Retention Gap Research Articles

Improvement of Care Cascade for Hypertension and Diabetes in Rural China: Protocol for an Implementation Study.

The management of hypertension and diabetes poses significant challenges to China's healthcare system, necessitating seamless patient progression through screening, diagnosis, management, and control. Utilizing the care cascade model, this study aims to systematically identify patient drop-offs and devise strategies to address healthcare delivery bottlenecks for hypertension and diabetes in rural China. This study consists of three phases. In Phase 1, qualitative interviews are conducted to explore healthcare experiences and identify determinants across the care cascade. Phase 2 involves systematically assessing barriers identified in Phase 1 and collaborating with local stakeholders using intervention mapping and co-design to generate interventions and implementation strategies. Phase 3 is a cluster randomized controlled trial involving 48 villages, randomly assigned in a 1:1 ratio, to compare changes in hypertension and diabetes care. Intervention villages will implement interventions developed in Phase 2 for 1 year, while control villages will continue with usual care. Primary outcomes include between-group differences in achieving blood pressure and glycemic targets, along with service and implementation outcomes. This study aims to identify the stage with the largest patient retention gap in the care cascade and develop intervention strategies through participatory co-design with practitioners, emphasizing feasible, low-cost approaches. The pragmatic cluster RCT will assess strategy effectiveness, offering valuable insights for practical interventions to enhance hypertension and diabetes care in rural settings, potentially shaping impactful programs and improving healthcare outcomes. Trial Registration: ClinicalTrials.gov. identifier: NCT06141278.

The effect of proactive, interactive, two-way texting on 12-month retention in antiretroviral therapy: Findings from a quasi-experimental study in Lilongwe, Malawi.

Retaining clients on antiretroviral therapy (ART) is challenging, especially during the first year on ART. Mobile health (mHealth) interventions show promise to close retention gaps. We aimed to assess reach (who received the intervention?) and effectiveness (did it work?) of a hybrid two-way texting (2wT) intervention to improve ART retention at a large public clinic in Lilongwe, Malawi. Between August 2021-June 2023, in a quasi-experimental study, outcomes were compared between two cohorts of new ART clients: 1) those opting into 2wT who received automated, weekly motivation short messaging service (SMS) messages and response-requested appointment reminders; and 2) a matched historical cohort receiving standard of care (SoC). Reach was defined as "the proportion clients ≤6 months of ART initiation eligible for 2wT". 2wT effectiveness was assessed in time-to-event analysis. Retention was presented in a Kaplan-Meier plot and compared between 2wT and SoC using a log-rank test. The effect of 2wT on ART dropout (lost to follow-up or stopped ART) was estimated using Fine-Gray competing risk regression models, adjusting for sex, age and WHO HIV stage at ART initiation. Of 1,146 clients screened, 501 were eligible for 2wT, a reach of 44%. Lack of phone (393/645; 61%) and illiteracy (149/645; 23%) were the most common ineligibility reasons. Among 468 participants exposed to 2wT, 12-month probability of ART retention was 91% (95% CI: 88% - 94%) compared to 76% (95% CI: 72% - 80%) among 468 SoC participants (p<0.001). Compared to SoC, 2wT participants had a 65% lower hazard of ART dropout at any timepoint (sub-distribution hazard ratio 0.35, 95% CI: 0.24-0.51; p<0.001). 2wT did not reach all clients. For those who opted-in, 2wT significantly increased 12-month ART retention. Expansion of 2wT as a complement to other retention interventions should be considered in other low-resource, routine ART settings.

Study on Migrants Found in Migration Solutions from Commercially Available Polyethylene Products

Migrants found in migration solutions obtained from commercially available polyethylene products that may contain food were studied and analysed via liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC-QTOF) for non-target screening and LC-MS/MS for quantifying 14 substances in migration solutions. Furthermore, an analytical approach based on the retention gap was developed for accurate separation techniques using LC-MS/MS. Irganox 1076 was detected at a maximum of 1.5 mg/kg, which was 1/4 of the Specific Migration Limit in the EU, in nine commercially available plastic bags tested. This is in accordance with European Regulation No 10/2011/EU. Furthermore, migration of Erucamide and Irgafos 168-oxide was confirmed.

