Dendritic cells in bone marrow at diagnosis and after chemotherapy in adult patients with acute myeloid leukaemia.

Dendritic cells (DCs) develop in the bone marrow from haematopoietic progenitor cells. Two subsets, plasmacytoid DCs (pDCs) and myeloid DCs (mDCs), have been identified. Little is known regarding DC levels in bone marrow of patients with acute myeloid leukaemia (AML) before and after chemotherapy. We investigated relative pDC and mDC levels in bone marrow from 37 hospital controls and 60 patients with AML [at diagnosis, complete remission (CR) and follow-up] using four-colour flow cytometry. The pDC immunophenotype was characterized as lin-/HLA-DR+/CD123 +  and mDC as lin-/HLA-DR+/CD11c+. In 69% of patients with AML, no DCs were detected at diagnosis. At CR, mDC levels were the same in patients with AML and hospital controls while pDC levels were slightly lower. There was no association between minimal residual disease or survival rates and DC levels. Patients with low mDC levels at CR were more likely to suffer from complicated infections, although the difference was not statistically significant. Altogether, there was a profound decrease in DC levels in patients with AML at diagnosis. DC levels increased at CR and were higher than in hospital controls after post-remission therapy, suggesting that DCs recover after repeated chemotherapy. There may be an association between mDC levels and infectious complications.

Growth, carcass characteristics, and profitability of organic versus conventional dairy beef steers.

Bull calves (n=49), born at the University of Minnesota West Central Research and Outreach Center (Morris) between March and May 2011, were used to compare growth measurements and profitability of conventional and organic dairy steers. Calves were assigned to 1 of 3 replicated groups at birth: conventional (CONV; n=16), organic (pasture and concentrate; ORG; n=16), or organic grass only (GRS; n=17), and analysis of variables was on a pen basis. Breed groups of calves were Holstein (HO; n=9); Holsteins (n=11) maintained at 1964 breed average level; crossbreds (n=19) including combinations of HO, Montbéliarde, and Swedish Red; and crossbreds (n=10) including combinations of HO, Jersey, Swedish Red, and Normande. The CONV steers were fed a diet of 80% concentrate and 20% forage. The ORG steers were fed a diet of organic corn, organic corn silage, and at least 30% of their diet consisted of organic pasture during the grazing season. The GRS steers grazed pasture during the grazing season and were fed high-quality hay or hay silage during the nongrazing season. Intakes of a total mixed ration were recorded daily with herd management software. A profit function was defined to include revenues and expenses for beef value, feed intake, pasture intake, health cost, and yardage. The GRS (358.6 kg) steers had lesser total gains from birth to slaughter than ORG (429.6 kg) and CONV (534.5 kg) steers. Furthermore, the GRS (0.61 kg/d) steers had lesser average daily gain from birth compared with ORG (0.81 kg/d) and CONV (1.1 kg/d) steers. The GRS and ORG steers had smaller rib eye area (49.5 and 65.8 cm(2), respectively) compared with CONV (75.4 cm(2)) steers. For profitability, GRS steers had 43% greater profit than CONV steers due to organic beef price premiums and lower feed costs. On the other hand, ORG steers had substantially less profit than CONV steers. The higher cost of production for the ORG steers is due to the extreme high value of organic corn. The results of the current study illustrate the economic potential of alternative strategies for growing and marketing male offspring of organic dairy cattle in the Midwest.

Fatty acid profiles, meat quality, and sensory attributes of organic versus conventional dairy beef steers.

