Sample preparation (Chemistry)

Headspace solid phase microextraction (HS-SPME) was optimized for the analysis of pesticides with gas chromatography electron capture detection (GC-ECD) and high-resolution mass spectrometry. Factors influencing the extraction efficiency such as fiber type, extraction mode and temperature, effect of ionic strength, stirring and extraction time were evaluated. The lowest pesticide concentrations that could be detected in spiked aliquots after HS-SPME-GC-ECD ranged from 0.0005 to 0.0032 μg L − 1 . Consequently hexachlorobenzene, trans-chlordane, 4,4′-DDD and 4,4′-DDE were detected in water samples after HS-SPME at concentrations ranging from 2.4 to 61.4 μg L − 1 that are much higher than the 0.1 μg L − 1 maximum limit of individual organochlorine pesticides in drinking water set by the European Community Directive. The same samples were cleaned with ISOLUTE C 18 SPE sorbent with an optimal acetone/n-hexane (1:1 v/v) mixture for the elution of analytes. No pesticides were detected after SPE clean-up and pre-concentration. Precision for both methods was satisfactory with relative standard deviations less than 20%. This work demonstrated the superiority of HS-SPME as a sample clean-up and pre-concentration technique for pesticides in water samples as well as the need to identify and control point sources of pesticides.

Headspace solid phase microextraction (HS-SPME) was optimized for the analysis of pesticides with gas chromatography electron capture detection (GC-ECD) and high-resolution mass spectrometry. Factors influencing the extraction efficiency such as fiber type, extraction mode and temperature, effect of ionic strength, stirring and extraction time were evaluated. The lowest pesticide concentrations that could be detected in spiked aliquots after HS-SPME-GC-ECD ranged from 0.0005 to 0.0032 μg L − 1 . Consequently hexachlorobenzene, trans-chlordane, 4,4′-DDD and 4,4′-DDE were detected in water samples after HS-SPME at concentrations ranging from 2.4 to 61.4 μg L − 1 that are much higher than the 0.1 μg L − 1 maximum limit of individual organochlorine pesticides in drinking water set by the European Community Directive. The same samples were cleaned with ISOLUTE C 18 SPE sorbent with an optimal acetone/n-hexane (1:1 v/v) mixture for the elution of analytes. No pesticides were detected after SPE clean-up and pre-concentration. Precision for both methods was satisfactory with relative standard deviations less than 20%. This work demonstrated the superiority of HS-SPME as a sample clean-up and pre-concentration technique for pesticides in water samples as well as the need to identify and control point sources of pesticides.

tApplication of a new carbon-based sorbent was studied for the first time for extraction and quantificationof amphetamine and methamphetamine as model analytes by means of electromembrane surroundedsolid phase microextraction (EM-SPME). Since the basis of this microextraction method is adsorptionof target analytes on the sorbent surface (after transferring across a supported liquid membrane) in anelectrical field, the sorbent, which also performs the electrical potential, should have a conductive nature.On the other hand, using a synthesized fiber is a suitable solution to eliminate the interfering compoundsexisting in the fiber. To extract the model analytes from acidic sample solution through a thin layer oforganic phase and into the aqueous acceptor phase and their final adsorption, 150 V electrical potentialwas applied for 15 min. Regardless of the high sample cleanup ability of the proposed method, whichmakes the analysis of complicated biological fluids possible, admissible extraction recoveries (9.0–18.8%)and suitable detection limits (less than 2.0 ng mL−1) were obtained. Repeatability and reproducibilityof the method were studied and intra- and inter-assay precisions were in the ranges of 2.0–7.3% and7.5–12.5%, respectively. Coefficients of determination larger than 0.9964 were achieved by scrutinizingof the linearity up to 500 ng mL−1and calibration curves were utilized for quantification of analytes ofinterest in human urine and whole blood samples.

