Simultaneous extraction of tetracycline, macrolide and sulfonamide antibiotics from agricultural soils using pressurised liquid extraction, followed by solid-phase extraction and liquid chromatography-tandem mass spectrometry

The veterinary antibacterial agents chlortetracycline (CTC), oxytetracycline (OTC), sulfadiazine (SDZ), erythromycin (ERY) and tylosin (TYL A, B, C and D) were extracted from soil using pressurized liquid extraction (PLE). Citric acid (pH 4.7) and methanol was used as extraction buffer, followed by tandem-solid-phase extraction (SPE) clean-up (SAX + HLB) for all compounds. For quantification two slightly different methods were employed using LC-MS-MS with MRM detection. The soil extraction method was validated using a loamy sand soil and a sandy soil, representing two typical Danish agricultural soils. Recoveries were 50-80% for the tetracyclines (CTC and OTC) and sulfadiazine (SDZ) and 60-100% for the macrolides (TYL and ERY). Limits of detection for the soil extraction method (LOD(soil)) were 0.6-5.6 microg kg(-1) soil for CTC and OTC, 0.9-2.9 microg kg(-1) soil for SDZ and 2.4-5.5 microg kg(-1) soil for TYL A and ERY. Furthermore, the method was applied to field samples taken from two agricultural fields fertilised with liquid manure containing CTC and TYL A. These results showed a decline in the content of antibacterial agents throughout the sampling period of 155 days from 10 to 15 microg CTC kg(-1) soil and 20-55 microg TYL A kg(-1) soil to below or near the LOD(soil) listed above. Finally, the method was applied to barley grains harvested from the fields. None of the antibacterial agents were measured in grain samples, but recoveries for spiked grain samples were similar to soil recoveries.

Simultaneous determination of pyrimethamine, sulfadiazine and N-acetyl-sulfadiazine in plasma for monitoring infants in treatment of congenital toxoplasmosis

A method for the simultaneous determination of pyrimethamine, sulfadiazine and its metabolite N-acetyl-sulfadiazine in small plasma samples from neonates in treatment for congenital toxoplasmosis has been developed. In this method only 25 microl of plasma is used and a simple sample preparation based on protein precipitation and centrifugation provides highly reliable data as the recovery is about 100% and the precision is good. The analysis is performed using high performance liquid chromatography with UV and mass spectrometric (MS) detection. Pyrimethamine was found to give a linear response using MS detection in the range 0.02-5 microg/ml. Sulfadiazine and its metabolite N-acetyl-sulfadiazine were preferably analysed by UV at 269 nm in the concentration ranges 0.2-200 microg/ml for sulfadiazine and 0.2-50 microg/ml for N-acetyl-sulfadiazine.

Isolation, structural elucidation and in vitro activity of 2-acetyl-2-decarboxamido-oxytetracycline against environmental relevant bacteria, including tetracycline-resistant bacteria

2-Acetyl-2-decarboxamido-oxytetracycline (ADOTC) is a major impurity of oxytetracycline (OTC) produced as a side product during fermentation. ADOTC was isolated from OTC and other impurities using preparative HPLC. The preparative column was an Xterra MS, C18 chromatographic column (100 mm x 19 mm i.d., 5 microm), and the mobile phase contained methanol-water (27:73 (v/v)) with 0.08 M formic acid added. The flow rate was 9.0 ml/min. It was possible to isolate few milligram ADOTC in a day. The compound was unambiguously identified using NMR and MS-MS. The anti-microbial activity against activated sludge bacteria was determined giving a potency of only 3% of that of OTC. With tetracycline-resistant bacteria, no anti-microbial activity was observed, indicating a mode of action similar to that of OTC.

