Safety risk categorization of organic extractables associated with polymers used in packaging, delivery and manufacturing systems for parenteral drug products.

PURPOSE: To develop and justify a Risk Evaluation Matrix for estimating the safety risk associated with extractables from plastic materials used in pharmaceutical applications and to apply that matrix to approximately 510 extractables to assess the risk that they would accumulate in drug products at levels sufficiently high to affect patient safety. METHOD: The Risk Evaluation Matrix considers toxicological, availability and solubility characteristics of extractables. Safety Risk categories were established based on certain scaled values for these characteristics, Total Risk Scores were calculated for each extractable and the extractables were categorized with respect to their safety risk based on these calculations. RESULTS: The Total Risk Scores were normally distributed around a value of 20 to 23, corresponding to safety risk categories of moderate and intermediate risk. The range in Risk Scores defined by the mean ± one standard deviation encompassed the entire region of moderate and intermediate risk. Approximately 15% of the extractables were categorized as lowest risk while 3% of the extractables were categorized as highest risk. CONCLUSIONS: Categorization of extractables could facilitate the selection of materials for use in pharmaceutical systems, the analytical testing of extracts and the selection of target extractables.

Controlled Extraction Studies Applied to Polyvinyl Chloride and Polyethylene Materials: Conclusions from the ELSIE Controlled Extraction Pilot Study.

The effective management of leachables in pharmaceutical products is a critical aspect of their development. This can be facilitated if extractables information on the materials used in a packaging or delivery system is available to assist companies in selecting materials that will be compatible with the drug product formulation and suitable for the intended use. The Extractables and Leachables Safety Information Exchange (ELSIE) materials working group developed and executed a comprehensive extraction study protocol that included a number of extraction solvents, extraction techniques, and a variety of analytical techniques. This was performed on two test materials, polyethylene (PE) and polyvinyl chloride (PVC), that were selected due to their common use in pharmaceutical packaging. The purpose of the study was to investigate if the protocol could be simplified such that (i) a reduced number or even a single extraction technique could be used and (ii) a reduced number of solvents could be used to obtain information that is useful for material selection regardless of product type. Results indicate that, at least for the PVC, such reductions are feasible. Additionally, the studies indicate that levels of extractable elemental impurities in the two test materials were low and further confirm the importance of using orthogonal analytical detection techniques to gain adequate understanding of extraction profiles.

Identification and quantification of medical device extractables and leachables via non-target analysis (NTA); Analytical uncertainty.

Leachables are substances that are leached from a medical device during its clinical use and are important due to the patient health-related effects they may have. Thus, medical devices are profiled for leachables (and/or extractables as probable leachables) to assess their potential impact on patient health and safety. This profiling is accomplished by screening extracts or leachates of the medical device for released organic substances via non-targeted analysis (NTA) employing chromatographic methods coupled with mass spectrometric detection. Chromatographic mass spectral response factors (RFs) for extractables and leachables vary significantly from compound to compound, complicating the quantitation of these compounds and the application of assessment strategies such as the Analytical Evaluation Threshold (AET). The analytical uncertainty resulting from response factor variation can be expressed in terms of an uncertainty factor (UF), which estimates the magnitude of response factor variation. This manuscript discusses the concept and impact of analytical uncertainty and provides best practice recommendations for the calculation and use of the uncertainty factor, UF.

Standardization of Chromatographic Screening Methods for Organic Extractables and Leachables by Managing Outcomes.

Drug products and medical devices can contain leachable impurities that could adversely affect patient health during their clinical use. To establish patient exposure to leachables, drug products and packaging, manufacturing system, or medical device extracts are analytically screened for leachables or extractables. For organic extractables/leachables, the screening process typically involves a chromatographic separation coupled with an information-rich detection method. Information contained in the detector response (e.g., the chromatographic peak) is processed to establish quantities and to elucidate identities for the detected compounds. Organic extractables and leachables screening methods and procedures have proliferated with little, if any, attempt at standardization, creating the situation in which virtually every testing laboratory has their own analytical testing and data processing methodology. This raises the possibility that two different labs screening the same extract or drug product would report extractables or leachables profiles that differ in the number of compounds reported, the identities of the reported compounds, and the extracted (or leached) amounts of the identified compounds. Although standardization of the screening methods and procedures themselves would reduce lab-to-lab variation, such an approach would be difficult to implement. Thus, standardization of the screening outputs by setting quality standards for the outputs is considered. For example, the method's ability to detect a broad cross-section of potential extractables/leachables is established by testing a test mixture of representative compounds. Additionally, this author proposes that reported compound identities should be confident to be used in safety risk assessment; use of lower quality identities requires that the lower quality be accounted for in the assessment, perhaps by use of an uncertainty factor. Similarly, it is proposed that reported concentrations should be semi-quantitative to be used in safety risk assessment; use of lower quality concentrations requires that the lower quality be accounted for in the safety risk assessment, perhaps by use of an uncertainty factor.