Differentiation ofanimalsourcesofgelatinisrequiredformanyreasonssuchassomeanxietiesabout
bovine spongiformencephalopathyorabanonconsumingporcinegelatininsomereligions.Inthe
present work,anefficient methodisintroducedfordeterminationofanimaloriginofgelatinsamples.
The basisofthisprocedureistheapplicationofpulsedelectric field forextraction,preconcentration,and
analysisofderivatizedaminoacidsingelatin.Tothisend,afterderivatizationofaminoacidsofinterest
by meansof o-phthalaldehyde(OPA)forenhancingtheirultraviolet(UV)absorbanceaswellas
increasing theirlipophilicities,a137Velectric field wasappliedfor20minwith10min
1 frequency
to maketheanalytesmigratethrougha200 mm organicliquidmembraneintoanaqueousacceptor
phase. Finally,theacceptorphasewasanalyzedbyHPLC-UV.Theproposedtechniqueofferedahigh
efficiency foranalysisofaminoacids,regarding43%and79%asextractionrecoveriesand25ngmL
1
and 50ngmL
1 as limitsofdetection(LODs)forasparagineandglutamine,respectively.Therefore,due
to samplecleanupabilityoftheproposedmethodandobtainedpreconcentrationfactors(29and53for
asparagine andglutamine,respectively),itcouldbecarriedoutfordifferentiationofanimaloriginsof
gelatin samples,evenifonlysmallamountsofsamplesareavailableorincomplicatedmediaof
foodstuffs andmedicament.

Chemical substances that are either produced by nature or by humankind have a consequence on the environment when they are accumulated to a great extent. One of nature’s major problem is that of the eutrophication of surface waters, which is caused by inorganic and organic phosphorus compounds and, in particular, from a group known as Inositol Phosphates. There are six different forms of these inositols and are commonly found in soil and sediment samples. The conducted project was aimed to develop an analytical method that could efficiently analyze and separate all six with repeatable results. As such, soil samples were collected two times from two forest locations and two crop field locations. The first time the soil samples were left overnight to dry in a drying oven while on the second time, the samples left to dry at room temperature. When the samples were considered dry enough, they processed to reach grain size and extracted with a mixture of NaOH and Titriplex® III. The extracted soil samples, the standard solutions containing inositols, and the spiked extracted soil samples with inositol solution were all analyzed with an instrumental combination of a Capillary Electrophoresis instrument coupled manually to an Electrospray mass spectrometer, where the first was operated at reversed mode and the second at negative mode. To achieve the best feasible separation, several background electrolyte solutions were created along with a large number of sheath liquids regulated by an LC pump, two Capillary Electrophoresis methods, and twenty-five distinct MS methods, all tested through extensive screening to obtain the best possible combination of parameters. Out of the obtained results from the runs, four background electrolyte solutions, two MS methods, one sheath liquid controlled by one specific flow rate, and one Capillary Electrophoresis method exhibited promising potentials with a satisfying outcome. However, the intense pulsation of the spray cone observed for many of the runs, the manual protrusion of the Capillary Electrophoresis fused silica capillary, and some random errors, the repeatability of the method is called into question.

In the present work, a simple and portable analysis device was designed for the first time for the
determination of lead ions as the model analyte. The basis of the lead analysis is its extraction and preconcentration
in an acceptor droplet via the application of an electrical field. The acceptor droplet is a KI
solution and therefore, the formation of a yellow precipitation of PbI2 was a sign of the presence of lead
ion in the solution. Following this, digital picture of the final acceptor droplet was analyzed by
investigating its Red-Green-Blue (RGB) components. The results show that the RGB intensities of the
acceptor phase are proportionate to the lead concentration in the sample solution. Also, a 9.0 V battery
was used to apply the electrical field, and other effective parameters, such as the type of organic liquid
membrane, pH of the sample solution, and the extraction time, were considered to obtain the optimal
conditions. The model analyte was determined by extracting it from a 100 mL sample solution across a
thin layer of 1-octanol, immobilized in the pores of a polypropylene membrane sheet, and into the
acceptor droplet via applying a 9.0 V electrical potential for 20 min. The device is capable of determining
lead ions down to 20.0 ng mL
1, with admissible repeatability and reproducibility (the intra- and interassay
precision ranged between 3.8–7.0% and 9.8–11.9%, respectively). Also, we calculated error% for
the model analyte in the range of
8.5 to +4.5, which suggests that the chip offers acceptable accuracy
for the analysis of lead ions. The linearity was studied in the range of 50.0–1500 ng mL
1, with a
correlation coefficient of 0.9994. Finally, the designed device was used for the analysis of lead in real
samples