Connecting in the Online Classroom: Building Rapport Between Teacher and Students by Rebecca A. Glazier

Reviewed by: Connecting in the Online Classroom: Building Rapport Between Teacher and Students by Rebecca A. Glazier Heather E. Yates Rebecca A. Glazier. Connecting in the Online Classroom: Building Rapport Between Teacher and Students. Baltimore. Johns Hopkins University Press, 2021. 251pp $29.95. ISBN 9781421442655 (paperback), ISBN 9781421442662(e-book). The COVID-19 global pandemic redirected our collective focus to the methods of online teaching in a way that no other modern event has. The entire educational infrastructure was temporarily suspended. The public health crisis demanded that universities rapidly migrate courses, in the middle of the academic term, to online instructional formats. It was hurried, at times chaotic, and most everyone was pushed beyond their professional (and personal) capacities. The emergency presented some challenges that compounded some standing concerns about higher education and revealed new ones about declining college enrollment. In cases where university campuses suspended in-person operations and performed rapid pivots to digital spaces, faculty were students' primary, and sometimes, only connection with the university. The demands of the unusual circumstances uncovered an entirely new set of concerns for student learning and retention. The disruption partly reinvigorated a public discourse about the necessities of online teaching and learning, but it also accelerated another lurking problem: an online retention crisis. Much of the discussion around student retention settles on the needs of traditional students, meaning those who are physically present on campuses, while the needs of online students get pushed to the periphery. As it relates to retention issues, online teaching can suffer from negative stereotypes and mischaracterizations that give way to myths of detached, sterile environments devoid of meaningful human interactions, making the face-to-face classroom a preferred method of instruction (Palloff & Pratt, 2013). For students, some may think online classes are 'easier' than in-person courses (Young, 2006). In view of these challenges, Rebecca Glazier, professor of political science at the University of Arkansas-Little Rock, authored Connecting in the Online Classroom: Building Rapport Between Teacher and Students. The book stands out from a sizeable literature concerning online teaching because it is not simply a best-practices guide to improving online pedagogy. It goes beyond that framework to reconstruct how we think about online teaching by offering a balanced treatment of students and professors in the online experience. One of the book's significant contributions is its focus on the lagging retention of online students in higher education. It also effectively dismantles the negative stereotypes associated with online teaching and, more generally, online classes. The book methodically and critically examines the issue of lagged online retention rates. Beyond the best-practices component, the book proposes evidence-based solutions on how best to address the online retention problem. The book's many strengths include its appeal to a wide audience, its applications across academic disciplines, and its utility for any level of teaching expertise. Glazier expertly describes the online retention gap as the differences in retention of student enrollments in online and in-person classes. Glazier observes that colleges commonly struggle with retaining online students more than any other student population. This digital retention gap is further characterized by Glazier's observation that students who want to succeed in a face-to-face classroom, but have limited options, are dropping out of online classes. The problem manifests in an [End Page 407] observable retention gap in enrollments between online and in-person classes where the in-person classes are enjoying more successful retention rates. While online students comprise a significant portion of the college population, many efforts to retain them get folded into traditional retention strategies. There are reasons why universities invest substantial amounts of capital to keep students on campus by focusing on positive student interactions and experiences within those physical spaces, which routinely enlist the energies of the faculty, staff, and the campus environment (Millea et al., 2018). However, an unintentional negative impact of this means that online students are rendered virtually invisible, which effectively relegates them to a second-class status on campuses. In addressing the online retention gap, Glazier provides a straight-forward, yet significant solution: rapport. The author shows the positive influence that human connectedness in digital learning spaces has on student...

Breaking Barriers: How Libraries Can Better Support Female Architecture Students for Professional Success

This study investigates the role academic libraries can play in narrowing the retention gap between the number of women graduating with a degree in architecture and the number of women currently in the architecture profession. Recommendations to libraries are made based on the existing literature and survey data. The findings of this study aim to propose solutions in the form of services and resources that libraries may provide to best support female architecture students. The findings shed light on four areas: 1. The importance of increasing students’ access to role models and mentors; 2. The need to bring more awareness to available academic tools; 3. The urge to diversify the material taught in the curriculum; 4. The value of sponsoring and hosting diversity-related events and programs. The proposed efforts will further empower women in architecture schools and can also benefit the broader community of minority groups by serving as a resource of recommendations for supporting the underrepresented communities in a profession.

