Hydrogen peroxide-sodium hydrosulfite chemiluminescence system combined with high-performance liquid chromatography for determination of 1-hydroxypyrene in airborne particulates

In this research, a highly sensitive chemiluminescence method based on a sodium hydrosulfite (NaHSO₃)-hydrogen peroxide (H₂O₂) reaction for the determination of 1-hydroxypyrene (1-OHP) was developed. The response of this system was linear in the range from 0.5 to 50 pmol (R² = 0.9983). The limit of detection for 1-OHP was 100 fmol (S/N = 3). 1-OHP in airborne particulates was well separated from interfering compounds using an ODS column with 75% methanol as the mobile phase in isocratic mode. The proposed method was successfully applied to determine the 1-OHP in airborne particulates collected in Kanazawa, Japan. The average concentration of 1-OHP in the atmosphere was 2.0 pg/m³ (9.2 fmol/m³).     

Improved method for the determination of kynurenic acid in rat plasma by column-switching HPLC with post-column fluorescence detection

Kynurenic acid (KYNA), an endogenous antagonist of ionotropic glutamate and α7 nicotinic receptors, was fluorometrically determined by column-switching high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC system consists of two octadecyl silica (ODS) columns, both of which are connected with an anion-exchange column (trapping column). Following sample injection onto the HPLC column, KYNA was separated on the first ODS column with a mobile phase of H₂O/acetonitrile (95/5) containing 0.1% acetic acid. The peak fraction of KYNA was trapped on the anion-exchange column by changing the position of a six-port valve and then introduced into the second ODS column. Subsequently, KYNA was detected fluorometrically as a fluorescence complex formed with zinc ion which was pumped constantly. Instrumental limit of detection was approximately 0.16 nM, which corresponded to 8.0 fmol (per 50 μl injection, signal to noise ratio 3), and the limit of quantification was 0.53 nM (signal to noise ratio 10). Intra- and inter-day relative standard deviations were 1.1-3.9% (n = 3) and 3.0-5.3% (n = 3), respectively. The peak of KYNA in rat plasma was clearly detected by the proposed column-switching HPLC system after a facile pretreatment procedure. Intra- and inter-day relative mean errors were −1.6-1.4% (n = 3) and −2.4 to −0.4% (n = 3), respectively, with a satisfactory precision (within 5.0%). A calibration curve for the determination of KYNA showed a good linearity (r² > 0.999) in the range of 25-200 nM. The KYNA concentrations in the plasma of male Sprague-Dawley rats (8-week-old) were 44 ± 5.5 nM (mean ± S.E., n = 5). In ketamine-treated rats, which are animal models of schizophrenia, the plasma KYNA concentrations were significantly increased compared with those in the control rats (p < 0.05).     

On-line preconcentration of trace carcinogenic polycyclic aromatic hydrocarbons (PAHs) in microcolumn liquid chromatography via large volume injection

The ability and efficiency of micro precolumns made of C30 particles, monolithic silica C18 stationary phase and quartz wool coated with C30, which act as novel solid phase absorbing materials, for the on-line enrichment of aqueous polycyclic aromatic hydrocarbons (PAHs) in microcolumn liquid chromatography (LC) was investigated. The enrichment unit was designed in such a way that micro precolumns were directly connected to a 6-port micro injection valve via fused-silica tubing (0.05 mm I.D.) in order to minimize band broadening of the samples, and the enrichment efficiency of the three materials was tested using 14 PAHs, which are selected by the US Environmental Protection Agency (US EPA), as the analytes. The separation of PAHs was evaluated by using laboratory-made C30 or ODS capillary columns and the results were compared. There were no significant differences showed from the separation of PAHs in terms of peak signal between the C30 and ODS capillary columns, but the C30 capillary column was chosen for the following experiment due to its ability to produce better repeatability than the ODS column. By using the three kinds of precolumn materials, results showed that the precolumn packed with C30 particles as well as the capillary monolithic C18 precolumns (0.1 or 0.2 mm I.D.) provided better recovery than those of the quartz wool's. As long as the recovery and separation of the PAHs were concerned, 0.1 mm I.D. monolithic C18 precolumn showed the best results and the R.S.D.s (N = 7) for the retention time, peak area and peak height were between 0.70-1.5, 2.3-5.8 and 2.4-6.6%, respectively. Large volume injection up to 0.5 mL, i.e. 2500-fold enrichment, was possible and no negative effect on the separation profile was found. The LOD (S/N = 3) were between 0.10 and 4.6 pg mL⁻¹, while the LOQ (S/N = 10) were in the range of 0.32-15 pg mL⁻¹, which showed that the system is comparable to many major analytical techniques and is sensitive enough for the trace analysis of PAHs in environmental samples. The system was then applied to the determination of trace PAHs present in soil sample which was randomly taken from a nearby highway.     

