Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications. A systematic review and meta-analysis of the management outcome studies.

BACKGROUND: Multiple-detectors computed tomographic pulmonary angiography (CTPA) has a higher sensitivity for pulmonary embolism (PE) within the subsegmental pulmonary arteries as compared with single-detector CTPA. Multiple-detectors CTPA might increase the rate of subsegmental PE diagnosis. The clinical significance of subsegmental PE is unknown. We sought to summarize the proportion of subsegmental PE diagnosed with single- and multiple-detectors CTPA and assess the safety of diagnostic strategies based on single- or multiple-detectors CTPA to exclude PE. PATIENTS AND METHODS: A systematic literature search strategy was conducted using MEDLINE, EMBASE and the Cochrane Register of Controlled Trials. We selected 22 articles (20 prospective cohort studies and two randomized controlled trials) that included patients with suspected PE who underwent a CTPA and reported the rate of subsegmental PE. Two reviewers independently extracted data onto standardized forms. RESULTS: The rate of subsegmental PE diagnosis was 4.7% [95% confidence interval (CI): 2.5-7.6] and 9.4 (95% CI: 5.5-14.2) in patients that underwent a single- and multiple-detectors CTPA, respectively. The 3-month thromboembolic risks in patients with suspected PE and who were left untreated based on a diagnostic algorithm including a negative CTPA was 0.9% (95% CI: 0.4-1.4) and 1.1% (95% CI: 0.7-1.4) for single- and multiple-detectors CTPA, respectively. CONCLUSION: Multiple-detectors CTPA seems to increase the proportion of patients diagnosed with subsegmental PE without lowering the 3-month risk of thromboembolism suggesting that subsegmental PE may not be clinically relevant.

Salmonella enterica serovar typhimurium trxA mutants are protective against virulent challenge and induce less inflammation than the live-attenuated vaccine strain SL3261.

In Salmonella enterica serovar Typhimurium, trxA encodes thioredoxin 1, a small, soluble protein with disulfide reductase activity, which catalyzes thiol disulfide redox reactions in a variety of substrate proteins. Thioredoxins are involved as antioxidants in defense against oxidative stresses, such as exposure to hydrogen peroxide and hydroxyl radicals. We have made a defined, complete deletion of trxA in the mouse-virulent S. Typhimurium strain SL1344 (SL1344 trxA), replacing the gene with a kanamycin resistance gene cassette. SL1344 trxA was attenuated for virulence in BALB/c mice by the oral and intravenous routes and when used in immunization experiments provided protection against challenge with the virulent parent strain. SL1344 trxA induced less inflammation in murine spleens and livers than SL3261, the aroA mutant, live attenuated vaccine strain. The reduced splenomegaly observed following infection with SL1344 trxA was partially attributed to a reduction in the number of both CD4(+) and CD8(+) T cells and B lymphocytes in the spleen and reduced infiltration by CD11b(+) cells into the spleen compared with spleens from mice infected with SL3261. This less severe pathological response indicates that a trxA mutation might be used to reduce reactogenicity of live attenuated vaccine strains. We tested this by deleting trxA in SL3261. SL3261 trxA was also less inflammatory than SL3261 but was slightly less effective as a vaccine strain than either the SL3261 parent strain or SL1344 trxA.

An interaction between the cytochrome P450 probe substrates chlorzoxazone (CYP2E1) and midazolam (CYP3A).