Accurate or Protective: What is the Goal of Non-targeted Extractables and Leachables Quantitation and Identification?

Leachables are quantified and identified to enable their quantitative toxicological safety risk assessment (qTSRA). The leachable's reported concentration and identity must meet certain quality expectations to be suitable for qTSRA. In this Correspondence, the author considers accuracy and protectiveness as competing key quality attributes and suggests that protectiveness is the proper quality attribute for qTSRA as qTSRA is based on the foundation that a leachable's potential adverse effect on patient health and safety must not be under-estimated. Considering this conclusion, means of making concentration estimates and proposed identities protective are discussed.

A Practical Derivation of the Uncertainty Factor Applied to Adjust the Extractables/Leachables Analytical Evaluation Threshold (AET) for Response Factor Variation.

The analytical evaluation threshold (AET) establishes which chromatographic peaks, produced during organic extractables/leachables (E&L) screening, require toxicological safety risk assessment because the peaks are associated with compounds of potentially unacceptable toxicity. Thus, the AET protects patient safety as its proper application ensures that all potentially unsafe E&L are necessarily assessed. Generally, application of the AET involves the presumption that all organic E&L have the same detector response factor, an assumption that is not valid for any of the detection methods commonly used in E&L screening. Thus, the AET's ability to be protective is compromised for poorly responding compounds, as they will appear to be below the AET when in fact they are not. This unacceptable outcome is addressed by adjusting the AET with an uncertainty factor (UF) whose value is dictated by the magnitude of response factor variation, with a larger variation resulting in a larger UF and a lower adjusted AET. Although the concept of the UF is straightforward, setting a generally accepted, scientifically valid, and practical value for the UF has been challenging. In this article, a database of relative response factors obtained for nearly 1200 E&L via the most commonly applied chromatographic screening methods (gas chromatography/mass spectrometry [GC/MS], liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization [LC/MS-APCI], and LC/MS with electrospray ionization [LC/MS-ESI]) is used to justify UFs for these methods, individually and as a combined practice, based on the practical principle of "the point of diminishing returns". Using this concept results in nearly 92% of the compounds in the database being properly flagged as above an AET adjusted with a UF = 3. Ninety-five percent (95%) coverage of the compounds can be achieved when a UF of 4 is applied to the combination of GC/MS and LC/MS methods or with other combinations of UF values applied to the various methods individually. Coverage is increased to 97% when a UF of 4 is individually applied to the GC/MS method and a UF of 10 is individually applied to the LC/MS methods. Furthermore, the available data suggest that application of both APCI and ESI ionization in LC/MS screening (as opposed to either method separately) provides the greatest coverage of E&L.

Is Retention Time and/or Structure Matching a Solution to the Challenge of Providing Quantitative Data When Screening for Extractables and Leachables by GC/MS?

Leachables can potentially and adversely affect patient safety. Thus, drug products and medical devices are chromatographically screened for organic leachables (and extractables), establishing these compounds' identity and quantity. Accurate quantitation of extractables and leachables is challenging given compound-to-compound variation in response factors. One proposed means for managing variation and improving quantitation accuracy is the use of retention time (RT) and structure to match analytes with their most relevant quantitation surrogate. Although the scientific basis for relationships between RT and structure versus response is unclear, the use of matching was investigated using databases of response factors (RFs) or relative response factors (RRFs), RTs, and structures for extractables/leachables. Gas chromatography with mass spectrometry (MS) detection was investigated as response variation in this technique is less than with other screening methods such as liquid chromatography with MS detection. The overall RF variation across RT and structure makes it difficult to establish whether RT and response or structure and response can be correlated. Rigorous statistical analysis of the data concludes that there are no discernible relationships between these quantities; however, casual visual examination suggests that subtle relationships might exist. The effect that RT or structure matching could have on quantitation accuracy was considered, presuming that the visual trends were real. Under this presumption, it was estimated that RT matching could at most improve quantitation accuracy by 25%, and that structure matching could improve accuracy by at most 50%. However, these improvements do not address the response variation that is independent of RT or structure, and thus it is concluded that RT or structure matching are not viable solutions to RF variation. Rather, it is recommended that databases of authentic RRFs be aggressively populated to provide accurate quantitation. Compounds for which authentic RRFs cannot be secured are most effectively quantified using the median RRF.