Meat from Holstein and crossbred organic and conventional dairy steers were evaluated and compared for fatty acid profiles, meat quality, sensory attributes, and consumer acceptance. Bull calves (n=49) were randomly assigned to 1 of 3 replicated groups: conventional (CONV), organic (ORG, pasture + concentrate), or grass-fed organic (GRS) and were born at the University of Minnesota West Central Research and Outreach Center (Morris, MN) between March and May 2011. The CONV steers (n=16) were fed a diet that contained 80% concentrate and 20% forage, and ORG steers (n=16) were fed a diet of organic corn, organic corn silage, and organic protein supplement. Furthermore, ORG steers consumed at least 30% of diet dry matter of high-quality organic pasture during the grazing season. The GRS steers (n=17) consumed 100% forage from pasture during the grazing season and high-quality hay or hay silage during the nongrazing season. The ORG steers had fat that was greater in oleic acid (C18:1) than the GRS and CONV steers (47.1, 36.1, and 39.9%, respectively). The GRS steers (21.9%) were lower for monounsaturated fat than the ORG (42.1%) and CONV (40.4%) steers. Furthermore, the GRS steers tended to have greater n-3 fat and had lower n-6 fat than the ORG and CONV steers. Consequently, the GRS (1.4%) steers had a lower n-6-to-n-3 fat ratio than the ORG (12.9%) and CONV (10.0%) steers. The GRS (2.6 kg) steers had steaks that were not different for Warner-Bratzler shear force than ORG (2.3 kg) steaks; however, the GRS steaks tended to have greater shear force than the CONV (2.0 kg) steaks. The 3 steer group had steaks that were not different for color brightness (L*; 0 = black and 100 = white) and yellowness/blueness (b*; positive values = yellow and negative values = blue) values; however, the GRS (10.5) steaks had lower redness/greenness (a*; positive values = red and negative values = green) values than CONV (14.5) steaks. For sensory attributes (0- to 120-point scale), no differences were observed for ORG (71.3) and CONV (69.2) steers for overall consumer liking of the beef; however, the GRS (56.3) steers had the lowest overall liking among beef consumers. The ORG (73.3) steers had greater flavor liking than the GRS (56.8) and CONV (69.2) steers. Conversely, the GRS (6.3) steers had the highest scores for off-flavor (0- to 20-point scale) compared with the ORG (3.9) and CONV (4.1) steers. The results of the current study suggest that a potential market may exist for organic grass-fed dairy steers in the United States, but quality and consistency of the beef needs to be improved.

Whole-milk feeding duration, calf growth, and profitability of group-fed calves in an organic production system.

The objective of this study was to evaluate the effect of early-life feeding duration on growth and economics of group-fed organic dairy calves. Heifer calves born during the spring of 2011 (n = 67) and the spring of 2012 (n = 57) were used to evaluate the effect of weaning age, growth, and profitability of group-fed calves fed once per day in an organic dairy production system. Calves were assigned to replicate feeding groups of 10 in super hutches by birth order, and were born at the University of Minnesota West Central Research and Outreach Center, Morris organic dairy. Breed groups were Holsteins (n = 15) selected for high production, Holsteins (n = 23) maintained at 1964 breed-average level, crossbreds (n = 54) including combinations of Holstein, Montbéliarde, and Swedish Red, and crossbreds (n = 32) including combinations of Holstein, New Zealand Friesian, Jersey, and Swedish Red. Groups of calves were weaned at 30 (EW, early weaning), 60 (MW, mid weaning), or 90 (LW, late weaning) d of age, and groups were fed 1.5% of birth weight of 13% total solids organic whole milk once daily and weaned when the group of 10 calves consumed an average of 0.91 kg of organic calf starter per calf per day for 4 consecutive days. Body measurements were recorded at birth, weekly during the preweaning period, at weaning, and monthly thereafter. Profitability was estimated as a function of the total cost for organic milk and organic calf starter for weaning groups to weaning and to the first 90 d of age. Preweaning group performance was weaning age, EW: 47.6d, MW: 64.5d, LW: 93.7d; weaning weight, EW: 61.8 kg, MW: 79.2 kg, LW: 108.1 kg; and gain per day, EW: 0.51 kg/d, MW: 0.63 kg/d, LW: 0.75 kg/d. Body weight (BW) did not differ among weaning groups at 90 d of age; however, MW calves had lower 120-d BW than did LW calves. The EW calves did not differ from either MW or LW calves for 120-d BW. Total feed costs to weaning for groups were $1,092.97 for EW calves, $1,871.24 for MW calves, and $2,956.64 for LW calves. The cost per kilogram of gain was higher for the EW ($5.54) group of calves than for the MW ($4.60) or LW ($4.14) groups during the preweaning period. Total costs and cost per kilogram of gain for the first 90 d of age were lowest for EW ($1,595.59, $3.02) calves and highest for LW ($2,956.64, $4.13) calves, respectively.

