Storage Of Standards Research Articles

Establishment of Technical Standard Database for Surface Engineering Construction of Oil and Gas Field

In recent years, oil and gas field surface engineering construction projects tend to be large in scale, large in quantity, and short in cycle. The task of surface construction management has increased significantly. In the process of project construction, corresponding standards and specifications are required to provide sufficient technical guidance and support for design, construction, and management personnel to ensure project management and control towards compliance, safety, and quality. However, the oil and gas field engineering standards are numerous and specialized, involving different levels of national standards, enterprise standards, and industry standards, which leads to the inefficiency of the actual use of standards and specifications. To solve them, this paper uses knowledge graph technology, OCR recognition, and natural language processing technology to conduct systematic research on the knowledge classification mechanism, data extraction, database construction mechanism, data structuring, and intelligent retrieval matching of oil-gas field surface engineering construction standards. In this study, the structured identification, storage, and information warehousing of standards are realized, and a highly sharable library of standards and specifications is formed, which realizes the intelligent retrieval and pushing of technical standards for surface engineering construction. This paper creates conditions for the realization of intelligent push and benchmarking management of standards and specifications, providing support for digital transformation and intelligent development of oil–gas fields.

Long-term stability of molecular doped epigraphene quantum Hall standards: single elements and large arrays (R K/236 ≈ 109 Ω)

In this work we investigate the long-term stability of epitaxial graphene (epigraphene) quantum Hall resistance standards, including single devices and an array device composed of 236 elements providing R K/236 ≈ 109 Ω, with R K the von Klitzing constant. All devices utilize the established technique of chemical doping via molecular dopants to achieve homogenous doping and control over carrier density. However, optimal storage conditions and the long-term stability of molecular dopants for metrological applications have not been widely studied. In this work we aim to identify simple storage techniques that use readily available and cost-effective materials which provide long-term stability for devices without the need for advanced laboratory equipment. The devices are stored in glass bottles with four different environments: ambient, oxygen absorber, silica gel desiccant, and oxygen absorber/desiccant mixture. We have tracked the carrier densities, mobilities, and quantization accuracies of eight different epigraphene quantum Hall chips for over two years. We observe the highest stability (i.e. lowest change in carrier density) for samples stored in oxygen absorber/desiccant mixture, with a relative change in carrier density below 0.01% per day and no discernable degradation of quantization accuracy at the part-per-billion level. This storage technique yields a comparable stability to the currently established best storage method of inert nitrogen atmosphere, but it is much easier to realize in practice. It is possible to further optimize the mixture of oxygen absorber/desiccant for even greater stability performance in the future. We foresee that this technique can allow for simple and stable long-term storage of polymer-encapsulated molecular doped epigraphene quantum Hall standards, removing another barrier for their wide-spread use in practical metrology.

Reference Standards to Support Quality of Synthetic Peptide Therapeutics

PurposePeptides are an important class of therapeutics. Their quality is evaluated using a series of analytical tests, many of which depend on well-characterized reference standards to determine identity, purity, and strength.ObjectiveDiscuss approaches to producing peptide reference standards, including vialing, lyophilization, analytical testing and stability studies.MethodsCase studies are used to illustrate analytical approaches to characterize reference standards, including methods for value assignment, content uniformity, and identity testing. Methods described include NMR, mass spectrometry, and chromatography techniques for identity testing and HPLC and GC methods for assessing peptide content and impurities.ResultsThis report describes the analytical strategy used to establish peptide reference standard and illustrates how results from multiple labs are integrated to assign a value to the final lyophilized vial. A two-step process for value assignment is described, which uses a mass balance approach to assign a quantitative value to a bulk peptide material. The bulk material is then used as a standard to assign a final value to the vialed material. Testing to confirm peptide identity and to ensure consistency of the vialed material is also described. Considerations for addressing variability, identifying outliers, and implementing stability studies are also presented.ConclusionThe methods and case studies described provide a benchmark for best practices in establishing the preparation, analytical testing, handling, and storage of peptide reference standards for the pharmaceutical industry. Some peptide features, such as chiral or isobaric amino acids, may require additional techniques to ensure a full characterization of the peptide reference standard.