In vitro reactivity of carboxylic acid-CoA thioesters with glutathione

The chemical reactivity of acyl-CoA thioesters toward nucleophiles has been demonstrated in several recent studies. Thus, intracellularly formed acyl-CoAs of xenobiotic carboxylic acids may react covalently with endogenous proteins and potentially lead to adverse effects. The purpose of this study was to investigate whether a correlation could be found between the structure of acyl-CoA thioesters and their reactivities toward the tripeptide, glutathione (gamma-Glu-Cys-Gly). The acyl-CoA thioesters of eight carboxylic acids (ibuprofen, clofibric acid, indomethacin, fenbufen, tolmetin, salicylic acid, 2-phenoxypropionic acid, and (4-chloro-2-methyl-phenoxy)acetic acid (MCPA)) were synthesized, and each acyl-CoA (0.5 mM) was incubated with glutathione (5.0 mM) in 0.1 M potassium phosphate (pH 7.4, 37 degrees C). All of the acyl-CoAs reacted with glutathione to form the respective acyl-S-glutathione products, with MCPA-CoA having the highest rate of conjugate formation (120 +/- 10 microM/min) and ibuprofen-CoA having the lowest (1.0 +/- 0.1 microM/min). The relative reactivities of the acyl-CoAs were dependent on the substitution at the carbon atom alpha to the acyl carbon and on the presence of an oxygen atom in a position beta to the acyl carbon and were as follows: phenoxyacetic acid > o-hydroxybenzoic acid--phenoxypropionic acid > arylacetic acid derivatives > 2-methyl-2-phenoxypropionic acid--2-phenylpropionic acid. For each acyl-CoA thioester, the overall hydrolysis rate was determined as the time-dependent formation of parent compound. A linear trend was observed when comparing the reactivities of the acyl-CoAs with glutathione with the corresponding overall hydrolysis rates. Thus, the most reactive compound (MCPA-CoA) was also the compound with the highest rate of hydrolysis and the least reactive compounds (ibuprofen-CoA, clofibryl-CoA) were also the compounds least susceptible to hydrolysis.

Recent applications of microemulsion electrokinetic chromatography

Microemulsions are used in a similar way as micellar solutions are used for separations in capillary electrophoresis. Within the last approximately six years, a number of papers have appeared in the literature in which the separation characteristics of microemulsion electrokinetic chromatography (MEEKC) have been investigated. The total number of papers dealing with MEEKC is now close to 100. One of the major fields of application for MEEKC has been the characterization of the lipophilicity of chemical substances but the technique has also been applied for the analysis of substances within the fields of natural products, pharmaceuticals, vitamins, peptides, proteins, and nucleic acid bases as well as nucleosides. An overview of the applications is given together with the microemulsions used for each application.

Are caveolae involved in clathrin-independent endocytosis?

In addition to endocytosing molecules via clathrin-coated pits, cells also internalize membrane and fluid by a clathrin-independent endocytic mechanism. In this article we search for the equivalent of clathrin-coated pits in clathrin-independent endocytosis, and discuss some pitfalls in the interpretation of electron micrographs. We also discuss how the early steps in clathrin-independent endocytosis might be analysed morphologically, and we argue that caveolae are not involved in clathrin-independent endocytosis.

Quantitative analysis of oxytetracycline and its impurities by LC-MS-MS

A liquid chromatographic-tandem mass spectrometric method using an Xterra MS C(18) chromatographic column ( 100 mm x 2.1 mm i.d., 3.5microm) that allows complete separation of oxytetracycline (OTC) and the impurities: 4-epi-oxytetracycline (EOTC), tetracycline (TC), 4-epi-tetracycline (ETC), 2-acetyl-2-decarboxamido-oxytetracycline (ADOTC), alpha-apo-oxytetracycline (alpha-AOTC) and beta-apo-oxytetracycline (beta-AOTC) was developed. Gradient elution was used and calibration curves were obtained using the scan mode selected reaction monitoring (SRM). Acceptable correlations were obtained for OTC, TC, EOTC and ADOTC whereas the correlations of alpha-AOTC and beta-AOTC were less accurate resulting in higher limits of quantification (LOQ) and limits of detection (LOD) relative to the other compounds. The intraday and interday accuracy varied for all the compounds from 90 to 112% and the intraday and interday precision were lower than 7.1%. The method was applied for analysis of commercial available ointments containing OTC resulting in an acceptable quantification of OTC and the impurities in the drug preparations. The advantage of this method compared to the other separation methods is an empty separation window right after the large peak corresponding to OTC in the chromatogram, which facilitates an accurate determination of ADOTC and the other impurities.

Determination of lisinopril in dosage forms and spiked human plasma through derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) followed by spectrophotometry or HPLC with fluorimetric detection