Development of an analytical method to determine avermectins in water, sediments and soils using liquid chromatography-tandem mass spectrometry.

A comprehensive analytical multi-residue method has been developed for the determination of seven avermectins (abamectin, doramectin, ivermectin, emamectin benzoate, eprinomectin, moxidectin and selamectin) in surface water, sediment and soil samples. Solid samples were extracted applying pressurised liquid extraction followed by a solid-phase extraction (SPE) clean-up step. For aqueous samples, extraction was done utilising only SPE. All compounds were measured using liquid chromatography coupled to tandem mass spectrometry using atmospheric pressure chemical ionisation. The recoveries were 38-67% (relative standard deviation: 9-26%), 63-88% (16-23%) and 63-80% (9-15%) for spiked Rhine water, spiked sediment and spiked soil samples, respectively, and limit of quantifications were 2.5-14 ngl(-1) in water and 0.5-2.5 ngg(-1) in soil and sediment.

Discriminant function analysis as decision support system for the diagnosis of acute leukemia with a minimal four color screening panel and multiparameter flow cytometry immunophenotyping.

Despite several recommendations for standardization of multiparameter flow cytometry (MFC) the number, specificity and combinations of reagents used by diagnostic laboratories for the diagnosis and classification of acute leukemias (AL) are still very diverse. Furthermore, the current diagnostic interpretation of flow cytometry readouts is influenced arbitrarily by individual experience and knowledge. We determined the potential value of a minimal four-color combination panel of 13 monoclonal antibodies (mAbs) with a CD45/sideward light scatter-gating strategy for a standardized MFC immunophenotyping of the clinically most relevant subgroups of AL. Bone marrow samples from 155 patients with acute myeloid leukemia (AML, n=79), B-cell precursor acute lymphoblastic leukemia (BCP-ALL, n=29), T-cell precursor acute lymphoblastic leukemia (T-ALL, n=12) and normal bone marrow donors (NBMD, n=35) were analyzed. A knowledge-based learning algorithm was generated by comparing the results of the minimal panel with the actual diagnosis, using discriminative function analysis. Correct classification of the test sample according to lineage, that is, BCP-ALL, T-ALL, AML and differentiation of NBMD was achieved in 97.2% of all cases with only six of the originally applied 13 mAbs of the panel. This provides evidence that discriminant function analysis can be utilized as a decision support system for interpretation of flow cytometry readouts.

Quality assurance of the donation process.

The quality of the organs harvested from a deceased donor is of critical importance for the outcome of the transplantations. During 2005, a quality assurance project was initiated to evaluate the donor management, harvest operation, and flow of information during the donation process. Three kinds of questionnaires were used in each donation. They were completed by the transplant coordinator, the harvesting surgeon, and the surgeons performing the liver and kidney transplantations. Feedback is given to the harvesting teams within 2 weeks after the procedures. The most important findings related to missed information concerning organ abnormalities or organ damage from the procurement operation. Procurement of organs from a deceased donor involves a complex chain of events. Based on our experiences in this 1-year project, we believe that standardized registration of the various parts of the process and structured feedback to the staff give possibilities to improve performance. After minor modifications, this method for quality assurance has been introduced as a permanent part of our donation procedure. We believe that this strategy can help to detect weaknesses and improve transplant outcomes.

Changing donation pattern in central Sweden.

Since 1990, the Organisation for Organ donation in Central Sweden has registered the numbers of donations at the various hospitals in the area. During this period, a significant decrease in donation rate was observed in the large hospitals, while there was an increase in donation rate in the smaller hospitals. Taken together, the small hospitals are now at least as important as the large hospitals. Possible reasons for the observed change in donation pattern are discussed.

Flow cytometric follow-up of minimal residual disease in bone marrow gives prognostic information in children with acute lymphoblastic leukemia.