A highly sensitive HPLC method with automated on-line sample pre-treatment and fluorescence detection for determination of reboxetine in human plasma

A fully automated, rapid and highly sensitive HPLC method with automated sample pre-treatment by column-switching system and fluorescence detection has been developed for the trace quantitative determination of the new antidepressant reboxetine (RBX) in human plasma. A simple pre-column derivatization procedure with 7-flouro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-F) reagent was employed. Paroxetine (PXT) was used as an internal standard. Plasma samples containing both RBX and PXT, after filtration, were derivatized by heating with NBD-F in borate buffer of pH 8 at 70 °C for 30 min. The derivatized plasma samples were injected into the HPLC system where an on-line sample clean up was achieved on the pre-treatment column (Co-sense Shim-pack MAYI-ODS) with a washing mobile phase (acetonitrile:2% acetic acid; 40:60, v/v) at a flow rate of 5 mL min⁻¹ for 1 min. After an automated on-line column switching to the analytical Hypersil phenyl 120A column (250 mm × 4.6 mm, 5 μm), the separation of the derivatized RBX and PXT was performed using a mobile phase consisting of sodium acetate buffer (pH 3.5):tetrahydrofuran:acetonitrile (55:35:10, v/v/v) at a flow rate of 2.0 mL min⁻¹. The eluted derivatives were monitored by a fluorescence detector set at an excitation wavelength of 470 nm and an emission wavelength of 530 nm. Under the optimum chromatographic conditions, a linear relationship with good correlation coefficient (r = 0.9995, n = 5) was found between the peak area ratio of RBX to PXT and RBX concentration in the range of 2-500 ng mL⁻¹, with limits of detection and quantification of 0.5 and 1.7 ng mL⁻¹, respectively. The intra- and inter-day precisions were satisfactory; the relative standard deviations were 2.25 and 3.01% for the intra- and inter-day precisions, respectively. The accuracy of the method proved as the mean recovery values were 100.11 ± 2.24% and 100.99 ± 2.98% for the intra- and inter-day assay runs, respectively. The proposed method involved simple and minimum sample preparation procedure and short run-time (<12 min) and therefore it can be applied to the routine therapeutic monitoring and pharmacokinetic studies of RBX.     

Determination of perfluorooctanoic acid and perfluorooctane sulfonate by automated in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

We have developed a simple, rapid, and sensitive method for the determination of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) by on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC-MS). PFOA and PFOS were separated within 10 min by high-performance liquid chromatography using an Inertsil ODS-3 column and 10 mM ammonium acetate/methanol (35/65, v/v) as a mobile phase at a flow rate of 0.25 mL min⁻¹. Electrospray ionization conditions in the negative ion mode were optimized for MS detection of PFOA and PFOS. The optimum in-tube SPME conditions were 20 draw/eject cycles with a sample size of 40 μL using a CP-Pora PLOT amine capillary column as the extraction device. The extracted compounds could be desorbed easily from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC-MS method, good linearity of the calibration curve (r = 0.9990 for PFOA, r = 0.9982 for PFOS) was obtained in the range of 0.05-5 ng mL⁻¹ each compound. The detection limits (S/N = 3) for PFOA and PFOS were 1.5 and 3.2 pg mL⁻¹, respectively. The method described here showed about 100-fold higher sensitivity than the direct injection method. The within-day and between-day precisions (relative standard deviations) were below 3.7 and 6.0%, respectively. This method was applied successfully to the analysis of PFOA and PFOS in environmental water samples and to the elution test from a Teflon^®-coated frying pan without interference peaks. The recoveries of PFOA and PFOS spiked into river samples were above 81%, and PFOA was detected at pg mL⁻¹ levels in environmental water samples and eluate from the frying pan.     