A Safety Risk-Based Extractables and/or Leachables Qualification Strategy for Packaged Drug Products.

During storage and distribution of a packaged drug product, chemical substances present in or on the packaging may leach into the drug product, potentially adversely affecting the drug product's key quality attributes, including safety. Thus, the packaging is profiled for extractables as potential leachables and/or the drug product is profiled for leachables over shelf life via the process of chemical characterization. In so doing, the packaging and the packaged drug product are qualified as being suited for their intended use. It is reasonable to propose that the extent of chemical characterization required to qualify the packaging and the packaged drug product depends on the risk that leached substances could adversely affect drug product quality; the higher the risk, the more extensive and rigorous the required qualification. Although regulatory guidance supports and advocates such a risk-based approach to chemical characterization, the existing guidance is founded on an overly simplified approach to risk assessment, leading to incongruous risk classifications for certain classes of drug products. Furthermore, the existing guidance no longer links risk to current requirements concerning the extent of chemical characterization necessary to secure regulatory approval of drug product applications. To address these circumstances, this manuscript proposes and justifies a risk classification process (risk evaluation matrix) for drug products and packaging and a risk-based approach to chemical characterization requirements, linking risk to the degree and rigor of the chemical characterization process and establishing chemical characterization requirements for individual risk classes.

The Implications of Chromatographically Screening Medical Products for Organic Leachables Down to the Analytical Evaluation Threshold Adjusted for Response Factor Variation.

A drug product is chromatographically screened for organic leachables, derived from the product's packaging system, as leachables might adversely impact the health of a patient to whom the drug product is administered. Similarly, medical device and packaging system extracts are chromatographically screened for organic extractables as probable leachables. To be protective of patient health, the screening methods must produce recognizable responses for all potentially unsafe substances. To be efficient, the screening methods should provide a means of differentiating between the responses linked to likely to be safe substances and to potentially unsafe substances. The analytical evaluation threshold (AET) was established as a means of differentiating chromatographic peaks, based on concentration, that are unlikely to be unsafe (and thus do not need safety assessment) and that are possibly unsafe (and thus require safety assessment). Thus, the AET manages the competing objectives of protection and efficiency. Although the AET is based on concentration, it is applied based on response. As no chromatographic detection method applied to extractables and leachables screening produces a uniform response to all potential analytes (thus, the magnitude of the response differs across analytes), the objectives of protection or efficiency can be compromised by false negatives and positives. To ensure protection at the expense of efficiency, the AET can be adjusted to address response variation. This article addresses the practical issue that the protectiveness of the AET is affected both by response factor bias and variation and thus correction for only variation is incomplete and ineffective. The article illustrates the proper adjustment of the AET for bias and variation.

Identification and Quantitation Classifications for Extractables and Leachables.

Extractables and leachables (E&L) are identified and quantified so that their impact on patient safety can be established and assessed. The uncertainty in the impact assessment is affected by the uncertainty in the substance's experimentally determined identity and concentration. Thus, these experimentally determined quantities must be reported not only in terms of their absolute result but also in terms of the uncertainty in the result, which is based on the amount and rigor of the information on which the result is based. In this way, the impact assessment can be tempered to account for the uncertainty in its input data. To facilitate the assignment and reporting of uncertainty, classification hierarchies are proposed and discussed for both identification and quantitation. Both hierarchies establish levels or degrees of identification and quantitation based on the uncertainty of the result and contain descriptions of the quality and quantity of information required to achieve a certain level within the hierarchy. The minimal levels that must be achieved to support impact assessment are also established.

Identifying and Mitigating Errors in Screening for Organic Extractables and Leachables: Part 3-Considering Errors of Implementation and the Use of a Database to Judge and Promote Good Science and Efficient Practices.