AIMS: The use of multiple probe substrates to evaluate the activity of drug metabolizing enzymes requires that there are no inter-substrate interactions. As part of a series of studies to develop a clinically useful collection of probe substrates that could be given alone or in any combination, we observed an interaction between midazolam (MDZ) and another component of the six-drug cocktail. Published data indicated that the interacting component was likely to be chlorzoxazone. This was investigated as part of a second study. The data relating to the interaction from both studies are reported here. METHODS: Both studies were performed in 16 healthy subjects. All treatments were given orally after an overnight fast. In study 1, which was performed to a four-period, open, crossover design, subjects received on separate occasions MDZ 5 mg, diclofenac 25 mg, a four drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg and chlorzoxazone 250 mg) and a six drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg, chlorzoxazone 250 mg, diclofenac 25 mg and MDZ 5 mg). In study 2, which was performed to a two-period, open, crossover design, subjects received a five drug cocktail (as the six drug cocktail in the first study, but without chlorzoxazone and with diclofenac dose increased to 50 mg) and a six drug cocktail (as five drug cocktail, with chlorzoxazone 250 mg). In both studies, blood samples were taken for measurement of plasma MDZ and 1-hydroxy MDZ (1-OH MDZ) concentrations. In study 1, blood samples were taken up to 12 h post-dose while in study 2 a single sample was taken 2 h after dosing. In study 1, the potential interaction between MDZ and the other components of the six drug cocktail was assessed by comparing AUClast ratios (1-OH MDZ/MDZ) between the two treatments. Additionally, a single sampling timepoint of 2 h post-dose for determination of concentration, rather than AUC, ratios was established. The 2 h plasma concentration ratios from studies 1 and 2 were combined and a pooled analysis performed to compare ratios within each study (to determine the change in ratio when MDZ was dosed with and without chlorzoxazone) and between studies (to determine the consistency of the ratios when MDZ was given either as part of the two six drug cocktails or when given alone and as part of the five drug cocktail). RESULTS: In study 1, both the AUClast ratio and the 2 h post-dose plasma concentration ratio were reduced when MDZ was given as part of the six drug cocktail in comparison with those for MDZ alone. This was the result of an increase in MDZ, rather than decrease in 1-OH MDZ, concentrations and was considered to result from a reduction in first pass metabolism of MDZ. The geometric mean AUClast values (with 95% CI) for MDZ were 95.6 (79.0, 115.7) and 160.4 (133.6, 192.6) microg l(-1) h when given alone and as part of the six drug cocktail, respectively. The corresponding values for 1-OH MDZ were 789.6 (697.6, 893.6) and 791.4 (701.7, 892.6) microg l(-1) h. The ratio of adjusted geometric mean AUClast ratios for the two treatments was 1.82 (90% CI 1.48, 2.23, P < 0.001). The pooled plasma 1-OH MDZ/MDZ ratio data from both studies showed that the differences in MDZ metabolism observed in study 1 were replicated in study 2. The adjusted geometric mean 1-OH MDZ/MDZ ratios when MDZ was given alone and as part of the six drug cocktail were 7.79 and 4.59, respectively, for study 1 (ratio 1.70, 95% CI 1.36, 2.11, P < 0.001) and 7.64 and 4.60 for study 2 (ratio 1.66, 95% CI 1.34, 2.06, P < 0.001). These data indicate that when given orally chlorzoxazone interacts with MDZ, increasing plasma MDZ concentrations. In contrast, there was no difference between the plasma 1-OH MDZ/MDZ ratios when MDZ was given alone and as part of the five drug cocktail indicating that there were no interactions between MDZ and any of the other components of that cocktail. CONCLUSIONS: Chlorzoxazone appears to significantly influence the pharmacokinetics of oral MDZ, probably through inhibition of first pass metabolism by CYP3A in the GI tract. Data from these studies and literature evidence showing a further interaction between chlorzoxazone and CYP1A2 substrates and questions concerning the specificity of chlorzoxazone as a probe substrate for CYP2E1, indicate that the use of chlorzoxazone in multisubstrate probe cocktails should be avoided.

Quantitative analysis of pharmaceuticals in biological fluids using high-performance liquid chromatography coupled to mass spectrometry: a review.

1. The development of bio-analysis of drug molecules over the last 10 years is reviewed, focusing on advances in sample preparation, liquid chromatography and detection. 2. Developments have led to improvements in detection sensitivity, enhancements in specificity and increased capacity. 3. Emerging technologies such as monolithic column chromatography and miniaturized chip-based systems are discussed.

A clinical trial on a plate? The potential of 384-well format solid phase extraction for high-throughput bioanalysis using liquid chromatography/tandem mass spectrometry.

The application of 384-well format solid phase extraction (SPE) for bioanalysis using liquid chromatography/tandem mass spectrometry (LC/MS/MS) is reported and a 384-well SPE method for the 5-HT agonist sumatriptan in human plasma described. Plasma samples were extracted on a prototype low-density polyethylene 384-well SPE block using a packed bed of 5 mg Oasistrade mark HLB. Liquid handling was automated by a combination of a robotic sampler processor and a 96/384 multi-channel dispensing station. Samples and SPE reagents were drawn through the SPE block by centrifugation. The extracts were analysed by LC/MS/MS with thermally and pneumatically assisted electrospray ionisation and selected reaction monitoring. The method is used to illustrate and discuss the feasibility and viability of sample preparation techniques in high-density microtitre plate format for routine bioanalysis.