Determination of water soluble trace metals in airborne particulate matter using a dynamic extraction procedure with on-line inductively coupled plasma optical emission spectrometric detection

A novel continuous-flow system for the dynamic extraction of water soluble metal fractions in airborne particulate matter (APM) with subsequent inductively coupled plasma optical emission spectrometric (ICP-OES) analysis of derived extracts is presented. The fully automated extraction system with on-line multi-element detection offers enhanced sensitivity when compared to batch-wise counterparts; additionally it provides information about the extraction process. With the developed procedure detection limits in the order of 1.5 (Ba) to 8.0 (Ni) ng extractable mass per investigated sample could be achieved, which translates to method detection limits for soluble metal concentrations in APM ranging from 0.2 ng m⁻³ (Ba) to 0.9 ng m⁻³ (Fe). Reproducibility of analysis was determined by replicate measurement (n = 6) of an APM sample with an aerodynamic diameter ≤10 μm (PM10), derived results varied between 3.5% (Mn) and 12.1% (Ni) relative standard deviation. Method validation was accomplished by comparison of extracted soluble and remaining non-soluble fractions with the total metal contents of the investigated PM10 samples, showing an excellent mass balance for all elements. Application of the developed procedure for the analysis of water soluble metal fractions in PM10 samples (n = 16) from Linz (Austria) indicated a high variability of extractable fractions ranging from 11.7 ± 7.2% (Fe) to 48.8 ± 15.4% (Mn) of the total metal contents.     

Determination of dye precursors in hair coloring products by liquid chromatography with electrochemical detection

The simultaneous determination of seven aminophenols, resorcinol and p-phenylenediamine in hair coloring products was performed by liquid chromatography (HPLC) with amperometric detection (ED). The aminophenols were separated on a ODS C18 reversed-phase column by isocratic elution with a mobile phase based on 0.1 M acetate buffer pH 4.5-methanol (90:10%, v/v) at a flow rate 0.8 mL min⁻¹. The limit of detection (S/N = 3) for the aminophenols was in the 15-40 pg (injected mass) range at an applied potential of 0.950 V versus Ag/AgCl. Peak heights for the aminophenols and the two others compounds were found to be linearly related to the amount injected, from 0.3 to 300 ng (r > 0.994-0.999).The relative standard deviation (R.S.D., n = 10) for 1 ng injected was comprised in the range from 2.5 to 6.2%, depending on the aminophenol tested. The present method minimizes troublesome and time-consuming pretreatment procedures and it was applied to the determination of aminophenols, resorcinol and phenylenediamine in hair coloring formulations.     

Automatic on line preconcentration and determination of lead in water by ICP-AES using a TS-microcolumn

A simple, sensitive, low-cost and rapid, flow injection system for the on-line preconcentration of lead by sorption on a microcolumn packed with silica gel funtionalized with methylthiosalicylate (TS-gel) was developped. The metal is directly retained on the sorbent column and subsequently then eluted from it by EDTA. Five variables (sample flow rate, eluent flow rate, eluent concentration, pH and buffer concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Box-Behnken designs. The optimum conditions established were applied to the determination of lead by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The proposed method has a linear calibration range from 10 to at least 500 ng ml⁻¹ of lead. At a sample frequency of 24 h⁻¹ and a 120 s preconcentration time, the enrichment factor was 41, the detection limit was 15.3 ng ml⁻¹ (S/N=3) and the precision, expressed as relative standard deviation, was 0.9% (at 100 ng ml⁻¹). Validation of the developed method was carried out against electrothermal atomic absorption spectrometry analysis without statistically significant differences between the proposed method and the atomic absorption method.     