Spectral properties and stability of selected carotenoid and chlorophyll compounds in different solvent systems

A quick, accurate, and low-cost analytical method for the assessment of bioactive leaf pigments, such as carotenoids and chlorophylls, can be beneficial for plant growers and consumers. The objective of this study was to learn about the thermal stability of major plant pigments and investigate the potential for rapid extraction and quantification of individual compounds in leafy greens. In this study, the spectral properties and chemical stability of violaxanthin, neoxanthin, lutein, zeaxanthin, β-carotene, and chlorophyll a and b pigments were examined in different solvent systems. Within the same solvent system, bathochromic shifts were observed in the analysis of carotenoids that contain a higher number of conjugated double bonds. Depending on the solvent system, pigments exhibited different degrees of stability. The results from this study can be used to identify an ideal solvent system for the storage of pigment standards and for the analysis of these pigments in leaf samples using UV-VIS spectroscopy.

Antibiotic standards stored as a mixture in water: methanol are unstable at various temperatures irrespective of pH and glass container silanization

ABSTRACT It is well-established that antibiotics stored individually at their optimal pH and in appropriate solvents are stable over time. However, limited information exists on the stability of antibiotics from multiple classes when prepared and stored as a mixture prior to multiresidue analysis by mass spectrometry. This study tested the stability of antibiotic standard mixtures from eight classes [amphenicols, tetracyclines, sulfonamides, quinolones, macrolides, β-lactams, lincosamides and miscellaneous (i.e., trimethoprim)] in relation to the water:methanol ratio, presence of sodium hydroxide base (to solubilise quinolones), storage temperature, and container type including plain and silanized glass vials. Antibiotics were analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. Several antibiotics, mainly quinolones, tetracyclines and macrolides, were unstable when stored as mixtures for one week regardless of the water:methanol ratio, storage temperature (4, −20 or −80 °C) and presence/absence of sodium hydroxide. Silanization of glassware improved the storage stability of quinolones and macrolides but reduced the stability of tetracyclines and other antibiotics including florfenicol amine, penicillin G, erythromycin and sulfadiazine. Our results show that several antibiotics in water:methanol are unstable when stored as a mixture and suggest a limited advantage of using base or silanized glass vials for the preparation and storage of antibiotic standards mixed together. Freshly prepared antibiotic standard mixtures are recommended for multi-residue quantitation of antibiotics. Abbreviations AMOX: amoxicillin; AMP: ampicillin; AZ: azithromycin; CAP: chloramphenicol; CE: collision energy; CTC: chlortetracycline; CIP: ciprofloxacin; DOX: doxycycline; ENO: enoxacin; ENRO: enrofloxacin; ERYTH: erythromycin; FF: florfenicol; FFA: florfenicol amine; FLU: flumequine; HDPE: high-density polyethylene; LC-MS/MS: liquid chromatography–tandem mass spectrometry; LIN: lincomycin; MRM: multiple reaction monitoring; NOR: norfloxacin; OFL-D3: ofloxacin-D3; OXO: oxolinic acid; OTC: oxytetracycline; PEN-G: penicillin G; PEN-V: penicillin V; ROX: roxithromycin; SDM: sulfadimethoxine; SDZ: sulfadiazine; SMX: sulfamethoxazole; SMZ-D4: sulfamethazine-D4; SSZ: sulfasalazine; TC: tetracycline; TAP: thiamphenicol; TILM: tilmicosin; TRIM: trimethoprim; TL: tolerance limit; VIRG: virginiamycin; UPLC-MS/MS: ultra-high pressure liquid chromatography–tandem mass spectrometry.

Designing working standards for stable H, C, and O isotope measurements in CO2 and H2 O.

We address here the selection, preparation, calibration, storage, and use of carbonate and water working standards (WSs) for stable H, C, and O isotope measurements requiring the best possible precision and accuracy vs international reference materials (iRMs). This may be of interest for laboratories working intensively in the domains of the carbon and water cycles and of paleoclimate. Defining a WS for stable C and O isotope studies requires combining mineralogical, physical, chemical (low Mg- and trace-carbonate), and isotopic measurements to select a carbonate fit for purpose; for water, two distinct deionized or distilled waters, with high and low δ2 H and δ18 O values, respectively, are normally used. In both cases, a strict protocol must be followed to properly qualify the WS vs the current international isotopic scales, and much attention must be paid to calculating rigorous estimates of final uncertainties on these scales. Two specific protocols for the selection of carbonate and water WSs are detailed. Equations for a proper estimate of uncertainties are proposed. The selection of WSs involves a preselection of potentially suitable materials based on initial estimates of their mineralogical, chemical, and isotopic properties and long-term stability, based on literature or previous measurements. Their precise characterization vs international isotopic scales requires a thorough analytical work in a correct sequence. When properly carried out, the proposed protocols should permit WSs to be obtained, defined vs the VSMOW and VPDB scales, with uncertainties comparable with those achieved for the characterization of iRMs.