Automated protein precipitation by filtration in the 96-well format.

The use of automated protein precipitation by filtration in the 96-well format as a rapid sample preparation technique for high throughput bioanalysis using liquid chromatography tandem mass spectrometry is reported. A robotic sample processor is used to aspirate sequentially a plasma sample and acetonitrile separated by air gaps. These are then mixed by being dispensed into individual channels of a 96-well filter block. The resulting supernatant is separated from the precipitated plasma proteins by the application of gentle vacuum using a custom manifold. The filtered supernatants are collected into a deep well microtitre plate, evaporated to dryness using a heated 96-well dry down station and reconstituted in water prior to analysis. The efficiency of the extraction procedure is measured by the Lowry method for determining protein concentration. This method was used to optimise both the volume and the order of reagent addition, and to compare several prototype 96-well filter blocks. Using the optimised procedure a specific, precise and accurate method was developed for the beta-agonist salbutamol in rabbit plasma with a calibration range of 1 to 100 ng/ml from 100 microl of sample.

Determination of a 'GW cocktail' of cytochrome P450 probe substrates and their metabolites in plasma and urine using automated solid phase extraction and fast gradient liquid chromatography tandem mass spectrometry.

A mass spectrometry based method for the simultaneous determination of an in vivo Greenford-Ware or 'GW cocktail' of CYP450 probe substrates and their metabolites in both human plasma and urine is described. The probe substrates, caffeine, diclofenac, mephenytoin, debrisoquine, chlorzoxazone and midazolam, together with their respective metabolites and stable isotope labelled internal standards, are simultaneously extracted from the biological matrix using solid phase extraction in 96-well microtitre plate format, automated by means of a custom built Zymark robotic system. The extracts are analysed by fast gradient high performance liquid chromatography (HPLC) with detection by tandem mass spectrometry (MS/MS) using thermally and pneumatically assisted electrospray ionisation in both positive and negative ion modes and selected reaction monitoring. The methods are specific, accurate and precise with intra- and inter-assay precision (%CV) of less than 15% for all analytes.

Determination of the enantiomers of salbutamol and its 4-O-sulphate metabolites in biological matrices by chiral liquid chromatography tandem mass spectrometry.

Sensitive, mass spectrometry based bioanalytical methods are described for the determination of the R- and S-enantiomers of the beta-agonist salbutamol (albuterol) and its 4-O-sulphate metabolite in human plasma and urine. In both methods samples are prepared by 96 well format solid phase extraction using a custom built robotic system. Extracts are then analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS) using a teicoplanin-based chiral stationary phase and selected reaction monitoring. The methods are accurate (bias < +/- 10%), precise (%CV < 11%) and sensitive, providing lower limits of quantitation (LLoQ) in plasma of 100 pg/mL and 5 ng/mL for the enantiomers of salbutamol and its 4-O-sulphate metabolite, respectively. By restricting the chiral method for plasma to the enantiomers of salbutamol only, it was possible to revalidate at an improved LLoQ of 25 pg/mL. A high throughout LC-MS/MS method has also been developed for racemic salbutamol only, which uses a similar extraction procedure but a conventional C8 column. The method has a reduced analysis time of three minutes per sample and using a high sensitivity, triple quadrupole mass spectrometer provides an LLoQ of 5 pg/mL based on extraction of 0.5 mL of plasma.

Determination of the glucocorticoid fluticasone propionate in plasma by automated solid-phase extraction and liquid chromatography-tandem mass spectrometry.

A sensitive, robust and high throughput mass spectrometry based method is described for the determination of the glucocorticoid fluticasone propionate in plasma. The method employs solid-phase extraction in 96 well microtitre plate format which has been automated by means of a custom built Zymark robotic system. The extracts are analysed by liquid chromatography-tandem mass spectrometry using thermally and pneumatically assisted electrospray ionisation and selected reaction monitoring. The method is both accurate and precise with both intra- and inter-assay precision (C.V.) of less than <6%. The method provides a lower limit of quantification of 20 pg/ml from 0.5 ml of human plasma, sufficient to monitor systemic concentrations of inhaled fluticasone propionate at therapeutic doses.