In the present work, the effect of application of voltage steps on extraction efficiency of pulsed electromembrane
extraction (PEME) was investigated for the first time. The effects of voltage variations
including initial and final voltages, number of steps between the initial and final voltages as well as their
time durations were studied on the extraction efficiencies of three different classes of analytes. These
classes include amitriptyline (AMI) and nortriptyline (NOR) as more hydrophobic analytes, diclofenac
(DIC) and mefenamic acid (MEF) as acidic drugs and salbutamol (SB) and terbutaline (TB) as hydrophilic
compounds. It was anticipated that the application of high voltages is not necessary at the beginning
of the extraction, since large amounts of target analytes exist around the supported liquid membrane
(SLM)/sample solution interface. So, they could be easily transferred into the acceptor phase utilizing
lower voltages. Results showed that the benefits of voltage-step PEME (VS-PEME) are more obvious
in systems with low electrical resistance (regarding the SLM composition). Efficiencies of VS-PEME for
extraction of AMI and NOR (96% and 89% for AMI and NOR, respectively) were comparable with those
achieved from applying a constant voltage (95% for AMI and 83% for NOR). However, recoveries from
the VS-PEME of DIC and MEF (53% and 44% for DIC and MEF, respectively) were significantly higher than
those from the application of a constant voltage (33% for DIC and 31% for MEF). Also, recoveries obtained
from the VS-PEME for SB and TB were approximately 3 orders of magnitude greater than those from a
constant voltage. Moreover, it was demonstrated that in all cases analytes could effectively be extracted
at the beginning of extraction by applying low voltages.

Africa as a continent has its unique challenges for analytical chemists in sample preparation for chromatographic analyses. The areas of agriculture, environment, food and health provide formidable challenges when it comes to method development, for example, drought can result in inadequate supplies of good quality water. The testing of water quality necessitates the development of assay methods that can be employed to not only determine the quantities of pesticides associated with malaria and tsetse fly eradication programmes, but also to monitor mycotoxins or neurotoxins. Urbanisation has also meant that endocrine disruptors such as phthalate esters need to be monitored. This review will profile some of the activities by analytical chemists practising in the African continent, who seek to address some of the challenges in sample preparation for chromatographic analyses.

Understanding the biogeochemical behaviour of arsenic in the weathering and shallow subsurface environment depends critically upon determining the nature and distribution of the chemical species present in natural waters. To this end, coupled ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS) is widely used, though species fractionation during ultrasonic nebulization, and matrix-dependent ionization in the plasma are analytical issues that need to be addressed. Hexapole collision cell technology is shown to be effective in suppressing chloride-based polyatomic interferences. Irrespective of the analytical technique used, As(III)/As(V) ratios of natural waters may change substantially during storage due to (1) differential adsorption of arsenic species on hydrated ferric oxides (HFOs); and (2) microbial activity. A wide range of apparently contradictory speciation changes observed by various workers can be rationalized in terms of the differences of microbial consortia present in different water samples. Arsenic speciation in certain water types can be stabilized for days or even weeks by combined filtration, acidification and refrigeration whilst the addition of EDTA and the use of 0.1 µm filters is indicated for iron-rich waters and waters with high activities of redox-active bacteria, respectively. Although the use of hydrochloric acid has been reported elsewhere as resulting in the apparent oxidation of As(III), we show that for certain water types it acts as an extremely effective preservative of arsenic speciation.

Capillary array instrument was applied to transcript profiling of the yeast genomic DNA using GeneCalling chemistry. The instrument integrated a 12-capillary array for DNA separation with a replaceable sieving matrix, laser-induced fluorescence detection and an automated microfraction collector. The DNA fractions, exiting the separation capillaries, were continuously deposited in a 1536-well collection plate made of agarose gel. DNA fragments recovered from selected fractions were cloned and then sequenced. Over 80% of theoretically predicted fragments could be recovered in the collected fractions, cloned and sequenced with an average redundancy of threefold. Excellent correlation of the experimentally obtained sequences with the theoretically predicted gene fragments demonstrated the suitability of capillary array electrophoresis for micropreparative recovery of DNA fragments. This approach, useful especially for rapid DNA expression profiling of unknown genes for nonsequenced organisms, demonstrates the practical capability of the prototype multicapillary fraction collector.

Capillary array instrument was applied to transcript profiling of the yeast genomic DNA using GeneCalling™ chemistry. The instrument integrated a 12-capillary array for DNA separation with a replaceable sieving matrix, laser-induced fluorescence detection and an automated microfraction collector. The DNA fractions, exiting the separation capillaries, were continuously deposited in a 1536-well collection plate made of agarose gel. DNA fragments recovered from selected fractions were cloned and then sequenced. Over 80% of theoretically predicted fragments could be recovered in the collected fractions, cloned and sequenced with an average redundancy of threefold. Excellent correlation of the experimentally obtained sequences with the theoretically predicted gene fragments demonstrated the suitability of capillary array electrophoresis for micropreparative recovery of DNA fragments. This approach, useful especially for rapid DNA expression profiling of unknown genes for nonsequenced organisms, demonstrates the practical capability of the prototype multicapillary fraction collector.