Two sensitive, simple and specific methods based on spectrophotometry and reversed-phase HPLC with fluorimetric detection are described for the determination of lisinopril in dosage forms as well as in spiked human plasma using solid phase extraction (SPE) procedures. Both methods are based on the derivatization of lisinopril with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in borate buffer of pH 9 to yield a yellow, fluorescent product. The spectrophotometric method depends on measuring the formed yellow color at 470 nm after optimization of the reaction conditions. The HPLC method is based on measurement of the derivatized product using fluorescence detection at 540 nm (excitation at 470 nm). The separation of the derivatized drug, the excess reagent and the internal standard (bumetanide) was performed on a reversed-phase ODS column using isocratic elution with methanol-0.02 M sodium dihydrogen phosphate, pH 3.0 (55:45, v/v) at a flow rate of 1.0 ml/min. The calibration graphs were linear over the concentration ranges 2-20 or 0.02-3.2 microg/ml of lisinopril with minimum detectability of 0.3 and 0.008 microg/ml (6.1 x 10(-7) and 1.7 x 10(-8)M) for the spectrophotometric and the HPLC methods, respectively. The proposed methods were applied without any interference from the tablet excipients for the determination of lisinopril in dosage forms, either alone or co-formulated with hydrochlorothiazide. Furthermore, the use of the HPLC method was extended to the in vitro determination of the drug in spiked human plasma. Interference from endogenous amino acids has been overcomed by using the solid phase extraction technique, the percentage recovery (n=6) was 101.6+/-3.35.

On-line turbulent-flow chromatography–high-performance liquid chromatography–mass spectrometry for fast sample preparation and quantitation

A sensitive and selective liquid chromatography-mass spectrometry method has been developed for the simultaneous identification and quantitation of drug substances and metabolites in rat plasma. The method combines on-line turbulent-flow chromatography, high-performance liquid chromatography and mass spectrometry. This combination is considered to be a new approach suitable for fast bio-analysis in drug discovery. Dextromethorphan, and its two metabolites, dextrorphan and 3-methoxymorphinan served as model substances. The analytes present in plasma were collected on a Cyclone column using turbulent-flow chromatography and were subsequently transferred on-line to and focused on an X-Terra MS C8 column. The analytes were eluted by a linear gradient and detected by a fast scanning mass spectrometer. The detector response was quadratic and the dynamic range was estimated to be 0.5-100 ng/ml plasma or 12.5 pg to 2.50 ng injected into the system.

Spectrophotometric determination of propranolol in formulations via oxidative coupling with 3-methylbenzothiazoline-2-one hydrazone

A simple spectrophotometric method has been developed for the determination of propranolol hydrochloride in pure as well as in dosage forms. The method is based on the oxidative coupling reaction with 3-methylbenzothiazoline-2-one hydrazone. A mixture of an acidic solution of the chromogenic agent and the drug upon treatment with ceric ammonium sulfate produces an orange color peaking at 496 nm. The absorbance-calibration plot was linear over the range 1-10 microg/ml with minimum detectability (S/N=2) of 0.1 microg/ml (3.38x10(-7) M). The molar absorbitivity was 3.195x10(3) l/M/cm with correlation coefficient (n=10) of 0.9999. The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. The proposed method was applied successfully to the determination of propranolol in its dosage forms. A proposal of the reaction pathway was presented.

Determination of octanol-water partition coefficients for carbonate esters and other small organic molecules by microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) was assessed as a tool for determination of octanol-water partition coefficients using 34 solutes encompassing 8 carbonate esters. It was confirmed that microemulsions containing 1.44-2.88% w/w SDS, 6.49% w/w 1-butanol, and 0.82% w/w n-heptane constitute a good model of octanol-water partitioning in the pH range of 1.4-7.4. Use of the migration index concept led to improved repeatability of the MEEKC method compared to the use of retention factors. Using a dynamical coating, a high electroosmotic flow at pH 1.4 and 4.75 was achieved expanding the practical pH working range of the MEEKC system. The correlation obtained between the migration index and log P was unaffected by pH indicating that the properties of the microemulsion droplets and, thus, partitioning are independent of pH. No evidence for congeneric behavior was found for the sample set comprising solutes with different hydrogen bonding properties suggesting that simple reference compounds can be used as calibrators. Lipophilicity estimates for the series of carbonate esters were obtained. The increase in lipophilicity with chain length was smaller than expected from the Hansch substituent constant, pi.