Use of liquid chromatography-tandem mass spectrometry for the quantitative and qualitative analysis of an antipsychotic agent and its metabolites in human plasma and urine.

The use of liquid chromatography-tandem mass spectrometry (LC-MS-MS) for the quantitative analysis of an 'atypical' antipsychotic agent in human plasma is described. The method uses atmospheric pressure chemical ionisation, and offers increased sensitivity, selectivity and speed of analysis over an existing high-performance liquid chromatography method using fluorescence detection. This method enabled same day turn around of results for in excess of 100 samples, including sample preparation, data acquisition and processing. LC-MS-MS was also used to detect and characterise known and unknown in vivo metabolites of the drug in human urine and plasma, using electrospray ionisation.

Identification of urinary and biliary conjugated metabolites of the neuromuscular blocker 51W89 by liquid chromatography/mass spectrometry.

Cisatracurium, (1R, 1'R, 2R, 2'R)-2,2-[1,5-pentanediylbis-[oxy(3-oxo- 3,1-propanediyl]]bis[1-[(3,4-dimethoxyphenyl)-methyl]-1,2,3,4- tetrahydro-6,7-dimethoxy-2-methylisoquinolinium] dibenzenesulphonate (51W89), is an intermediate-acting neuromuscular blocking agent. 51W89 is one of ten isomers contained in Tracrium (atracurium besylate) and represents approximately 15 percent of the atracurium mixture. Clinical studies have indicated that 51W89 is more potent and is significantly weaker as a histamine releaser than atracurium. In vitro studies in human plasma have shown that, like atracurium, 51W89 spontaneously degrades at physiological pH by Hoffmann elimination to form laudanosine and the quaternary monoacrylate. Subsequent ester hydrolysis of the monoacrylate generates the monoquaternary alcohol. In rat plasma, 51W89 is also metabolized by non-specific carboxylesterases to the monoquaternary alcohol and the monoquaternary acid, the former being rapidly hydrolysed further to the more stable acid. It has been reported that laudanosine can be further metabolized via N-dimethylation to yield tetrahydropapaverine. The rate-limiting step in the degradation of 51W89 in human plasma is Hofmann elimination, whilst in rat plasma, the action of non-specific carboxylesterases is rate limiting. As part of the development of 51W89, the disposition of 14C-51W89 following a single intravenous bolus dose was studied in various animal species and humans. In the present work, we describe the identification of 51W89 metabolites in urine and bile from these studies by high performance liquid chromatography/mass spectrometry using pneumatically-assisted electrospray ionization coupled to an on-line radioactivity monitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of microcystins from laboratory cultures and environmental samples of Microcystis aeruginosa and from an associated animal toxicosis.

Six microcystins were identified in a laboratory culture of the cyanobacterium (blue-green alga) Microcystis aeruginosa PCC 7813 using high-performance liquid chromatography coupled with diode array detection (HPLC-DAD) and mass spectrometry (LC-MS). The toxins were purified and further characterized by amino acid analysis and tandem mass spectrometry (MS-MS). The presence of the previously reported microcystin-LR and microcystin-LY was confirmed. Two further microcystins were characterized as microcystin-LW and microcystin-LF. Another two toxins were partially characterized and are believed to be an analog of microcystin-LR (molecular weight 1008) and microcystin-LM (molecular weight 969). Natural bloom material of M. aeruginosa collected from 2 reservoirs was found to have similar microcystin profiles using HPLC-DAD and LC-MS, indicating the widespread occurrence of these microcystin variants. In addition, the presence of 5 of the microcystins was confirmed in the rumen contents of a lamb by LC-MS and LC-MS-MS, providing the first report of microcystins identified in an animal suspected of being poisoned by cyanobacterial hepatotoxins.

Determination of the acylcoenzyme A cholesterol acyltransferase inhibitor 447C88 in plasma using gas chromatography-mass spectrometry and liquid chromatography atmospheric pressure chemical ionisation tandem mass spectrometry.