Global Research Alliance N2 O chamber methodology guidelines: Recommendations for air sample collection, storage, and analysis.

Certain aspects in the collection, handling, storage, and subsequent analysis of discrete air samples from non-steady-state flux chambers are critical to generating accurate and unbiased estimates of nitrous oxide (N2 O) fluxes. The focus of this paper is on air sample collection and storage in small vials (<12ml) primarily for gas chromatography (GC) analysis. Sample integrity is assured through following simple procedures including storage under pressure and analysis within a few months of collection. Concurrent storage of standards in an identical manner to samples is recommended and allows the storage period to be reliably extended. In the laboratory, an autosampler is typically used in batch analysis of ∼200 sequentially analyzed samples by GC with an electron capture detector (ECD). Some comparisons are given between GC and alternatives including optical N2 O detectors that are increasingly being used for high-precision N2 O measurement. The importance of calibration and traceability of gas standards is discussed, where high-quality standards ensure the most accurate assessment of N2 O concentration and comparability between laboratories. The calibration allows a consistent and best estimate of flux to be derived.

МОДЕЛЬ АНАЛИЗА РЕЗУЛЬТАТОВ СКАНИРОВАНИЯ ГЕОМЕТРИИ СОПЛОВЫХ АППАРАТОВ ТУРБИН

Traditionally, the blades of gas turbine engines are assembled manually using special techniques (sorting by mass or by several geometric parameters). The use of manual assembly leads to the need to perform reassembly of units and is characterized by non-optimal operating parameters achieved. The data obtained from the scanners when monitor-ing the geometry of the blades can be used to improve the quality of the assembly processes of compressors and engine turbines. In particular, parts can be picked based on key parameters. The results of the work will automate the receipt of such parameters. The paper presents a mathematical model for performing a computer calculation of the flow area of turbine nozzles. The model is used to work with objects of *.stl format when processing data after scanning. With the use of the developed model, the calculations will not depend on the qualifications of the controller, and the proposed approach will not require a unique adjustment and expensive repair and storage of standards for all standard sizes of nozzles. The calculation was carried out in three sections, which increases the accuracy of the calculations while reducing the complexity and cost of measurement. An increase in the number of sections practically does not increase the complexity of calculations, so there are no significant restrictions on the performance of virtual measurements in four or more sections. The model is implemented in the mathematical package MATLAB. The model was tested by the example of processing the STL model of the sector of the turbine nozzle blades.

Ensuring the stability of primary mass standards during the implementation of the new definition of the kilogram

In November 2018 the General Conference on Weights and Measures (CGPM) will meet and are likely to ratify the revision of the international system of units (SI). This represents a major change to the way the base SI units are defined and realised, a major consequence being that the last of the definitions based on a material artefact, the international prototype of the kilogram, will be “retired” and the “new” kilogram will be realised in terms of the Planck constant via the Kibble balance or X-ray crystal density (XRCD) experiment. While the revision of the SI and the redefinition of the kilogram will almost certainly be endorsed by the CGPM there are issues around the current agreement of the Kibble balance and XRCD experiments. This will mean that in order to implement the kilogram redefinition a consensus value for the “new” kilogram will need to be adopted in order that a consistent value for the SI unit of mass be maintained. In order to maintain this consistency the storage, monitoring and use of current primary mass standards will be critical and this paper outlines ways in which the stability of artefact based mass standards can be optimised by careful storage and monitoring using surface analysis techniques and quartz crystal microbalance technology.

Solid Phase Microextraction On-Fiber Derivatization Using a Stable, Portable, and Reusable Pentafluorophenyl Hydrazine Standard Gas Generating Vial.