Identification of the amino acids of human serum albumin involved in the reaction with the naproxen acyl coenzyme A thioester using liquid chromatography combined with fluorescence and mass spectrometric detection

Xenobiotic carboxylic acids, that via their metabolites covalently modify proteins, have been associated with serious side effects in man. Such reactive metabolites may be acyl glucuronides or alternatively, the corresponding acyl-CoA thioesters. In this study, the reaction of a model xenobiotic acyl-CoA, the naproxen-CoA, with human serum albumin (HSA), was characterized by high-performance liquid chromatography employing fluorescence and mass spectrometric detection. One mM naproxen-CoA was incubated for 6h with HSA (0.45 mM) at 37 degrees C in a 0.1M phosphate buffer (pH 7.4). The tryptic digest of the reduced and alkylated protein was analyzed in order to identify the amino acids in the sequence that were covalently modified with naproxen. Fluorescent peptides, that represented naproxen-modified peptides, were characterized using HPLC-MS-MS and HPLC-MS in zoom scan mode, which provided information on the structure and the charge of the modified peptides. The naproxen-CoA reacted predominantly with lysine 199, lysine 541, and lysine 351, which was in agreement with the binding pattern that has previously been reported for the reactive acyl glucuronides and their reaction with HSA.

A sequential high-yielding large-scale solution-method for synthesis of philanthotoxin analogues

A general, improved procedure for rapid synthesis of philanthotoxin analogues, a pharmacologically important class of polyamine conjugates, is described. The solution-phase procedure is illustrated by gram-scale synthesis of philanthotoxins PhTX-343 and PhTX-12. Selectively protected polyamines are coupled to N(alpha)-Fmoc-protected amino acid pentafluorophenyl esters. After removal of the N(alpha)-Fmoc group, the amine is coupled with carboxylic acid pentafluorophenyl esters. Deprotection followed by a rapid and efficient purification by vacuum liquid chromatography on octadecylsilyl silica (RP-18 phase) gave the philanthotoxin analogues in 74-78% overall yield.

From experimental design to uncertainty estimation for the European Pharmacopoeia HPLC analysis of human insulin

In this paper the process from experimental design (e.g. ruggedness test) to uncertainty estimation is described. The uncertainty estimate was calculated for the peak area of insulin plus A21 desamido insulin resulting from an HPLC analysis of a sample of an injectable human insulin preparation, Actrapid HM 100 IU ml(-1) (Novo Nordisk A/S). The analytical method used was the European Pharmacopoeia assay. (4) An expanded uncertainty (1) of 1.8% (of the area from the HPLC analysis) at an approximately 95% confidence level was found and confirmed by a validation study. This uncertainty refers to the peak area of the analyte from a single injection of the sample. The input parameters to the uncertainty estimate were found from a factorial experimental design (e.g. ruggedness test) consisting of 9 factors applied to the HPLC analysis. The input parameters were chosen to cover the probable contributors to the variability of the measured area of the HPLC analysis, including the sample preparation, but excluding uncertainty deriving from the reference material(s).

Characterization of mixtures of recombinant human cytochrome p450s as a screening model for metabolic stability in drug discovery

1. Recombinant human cytochrome p450 (rhCYP) has become an important screening model in drug metabolism studies due to the high cost of human and animal hepatic tissue. Until now, rhCYPs have been evaluated and used as separate forms, but a mixture of CYP forms comparable with the human liver could be of value in early drug discovery. 2. In the present study, rhCYP2C9, rhCYP2D6 and rhCYP3A4 co-expressed with reductase in Escerichia coli were mixed and evaluated with regards to kinetic properties (K(m) and V(max)). Furthermore, antioxidant was added to investigate whether a free radical scavenger would affect the kinetic parameters. Results were compared with data obtained in human liver microsomes (HLM). 3. Results showed a good correlation between mixed rh CYP data and HLM data for K(m) and V(max). K(m) varied < 3-fold between matrices for CYP2C9 and CYP3A4, whereas the K(m) for CYP2D6 varied up to 4.5-fold. V(max) differed up to 3-fold between matrices for the CYP forms investigated. However, the discrepancy in V(max) may depend on the anticipated level of each form in HLM. The addition of antioxidant increased V(max) for CYP2C9 and CYP2D6 by 75 and 50%, respectively, whereas V(max) for CYP3A4 was unchanged. 4. In conclusion, the rhCYP mixture shows promising results as a predictor of CYP kinetic parameters. Furthermore, addition of antioxidant can in certain cases increase catalytic activity.