Gross Anatomical Knowledge Loss in Fourth‐Year Nursing Students

Human anatomy and physiology are considered a cornerstone of health‐related professional education and serve as a prerequisite for future nursing courses (McVicar et al., 2015). Numerous research studies show great difficulty in transferring fundamental knowledge of these courses to clinical and subsequent years of these disciplines (Bhangu et al., 2010; Narnaware and Neumeier, 2020; Narnaware, Y. 2021a). However, most of the knowledge acquisition, transfer/lost, and retention studies have been carried out in medical and allied health students and have been assessed rarely in nursing students. We have previously shown that the second‐and third‐year nursing students lose approximately 29.0% and 31.0% of their second and third‐year anatomical knowledge, retaining about 71.0% and 69.0% within two years (Narnaware and Neumeier, 2020; Narnaware and Neumeier, 2020b). However, anatomical knowledge transfer/loss, retention, and application in fourth‐year nursing students have not been assessed yet. The present study's main objective, therefore, is to assess the anatomical knowledge loss among fourth‐year nursing students and determine if the retention level is organ system‐specific. To evaluate the knowledge loss in fourth‐year nursing students, they were quizzed on eleven anatomy organ systems using the online quizzing system Kahoot. Each Kahoot quiz included nine to eleven knowledge and comprehension level multiple‐choice questions. These scores were compared to first‐year quiz scores on the same content to determine overall knowledge loss over the fourth year. Data were statistically analyzed using SPSS II, and means were compared using two‐way ANOVA. The scores are shown for each organ system by reporting the mean and standard deviation (±SD). Statistical significance was set at P &lt; 0.05 for all tests. The results show that there was a significant decrease in the overall mean score from 83.05 ± 8.34 (± SD) in the first year to 53.9 ± 9.4 (±SD) in the fourth year (P=0.0001) (Figure 1). This equates to a 29.6% loss and 70.4% overall retention of anatomical knowledge over two years. However, there was no significant difference in mean scores between the third‐year and four‐year nursing students. The mean score in fourth‐year nursing students was higher by approximately 3.4% than the third‐year students. System‐specific knowledge loss shown in table 1 was highest for the head and neck lymphatic (55.7%), cranial nerves (44.1%), lymphatic (37.6%), and special senses (37.0%). This system‐specific knowledge loss was followed by the integumentary system (28.2%), vascular system (27.6%), muskulo‐skeletal (26.6%), and nervous system (25.1%). The loss was the lowest for the genitourinary system (21.2%), respiratory system (13.9%), and gastrointestinal system (12.0%). The present study reveals that nursing students lost more knowledge in the fourth‐year than first‐year and comparatively less than third‐year but retained much higher anatomical knowledge than medical and allied health students reported. This study provides knowledge retention for different body systems. It also identifies where nursing students' knowledge retention gaps exist so that those can be addressed by developing a robust interventional strategy for nursing students in the future.

Don’t Be Too Political: Depoliticization, Sexual Orientation, and Undergraduate STEM Major Persistence

ABSTRACT Lesbian, gay, bisexual, and queer (LGBQ) students persist in STEM majors at a lower rate than their heterosexual peers. This study posits that heteronormativity, as an instance of depoliticization in STEM affecting LGBQ students, could be a primary contributing factor. Using national, longitudinal data from the Higher Education Research Institute (HERI) at UCLA, this study tested LGBQ-related college experiences to determine if they help explain the retention gap between LGBQ STEM students and their heterosexual peers. Through multilevel regression modeling, we found that LGBQ status is not a significant predictor of retention in STEM after controlling for LGBQ-related experiences. The results suggest that LGBQ-related and other politicized experiences predict lower retention in STEM for heterosexual students, meaning a culture of depoliticization in STEM may be detrimental to more students than those in minoritized social identity groups.

Occurrence of Mineral Oil Hydrocarbons in Omega-3 Fatty Acid Dietary Supplements.

