In-house Reference Standard Research Articles

Potential of external (in air) particle induced gamma-ray emission method for the preparation of isotopic composition of boron in-house reference standard in boron carbide matrix for quality control work

In-house reference standards for isotopic compositions of boron in natural and enriched boron carbide matrix were prepared using external PIGE methods.

International standards for monoclonal antibodies for assessing the biological activity of medicines: A status update

Scientific relevance. The clinical effects and the expiration of patents for original (reference) biotechnological medicines based on monoclonal antibodies (mAbs) stimulated the development of biosimilar mAbs. The quality profile of a biosimilar mAb should correspond to the quality of the reference medicinal product. When demonstrating biosimilarity and determining the activity of medicines as part of batch quality control, analysts should study the biological properties of mAbs using suitable reference standards. The lack of international standards (ISs) makes mAb manufacturers use in-house reference standards. There is a risk of obtaining non-uniform quality and efficacy data because of the use of in-house reference standards, the heterogeneity and structural complexity of mAbs, and the relationship between the biological activity and efficacy of mAbs.Aim. This study aimed to analyse the relevance of and need for ISs for the biological activity of biotherapeutic mAbs and to define the role of reference medicinal products and ISs in assessing biosimilarity and testing medicines throughout their lifecycle.Discussion. This review covers the issues arising from the lack of ISs for assessing the biological activity of mAbs and the role and significance of reference products and ISs for biosimilars. The authors describe the specifics of studying the biological properties of mAbs and summarise the data on the need to develop and use ISs for the standardisation of biological tests. This review presents the results of studies on the first ISs established by the World Health Organisation to assess the biological activity of mAbs; these results suggest the need to standardise mAbs using ISs to ensure the quality, safety, and efficacy of mAb therapy.Conclusions. The use of ISs for mAbs plays a key role in harmonising biological activity assessments. Publicly available ISs serve as primary standards for the calibration of secondary reference materials. Moreover, ISs are required for the harmonisation of activity evaluation (in IU) between laboratories and for the consistency of the activity of various medicinal products from different manufacturers that share the same INN. The use of ISs by mAb manufacturers will contribute to ensuring the quality of mAbs and clinical monitoring of the effectiveness of their use.

Pollen allergen products: current standardisation issues

Scientific relevance. Pollen allergen medicines are in high demand, and their therapeutic benefits directly correlate with their standardisation. Better diagnosis and treatment of allergic diseases require state-of-the-art procedures for assessing the allergenic activity of pollen allergen products using reference standards and physicochemical testing methods.Aim. The study aimed at developing methodological approaches to the standardisation of pollen allergen products in order to shift to measuring their potency in allergenic activity units (AAU) and bring their quality in line with the requirements of the State Pharmacopoeia of the Russian Federation.Materials and methods. The study used pollen allergen reference standards by Microgen, the WHO International Standard for timothy grass (Phleum pratense) pollen extract, a gel filtration standard kit of molecular weight markers ranging from 1.35 to 670 kDa, bovine serum albumin, serum samples with specific IgE obtained from donors sensitised to the study pollen allergens, labelled anti-human IgE antibodies, and reference standards for determining residual volatile solvents by gas chromatography. The identification of in-house reference standards for the potency of pollen allergens involved Western blotting (for allergenic components). The total protein content was determined by Bradford’s assay. In addition, the authors used high-performance liquid chromatography to study protein fractions and gas–liquid chromatography to determine the content of residual organic solvents.Results. To substitute the existing method of non-specific characterisation of allergenic activity in protein nitrogen units (PNU), the authors developed and tested a new method to control allergenic activity in allergenic activity units (AAU) based on an in vitro competitive enzyme-linked immunosorbent assay (ELISA) procedure developed and validated in this study. Furthermore, the authors developed and certified 15 primary in-house reference standards with allergenic activity established in AAU/mL using skin tests in vivo. The experimental data were analysed to standardise the allergenic activity of the pollen allergens manufactured by Microgen. The authors developed physicochemical methods for the certification of in-house reference standards and validated these methods in accordance with the State Pharmacopoeia of the Russian Federation. The study involved selecting chromatographic separation conditions for residual organic solvents (acetone and diethyl ether) and establishing system suitability criteria for the chromatographic system. The allergenic activity of secondary in-house reference standards was certified against that of primary in-house reference standards using competitive ELISA. Thus, the authors managed to shift to the standardisation of pollen allergen products in vitro.Conclusions. The authors developed their competitive ELISA-based method to standardise pollen allergen products by comparing the inhibition of immune responses to a product and a standard. The study demonstrated the feasibility of substituting allergenic activity quantification (in AAU) for protein nitrogen content determination (in PNU) and showed the first example of using AAU for the certification of in-house reference standards. Additionally, the authors developed and validated an analytical procedure for determining the content of residual organic solvents in pollen allergen products by gas–liquid chromatography.