Chemical reactivity of the naproxen acyl glucuronide and the naproxen coenzyme A thioester towards bionucleophiles

Drugs may be metabolised to reactive electrophilic species that spontaneously react with proteins. The presence of such drug-protein adducts has been associated with drug toxicity. In this study, the reactivity of the major metabolite of naproxen--the 1-beta-O-glucuronide (Nap-GlcU)--was compared to the corresponding naproxen coenzyme A (Nap-CoA) thioester. The reactivity of the two metabolites was assessed in vitro in a phosphate buffer (pH 7.4; 0.1 M) at 37 degrees C towards the model bionucleophiles glutathione and human serum albumin (HSA). The reaction between the electrophilic species (Nap-GlcU and Nap-CoA) and glutathione forming the Nap-glutathione conjugate was monitored using LC-MS-MS and LC-UV, respectively. It was shown that Nap-CoA resulted in an approximate 100-fold higher formation of Nap-glutathione conjugate than Nap-GlcU. The presence of Nap-CoA also resulted in acylated HSA with a rate and a yield that was significantly higher than reported for Nap-GlcU. In summary, the data suggest that CoA metabolites may be more reactive species than acyl glucuronides that previously have been associated with severe drug related side effects in vivo.

In vivo release of bupivacaine from subcutaneously administered oily solution. Comparison with in vitro release

A non-randomized cross-over study was performed with bupivacaine HCl (5 mg x ml(-1)) aqueous solution and bupivacaine free base (4.44 mg x ml(-1)) in Viscoleo/castor oil 2:1 (v/v) administered s.c. to male Wistar rats. Plasma levels were analyzed by LC-MS. Plasma profiles obtained after administration of oily solution showed a prolonged bupivacaine release with lower peak plasma levels as compared to administration of an aqueous formulation applied in the same compartment. t(1/2), t(max), C(max) and AUC(0-infinity) for the aqueous solution were 63+/-8 min, 19+/-16 min, 194+/-46 ng x ml(-1) and 25,000+/-3000 ng min x ml(-1), respectively, while the corresponding data for the oil solution were 368+/-89 min, 334+/-186 min, 36+/-25 ng x ml(-1) and 25,000+/-6000 ng x min x ml(-1). The present data indicate the potential of designing an oil formulation of bupivacaine with a prolonged local analgetic effect exhibiting a minimum of systemic toxicity. In vivo release of bupivacaine from the oil solution was evaluated by a numerical deconvolution method. In vivo release kinetics was found to be first-order and corresponded well with in vitro release kinetics found using a rotating dialysis cell. This led to establishment of an in vitro/in vivo correlation for this particular formulation.

Stereospecific pH-dependent degradation kinetics of R- and S-naproxen-beta-l-O-acyl-glucuronide

The hydrolysis and acyl migration of biosynthetic S-naproxen-beta-l-O-acyl glucuronide (I) and R-naproxen-beta-l-O-acyl glucuronide (II) was followed by HPLC. Nine first-order kinetic rate constants for the hydrolysis and acyl migration between the beta-l-O-acyl glucuronide, its alpha/beta-2, alpha/beta-3-, alpha/beta-4-, and alpha-1-O-acyl isomers and naproxen aglycone were determined for I and II at pH 7.00, 7.40 and 8.00 at 37 degrees C by kinetic simulation. For I the 3-O-acyl isomer was the most stable isomer as the pseudo-equilibrium ratio for the major acyl-migrated isomers was 1:1.5:0.9 (2-O-acyl isomer:3-O-acyl isomer:4-O-acyl isomer). The 3- and 4-O-acyl isomers of II were equally stable as the pseudo-equilibrium ratio for the major acyl-migrated isomers was 1:1.4:1.4 (2-O-acyl isomer:3-O-acyl isomer:4-O-acyl isomer). For both I and II, the pseudo-equilibrium ratio between the major 2-O-acyl isomer and the minor alpha-l-O-acyl isomer was 10:1 (2-O-acyl isomer:alpha-l-O-acyl isomer). The pseudo-equilibrium found for the major acyl-migrated isomers of I and II in the present study corresponds with the pattern previously published for R- and S-ketoprofen-beta-l-O-acyl glucuronide acyl-migrated isomers, suggesting that these findings may be general for acyl-migrated beta-l-O-acyl glucuronides of enantiomeric 2-arylpropionic acids.

Pain, sedation and morphine metabolism in cancer patients during long-term treatment with sustained-release morphine

BACKGROUND

Morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G) are the two most important metabolites of morphine. Both are pharmacologically active, however, with different effects. M-6-G has been demonstrated capable of inducing anti-nociception and sedation, and M-3-G may induce behavioural excitation and possibly antagonise anti-nociception. Their impact on pharmacodynamics in patients in long-term treatment with oral morphine remains to be settled.

METHODS

Forty-two cancer patients treated with oral sustained-release (SR) morphine were assessed for pain, sedation and other side effects related to morphine treatment. Blood samples were analysed for morphine, M-3-G and M-6-G by high-performance liquid chromatography (HPLC).