Substances leached from pharmaceutical manufacturing systems, packages, and/or medical devices can be administered to a patient during a clinical therapy and can adversely affect the therapy and/or patient safety. Thus, extracts or drug products are chromatographically screened to discover, identify, and quantify these unspecified foreign impurities. Although screening methods have achieved a high degree of technical and practical sophistication, they are not without issues in terms of accomplishing these three functions. In this third (and last) part of the series, errors of implementation are addressed. An error of implementation occurs when a capable method and/or a proper data processing procedure is implemented in such a way that the intrinsic capabilities of either the method or the processing procedure (or both) are compromised. System suitability assessment establishes that a method, as executed at the time of use, has been properly set up and implemented, thus revealing errors of implementation. System suitability data, captured in a database, can be processed to establish trends in system performance, where trends in declining performance can establish a system's useful operating lifetime, serve as an early warning of imminent system failure, and/or act as a trigger for system maintenance. Additionally, this manuscript considers how the existence, size, and use of a chromatographic database provides a measure of a testing laboratory's level of "good science". Lastly, the manuscript considers the database as an enabler of advances in information management and impact assessment.

Materials in Manufacturing and Packaging Systems as Sources of Elemental Impurities in Packaged Drug Products: An Updated Literature Review.

Elemental impurities in drug products arise from different sources and via a number of different means, including leaching of elemental entities (including the elements themselves or element-containing compounds) from the drug product's manufacturing or packaging systems. Thus, knowledge about the presence, level, and likelihood of leaching of elements in manufacturing and packaging systems is relevant to understanding how these systems contribute to a drug product's total elemental impurity burden. To that end, this manuscript updates a previous review of available literature on elemental entities in pharmaceutically relevant polymers and the presence of these elemental entities in material extracts and/or drug products. This updated review contains the information that has been published subsequent to the publication of the initial review and considers two questions: (1) What elemental entities are present in the relevant polymers and materials and at what levels are they present? (2) To what extent are these elemental entities leached from these materials under conditions relevant to the manufacturing and storage/distribution of solution drug products? The compiled recent data reaffirms the conclusions drawn from the original review: (1) Elemental entities are present in the materials used to construct packaging and manufacturing systems as these materials either contain these elemental entities as additives or are exposed to the elemental entities during their production. (2) Unless the elemental entities were parts of the materials themselves (e.g., SiO2 in glass) or intentionally added to the materials (e.g., metal stearates in polymers), their incidental amounts in the materials were generally low. (3) If elemental entities were present in materials and systems, generally only a very small fraction of the total available amount of the entity could be leached under conditions that were relevant to the packaged drug products. Thus, although sources of certain elemental impurities may be ubiquitous in the natural environment, they were not ubiquitous in materials used in pharmaceutical packaging and manufacturing systems and when they were present, they were not extensively leached under relevant conditions of use for those systems. This conclusion, supported by an ever-increasing body of literature, suggests that in general the manufacturing and packaging systems, by themselves, do not contribute sufficiently large quantities of elemental impurities that the impurities pose a meaningful threat to patient safety. Furthermore, this conclusion should be considered when standards are developed for the characterization and qualification of manufacturing systems, packaging systems, and their associated materials and components of construction.

Correcting the Analytical Evaluation Threshold (AET) and Reported Extractable's Concentrations for Analytical Response Factor Uncertainty Associated with Chromatographic Screening for Extractables/Leachables.

It is generally acknowledged that quantitation in extractables and leachables (E&L) can be variably reproducible and accurate, depending on the quantitation approach taken. This is especially true for "simple" quantitation, which is the practice of estimating an analyte's concentration based on its response relative to that of an internal standard that has been added to the sample in a known amount. Simple quantitation is prone to error and variation as it is based on the largely false premise that the response factors for all extractables, leachables, and internal standard candidates are the same. It has been proposed that this uncertainty (inaccuracy and variation) be accounted for by adjusting two key parameters in E&L assessment, the reported concentrations themselves and the analytical evaluation threshold (AET) via an uncertainty factor (UF). This paper examines quantitation variation and discusses the means of establishing and utilizing the UF to adjust the AET to lower values and to adjust reported concentrations to higher values, enabling an impact assessment performed with this data to be more protective of patient safety. Although adjustment of the AET lower with the UF is supported, flaws in the concept of using the UF to adjust reported concentrations upward are considered, and it is recommended that the UF not be used in this manner. Rather, E&L quantitation should be based on compound-specific relative response factors, collected and collated in an E&L database.