Using flow cytometry (FC) and live gate (LG) analysis we have followed levels of minimal residual disease (MRD) in the bone marrow (BM) of 70 consecutive patients with childhood acute lymphoblastic leukemia (59 B precursor ALL and 11 T-ALL) treated according to the Nordic (NOPHO-92) protocols. Thorough studies of B and T cell antigen expression patterns in normal BM performed during BIOMED 1 Concerted Action on MRD, made it possible to tailor individual protocols of marker combinations for follow-up in 97% of patients. In 12% of LG analyses, the numbers of cells exceeded 10(6) and in 82% exceeded 10(5), giving the sensitivity level of MRD detection 10(-5) and 10(-4), respectively. The median follow-up time was 53 months. Patients with MRD levels > or = 0.01% at follow-up time-points during and after first induction, and at the end of treatment had significantly lower disease-free survival by comparison to patients with MRD values <0.01%. Seven of nine patient with recurrence in the BM showed under treatment persisting MRD levels > or = 0.01% of BM cells. This was also observed in another two patients with infant leukemia who relapsed. In conclusion, the investigation of levels and the dynamics of MRD by sensitive and quantitative FC can provide a basis for further clinical studies for at least upgrading of therapy.

Flow cytometry and allele-specific oligonucleotide PCR are equally effective in detection of minimal residual disease in ALL.

The analysis of minimal residual disease (MRD) has assumed a growing role in the follow-up of patients with acute lymphoblastic leukemia (ALL). We have applied multiparameter flow cytometry (FC) with 'live-gate' analysis and allele-specific oligonucleotide (ASO)-PCR detecting leukemia-specific T cell receptor gamma and delta gene rearrangements for MRD follow-up in 30 ALL patients. The comparison of results obtained in 89 follow-up samples from 23 patients showed significantly consistent results in 70 samples (78%); (P < 0.001). Bone marrow samples taken during the first phase of treatment (during or immediately after induction) showed a lower level of consistency when compared to samples taken during later phases of treatment (69% vs 85% consistent results, respectively). Some of the discrepant results were due to low cellularity of the samples obtained for FC and some due to the presence of PCR inhibitors. Of 29 patients evaluated at the end of the induction treatment, 18 (62%) had detectable levels of MRD and six of these patients suffered relapse. In all these patients MRD levels by FC increased preceding relapse. Our results suggest that FC offers a MRD detection tool that can be easily applied in clinical practice and is as informative as molecular methods.

Analysis of minimal residual disease in childhood acute lymphoblastic leukemia: comparison between RQ-PCR analysis of Ig/TcR gene rearrangements and multicolor flow cytometric immunophenotyping.

Detection of minimal residual disease (MRD) in follow-up samples from patients with ALL is essential for evaluation of treatment response. We applied multicolor flow cytometry and real-time quantitative PCR (RQ-PCR) to compare MRD results in 71 follow-up samples from 22 children treated for ALL. When results obtained by flow cytometry and RQ-PCR were grouped into positive-negative categories, a significant level of agreement was found in 72% of samples (P<0.001). However, if a cutoff level of 0.01% was applied, the concordance was 89%. MRD could be quantified in 19 samples by both methods, showing a strong correlation (P<0.01). Nevertheless, MRD levels differed more than five-fold between both methods in 4/19 samples. In 20 (28%) samples, the two techniques showed discordant results. Most discordant results (17/20) were due to the limited sensitivity of flow cytometry analysis within the range 0.01-0.001%; remaining discordant results were due to the instable or subclonal IG/TCR gene rearrangements or a limited quantitative range of the applied RQ-PCR targets. Although concordant results could be obtained by flow cytometry and RQ-PCR analysis, MRD levels may differ. Therefore, MRD data obtained by these two techniques are not yet easily exchangeable.

BIOMED-1 concerted action report: flow cytometric characterization of CD7+ cell subsets in normal bone marrow as a basis for the diagnosis and follow-up of T cell acute lymphoblastic leukemia (T-ALL).

