastric content were diluted with water to 4-fold and 500-fold and measured, respectively.
Keywords: Cyanide; Gold; Electrospray ionization; Tandem mass spectrometry; Urine
Mapping vortex-like hydrodynamic flow in microfluidic networks using fluorescence correlation spectroscopy by Ke Liu; Yu Tian; Sean M. Burrows; Randall D. Reif; Dimitri Pappas (pp. 85-90).
The ability to quickly measure flow parameters in microfluidic devices is critical for micro total analysis system (μTAS) applications. Macrofluidic methods to assess flow suffer from limitations that have made conventional methods unsuitable for the flow behavior profiling. Single molecule fluorescence correlation spectroscopy (FCS) has been employed in our study to characterize the fluidic vortex generating at a T-shape junction of microscale channels. Due to its high spatial and temporal resolution, the corresponding magnitudes relative to different flow rates in the main channel can be quantitatively differentiated using flow time ( τF) measurements of dye molecules traversing the detection volume in buffer solution. Despite the parabolic flow in the channel upstream, a heterogeneous distribution of flow has been detected across the channel intersection. In addition, our current observations also confirmed the aspect of vortex-shaped flow in low-shear design that was developed previously for cell culture. This approach not only overcomes many technical barriers for examining hydrodynamic vortices and movements in miniature structures without physically integrating any probes, but it is also especially useful for the hydrodynamic studies in polymer-glass based micro -reactor and -mixer.
Keywords: Fluorescence correlation spectroscopy (FCS); Microfluidics; Vortex; Diffusion time (; τ; D; ); Flow time (; τ; F; ); Rhodamine 110
Enhanced surface plasmon resonance by Au nanoparticles immobilized on a dielectric SiO2 layer on a gold surface by Jaeyeon Jung; Kyunga Na; Jonghwan Lee; Ki-Woo Kim; Jinho Hyun (pp. 91-97).
This paper introduces strategies for enhancement of a surface plasmon resonance (SPR) signal by adopting colloidal gold nanoparticles (AuNPs) and a SiO2 layer on a gold surface. AuNPs on SiO2 on a gold surface were compared with an unmodified gold surface and a SiO2 layer on a gold surface with no AuNPs attached. The modified surfaces showed significant changes in SPR signal when biomolecules were attached to the surface as compared with an unmodified gold surface. The detection limit of AuNPs immobilized on a SPR chip was 0.1ngmL−1 for the prostate-specific antigen (PSA), a cancer marker, as measured with a spectrophotometer. Considering that the conventional ELISA method can detect ∼10ngmL−1 of PSA, the strategy described here is much more sensitive (∼100 fold). The enhanced shift of the absorption curve resulted from the coupling of the surface and particle plasmons by the SiO2 layer and the AuNPs on the gold surface.
Keywords: Enhancement; Gold nanoparticles (AuNPs); Prostate-specific antigen (PSA); Silica (SiO; 2; ); Surface plasmon resonance (SPR)
Development of a surface plasmon resonance-based assay for the detection of Corynebacterium pseudotuberculosis infection in sheep by Sharon Stapleton; Bernard Bradshaw; Richard O’Kennedy (pp. 98-104).
Caseous lymphadenitis (CLA), a disease affecting sheep and goats, is caused by Corynebacterium pseudotuberculosis and is difficult to detect, especially at early stages in its development. A surface plasmon resonance-based biosensor assay for the detection of antibodies to the phospholipase D (PLD) exotoxin of C. pseudotuberculosis in sheep serum was successfully generated. It employed a recombinant form of PLD, which was immobilised, and all aspects of the assay including minimisation of non-specific binding, and the regeneration of the chip, were optimised. The applicability of the assay was initially demonstrated using sera collected from experimentally infected sheep and from sheep with no prior history of infection. The assay was then evaluated on a panel of clinical samples and the results obtained compared very favourably to those obtained by a double sandwich ELISA (over 90% similarity) and clearly verified its analytical value.