Omega-3 fatty acid dietary supplements have become increasingly popular with consumers due to their multiple health benefits. In this study, the presence of mineral oil hydrocarbons (MOH) was investigated in seventeen commercial samples of such supplements, characterized by different formulations. The analyses were performed using on-line liquid chromatography–gas chromatography (with flame ionization detection), which is considered the most efficient method for the determination of MOH in foodstuffs. Analyte transfer was performed by using the retention gap technique, with partially concurrent solvent evaporation. Various degrees of mineral oil saturated hydrocarbon contamination (from 2.4 ppm to 375.7 ppm) were found, with an average value of 49.9 ppm. Different C-number range contaminations were determined, with the >C25–≤C35 range always found with an average value of 26.9 ppm. All samples resulted free of mineral oil aromatic hydrocarbons, except for two samples in which a contamination was found at the 9.9 and 6.6 ppm levels, respectively.

Improved chromatographic performance in red chilli powder pesticide residue quantitation byretention gap introduction in gas chromatography tandem mass spectrometry.

The online version contains supplementary material available at 10.1007/s13197-021-05177-3.

Early Detection of Poor Academic Performers Using Machine Learning Predictive Modeling

The student's academic development, retention, and attainment gap are considered as the common key factors that influence the institutional academic performance. In this regard, educational institutions are focusing to reduce the attainment gap between good, average, and poor performing students. Two different datasets are taken for this study. Students' data is collected through questionnaire, and Dataset 1 (D1) is created. The second dataset (D2) is taken from the repository. Both the datasets have been preprocessed followed by attribute selection and predictive modeling. In this study, predictive models have been built, and the learners are classified as high, average, and low performers based on their academic scores as well as on their demographic characters. The three classifier models are applied on the datasets. Based on the evaluation measures, the best classifier is identified. This early identification of low performance students will help the educators as well as the learners to put a special care to enhance the learning process as well as to improve the academic performance.

Physiological Knowledge Retention in Second‐Year Nursing Students

Despite anatomy and physiology being foundational courses in medical, nursing, and allied -health care programs, there is growing concern that the knowledge in these courses is not being retained by students over time. Numerous studies have demonstrated the difficulty of medical, allied health, and nursing students to retain and apply anatomical knowledge in their future years of study (Doomernik et al., 2017). However, physiological knowledge retention has not been studied as extensively as anatomical knowledge retention in health care disciplines, with very few studies focusing on nursing students (Aari et al., 2004). Of those studies, most are carried out after graduation (Aari et al., 2004) or are focused on a single or limited number of organ systems (Pourshanazari et al., 2013). We have previously shown that nursing students retained 92.0% of their first-year physiological knowledge, losing 8.% within 4-months (Narnaware and Neumeier, 2020a). The present study aims to determine the level of physiological knowledge retained by nursing students in the second year. To answer this question, nursing students were quizzed on ten organ systems using the on-line quizzing system Kahoot. Each Kahoot quiz included nine to eleven knowledge and comprehension level multiple-choice questions. These scores were compared to first-year quiz scores on the same content to determine overall knowledge retention over a year. Data were statistically analyzed and means were compared using 2-sample t-tests. The scores are described for each organ system by reporting the mean and standard deviation (±SD). Statistical significance was set at P < 0.05 for all tests. The mean score of questions from all organ systems in year one was 62.9 ± 10.5 (±SD). Comparing that score to matched test items evaluated in the pathophysiology course, there is a decrease in the overall mean score from 62.9 ± 10.5 (±SD) to 47.9 ± 9.2 (±SD). This equates to an 85.0% retention rate, or 15.0% knowledge loss within a year. Organ-specific knowledge retention was highest for digestive physiology (97.37%), respiratory physiology (92.32%), fluid and electrolyte physiology (90.41%), inflammation (85.99%), reproductive physiology (83.55%), and vascular physiology (85.22%). This was followed by renal physiology (83.37%) and blood (82.49%). Retention was comparatively lower for endocrine physiology (79.47%) and defenses (70.42%). These results demonstrate a high level of knowledge retention overall, with variations in retention being system-specific. The level of knowledge retention in this study was significantly higher than previous rates reported in medical and allied-health students (Pourshanazari et al., 2013) and is significantly higher than anatomical knowledge retention levels in the same population (Narnaware and Neumeier, 2020b). This study identifies where nursing students' knowledge retention gaps exist which will help to develop an interventional strategy for nursing students in the future.