Fluorimetric determination of aminocaproic acid in pharmaceutical formulations using a sequential injection analysis system

A sequential injection analysis (SIA) methodology for the fluorimetric determination of aminocaproic acid in pharmaceutical formulations is proposed. The developed analytical procedure is based on the derivatisation reaction of the aminocaproic primary amine with o-phthalaldehyde (OPA) and N-acetylcysteine (NAC) and fluorimetric detection of the formed product (λ_ex = 350 nm; λ_em = 450 nm). The implementation of a SIA flow system allowed for the development of a simple, fast and versatile automated methodology, which exhibits evident advantages regarding the US Pharmacopoeia 24 (USP 24) reference procedure. By combining the SIA time-based sample insertion with a subsequent zone sampling approach, which permitted to select for detection of a well-defined sample zone, it was possible to implement an on-line dilution strategy that enabled the expansion of the analytical working range of the methodology, and thus its application in dissolution studies, without manifold re-configuration.Linear calibration plots were obtained for aminocaproic acid concentrations up to 6 × 10⁻⁵ mol l⁻¹. The developed methodology exhibit a good precision, with a R.S.D. < 2.0% (n = 15) and the detection limit was 2.5 × 10⁻⁷ mol l⁻¹. The obtained results complied with those furnished by the reference procedure with a relative deviation lower than 1.2%. No interference was found.     

A microfluidic chip based liquid-liquid extraction system with microporous membrane

A robust and simple approach for microfabricated chip based liquid-liquid extraction was developed for on-chip sample pretreatment. The chip based extraction system was composed of two microfabricated glass plates with a microporous membrane sandwiched in between. A simple bonding approach using epoxy was used to achieve bonding and sealing of the L-L extraction chip. Gravity was employed to drive the aqueous and organic flows through separate channels in the extraction system, separated by the membrane. During extraction, the analyte in an aqueous sample stream was transferred through the membrane into the organic stream. The fluorescence intensity of the analyte extracted into the organic stream was monitored in situ by a laser induced fluorescence detection system. The performance of the system was demonstrated using an aqueous solution of butyl rhodamine B (BRB) and isobutanol as sample and extractant, respectively. The system proved to be an efficient means for achieving chip based microporous membrane liquid-liquid extraction. The precision of fluorescence measurements was 1.5% R.S.D. (n = 4). A linear response range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M BRB was obtained with a regression equation: I = 8.00 × 10⁶ C + 4.91. An enrichment factor of ca. 3 was obtained with an extraction efficiency of 69%.     

Determination of traces of palladium in stream sediment and auto catalyst by FI-ICP-OES using on-line separation and preconcentration with QuadraSil TA

A flow injection analysis (FIA) method using on-line separation and preconcentration with a novel metal scavenger beads, QuadraSil™ TA, has been developed for the ICP-OES determination of traces of palladium. QuadraSil TA contains diethylenetriamine as a functional group on spherical silica beads and shows the highest selectivity for Pd(II) at pH 1 (0.1 mol l⁻¹ hydrochloric acid) solution. An aliquot of the sample solution prepared as 0.1 mol l⁻¹ in hydrochloric acid was passed through the QuadraSil TA column. After washing the column with the carrier solution, the Pd(II) retained on the column was eluted with 0.05 mol l⁻¹ thiourea solution and the eluate was directly introduced into an ICP-OES. The proposed method was successfully applied to the determination of traces of palladium in JSd-2 stream sediment certified reference material [0.019 ± 0.001 μg g⁻¹ (n = 3); provisional value: 0.0212 μg g⁻¹] and SRM 2556 used auto catalyst certified reference material [315 ± 4 μg g⁻¹ (n = 4); certified value: 326 μg g⁻¹]. The detection limit (3σ) of 0.28 ng ml⁻¹ was obtained for 5 ml of sample solution. The sample throughputs for 5 ml and 100 μl of the sample solutions were 10 and 15 h⁻¹, respectively.     