Solid phase microextraction (SPME) on-fiber derivatization methods have facilitated the achievement of lower detection limits and targeted analysis of various substances that exhibit poor chromatographic behavior, thermal instability, or high reactivity while limiting the use of organic solvents. However, previously developed on-fiber derivatization methods have been hindered by poor loading reproducibility and standard lifetime due to derivatization reagent reactivity. In addition, this reactivity often results in these reagents demonstrating toxic effects, complicating handling and standard formulation. To address this, a reusable standard gas generating vial containing pentafluorophenyl hydrazine (PFPH) has been developed. With this development, SPME fibers can now be reproducibly loaded with derivatization reagent, from an easy to use and safe platform. Validation of the vial using C4-C9 linear aldehyde standards as target analytes demonstrated intrabatch vial reproducibility (2% relative standard deviation (RSD), n = 4), along with PFPH headspace stability over a period of 11 weeks, facilitating reduced reagent consumption due to standard longevity. In addition, reproducibility of the derivatization reaction was observed over 1 week (RSD < 9%), and the linear concentration range was evaluated using headspace extractions from aqueous aldehyde solutions (R(2) > 0.996, 10-200 ppb v/v). Finally, the PFPH-generating vial was applied to the monitoring of volatile aldehydes generated during meat spoilage, as well as an on-site application where the free and total concentration of formaldehyde was determined in car exhaust using a portable GC/MS. To the best of our knowledge, the standard gas generating vial proposed in this work is the first documented device for the long-term storage of reusable headspace standards for a reactive, toxic, and otherwise unstable derivatization reagent standard.

Test on the Reliability of Gastight Syringes as Transfer/Storage Media for Gaseous VOC Analysis: The Extent of VOC Sorption between the Inner Needle and a Glass Wall Surface

A gastight syringe (GTS) is commonly used as a medium for transfer or storage of gaseous standards (or samples) in the analysis of volatile organic compounds (VOCs). In this study, the sorptive loss patterns of 21 VOCs were examined, using GTS as the transfer medium. The results of the test were evaluated with respect to a number of key variables including concentration, sampling volume, and physicochemical properties (molecular weight and boiling point). The VOCs with relatively high volatility (Group 1: aldehyde, ketone, ester, alcohol, and aromatic hydrocarbons (n = 12)) showed low sorptive losses with a mean (±SD) of 2.56 ± 2.87%, regardless of differences in the aforementioned key variables (p-value by t-test before and after using GTS = mean 0.15 ± 0.13). Conversely, the sorptive losses of seven semi-VOCs (Group 2: carboxyl and cresol (n = 9)) were significantly high, ranging from 18.0 ± 4.10% (propionic acid) to 65.4 ± 10.9% (n-heptanonic acid). In addition, we also measured the sorptive losses on the syringe needle (mean sorptive loss of Group 2 = 5.94 ± 5.63%). A linear regression analysis showed that the sorptive losses for Group 2 increased as molecular weight (or boiling point) increased, exhibiting a highly significant correlation (R(2) value (0.804 ± 0.084) and mean p-value (0.002 ± 0.003).

Multianalyte determination of 24 cytostatics and metabolites by liquid chromatography–electrospray–tandem mass spectrometry and study of their stability and optimum storage conditions in aqueous solution

A multianalyte liquid chromatography–electrospray–tandem mass spectrometry (LC–ESI–MS/MS) method for determination of 19 cytostatics and 5 metabolites, from 6 different therapeutic families, has been developed, and the structures of the main characteristic fragment ions have been proposed. Instrumental limits of detection and quantification are in the range 0.1–10.3 and 1.0–34.3ngmL−1, respectively. Moreover, the stability of the compounds in aqueous solution was investigated in order to establish the best conditions for preparation and storage of both calibration standards and water samples. Dimethylsulphoxide (DMSO) was selected as solvent for preparation of the stock solutions. At room temperature (25°C), 11 of the 24 target compounds were shown to be unstable in water (percentage of organic solvent 4%), with concentration losses greater than 20% in less than 24h. At 4°C (typical storage temperature for water samples) all compounds, except MTIC and chlorambucil, were stable for 24h, but the number of stable compounds decreased to 10 after 9 days. Freezing of the aqueous solutions improved considerably the stability of various compounds: after 3 months of storage at −20°C, 10 compounds, namely, 5-fluorouracil, carboplatin, gemcitabine, temozolomide, vincristine, vinorelbine, ifosfamide, cyclophosphamide, etoposide, and capecitabine, remained stable (in contrast to only carboplatin and capecitabine at 4°C). The addition of acid improved the stability of methotrexate and its metabolite hydroxy-methotrexate but not that of the rest of compounds. The addition of organic solvent (50% methanol or DMSO) prevented the degradation at 4°C of the otherwise unstable compounds oxaliplatin, methotrexate, erlotinib, doxorubicin, tamoxifen, and paclitaxel. To the authors' knowledge, five of the analytes investigated have never been searched for in the aquatic environment (imatinib, 6α-hydroxypaclitaxel, endoxifen, (Z)4-hydroxytamoxifen, and temozolomide), and for many of them the stability data provided, and even the analytical LC–MS/MS conditions, are the first ever published.