Anatomical Knowledge Retention in Third‐Year Nursing Students

Human anatomy and physiology are fundamental courses in medical, allied health and nursing disciplines, and serve as a prerequisite for future clinical (Turney et al., 2007). The mounting evidence suggests great difficulty in transferring fundamental knowledge of these courses to clinical and coming years of these disciplines (Bhangu et al., 2010; Narnaware and Neumeier, 2019, 2020). However, most of the knowledge acquisition, transfer/lost, and retention studies have been carried out in medical students and allied health students and have been assessed rarely in nursing students. We have previously shown that the second-year nursing students retained approximately 71.0% of their first anatomical knowledge, losing about 29% within a year (Narnaware and Neumeier, 2020). However, anatomical knowledge transfer/loss, retention, and its application in third-year nursing students has not been assessed yet. Therefore, the present study's main objective is to assess the anatomical knowledge retention among third-year nursing students and determine if the retention level is organ system-specific. To assess the knowledge retention in third-year, nursing students were quizzed on eleven anatomy organ systems using the on-line quizzing system Kahoot. Each Kahoot quiz included nine to eleven knowledge and comprehension level multiple-choice questions. These scores were compared to first-year quiz scores on the same content to determine overall knowledge retention over the third-year. Data were statistically analyzed using SPSS II, and means were compared using two-way ANOVA. The scores are described for each organ system by reporting the mean and standard deviation (±SD). Statistical significance was set at P < 0.05 for all tests. The results show that there was a significant decrease in the overall mean score from 83.05 ± 8.34 (± SD) in the first year to 51.6 ± 12.5 (±SD) in the third-year (P=0.001). This equates to a 31.4% loss andd 68.6% overall retention of anatomical knowledge over two years. However, there was no significant difference in mean scores between the second and third-year nursing students. The mean score in third-year nursing students was lower by approximately 3.0% than the second-year students. System-specific knowledge retention was highest for the gastrointestinal (87.4%), respiration (86.0%), special senses (82.7%). This system-specific retention was followed by the genitourinary system (78.9%), integumentary system (76.0%), and nervous system (74.9%). Retention was lowest for the musculoskeletal (59.7%), lymphatic (system plus head & neck) (57.5 - 58%), cranial nerves (57.4%) and vascular system (50.9%). The present study reveals that nursing students retain less knowledge than first-year and second-year students but retain much higher anatomical knowledge than reported in medical and allied health students. The researchers are now investigating knowledge retention and its application in fourth-year nursing students. This study provides knowledge retention for different body systems. It also identifies where nursing students' knowledge retention gaps exist so that those can be addressed by developing a robust interventional strategy for nursing students in the future.

Research Progress of Analysis of Mineral Oil Hydrocarbons using On-line High Performance Liquid Chromatography Coupled with Gas Chromatography

Abstract In the past decades, the application of on-line high performance liquid chromatography coupled with gas chromatography (HPLC-GC) has been rapidly developed for the quantitative analysis of mineral oil hydrocarbons (MOH). MOH are derived from petroleum and synthetic fuels, and cover a large range of boiling points, mainly consisting of mineral oil saturated hydrocarbons (MOSH) and aromatic hydrocarbons (MOAH). MOH can migrate into food and environment through a variety of pathways, consequently impose an adverse impact on human health. However, the analysis of MOH is challenging due to the limited selectivity and sensitivity of hydrogen flame ionization detector (FID). On-line HPLC-GC combines the high separation efficiency of HPLC with the equal-carbon-response detection of GC-FID, which solves the problems associated with selectivity and sensitivity of MOH analysis. The innovation of the retention gap, Y-piece interface, and solvent vapor exit (SVE) with which the HPLC-GC is equipped enables large-volume injection into GC-FID. By allowing the elution fractions from HPLC to be completely transferred into the GC, the analytical sensitivity of the MOH is enhanced by more than two orders of magnitude, and the contaminants introduced are minimized during the analytical procedure, ensuring the reproducibility and accuracy of the MOH analysis. In this paper, the research history of the interfaces used in on-line HPLC-GC and the matching conditions between HPLC and GC were described in detail, and the sample preparation methods for the removal of interferences and the enrichment of MOH based on HPLC-GC were reviewed. In addition, the limitations of HPLC-GC were summarized, and the future applications of this technology and the trends in the development of MOH analysis were prospected.