Analytical Ultracentrifugation-Calibrated Anion-Exchange Chromatography for Sensitive and Intact Determination of Osteopontin in Infant Formula and Dairy Products.

Osteopontin is a crucial protein ingredient that has been applied in fortified dairy products and infant formula. It has great significance to infant gut health and brain development. However, current techniques including enzyme-linked immunosorbent assay and liquid chromatography coupled with mass spectrometry are still facing the bottleneck of low sensitivity and indirect quantification. Moreover, the unavailable certified commercial OPN standard hinders its accurate quantification. Herein, a novel method of anion-exchange chromatography was established to determine OPN concentration in several dairy matrices. The polarity-reversed capillary isoelectric focusing was utilized to measure the exact isoelectric point (pI) to support method development for OPN separation. Analytical ultracentrifugation was used to calibrate the purity of intact OPN to develop an in-house reference standard. The method showed the merits of limits of detection to 0.04 mg/100 g, relative standard deviation of reproducibility <5% for 13 out of 14 tested matrices, and an average recovery rate of 101.3%. This method has shown the potential to be adopted as an international standard method for the quantification of intact OPN in infant formula and dairy products.

Botulinum toxin preparations: areas for improvement and issues of standardisation

Scientific relevance. Botulinum toxin preparations are a good example of using a deadly toxin as a unique therapeutic agent. However, there are many unresolved issues related to biotechnology, biological activity, interchangeability, and standardisation of botulinum toxin preparations. Aim. To review current opportunities for improving therapeutic botulinum toxin preparations.Discussion. This review covers botulinum toxin type A preparations and unresolved issues related to them. In the absence of international non-proprietary names recommended by the World Health Organisation or by the Board of the Eurasian Economic Commission, domestic and imported botulinum toxin type A preparations approved in Russia have only similarity-based grouping names. In addition, manufacturers name botulinum toxin preparations at their discretion. Therefore, classifying these preparations under a common nomenclature is essential for clear identification, adequate selection, and correct prescription. Several studies have shown significant variability across botulinum toxin type A preparations. Due to the identified differences in qualitative and quantitative characteristics, botulinum toxin type A preparations cannot be considered similar, which raises the issue of their interchangeability and bioequivalence. To resolve this issue, a unified classification and naming system for botulinum toxin preparations should be established and documented in regulatory standards. According to the literature, manufacturers of botulinum toxin preparations use in-house reference standards. Hence, the same activity unit resulting from toxicity and efficacy studies may express a different protein load for each botulinum toxin preparation. Keeping that in mind, the authors discuss the development of a single international potency standard for existing and pipeline botulinum toxin type A preparations. Conclusions. The article describes novel pharmaceutical compositions containing botulinum toxin, including those in late development. Summarised data from clinical studies on the safety, efficacy, and cost-effectiveness of botulinum toxin type A preparations can guide prescribing decisions.