Identifying and Mitigating Errors in Screening for Organic Extractables and Leachables: Part 1-Introduction to Errors in Chromatographic Screening for Organic Extractables and Leachables and Discussion of the Errors of Omission.

Substances leached from materials used in pharmaceutical manufacturing systems, packages, and/or medical devices can be administered to a patient as part of a clinical therapy. These leachables can have an undesirable effect on the effectiveness of the therapy and/or patient safety. Thus, relevant samples such as material extracts or drug products are chromatographically screened for foreign organic impurities, where screening is the analytical process of discovering, identifying, and quantifying these unspecified foreign impurities. Although screening methods for organic extractables and leachables have achieved a high degree of technical and practical sophistication, they are not without issues with respect to their ability to accomplish the aforementioned three functions. In this first part of a series of three manuscripts, the process of screening is examined, limitations in screening are identified, and the concept of using an internally developed analytical database to identify, mitigate, or correct these errors is introduced. Furthermore, errors of omission are described, where an error of omission occurs when a screening method fails to produce a recognizable response to an analyte present in the test sample. The error may be that no response is produced ("falling through the cracks") or that a produced response is not recognizable ("failing to see the tree for the forest"). In either case, proper use of a robust internal extractables/leachables database can decrease the frequency with which errors of omission occur. Examples of omission errors, their causes, and their possible resolution are discussed.

Identifying and Mitigating Errors in Screening for Organic Extractables and Leachables: Part 2-Errors of Inexact Identification and Inaccurate Quantitation.

Patients can be exposed to leachables derived from pharmaceutical manufacturing systems, packages, and/or medical devices during a clinical therapy. These leachables can adversely decrease the therapy's effectiveness and/or adversely impact patient safety. Thus, extracts or drug products are chromatographically screened to discover, identify, and quantify organic extractables or leachables. Although screening methods have achieved a high degree of technical and practical sophistication, they are not without issues in terms of accomplishing these three functions. In this Part 2 of our three-part series, errors of inexact identification and inaccurate quantitation are addressed. An error of inexact identification occurs when a screening method fails to produce an analyte response that can be used to secure the analyte's identity. The error may be that the response contains insufficient information to interpret, in which case the analyte cannot be identified or that the interpretation of the response produces an incorrect identity. In either case, proper use of an internal extractables and leachables database can decrease the frequency of encountering unidentifiable analytes and increase the confidence that identities that are secured are correct. Cases of identification errors are provided, illustrating the use of multidimensional analysis to increase confidence in procured identities. An error of inaccurate quantitation occurs when an analyte's concentration is estimated by correlating the responses of the analyte and an internal standard and arises because of response differences between analytes and internal standards. The use of a database containing relative response factors or relative response functions to secure more accurate analyte quantities is discussed and demonstrated.

Modeling of the solution interaction properties of plastic materials used in pharmaceutical product container systems.

Material/water equilibrium binding constants (Eb) were determined for 14 organic solutes and 17 plastic raw materials that could be used in pharmaceutical product container systems. Correlations between the measured binding constants and the organic solute's octanol/water and hexane/water partition coefficients were obtained. In general, while the materials examined exhibited a wide range of binding characteristics, the tested materials by and large fell within two broad classes: (1) those that were octanol-like in their binding characteristics, and (2) those that were hexane-like. Materials of the same class (e.g., polypropylenes) generally had binding models that were very similar. Rank ordering of the materials in terms of their magnitude of drug binding (least binding to most binding) was as follows: polypropylene < polyethylene < polyamide < styrene-ethylene-butylene-styrene < copolyester ether elastomer approximately equal to amine-terminated poly fatty acid amide polymer. The utilization of the developed models to estimate drug loss via sorption by the container is discussed.

How One Might Experimentally Determine if Container Closure Systems and Their Components and Materials of Construction Contribute Elemental Impurities To Packaged Pharmaceutical Drug Products.