Worldwide proficiency test for routine analysis of δ2H and δ18O in water by isotope‐ratio mass spectrometry and laser absorption spectroscopy

The interpretation of stable hydrogen and oxygen isotope data in isotope hydrology relies on accurate, high-precision analytical measurements of the (2)H:(1)H and (18)O:(16)O ratios in liquid H(2)O samples. A synthesis of the International Atomic Energy Agency (IAEA) worldwide proficiency test for analytical laboratories conducting routine analysis of δ(2)H and δ(18)O values in water (WICO2011) by isotope-ratio mass spectrometry (IRMS) and laser absorption spectroscopy (LAS) technology has been carried out. This test revealed that >96% of the 160 laboratory submissions provided acceptable results within ±2‰ for δ(2) H values and ±0.2‰ for δ(18)O values of the established reference values for four test waters, and no difference in outcomes based on IRMS vs. LAS technology was found for good performing laboratories. The leading cause of outliers appeared to be improper calibration or compromised storage of laboratory standard and primary reference waters; hence the importance of judicious storage of lab standards cannot be understated. The deprecated practice of single standard normalization was identified as a problem for some laboratories. We further recommend that laboratories strive to report parsimonious long-term precisions based upon control standards, and to improve quantification and correction for LAS instrumental drift and inter-sample carryover effects.

Evaluation of equipment and procedures for the transfer and storage of mass standards in inert gas

This paper reports on work to improve mass stability when transferring platinum/iridium, stainless steel and silicon artefacts between air and vacuum using inert gas (argon) as a transfer/storage medium. Work is underway to redefine the kilogram in terms of a fundamental constant of nature and this will involve realizing a kilogram in vacuum. The development of an effective traceability link to this kilogram in vacuum is therefore essential for dissemination of the mass scale in the future. The work reported here investigates the effect of cycling artefacts between air and vacuum compared with cycling artefacts between argon and vacuum. Additionally, the effect of transferring artefacts between short-term storage in air compared with short term-storage in argon is investigated. The results presented demonstrate improved stability in the artefacts that are transferred between storage in argon and vacuum compared with those that are transferred between storage in air and vacuum.

Mechanisms of degradation of DNA standards for calibration function during storage

Establishment of molecular diagnostics offering quantitative technology is directly associated with real-time polymerase chain reaction (PCR). This rapid, accurate and sensitive method requires careful execution, including reliable calibration standards. The storage of such standards is crucial to prevent nucleic acid decay and to ensure stable results using real-time PCR. In this study, a broad investigation of possible causes of DNA degradation during storage was performed, including GC-content of the fragments, long-term storage, rapid freeze-and-thaw experiments, genomic DNA and short DNA fragments of different species, the influence of shear stress and the effect of nuclease remaining after DNA isolation. Several known chemical DNA degradation mechanisms have been matched with the experimental data through a process of elimination. Protocols for practical application, as well as a theoretical model describing the underlying mechanisms of deviation of real-time PCR results due to decay of standard DNA, have been developed. Primary amines in the buffer composition, which enhance depurination of the DNA helix, and shear stress due to ice crystal formation, could be identified as major sources of interaction. This results in degradation of the standard DNA, as well as in the probability of occurrence of mismatches affecting real-time PCR performance.

Impact of Long-Term Storage on Stability of Standard DNA for Nucleic Acid-Based Methods

Real-time PCR is dependent upon a calibration function for quantification. While long-term storage of standards saves cost and time, solutions of DNA are prone to degradation. We present here the benchmark treatment for preservation of DNA standards, involving storage in 50% glycerol-double-distilled water, whereby a deviation of 0.2 threshold cycle (C(T)) values resulted after 100 days of storage.