Multiplex agglutination-PCR (ADAP) autoantibody assays compared to radiobinding autoantibodies in type 1 diabetes and celiac disease

Multiplex Antibody-Detection by Agglutination-PCR (ADAP) assay was compared to singleplex standard radiobinding assays (RBA) to detect autoantibodies against insulin (IAA), GAD65 (GADA), islet antigen-2 (IA-2A), ZnT8 (ZnT8A) and tissue transglutaminase (TGA). Serum samples from 273 (114F/158M), 15–73 years of age healthy controls and 227 (109F/118M) newly diagnosed type 1 diabetes children, 1–11 years of age, were analyzed in both assay systems.The original WHO standard 97/550 and in-house reference standards for RBA were compared to ADAP. The ADAP and RBA generated parallel reference standards in all assays except TGA. Lower detection limits were observed in the ADAP assay for GADA,IAA and ZnT8A, markedly for TGA, but not for IA-2A. The Receiver Operating Characteristics (ROC) curve AUC analyses for pairwise comparison of ADAP with RBA showed no difference for GADA (n.s.), ADAP greater AUC for IAA (p = 0.005), RBA greater AUC for IA-2A (p = 0.0004) and ZnT8A (p < 0.0001) while ADAP TGA had a greater AUC compared to both RBA TGA-IgG (p < 0.0001) and TGA-IgA (p < 0.0001). These data suggest that the ADAP and RBA assays are comparable with equal performance for GADA, better ADAP performance for IAA while the RBA showed better performance in both IA-2A and ZnT8A associated with greater heterogeneity in autoantibody levels. The simultaneous analysis of 5 different autoantibodies by ADAP in sample volume reduced to only 4 μL and at an increased lower detection limit in all assays except IA-2A makes the ADAP automated autoantibody assay a distinct advantage for high throughput screening.

Development of an in-house reference standard for anti-rabies immunoglobulin potency, to be used in the virus neutralisation test in a Vero cell culture

The development and use of new methods of quality control of medicines involve the use of a lot of reference materials in quality control testing. Specialists of the Russian Research Antiplague Institute “Microbe” have proposed an alternative methodological approach to determination of potency of anti-rabies immunoglobulin in cell culture, which requires the development of an in-house reference standard (RS) certified against the biological reference preparation (BRP) of the European Pharmacopoeia human rabies immunoglobulin. The aim of the study was to develop and evaluate the metrological characteristics of an in-house RS for anti-rabies immunoglobulin potency, to be used in the virus neutralisation test in a Vero cell culture. Materials and methods: The following materials were used in the study: equine rabies immunoglobulin, Vero continuous cell culture, fixed rabies virus (Moscow 3253Vero strain), human rabies immunoglobulin BRP of the European Pharmacopoeia. The potencies of the candidate in-house RS and rabies immunoglobulin samples were determined in the neutralisation test in cell culture. The results were recorded using a fluorescent microscope. Statistical processing was carried out in accordance with general chapter 1.1.0014.15 of the State Pharmacopoeia of the Russian Federation, 14th edition. Results: the certified value of the in-house RS potency was 180.8±18.8 IU/mL. The confidence limits were determined at the 0.95 probability level. The shelf life of the in-house RS is 1.5 years (when stored according to the sanitary regulation SanPiN 3.3686-21). The certified in-house RS was assigned with the number 41-01-20. A set of technical and operational documentation was developed and approved for the in-house RS. The developed in-house RS can be used for in vitro determination of anti-rabies immunoglobulin potency, expressed in international units, to confirm its compliance with the product specification file. Conclusions: the authors developed an in-house RS for anti-rabies immunoglobulin potency, to be used in the virus neutralisation test in cell culture, certified against the human rabies immunoglobulin BRP of the European Pharmacopoeia.

The First WHO International Standard for Harmonizing the Biological Activity of Bevacizumab.