RESULTS

Significant correlations were found between the daily dose of SR morphine and plasma morphine (M) (r = 0.535, P < 0.001), plasma M-6-G (r = 0.868, P < 0.001) and plasma M-3-G (r = 0.865, P < 0.001). There was no relationship between plasma morphine, M-6-G, M-6-G/M and pain and sedation scores. Seventy-nine percent of the patients suffered from dryness of the mouth, which was the most frequent side effect observed. Patients in this group had higher plasma morphine and M-6-G concentrations than patients who did not suffer from this side effect.

CONCLUSION

The plasma concentrations of morphine and its metabolites, M-3-G and M-6-G, are significantly correlated to the daily dose of SR morphine. Although M-6-G has analgesic properties, no associations were found between pain and plasma morphine and morphine metabolites. This may be due to the multitudinous factors affecting the dose-effect relationship. Patients with dryness of the mouth had higher concentrations of morphine and M-6-G than patients without this side effect.

Changing M3G/M6G ratios and pharmacodynamics in a cancer patient during long-term morphine treatment

A cancer patient receiving long-term oral sustained-release morphine treatment and periodically presenting with unusually high plasma M3G/M6G ratios is described. We found the patient's formation of M6G more unstable and perhaps delayed compared to the formation of M3G. There is no apparent explanation for this phenomenon and the high M3G/M6G ratios had no implications for the patient's pain experience or side effects from the morphine treatment.

Separation of hypericins and hyperforins in extracts of Hypericum perforatum L. using non-aqueous capillary electrophoresis with reversed electro-osmotic flow

The separation of the lipophilic compounds in extracts of Hypericum perforatum L. is demonstrated in a non-aqueous capillary electrophoresis system with reversed electro-osmotic flow. Solvent mixtures of methanol, dimethylsulfoxide and N-methylformamide were used for the electrophoresis media, with addition of ammonium acetate and sodium acetate as electrolytes. The flow was reversed by the addition of the polycation hexadimethrine bromide, and thus negative voltage was applied. The method shows baseline separation between the four hypericins-protopseudohypericin, pseudohypericin, protohypericin and hypericin-whereas total baseline separation between the two hyperforins-hyperforin and adhyperforin-was not achieved. Using a fused-silica capillary (30 cm x 25 microm ID) and a voltage of -25 kV the analysis time of the hypericins and hyperforins was obtainable within 3 min. Application of the method with a fused-silica capillary of a larger internal diameter (48.5 cm x 50 microm ID) and a voltage of -20 kV resulted in analysis times of 8 min, but also lower limits of detection. The maximal attainable voltage was applied in both cases. Simultaneous separation of the flavonoids-although less efficient-may also be achieved. The technique of non-aqueous capillary electrophoresis with reversed electro-osmotic flow provides a very fast technique to evaluate the composition of hypericins and hyperforins in extracts of Hypericum perforatum L.

Method optimisation with the use of uncertainty budgets

Uncertainty budgets can be used for a variety of situations, e.g. reporting the total uncertainty, calculating tolerance limits or method optimisation. In this paper it is demonstrated how the use of uncertainty budgets can help in reducing the total uncertainty of an analytical method, i.e. method optimisation. In this example it has been possible to reduce the total uncertainty of a concentration determination of hydrogen peroxide (by titration) from 2.7 x 10(-2) M to 3.93 x 10(-3) M (or to about a 1/7) by changing the traceability chain and working with more pure reagents.

A new sheathless electrospray interface for coupling of capillary electrophoresis to ion-trap mass spectrometry

A simple laboratory-made sheathless electrospray interface for coupling of capillary electrophoresis to ion-trap mass spectrometry (CE/MS) was developed. The interface was machined in-house and it was designed to be freely interchangeable with the commercially available ionization sources for the mass spectrometer. Sharpened fused-silica capillaries were coated with nickel by a simple electrodeless plating procedure and were used as all-in-one columns/emitters. The electrodeless plating produced a 2-5- micro m thick smooth nickel layer that lasted for more than 8 h of continuous electrospraying. The performance of the CE/MS interface was examined by using four cationic imipramine derivatives as test substances. Relative detection limits were calculated on the basis of the extracted ion electrophorograms and were in the range 6-130 nmol/L, corresponding to absolute detection limits in the range of 20-400 amol. The system was applied for analysis of impurities in an impure imipramine N-oxide preparation, and two of the impurities could be identified on the basis of online-MS(MS) spectra recorded in scan-dependent mode.