The European BIOMED-1 Concerted Action was initiated in 1994 to improve and standardize the flow cytometric detection of minimal residual disease (MRD) in acute leukemia (AL). Three different protocols were defined to identify the normal subsets of B, T and myeloid cells in bone marrow (BM), and were applied to the different types of AL in order to study aberrant immunophenotypes. Using sensitive acquisition methods ('live gate') T cell subsets in normal BM could be identified with five triple-stains: CD7/CD5/CD3, CD7/CD4/CD8, CD7/CD2/CD3, CD7/CD38/CD34 and TdT/CD7/surface or cytoplasmic (cy)CD3 (antibodies conjugated with FITC/PE/PECy5 or PerCP, respectively). The identification of T cell subsets in BM allowed definition of 'empty spaces' (ie areas of flow cytometric plots where normally no cells are found). All studied T-ALL cases (n = 65) were located in 'empty spaces' and could be discriminated from normal T cells. The most informative triple staining was TdT/CD7/cyCD3, which was aberrant in 91% of T-ALL cases. In most cases, two or more aberrant patterns were found. Apparently the immunophenotypes of T-ALL differ significantly from normal BM T cells. This is mostly caused by their thymocytic origin, but also the neoplastic transformation might have affected antigen expression patterns. Application of the five proposed marker combinations in T-ALL contributes to standardized detection of MRD, since cells persistent or reappearing in the 'empty spaces' can be easily identified in follow-up BM samples during and after treatment.

BIOMED-I concerted action report: flow cytometric immunophenotyping of precursor B-ALL with standardized triple-stainings. BIOMED-1 Concerted Action Investigation of Minimal Residual Disease in Acute Leukemia: International Standardization and Clinical Evaluation.

The flow cytometric detection of minimal residual disease (MRD) in precursor-B-acute lymphoblastic leukemias (precursor-B-ALL) mainly relies on the identification of minor leukemic cell populations that can be discriminated from their normal counterparts on the basis of phenotypic aberrancies observed at diagnosis. This technique is not very complex, but discordancies are frequently observed between laboratories, due to the lack of standardized methodological procedures and technical conditions. To develop standardized flow cytometric techniques for MRD detection, a European BIOMED-1 Concerted Action was initiated with the participation of laboratories from six different countries. The goal of this concerted action was to define aberrant phenotypic profiles in a series of 264 consecutive de novo precursor-B-ALL cases, systematically studied with one to five triple-labelings (TdT/CD10/CD19, CD10/CD20/CD19, CD34/CD38/CD19, CD34/CD22/CD19 and CD19/CD34/CD45) using common flow cytometric protocols in all participating laboratories. The use of four or five triple-stainings allowed the identification of aberrant phenotypes in virtually all cases tested (127 out of 130, 98%). These phenotypic aberrancies could be identified in at least two and often three triple-labelings per case. When the analysis was based on two or three triple-stainings, lower incidences of aberrancies were identified (75% and 81% of cases, respectively) that could be detected in one and sometimes two triple-stainings per case. The most informative triple staining was the TdT/CD10/CD19 combination, which enabled the identification of aberrancies in 78% of cases. The frequencies of phenotypic aberrations detected with the other four triple-stainings were 64% for CD10/CD20/CD19, 56% for CD34/CD38/CD19, 46% for CD34/CD22/CD19, and 22% for CD19/CD34/CD45. In addition, cross-lineage antigen expression was detected in 45% of cases, mainly coexpression of the myeloid antigens CD13 and/or CD33 (40%). Parallel flow cytometric studies in different laboratories finally resulted in highly concordant results (>90%) for all five antibody combinations, indicating the high reproducibility of our approach. In conclusion, the technique presented here with triple-labelings forms an excellent basis for standardized flow cytometric MRD studies in multicenter international treatment protocols for precursor-B-ALL patients.

Flow cytometric analysis of normal B cell differentiation: a frame of reference for the detection of minimal residual disease in precursor-B-ALL.