Several Bevacizumab products are approved for clinical use, with many others in late-stage clinical development worldwide. To aid the harmonization of potency assessment across different Bevacizumab products, the first World Health Organization (WHO) International Standard (IS) for Bevacizumab has been developed. Two preparations of a Bevacizumab candidate and comparator were assessed for their ability to neutralize and bind vascular endothelial growth factor (VEGF) using different bioassays and binding assays in an international collaborative study. Relative potency estimates were similar across different assays for the comparator or the duplicate-coded candidate sample. Variability in relative potency estimates was reduced when the candidate standard was used for calculation compared with various in-house reference standards, enabling harmonization in bioactivity evaluations. The results demonstrated that the candidate standard is suitable to serve as an IS for Bevacizumab, with assigned unitages for VEGF neutralization and VEGF binding activity. This standard coded 18/210 was established by the WHO Expert Committee on Biological Standardization, which is intended to support the calibration of secondary standards for product development and lifecycle management. The availability of IS 18/210 will help facilitate the global harmonization of potency evaluation to ensure patient access to Bevacizumab products with consistent safety, quality and efficacy.

Development of competitive inhibition ELISA as an effective potency test to analyze human rabies vaccines and assessment of the antigenic epitope of rabies glycoprotein

The potency of all modern tissue culture human rabies vaccines is measured based on the National Institute of Health (NIH) potency test that is laborious, time-consuming, involves large test variations and requires sacrifice of large number of animals. To circumvent these limitations, several researchers and WHO expert working groups have discussed development of alternative in vitro methods to replace the NIH potency test. Although several immunochemical methods have been proposed to quantify rabies glycoprotein (G-protein) using multiple murine monoclonal antibodies, we report an In vitro competitive inhibition ELISA (CIA) method based on the use of a neutralizing rabies glycoprotein site III directed novel therapeutic human rabies monoclonal antibody (RAB1) that shows equivalence to the mice NIH potency test in recognition of neutralization site of the glycoprotein. In vitro potency testing of WHO 7th International Standard for rabies vaccine (IS) by CIA using RAB1 and In-house reference standard (IHRS) as a standard to assess its suitability for the assessment of validation parameters showed accurate and precise values with <15% coefficient variance. The method was validated using 5PL standard curve with linearity r2 > 0.98 and LLOQ of 0.125 IU/mL indicating sensitivity of the method. The method was found to be precise, robust and accurate to quantitate intact rabies glycoprotein in final vaccine and showed a strong correlation (Pearson's r = 0.81) with the NIH potency values of licensed Vero cell rabies vaccine. The CIA test using RAB1 was able to accurately quantitate degradation of rabies vaccine and assess loss in antigenicity of lyophilized and reconstituted liquid rabies vaccine under thermal stress conditions. The method was able to differentiate between potent and reduced potency vaccine samples. The new in vitro competitive inhibition ELISA method using RAB1 thus can be a valid alternative to the NIH test.

Novel Method of Extraction for Radiocarbon Measurements of Atmospheric Carbon dioxide

ABSTRACTIn this paper, we present the first data from an alternative extraction method for atmospheric 14CO2 analysis, based on the direct trapping of whole air samples onto a molecular sieve zeolite (13X) trap, incorporated into a commercially available automated graphitization system. Results are presented for both inter-laboratory comparison samples and an in-house reference standard. The in-house reference was used to calculate the standard deviation of measurements (2.0‰). This newly developed method will facilitate faster sample processing and therefore lower cost per analysis, critical for scaling up such studies.

An in vitro functional assay to measure the biological activity of TB vaccine candidate H4-IC31