Determination of clenbuterol by capillary electrophoresis immunoassay with chemiluminescence detection

A competitive immunoassay for clenbuterol (CLB) based on capillary electrophoresis with chemiluminescence (CL) detection was established. The method was based on the competitive reaction of horseradish peroxidase (HRP)-labeled CLB (CLB-HRP) and free CLB with anti-CLB antiserum. The factors affecting the electrophoresis and CL detection were systematically investigated with HRP as a model sample. Under the optimal conditions, the tracer CLB-HRP and the immunoassay complex were separated, and the linear range and the detection limit (S/N = 3) for CLB were 5.0-40 nmol l⁻¹ and 1.2 nmol l⁻¹, respectively. The proposed method has been applied satisfactorily in the analysis of urine sample.     

Local factor analysis of rank-deficient reaction systems

A variety of biochemical and physical properties of proteins are regulated by calcium ion (Ca²⁺) binding with varying specificity and affinity. Calcium ion binding can adjust the phospholipid-protein interactions through changing the properties of phospholipid membrane. As an attractive detection technique, whole column imaging detection (WCID) coupled to capillary isoelectric focusing (cIEF) displays several advantages in the study of protein-ligand and protein-protein interactions, including fast and high-efficient separation, high resolution, and simple operation. In this study, a cIEF-WCID method was evaluated for studying the effect of Ca²⁺ binding on protein structural changes and phospholipid-protein interactions. Four proteins with different isoelectirc point (pI), trypsin inhibitor (pI = 4.5), β-lactoglobulin B (pI = 5.2), phosphorylase b (pI = 6.3), and trypsinogen (pI = 9.3), were used for this purpose. The targeted proteins exhibited altered cIEF profiles due to protein conformation changes resulting from the Ca²⁺ binding. The study showed that Ca²⁺ can be buried in the phospholipid membrane, modify the membrane property, and change the phospholipid-protein interactions. The utility of the cIEF-WCID technique demonstrates that the calcium binding plays a crucial role in the protein structural changes and the phospholipid-protein interactions, and elucidates the possible mechanisms involved in calcium-protein binding and calcium bound phospholipid-protein interactions.     

Enzymatic chemiluminescent assay of glucose by sequential-injection analysis with soluble enzyme and on-line sample dilution

This work reports a sequential-injection analysis (SIA) method for the enzymatic assay of glucose with soluble glucose oxidase (GOD) and on-line sample dilution with chemiluminescence (CL) detection. A zone of sample was aspirated in the holding coil of the SIA manifold and, if necessary, was diluted on-line by means of an auxiliary dilution conduit. Then, a zone of GOD was aspirated adjacent to the sample zone and a stopped-flow period was applied to allow the enzymatic reaction to proceed with production of hydrogen peroxide. Then, zones of a catalyst (Co(II) solution) and alkaline luminol were aspirated into the holding coil. Finally, the flow was reversed and the stacked zones were sent to a flow-cell located in front of a photomultiplier tube (PMT) that monitored the CL intensity. The linear dynamic range was 1 × 10⁻⁵-1 × 10⁻³ mol L⁻¹ glucose, the coefficient of variation at 8 × 10⁻⁵ mol L⁻¹ of glucose was s_r = 3.1% (n = 8), the limit of detection at the 3σ level was c_L = 1 × 10⁻⁶ mol L⁻¹ and the sampling frequency was 28 h⁻¹. With on-line dilution by a factor of 1/200, the linear range could be extended up to 0.2 mol L⁻¹ glucose. The advantages of the proposed method are the simple manifold and instrumentation used, the scope for automated on-line dilution, the low consumption of sample and reagents and the elimination of enzyme immobilisation procedures. The method was applied to the analysis of commercial drinks and honey with percent relative errors in glucose determination in the range 100 ± 6.1%.     