The safety aspects of elemental impurities in finished drug products are a topic of considerable importance in the pharmaceutical community, and guidelines such as ICH Q3D and USP <232> and <233> have been published to provide directions on how to assess finished drug products with respect to such impurities. Although a drug product's packaging system has been identified as a potential source of elemental impurities, comparable guidelines have not been established for assessing packaging systems and their materials and components of construction with respect to their potential to contribute leached elements to packaged drug products. In this commentary, the author considers the critical questions associated with selecting materials and components of construction and qualifying components and packaging with respect to their potential to add elemental impurities to packaged products and suggests means for accomplishing this objective.LAY ABSTRACT: Elemental impurities in drug products can adversely affect the drug product's quality attributes. Regulatory guidelines that establish how to assess drug products for elemental impurities have been published. Although the drug product's packaging system has been identified as a potential source of elemental impurities, no guidelines have been published to specifically address packaging. In this commentary, the author considers the key issues associated with elemental impurities derived from packaging and suggests means for selecting and qualifying packaging on the basis of extractable elements.

Application of Arrhenius Kinetics to Acceleration of Controlled Extraction Studies.

Pharmaceutical drug products are packaged in containers so that they can be manufactured, distributed, and stored. During these events in a drug product's life cycle, the drug product and its packaging could interact, resulting in substances leaching from the plastic and accumulating in the drug product. As the leached substances could adversely impact a key quality attribute of the drug product, drug products must be tested to establish which leachables are present and in what quantities.Because a drug product's lifetime can be long, it is common practice to accelerate leaching by using temperatures higher than clinical use conditions. While use of accelerated conditions is a well-accepted practice, there are questions with respect to the means by which the degree of acceleration can be calculated and justified. In this manuscript, experimental data from 10 case studies are used to evaluate commonly utilized, Arrhenius-based approaches to acceleration, and recommendations are made in terms of the proper approaches to be used for concentration and duration extrapolations. Specifically, when accumulation levels are projected from a clinical to an elevated temperature, the Arrhenius model formulated by ASTM for the accelerated aging of medical devices using a Q10 value of 1.5 most frequently provides the best fit to experimental leaching data. Alternatively, when contact durations are projected from a clinical to an elevated temperature, the Arrhenius model reflected in the empirically derived "factor 10 rule," developed for and applied to food contact packaging, most frequently provides the best fit to experimental leaching data.LAY ABSTRACT: Pharmaceutical drug products are packaged in containers so that they can be manufactured, distributed, and stored. During these events in a drug product's life cycle, the drug product and the plastic systems may interact, resulting in substances leaching from the plastic and accumulating in the drug product. As the leached substances could adversely impact a key quality attribute of the drug product, drug products must be tested to establish what leachables are present and in what quantities.Because a drug product's lifetime can be long, it is common practice to accelerate leaching by using temperatures higher than clinical use conditions. While use of accelerated conditions is a well-accepted practice, there are questions with respect to the means by which the degree of acceleration can be calculated and justified. In this manuscript, experimental data from 10 case studies are used to evaluate commonly utilized approaches to acceleration, and recommendations are made in terms of the proper approaches to be used for concentration and duration extrapolations.

Evaluation of the chemical compatibility of plastic contact materials and pharmaceutical products; safety considerations related to extractables and leachables.

A review is provided on the general topic of the compatibility of plastic materials with pharmaceutical products, with specific emphasis on the safety aspects associated with extractables and leachables related to such plastic materials.

Performance characteristics of an ion chromatographic method for the quantitation of citrate and phosphate in pharmaceutical solutions.

The performance of an ion chromatographic method for measuring citrate and phosphate in pharmaceutical solutions is evaluated. Performance characteristics examined include accuracy, precision, specificity, response linearity, robustness, and the ability to meet system suitability criteria. In general, the method is found to be robust within reasonable deviations from its specified operating conditions. Analytical accuracy is typically 100 +/- 3%, and short-term precision is not more than 1.5% relative standard deviation. The instrument response is linear over a range of 50% to 150% of the standard preparation target concentrations (12 mg/L for phosphate and 20 mg/L for citrate), and the results obtained using a single-point standard versus a calibration curve are essentially equivalent. A small analytical bias is observed and ascribed to the relative purity of the differing salts, used as raw materials in tested finished products and as reference standards in the analytical method. The assay is specific in that no phosphate or citrate peaks are observed in a variety of method-related solutions and matrix blanks (with and without autoclaving). The assay with manual preparation of the eluents is sensitive to the composition of the eluent in the sense that the eluent must be effectively degassed and protected from CO(2) ingress during use. In order for the assay to perform effectively, extensive system equilibration and conditioning is required. However, a properly conditioned and equilibrated system can be used to test a number of samples via chromatographic runs that include many (> 50) injections.