Potency assays for vaccine products are an important regulatory requirement, and are used to assess product quality and consistency prior to lot release for clinical testing. Ideally they measure an established correlate of efficacy or protection. In cases where there is no known correlate of protection, however, a functional assay that measures a biological response to a vaccine can be applied as a potency assay. Here we describe an in vitro assay which quantitatively measures human T cell activation as a biological response to the TB vaccine candidate H4-IC31. The Cytokine Secretion Assay (CSA) is based on the ability of peripheral blood mononuclear cells (PBMCs) from a Bacillus Calmette-Guérin (BCG)-vaccinated human donor to process and respond to H4-IC31. The ability of H4-IC31 to stimulate a cellular immune response is measured through the quantification of secreted IFNγ and is reported as relative stimulatory activity (RSA) compared to an in-house reference standard. The CSA is specific to the H4-IC31 vaccine, determines the RSA of H4-IC31 in the range of 50% to 150% of the reference standard, and is stability indicating as it detects differences in RSA between intact and heat treated H4-IC31. Although the CSA does not provide a link to clinical efficacy, it fulfills the critical requirements for a biological potency test to assess TB vaccine candidates and can be used along with biochemical and immunochemical assays to define a product profile during clinical development, while eliminating the use of animals for product testing.

Implementation of USP antibody standard for system suitability in capillary electrophoresis sodium dodecyl sulfate (CE-SDS) for release and stability methods

Capillary electrophoresis sodium dodecyl sulfate (CE-SDS) is widely used for purity analysis of monoclonal antibody therapeutics for release and stability to demonstrate product consistency and shelf life during the manufacturing and life cycle of the product. CE-SDS method development is focused on exploring the method capability to provide the information about the product purity and product related degradants (fragmentation, aggregation etc.). In order to establish the functionality of the instrumentation, software, and sample preparation; system suitability criteria need to be defined for analytical methods using a well characterized reference standard run under the same protocol and analysis as the test articles. Typically the reference standard is produced using a manufacturing process representative of the clinical material. The qualification, control, and maintenance of in-house reference standards are established through rigorous quality and regulatory guidelines. The U.S. Pharmacopeia (USP) has developed a monoclonal IgG System Suitability Reference Standard to be utilized for assessment of system suitability in CE-SDS methods.In this communication, we evaluate the system suitability acceptance criteria performance of the USP IgG standard using two methods, the recommended USP protocol provided in monograph <129> and a molecule specific Bristol-Myers Squibb (BMS) CE-SDS method. The results from USP IgG standard were compared with two in-house monoclonal antibody reference standards. The data suggest that the USP CE-SDS method may not be suitable for CE-SDS analysis for release and stability of monoclonal antibody therapeutics due to the high level of method induced partial reduction observed for all molecules tested. This high level of fragmentation observed utilizing the USP method will result in reporting lower purity levels, which will impact the overall quality assessment of the molecule. The system suitability criteria recommended by the USP method can be achieved by using the USP reference standard during the development and pre-validation stages. Furthermore, the USP reference standard does not offer significant advantages to existing SST criteria in the BMS method during release and stability testing, and therefore we propose use of the USP standard only during the optimization and pre-validation stages of method development.

Quality of Online Chat Reference Answers Differ between Local and Consortium Library Staff: Providing Consortium Staff with More Local Information Can Mitigate these Differences