During the last two decades, major progress has been made in the technology of flow cytometry and in the availability of a large series of monoclonal antibodies against surface membrane and intracellular antigens. Flow cytometric immunophenotyping has become a diagnostic tool for the analysis of normal and malignant leukocytes and it has proven to be a reliable approach for the investigation of minimal residual disease (MRD) in leukemia patients during and after treatment. In order to standardize the flow cytometric detection of MRD in acute leukemia, a BIOMED-1 Concerted Action was initiated with the participation of six laboratories in five different European countries. This European co-operative study included the immunophenotypic characterization and enumeration of different precursor and mature B cell subpopulations in normal bone marrow (BM). The phenotypic profiles in normal B cell differentiation may form a frame of reference for the identification of aberrant phenotypes of precursor-B cell acute lymphoblastic leukemias (precursor-B-ALL) and may therefore be helpful in MRD detection. Thirty-eight normal BM samples were analyzed with five different pre-selected monoclonal antibody combinations: CD10/CD20/CD19, CD34/CD38/CD19, CD34/CD22/CD19, CD19/CD34/CD45 and TdT/CD10/CD19. Two CD19- immature subpopulations which coexpressed B cell-associated antigens were identified: CD34+/CD22+/CD19- and TdT+/CD10+/CD19-, which represented 0.11 +/- 0.09% and 0.04 +/- 0.05% of the total BM nucleated cells, respectively. These immunophenotypes may correspond to the earliest stages of B cell differentiation. In addition to these minor subpopulations, three major CD19+ B cell subpopulations were identified, representing three consecutive maturation stages; CD19dim/CD34+/TdT+/CD10bright/CD22dim/CD45dim /CD38bright/CD20- (subpopulation 1), CD19+/CD34-/TdT-/CD10+/CD22dim/CD45+/CD38bright/ CD20dim (subpopulation 2) and CD19+/CD34-/TdT-/CD10-/CD22bright/CD45bright/ CD38dim/CD20bright (subpopulation 3). The relative sizes of subpopulations 1 and 2 were found to be age related: at the age of 15 years, the phenotypic precursor-B cell profile in BM changed from the childhood 'immature' profile (large subpopulations 1 and 2/small subpopulation 3) to the adult 'mature' profile (small subpopulation 1 and 2/large subpopulation 3). When the immunophenotypically defined precursor-B cell subpopulations from normal BM samples are projected in fluorescence dot-plots, templates for the normal B cell differentiation pathways can be defined and so-called 'empty spaces' where no cell populations are located become evident. This allows discrimination between normal and malignant precursor-B cells and can therefore be used for MRD detection.

Photochemotherapy of tumours with mesotetrahydroxyphenyl chlorin is pH dependent.

Human colon carcinoma cells of the WiDr line were incubated with the tumour-localizing and photosensitizing drug mesotetrahydroxyphenyl chlorin (mTHPC) at either pH 6.8, 7.2 or 7.8. The cellular uptake of the drug was found to be independent of the pH value. However, under conditions where the cells contained the same amount of the drug (i.e. after incubation at different pH values) and were exposed to light, their photosensitivity increased with decreasing pH value. Furthermore, the cells were more photosensitive at 4 degrees C than at 37 degrees C. The shoulder on the survive curves, observed for irradiation at 37 degrees C and at pH 7.2-7.8 was practically absent for irradiation at 4 degrees C and even at 37 degrees C when the light exposure took place at pH 6.8. The observations may be related to a reduced repair of photochemotherapy (PCT)-induced damage at 4 degrees C and at pH 6.8. The high PCT efficiency at pH 6.8 may contribute to the tumour selectivity of PCT with mTHPC.

pH-dependent spectral properties of HpIX, TPPS2a, mTHPP and mTHPC.