Analysis of heterocyclic amines in hair by on-line in-tube solid-phase microextraction coupled with liquid chromatography−tandem mass spectrometry

Mutagenic and carcinogenic heterocyclic amines (HCAs) are formed during heating of various proteinaceous foods, but human exposure to HCAs has not yet been elucidated in detail. To assess long-term exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in hair by automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Using a Zorbax Eclipse XDB-C8 column, 16 HCAs were analyzed within 15 min. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL sample at a flow rate of 200 μL min⁻¹ using a Supel-Q PLOT capillary column as an extraction device. The extracted HCAs were easily desorbed from the column by passage of the mobile phase, with no carryover observed. This in-tube SPME LC–MS/MS method showed good linearity for HCAs in the range of 10–2000 pg mL⁻¹, with correlation coefficients above 0.9989 (n = 18), using stable isotope-labeled HCA internal standards. The detection limits (S/N = 3) of 14 HCAs except for MeAαC and Glu-P-1 were 0.10–0.79 pg mL⁻¹. This method was successfully utilized to analyze 14 HCAs in hair samples without any interference peaks, with quantitative limits (S/N = 10) of about 0.17–1.32 pg mg⁻¹ hair. Using this method, we evaluated the exposure to HCAs in cigarette smoke and the suitability of using hair HCAs as exposure biomarkers.     

Analysis of trace levels of domoic acid in seawater and plankton by liquid chromatography without derivatization,using UV or mass spectrometry detection

Quantitation of trace levels of domoic acid (DA) in seawater samples usually requires labour-intensive protocols involving chemical derivatization with 9-fluorenylmethylchloroformate and liquid chromatography with fluorescence detection (FMOC–LC–FLD). Procedures based on LC–MS have been published, but time-consuming and costly solid-phase extraction pre-concentration steps are required to achieve suitable detection limits. This paper describes an alternative, simple and inexpensive LC method with ultraviolet detection (LC–UVD) for the routine analysis of trace levels of DA in seawater without the use of sample pre-concentration or derivatization steps. Qualitative confirmation of DA identity in dubious samples can be achieved by mass spectrometry (LC–MS) using the same chromatographic conditions. Addition of an ion-pairing/acidifying agent (0.15% trifluoroacetic acid) to sample extracts and the use of a gradient elution permitted the direct analysis of large sample volumes (100 μl), resulting in both high selectivity and sensitivity (limit of detection = 42 pg ml⁻¹ by LC–UVD and 15 pg ml⁻¹ by LC–MS). Same-day precision varied between 0.4 and 5%, depending on the detection method and DA concentration. Mean recoveries of spiked DA in seawater by LC–UVD were 98.8% at 0.1–10 ng ml⁻¹ and 99.8% at 50–1000 ng ml⁻¹. LC–UVD exhibited strong correlation with FMOC–LC–FLD during inter-laboratory analysis of Pseudo-nitzschia multiseries cultures containing 60–2000 ng DA ml⁻¹ (r² > 0.99), but more variable results were obtained by LC–MS (r² = 0.85). This new technique was used to confirm the presence of trace DA levels in low-toxicity Pseudo-nitzschia spp. isolates (0.2–1.6 ng ml⁻¹) and in whole-water field samples (0.3–5.8 ng ml⁻¹), even in the absence of detectable Pseudo-nitzschia spp. cells in the water column.     

Development and validation of a HPLC method for the determination of buprenorphine hydrochloride, naloxone hydrochloride and noroxymorphone in a tablet formulation

A simple isocratic reversed-phase high-performance liquid chromatographic method (RP-HPLC) was developed for the simultaneous determination of buprenorphine hydrochloride, naloxone hydrochloride dihydrate and its major impurity, noroxymorphone, in pharmaceutical tablets. The chromatographic separation was achieved with 10 mmol L⁻¹ potassium phosphate buffer adjusted to pH 6.0 with orthophosphoric acid and acetonitrile (17:83, v/v) as mobile phase, a C-18 column, Perfectsil Target ODS3 (150 mm × 4.6 mm i.d., 5 μm) kept at 35 °C and UV detection at 210 nm. The compounds were eluted isocratically at a flow rate of 1.0 mL min⁻¹. The average retention times for naloxone, noroxymorphone and buprenorphine were 2.4, 3.8 and 8.1 min, respectively. The method was validated according to the ICH guidelines. The validation characteristics included accuracy, precision, linearity, range, specificity, limit of quantitation and robustness. The calibration curves were linear (r > 0.996) over the concentration range 0.22-220 μg mL⁻¹ for buprenorphine hydrochloride and 0.1-100 μg mL⁻¹ for naloxone hydrochloride dihydrate and noroxymorphone. The recoveries for all three compounds were above 96%. No spectral or chromatographic interferences from the tablet excipients were found. This method is rapid and simple, does not require any sample preparation and is suitable for routine quality control analyses.     