A Review of:&#x0D; Meert, D.L., &amp; Given, L.M. (2009). Measuring quality in chat reference consortia: A comparative analysis of responses to users’ queries.” College &amp; Research Libraries, 70(1), 71-84.&#x0D; &#x0D; Objective – To evaluate the quality of answers from a 24/7 online chat reference service by comparing the responses given by local and consortia library staff using in-house reference standards, and by assessing whether or not the questions were answered in real time.&#x0D; &#x0D; Design – Comparative analysis of online chat reference transcripts.&#x0D; &#x0D; Setting – Large academic library in Alberta, Canada.&#x0D; &#x0D; Subjects – A total of online chat reference transcripts from the first year of consortium service were analyzed for this study. Of these, 252 were answered by local library staff and 226 from consortia (non-local) library staff.&#x0D; &#x0D; Methods – A stratified random sample of 1,402 transcripts were collected from the first year of consortium service (beginning of October to end of April). This method was then applied monthly, resulting in a sample size of 478 transcripts. In the first part of the study, responses were coded within the transcripts with a “yes” or “no” label to determine if they met the standards set by the local university library’s reference management. Reference transaction standards included questions regarding whether or not correct information or instructions were given and if not, whether the user was referred to an authoritative source for the correct information. The second part of the study coded transcripts with a “yes” or “no” designation as to whether the user received an answer from the staff member in “real time” and if not, was further analyzed to determine why the user did not receive a real-time response. Each transcript was coded as reflecting one of four “question categories” that included library user information, request for instruction, request for academic information, and miscellaneous/non-library questions. &#x0D; &#x0D; Main Results – When all question types were integrated, analysis revealed that local library staff met reference transaction standards 94% of the time. Consortia staff met these same standards 82% of the time. The groups showed the most significant differences when separated into the question categories. Local library staff met the standards for “Library User Information” questions 97% of the time, while consortia staff met the standards only 76% of the time. “Request for Instruction” questions were answered with 97% success by local library staff and with 84% success by consortia. Local library staff met the “Request for Academic Information” standards 90% of the time while consortia staff met these standards 87% of the time. For “Miscellaneous Non-Library Information” questions, 93% of local and 83% of consortia staff met the reference transaction standards. For the second part of the study, 89% of local library staff answered the questions in real time, as opposed to only 69% of non-local staff. The three most common reasons for not answering in real time (known as deferment categories) included not knowing the answer (48% local; 40% consortia), technical difficulty (26% local; 16% consortia), and information not being available (15% local; 31% consortia).&#x0D; &#x0D; Conclusion – The results of this research reveal that there are differences in the quality of answers between local and non-local staff when taking part in an online chat reference consortium, although these discrepancies vary depending on the type of question. Providing non-local librarians with the information they need to answer questions accurately and in real time can mitigate these differences.

HBeAg and hepatitis B virus DNA as outcome predictors during therapy with peginterferon alfa-2a for HBeAg-positive chronic hepatitis B

The aims of this study were to evaluate the usefulness of quantitative hepatitis B e antigen (HBeAg) values for predicting HBeAg seroconversion in patients treated with peginterferon alfa-2a and to assess the dynamic changes in quantitative HBeAg during therapy, compared with conventional measures of serum hepatitis B virus DNA. Data were analyzed from a large, randomized, multinational phase III registration trial involving 271 HBV-infected HBeAg-positive patients who received peginterferon alfa-2a plus oral placebo for 48 weeks. HBeAg levels were measured serially during therapy using a microparticle enzyme immunoassay validated with in-house reference standards obtained from the Paul Ehrlich Institute (PEIU/mL). In patients who achieved HBeAg seroconversion, levels of HBeAg consistently decreased during treatment and remained at their lowest level during the 24 weeks of posttreatment follow-up. After 24 weeks of treatment, 4% of patients with the highest levels of HBeAg (>or=100 PEIU/mL) achieved HBeAg seroconversion, yielding a negative predictive value of 96%, which was greater than that obtained for levels of HBV DNA (86%). Late responders to peginterferon alfa-2a could also be differentiated from nonresponders by continued decrease in HBeAg values, which were not evident by changes in HBV DNA. These analyses suggest quantitative HBeAg is a useful adjunctive measurement for predicting HBeAg seroconversion in patients treated with peginterferon when considering both sensitivity and specificity compared with serum HBV DNA.

Design and scaleup of downstream processing of monoclonal antibodies for cancer therapy: from research to clinical proof of principle

Murine monoclonal antibodies (mAb) from cell culture supernatants have been purified in order to acquire clinical grade for in vivo cancer treatment. The starting material was purified by high performance liquid chromatography (HPLC) systems ranging from the analytical scale process to a scaleup to 1 g per batch. Three columns (Protein A affinity chromatography with single-step elution, hydroxyapatite (HA) chromatography followed by linear gradient elution and endotoxin removing-gel chromatography), exploiting different properties of the mAb were applied. The final batches of antibody were subjected to a large panel of tests for the purpose of evaluating the efficacy of the downstream processing. The resulting data have allowed us to determine the maximum number of times the column can be used and to precisely and thoroughly characterize antibody integrity, specificity, and potency according to in-house reference standards. The optimized bioprocessing is rapid, efficient, and reproducible. Not less importantly, all the techniques applied are characterized by costs which are affordable to medium-sized laboratories. They represent the basis for implementing immunotherapeutic protocols transferable to clinical medicine.