Lower extracellular pH in tumors as compared to normal tissues has been proposed to be a factor contributing to the tumor selective uptake of several photosensitizers. Therefore, the pH dependence of absorption and fluorescence spectral properties of four different drugs relevant for photodynamic therapy (hematoporphyrin IX [HpIX], disulfonated meso-tetraphenylporphine [TPPS2a], meso-tetra(3-hydroxyphenyl)porphine [mTHPP] and meso-tetra(3-hydroxyphenyl)chlorin [mTHPC]) has been examined. Spectral analysis of the dyes dissolved in phosphate buffered saline (PBS) indicates pH-dependent modification in the physiologically important region (6.0-8.0) only in the case of HpIX. This modification is probably related to the protonation of carboxylic groups. Spectral changes of HpIX in PBS observed at acidic pH values < 5, as well as those of the rest of the drugs (inflection points of titration curves occurred at about 5.1, 3.8 and 2.4 for TPPS2a, mTHPP and mTHPC, respectively), are likely to be due to the protonation of imino nitrogens. The tumor localizing properties of mTHPP and mTHPC reported in the literature appear to be due to factors other than pH-dependent changes in the lipophilicity of the drugs.

Comparison of two extraction methods independently developed on two conceptually different automated supercritical fluid extraction systems for the determination of polychlorinated biphenyls in sediments.

Two extraction methods that independently have been developed on conceptually different automated supercritical fluid extraction systems, ISCO SFX 3560 (syringe pump and liquid trapping) and Hewlett-Packard 7680T SFE (reciprocating pump and solid-phase trapping), were compared for the extraction of polychlorinated biphenyls from two Swedish sediments. The results demonstrated that the high-temperature ISCO method in some cases yields a more exhaustive extraction, but also less clean extracts due to co-extraction of unwanted matrix components which are all present in the trapping solvent. The medium-temperature Hewlett-Packard method may sometimes cause problems with quantitative recoveries, but on the other hand it yields very clean extracts due to the extra selectivity resulting from collection on a solid-phase trap.

Analytical-scale microwave-assisted extraction.

Microwave-assisted extraction (MAE) is a process of using microwave energy to heat solvents in contact with a sample in order to partition analytes from the sample matrix into the solvent. The ability to rapidly heat the sample solvent mixture is inherent to MAE and the main advantage of this technique. By using closed vessels the extraction can be performed at elevated temperatures accelerating the mass transfer of target compounds from the sample matrix. A typical extraction procedure takes 15-30 min and uses small solvent volumes in the range of 10-30 ml. These volumes are about 10 times smaller than volumes used by conventional extraction techniques. In addition, sample throughput is increased as several samples can be extracted simultaneously. In most cases recoveries of analytes and reproducibility are improved compared to conventional techniques, as shown in several applications. This review gives a brief theoretical background of microwave heating and the basic principles of using microwave energy for extraction. It also attempts to summarize all studies performed on closed-vessel MAE until now. The influences of parameters such as solvent choice, solvent volume, temperature, time and matrix characteristics (including water content) are discussed.

On-line clean-up of pressurized liquid extracts for the determination of polychlorinated biphenyls in feedingstuffs and food matrices using gas chromatography-mass spectrometry.

This paper describes a fast and simple pressurized liquid extraction method for the determination of polychlorinated biphenyls (PCBs) in feedingstuffs and food matrices. The method is based on a simultaneous extraction/clean-up step requiring a minimum of sample handling. The final analysis was performed with gas chromatography-mass spectrometry. Seven PCBs (28, 52, 101, 118, 138, 153 and 180) were analyzed, all of which are indicator congeners that, according to European legislation should be included in the analytical monitoring program. The extracted matrices were spiked feed for poultry and two certified reference materials naturally contaminated with PCBs (cod-liver oil and milk powder), which showed excellent conformity with certified data.

Utilization of fat retainers in supercritical fluid extraction for the selective extraction of polychlorinated biphenyls from a model fat sample.

Two common fat retainers used in supercritical fluid extraction--basic alumina and the silica based adsorbent Florisil--were investigated using lard fat as model material. With a fat retainer in the extraction cell it was possible to obtain fat-free time windows. Activation by heating did not influence the length of the time windows, while deactivation of the retainers with 10% water (w/w) drastically decreased the fat retaining capabilities. The influence of modifier addition was also investigated. Finally, a method was developed, where basic alumina was utilized to selectively extract polychlorinated biphenyls (PCBs) from a model fat sample, containing PCBs, triglycerides and phospholipids. The PCBs could be quantitatively extracted in a totally fat-free time window.