Development of vial wall sorptive extraction and its application to determination of progesterone in human serum

A novel sample preparation method, vial wall sorptive extraction (VWSE), which uses a vial whose internal wall is coated with polydimethylsiloxane (PDMS), was developed. The method was applied to the determination of progesterone in human serum sample. Human serum sample (0.5 mL) spiked with progesterone-¹³C₂ was pipetted into the VWSE device and vortex mixing was performed for 30 min. Then, the serum sample was removed and the vial rinsed with purified water. Fifty microliter of methanol as liquid desorption (LD) solvent was pipetted into the VWSE device and vortex mixing was performed for 10 min. Then, the extract was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The correlation coefficient (r) of the calibration curve over the concentration range of 0.5–200 ng mL⁻¹ was 0.999. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.1 and 0.5 ng mL⁻¹, respectively. The relative recoveries were 97.9% (RSD: 4.4%, n = 6) and 102.8% (RSD: 1.1%, n = 6) for progesterone spiked at 5 and 50 ng mL⁻¹, respectively. This simple, accurate, sensitive, and selective analytical method is applicable to the trace analysis of a minute amount of sample.     

Flow injection wetting-film extraction system for flame atomic absorption spectrometric determination of cadmium in environmental waters

A newly simple flow injection wetting-film extraction system coupled to flame atomic absorption spectrometry (FAAS) has been developed for trace amount of cadmium determination. The sample was mixed on-line with sodium diethyl dithiocarbamate and the produced non-charged Cd(II)-diethyl dithiocarbamate (DDTC) chelate complex was extracted on the thin film of diisobutyl ketone (DIBK) on the inner wall of the PTFE extraction coil. The wetting-film with the extracted analyte was then eluted by a segment of the cover solvent, and transported directly to the FAAS for evaluation. All the important chemical and flow parameters were optimized. Under the optimized conditions an enhancement factor of 35, a sample frequency of 22 h⁻¹ and a detection limit of c_L = 0.7 μg l⁻¹ Cd(II) were obtained for 60 s preconcentration time. The calibration curve was linear over the concentration range 1.5-45.0 μg l⁻¹ Cd(II) and the relative standard deviation, R.S.D. (n = 10) was 3.9%, at 10.0 μg l⁻¹ concentration level. The developed method was successfully applied to cadmium determination in a variety of environmental water samples as well as waste-water sample.     

A reversed-phase high performance liquid chromatography coupled with resonance Rayleigh scattering detection for the determination of four tetracycline antibiotics

A new reversed-phase high performance liquid chromatography with resonance Rayleigh scattering detection (HPLC-RRS) was developed for simultaneous separation and determination of four tetracycline antibiotics (TCs). A good chromatographic separation among the compounds was achieved using a Synergi Fusion-RP column (150 mm × 4.6 mm; 4 μm) and a mobile phase consisting of methanol-acetonitrile-oxalic acid (5 mM) at the flow rate of 0.8 mL min⁻¹. Column temperature was 30 °C. The RRS signal was detected at λ_ex = λ_em = 370 nm. The recoveries of sample added standard ranged from 95.3% to 103.5%, and the relative standard deviation was below 2.79%. A detection limit of 2.12-5.12 μg mL⁻¹ was reached and a linear range was found between peak height and concentration in the range of 10.36-518.0 μg mL⁻¹ for oxytetracycline (OTC), 12.11-605.5 μg mL⁻¹ for tetracycline (TC), 11.79-589.5 μg mL⁻¹ for chlortetracycline (CTC) and 10.32-516.0 μg mL⁻¹ for doxycycline (DC). The linear regression coefficients were all above 0.999. The method has been applied successfully to the determination of OTC, TC, CTC, DC in pharmaceutical formulations and in honey. The method was simple, rapid and showed a better linear relation and high repeatability.