Keywords: Corynebacterium pseudotuberculosis; Caseous lymphadenitis; Surface plasmon resonance (SPR); Serum; Non-specific binding
Affinity-based microdialysis sampling using heparin for in vitro collection of human cytokines by Yuexi Wang; Julie A. Stenken (pp. 105-111).
Microdialysis sampling is a widely used method to sample from complex biological matrices. Cytokines are important signaling proteins that are typically recovered with low relative recovery values during microdialysis sampling. Heparin was included in the microdialysis perfusion fluid as an affinity agent to increase in vitro recovery of different cytokines through polyethersulfone (PES) microdialysis membranes with 100kDa molecular weight cutoff. No change in fluid volumes collected from the microdialysis probes occurred when heparin was included in the perfusion fluid up to concentrations of 10μM. The loss of heparin (10μM) across the dialysis membrane was minimal (2.7±0.9%, n=3). Additionally, heparin at these concentrations did not interfere with the cytokine immunoassays. The control and heparin-enhanced relative recoveries for five human cytokines using 0.1μM heparin in the microdialysis perfusion fluid flowing at 0.5μLmin−1 were ( n=3): interleukin-4 (IL-4), 4.2±0.5% and 7.2±3.1%; interleukin-6 (IL-6), 1.4±0.8% and 3.6±1.3%; interleukin-7 (IL-7), 1.3±0.8% and 4.8±1.8%; monocyte chemoattractant protein-1 (MCP-1), 9.0±1.6% and 19.5±2.7%; and tumor necrosis factor-α (TNF-α), 7.4±1.3% and 16.9±1.6%, respectively. Heparin increased the microdialysis sampling relative recovery of several human cytokines in vitro.
Keywords: Abbreviations; BSA; bovine serum albumin; EDTA; ethylenedinitrilotetraacetic acid; FBS; fetal bovine serum; IL-4; interleukin-4; IL-6; interleukin-6; IL-7; interleukin-7; MCP-1; monocyte chemoattractant protein-1; MWCO; molecular weight cutoff; PBS; phosphate buffered saline; RR; relative recovery; TNF-α; tumor necrosis factor-αMicrodialysis; Cytokines; Heparin; In vitro
Rapid, simultaneous determination of lopinavir and ritonavir in human plasma by stacking protein precipitations and salting-out assisted liquid/liquid extraction, and ultrafast LC–MS/MS by Francis Myasein; Elaine Kim; Jun Zhang; Huaiqin Wu; Tawakol A. El-Shourbagy (pp. 112-116).
Lopinavir and ritonavir are co-formulated in Kaletra® approved for the treatment of human immunodeficiency virus infection. A validated analytical method is mandatory for clinical development and therapeutic drug monitoring. Here we are reporting a method for rapid, simultaneous determination of lopinavir and ritonavir in human plasma with stacked protein precipitations and salting-out assisted extraction (SALLE), and ultrafast LC–MS/MS detection. With stacked protein precipitations and SALLE, the sample preparation for a 96-well plate can be completed within 20min by an automated pipette. Due to the unique cleanliness of SALLE extracts post double protein precipitations, the extracts were injected into an ultrafast liquid chromatography and tandem mass spectrometry system (LC–MS/MS) after simple dilution. An Agilent Zobax Extend-C18 Rapid resolution HT column (1.8μm, 2.1mm×30mm) was used for the separation. A mixture of acetonitrile:water (55:45, v/v) with 0.1% formic acid was used as the mobile phase. LC ran for approximately 48s at a flow rate of 0.5mLmin−1, tandem mass spectrometric data collection started at 15s and lasts for 30s. The method was validated with reference to Industry Guidance for Bioanalytical Method Validation and then used for clinical samples. The method is ultrafast, and robust. Results of incurred samples demonstrated excellent method of reproducibility. This ultrafast analysis speed did not compromise with the data quality. To our knowledge, this is the fastest analytical method for simultaneous determination of lopinavir and ritonavir.
Keywords: Salting-out; Ultrafast liquid chromatography; Sample preparation; High throughput; Lopinavir; Ritonavir