Detection of urinary gonadotropins in callitrichid monkeys with a sensitive immunoassay based upan a unique monoclonal antibody.

A radioimmunological method for measuring urinary luteinizing hormone (LH) and chorionic gonadotropin (CG) excretion in the family Callitrichidae is described. The method uses a monoclonal antibody that will be available in virtually unlimited quantity. Several polyclonal antisera that have been useful for the detection of callitrichid gonadotropins are near depletion. The monoclonal antibody-based RIA provided similar results when compared with the mouse Leydig cell bioassay for LH and a previously validated polyclonal antibody-based RIA. When the monoclonal antibody is used for immunodetection of Saguinus oedipus LH by non-reducing SDS-PAGE, a single entity is recognized that corresponds with the molecular weight range of bioactive LH and appears to be in the normal range for LH in nonhuman primates. LH and CG were detected by the monoclonal antibody-based RIA in urine from representatives of species from all genera of callitrichids. Hormonal profiles of daily urine samples revealed the detection of the preovulatory LH surge by both RIA methods in the cotton-top tamarin (Saguinus Oedipus) and pygmy marmoset (Cebuella pygmea) and the increase CG due to pregnancy in both species. Serial dilutions of midcycle and pregnancy urine from Saguinus, Callithrix, Leontopithecus, and Cebuella exhibited parallelism when compared with our in-house reference standard of rhesus monkey CG. Cultured Saguinus oedipus pituitary cells showed an increased release of LH when challenged by gonadotropin releasing hormone (GnRH) providing further support that the monoclonal antibody-based RIA measures LH in this species. © 1993 Wiley-Liss, Inc.

Determination of base metals in fine silver by electrothermal atomic absorption spectrometry with a fast temperature programme

Trace metals can be successfully determined in a silver nitrate matrix with a shortened temperature programme that includes an accelerated drying step and excludes a pyrolysis step. Analyte concentrations determined by this technique overlapped with the 95% confidence intervals for an in-house reference standard. Sensitivities for most elements are comparable to literature values. The matrix acts as a physical modifier for volatile elements by delaying atomization so that it occurs when more nearly isothermal conditions prevail. No matrix interferences are observed and the addition of other modifiers do not appear to be necessary. Determination of zinc require gas flow conditions that reduce the effects of high blank absorbances.

Immunocheraical investigation of allergens from Rhizopus nigricans

The allergenic proteins of mould, Rhizopus nigricans extract (RNE) were identified and characterized by crossed immunoelectrophoresis (CIE), thin-layer isoelectrofocusing (TLIEF) and RAST inhibition. CIE revealed that the extract contained at least 31 distinct antigens. On TLIEF the extract resolved into 22 bands in pI 3.5-6.8. Two important allergens, Rhiz IIIb and VIb were purified by a combination of ammonium sulfate precipitation, anion exchange chromatography on DEAE-Sephadex column and gel filtration. Twenty and 12 micrograms of Rhiz IIIb and Rhiz VIb were sufficient to give 50% RAST inhibition as against 43 micrograms of crude RNE. Rhiz IIIb and Rhiz VIb were found to be glycoproteins with molecular weights of 12,400 daltons and 14,200 daltons, respectively. Rhiz IIIb was found to be homogeneous on polyacrylamide gel electrophoresis (PAGE) and TLIEF with a pI of 4.8, while Rhiz VIb gave a single band on PAGE and resolved into two Coomassie blue stained bands with pI 3.6 and 3.8. It was possible to separate the components of RNE on fast protein liquid chromatography (FPLC) using an anion exchanger Mono Q column. The identification and characterization of the antigenic and allergenic proteins in the extract will be useful in standardization of RNE and in preparation of an in-house reference standard.