Two mass spectrometry-based methods are described for the determination of 447C88 (I), a novel inhibitor of acylcoenzyme A cholesterol acyltransferase (ACAT), in rat, dog and human plasma. The first method uses gas chromatography-mass spectrometry (GC-MS) with electron ionisation and selected-ion monitoring. The method employs solid-phase extraction of I from plasma and requires alkylation of I using iodoethane. The second method uses liquid chromatography-tandem mass spectrometry (LC-MS-MS) with atmospheric-pressure chemical-ionisation and selected-reaction monitoring. The LC-MS-MS method uses a simplified version of the extraction procedure used for GC-MS and does not require derivatisation of I. While both methods provide the necessary limit of quantitation of 0.5 ng/ml in human, dog and rat plasma with the required precision and accuracy, the LC-MS-MS assay offers increased sensitivity, selectivity and speed over the GC-MS assay. This allows a same day turn round of results for in excess of 100 samples, including sample preparation and data acquisition and processing.

Determination of erythromycin A in salmon tissue by liquid chromatography with ion-spray mass spectrometry.

A reverse-phase liquid chromatography/mass spectrometry (LC/MS) method, incorporating gradient elution, is described for the characterization of residual erythromycin A and its metabolites in salmon tissue. The method uses ion-spray, a mild atmospheric pressure ionization technique which provides an abundant protonated molecule well suited for selected ion monitoring experiments. Tandem mass spectrometry (MS/MS) using collision-induced dissociation was used to provide structural information. The LC/MS method was tested for the analysis of salmon tissue spiked with erythromycin A at levels between 0.01 and 1 p.p.m. A simple extraction and clean-up procedure, slightly modified from that described by Takatsuki et al. (J. Assoc. Off. Anal. Chem. 70, 708 (1987)), was used in this work. Using selected ion and selected reaction monitoring techniques, the LC/MS and LC/MS/MS methods provided detection limits of < 10 and 50 ng g-1, respectively. Confirmatory full-scan LC/MS and LC/MS/MS spectra were obtained at the 0.5 and 1 microgram g-1 levels, respectively. Using a combination of these techniques, the presence of residual erythromycin A was confirmed in the tissue of fish administered medicated feed containing the antibiotic. In addition, several metabolites and degradation products of erythromycin A, including anhydro-erythromycin and N-demethyl-erythromycin, were detected and where possible confirmed by comparison with authentic compounds. Although this analytical method has been shown to afford the necessary sensitivity and precision, application of these techniques to high-throughput quantitative analyses will require development of an improved clean-up procedure and preferably also of a suitable surrogate internal standard.

Detection of new 7-O-acyl derivatives of diarrhetic shellfish poisoning toxins by liquid chromatography-mass spectrometry.

A novel method for the detection of acylated diarrhetic shellfish poisoning toxins is reported. Direct determination of these compounds is possible using high performance liquid chromatography coupled with ion-spray mass spectrometry. An extract, purified from the digestive glands of toxic mussels (Mytilus edulis) contaminated with okadaic acid, dinophysistoxin-1, and a recently reported analog, dinophysistoxin-2, was also shown to contain small amounts of dinophysistoxin-3, a mixture of 7-O-acyl ester derivatives of dinophysistoxin-1. In addition, acyl ester derivatives of okadaic acid and dinophysistoxin-2 were also detected by direct LC-MS analysis and confirmed by analysis of their hydrolysis products. This is the first report of the detection of other naturally occurring 7-O-acyl esters similar to dinophysistoxin-3.

Synthesis, characterization, and Ca2+ antagonistic activity of diltiazem metabolites.

Diltiazem is a calcium antagonist widely used in the treatment of angina and hypertension. The contributions of metabolites of diltiazem to the vasorelaxant effects of diltiazem were investigated. The synthesis and spectroscopic characterization of eight major cis-diltiazem metabolites are described. Three of the compounds--N, O-didemethylated metabolite (21), O-demethylated metabolite (22), and diltiazem N-oxide (27)--have been recently reported and have not previously been synthesized. The identities of all eight synthetic metabolites have been verified with samples obtained from human urine using combined LC-MS/MS. The Ca2+ antagonistic activities of diltiazem and its metabolites (except 27) were studied on hamster aorta preparations depolarized with KCl. The order of potencies (IC50 +/- SE, microM) is as follows: diltiazem (0.98 +/- 0.47) greater than 17 (2.46 +/- 0.38) greater than or equal to 23 (3.27 +/- 1.02) greater than 26 (20.2 +/- 10.5) greater than 22 (40.4 +/- 15.4) greater than or equal to 25 (45.5 +/- 18.1) greater than 21 (112.2 +/- 33.2) greater than or equal to 24 (126.7 +/- 24.2). Structure-activity relationships are also discussed.