Long-term conservation of HCV RNA at 4 °C using a new RNA stabilizing solution

Protecting RNA from degradation, whilst maintaining its biological activity, is essential in molecular biology. However, RNA is very sensitive to degradation by ribonucleases, especially at temperatures above 0 °C. The stability of RNA was examined at 4 °C and −20 °C, in a new stabilizing solution consisting of a low-molarity mixture of chaotropic agents guanidinium and ammonium thiocyanate, a buffer for pH stabilization, phenol, and yeast RNA. Two substrates were tested for storage: RNA in human plasma positive for hepatitis C virus (HCV) and naked RNA (purified from HCV positive human plasma or transcribed in vitro). Stability was followed by viral load estimation, using an in-house competitive RT-PCR assay. Naked RNA purified from human plasma positive for HCV was stable at 4 °C for at least 24 months. An RNA standard transcribed in vitro was still viable after 36 months of storage at 4 °C. Human plasma dilutions positive for HCV were stable for at least 5 months in this solution when stored at 4 °C. It was concluded that the described stabilizing solution ensures long-term stability on naked RNA at 4 °C, and ideal for the storage of RNA controls and standards for molecular diagnosis, the solution may be used for preserving clinical samples prior to transport to a clinical laboratory.

High Preservation of DNA Standards Diluted in 50% Glycerol

Standard curves are important tools in real-time quantitative polymerase chain reaction (PCR) to precisely analyze gene expression patterns under physiologic and pathologic conditions. Handling of DNA standards often implies multiple cycles of freezing and thawing that might affect DNA stability and integrity. This in turn might influence the reliability and reproducibility of quantitative measurements in real-time PCR assays. In this study, 3 DNA standards such as murine tumor necrosis factor (TNF) alpha, interferon (IFN) gamma, and kainat-1 receptor were diluted in 50% glycerol or water after 1, 4, and 16 cycles of freezing and thawing and amplified copy numbers after real-time PCR were compared. The standards diluted in water showed a reduction to 83%, 55%, and 50% after 4 cycles, to 24%, 5%, and 4% after 16 cycles for kainat-1 receptor, TNFalpha, and IFNgamma standards, respectively, when compared with a single cycle of freezing and thawing. Interestingly, all cDNA samples diluted in 50% glycerol were amplified in comparable copy numbers even after 16 cycles of freezing and thawing. The effect of the standards undergoing different cycles of freezing and thawing on sample values was demonstrated by amplifying cDNA obtained from Borna disease virus infected and noninfected TNF-transgenic mice brain. This revealed significant differences of measured cDNA copy numbers using water-diluted DNA standards. In contrast, sample values did not vary using glycerol-diluted standards that were frozen and thawed for 16 times. In conclusion, glycerol storage of DNA standards represents a suitable tool for the accurate and reproducible quantification of cDNA samples in real-time PCR analysis.

High-performance liquid chromatography profiling of the major carotenoids in Arabidopsis thaliana leaf tissue

Carotenoids are extremely sensitive to a variety of physico-chemical attacks which may have a profound effect on their characteristic properties, thereby influencing the accurate identification and quantification of individual compounds. In this light, a comprehensive summary of the pitfalls encountered and precautions to be administered during handling and storage of authentic standards and samples was found to be incomplete. Furthermore, acceptable baseline separation of trans-lutein from trans-zeaxanthin and between the cis- and trans-forms of neoxanthin and violaxanthin has not been satisfactorily demonstrated. Hence the most optimal sample preparation and analytical steps were determined and a sensitive and reproducible method for the quantitative HPLC profiling of the principal carotenoids found in plant leaf tissue was developed. A reverse-phase C 30 column with a binary mobile solvent system was used for the baseline separation of eight of the major carotenoids and the two chlorophylls ( a and b) within 18 min. These compounds were identified via the use of authentic standards, their spectral characteristics and HPLC-atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) confirmation. This method has been successfully applied for the quantification of plant pigments in Arabidopsis thaliana wild-type (WT) leaf tissue and in two A. thaliana non-photochemical mutants, namely npq1 and npq2. These mutants have previously been well-characterised and provided valuable reference data as well as acting as internal controls for the assessment of our new method.

The cleaning of polymer colloids

The current state of knowledge of the cleaning of polymer colloids is reviewed with regard to a wide range of cleaning and characterisation techniques. The type, level and quantity of impurities involved with different polymer latex formulations varies widely. Even for similar formulations, differences in the nature and number of functional groups reported are often a consequence of sometimes subtle differences in the cleaning procedures employed. Not only may surface functionality be affected but also monomer and oligomer extraction procedures may lead to morphological changes in the particles. No single technique alone is likely to be able to remove all impurities. Care is needed to avoid the introduction of new impurities from the equipment, materials and water used as well as possible contamination from atmospheric carbon dioxide, bacteria and fungi. These factors also need to be considered in the storage of latex particle standards.