C60 and C70 fullerene isomers generated in flames. Detection and verification by liquid chromatography/mass spectrometry analyses.

Fullerenes C60 and C70, generated by combustion, have been shown previously to be produced in controlled laminar flames accompanied by other compounds having fullerene-like characteristics. Analysis of these additional compounds by high-performance liquid chromatography, coupled on-line with mass spectrometry has identified them as isomers of the C60 and C70 fullerenes. The newly observed isomers have characteristic UV spectra and are thermally unstable, undergoing conversion to the more stable fullerenes with a half-life of about 1 h in boiling toluene (111 degrees C). Isomers of C60 and C70 fullerenes previously have been studied theoretically, but not observed experimentally. The flame-generated material also contains C60O and C70O compounds, as well as C76 and higher carbon clusters.

Ionspray mass spectrometry of marine toxins. IV. Determination of diarrhetic shellfish poisoning toxins in mussel tissue by liquid chromatography/mass spectrometry.

An improved liquid chromatographic/mass spectrometric (LC/MS) method utilizing gradient elution and ion-spray ionization is described for the sensitive determination of okadaic acid and dinophysistoxin-1, the principal toxins implicated in cases of diarrhetic shellfish poisoning. The method was used to confirm the presence of both toxins, together with a recently identified isomer of okadaic acid, dinophysistoxin-2, in various samples of cultivated blue mussels (Mytilus edulis) from Canadian and European waters. The method provided a mass detection limit of 0.4 ng for each toxin, thus allowing detection of 40 ng per g of whole mussel tissue (or approximately 10 ng/g if only the digestive glands were used in the assay). Quantitative results obtained by LC/MS were in good agreement with those obtained by derivatization and high-performance liquid chromatography with fluorescence detection.

Comparison of liquid-junction and coaxial interfaces for capillary electrophoresis-mass spectrometry with application to compounds of concern to the aquaculture industry.

The application of capillary electrophoresis-mass spectrometry (CE-MS) to the analysis of compounds of concern to the aquaculture industry is reported. Two different approaches to coupling the CE column to an IonSpray atmospheric pressure ionization (API) interface, viz., a liquid-junction and a coaxial arrangement, are describe and compared with regard to ruggedness, ease of use, sensitivity and electrophoretic performance. The different injection modes used in three commercial capillary electrophoresis systems were also evaluated for their applicability to CE-MS. The use of CE-MS for the analysis of a variety of classes of antibiotics used in the fish aquaculture industry, such as the sulfonamides and their potentiators (e.g., trimethoprim), is demonstrated and was used to confirm the presence of these components in shellfish extracts at the low ppm level. CE-MS was also applied to the analysis of marine toxins such as saxitoxin and its analogues which are associated with paralytic shellfish poisoning, and also the toxins responsible for amnesic and diarrheic shellfish poisoning. Tandem mass spectrometry (MS-MS) was used to provide structural information on these analytes, and the ability to distinguish isomeric compounds based on their different migration and fragmentation characteristics using CE-MS-MS is demonstrated.

Ionspray mass spectrometry of marine toxins. III. Analysis of paralytic shellfish poisoning toxins by flow-injection analysis, liquid chromatography/mass spectrometry and capillary electrophoresis/mass spectrometry.

Ionspray mass spectrometry has been used to monitor the purification of saxitoxin, the parent compound in the family of toxins responsible for paralytic shellfish poisoning (PSP), from a strain of the dinoflagellate Alexandrium excavatum. Quantitative results obtained by flow-injection analysis are compared to those obtained by high-performance liquid chromatography with post-column oxidation and fluorescence detection. The coupling of liquid chromatography and capillary electrophoresis with ionspray mass spectrometry is described for the separation of mixtures of PSP toxins and the highly potent pufferfish toxin tetrodotoxin. Tandem mass spectrometry is used to provide the structural information, and the ability to distinguish isomeric PSP toxins both chromatographically and mass spectrometrically is demonstrated.