A Mixed Methods Study of Factors that Enhance Louis Stokes Mississippi Alliance for Minority Participation (LSMAMP) Students Degree Attainment in STEM

The purpose of this study was to advance the literature addressing best practices capable of bridging the retention and completion gap in STEM education for underrepresent minority students. Using a mixed-methods design, this article delineates Louis Stokes Mississippi Alliance for Minority Participation (LSMAMP) program experiences, instructional strategies, institutional practices and students’ persistence within the LSMAMP community. Five main themes emerged from the student interviews and survey results: (1) early exposure to STEM and familial support; (2) hands on involvement and academic intervention activities; (3) Peer group support; (4) institutional environment and infrastructural support; and (5) financial incentives. The top choices of faculty about institutional and instructional practices and learning strategies that enhance student learning and degree attainment were faculty mentoring, student opportunities to present research at or attend professional conferences, faculty advising, faculty tutoring/study sessions, peer tutoring, interactive lectures, and student opportunities to connect prior learning to new lecture content.

Solving the Puzzle to Lasting Impact of the National Diabetes Prevention Program.

To address the burden of type 2 diabetes, the Centers for Disease Control and Prevention (CDC) launched the National Diabetes Prevention Program (National DPP) in 2010 (1). The program promotes weight loss through lifestyle change, based on remarkable findings of 58% reduced cumulative incidence over 3 years in an efficacy trial (2). Major successes include reaching hundreds of thousands of at-risk individuals nationwide, robust outcomes, and widespread insurance coverage (1,3), but more work is needed to ensure lasting impact, and retention plays a critical part. This Commentary briefly reviews the new retention study by Cannon et al. (4), linkage to other critical pieces, and future directions. In considering solutions to a complex national problem, I seek to contribute my uniquely broad experience with the National DPP working as a lifestyle coach, securing funding, overseeing delivery, reaching disadvantaged populations, serving on state workgroups, rate setting, becoming a Medicare supplier, advocating to payers and legislators, and authoring over 20 peer-reviewed articles on the program. Beginning with doctoral training on a preceding translational study (5), I now lead a large pragmatic trial a decade later to improve retention with presessions to the National DPP (6). I am also ashamedly familiar with diabetes risks and lost over 50 pounds in my own personal journey with lifestyle change. With rigorous analysis of 41,203 participants across 581 organizations, Cannon et al. show incremental attrition that leaves only a third (32%) remaining by month 10 of the yearlong intervention (data not presented for months 11–12) (4). Racial/ethnic minority and younger individuals, and those lacking successful lifestyle change, drop out disproportionately more. The findings help replicate my early studies on retention gaps for these groups (7–9 …

Field courses narrow demographic achievement gaps in ecology and evolutionary biology.

Disparities remain in the representation of marginalized students in STEM. Classroom‐based experiential learning opportunities can increase student confidence and academic success; however, the effectiveness of extending learning to outdoor settings is unknown. Our objectives were to examine (a) demographic gaps in ecology and evolutionary biology (EEB) major completion, college graduation, and GPAs for students who did and did not enroll in field courses, (b) whether under‐represented demographic groups were less likely to enroll in field courses, and (c) whether under‐represented demographic groups were more likely to feel increased competency in science‐related tasks (hereafter, self‐efficacy) after participating in field courses. We compared the relationships among academic success measures and demographic data (race/ethnicity, socioeconomic status, first‐generation, and gender) for UC Santa Cruz undergraduate students admitted between 2008 and 2019 who participated in field courses (N = 941 students) and who did not (N = 28,215 students). Additionally, we administered longitudinal surveys to evaluate self‐efficacy gains during field‐based versus classroom‐based courses (N = 570 students). We found no differences in the proportion of students matriculating at the university as undecided, proposed EEB, or proposed other majors across demographic groups. However, five years later, under‐represented students were significantly less likely to graduate with EEB degrees, indicating retention rather than recruitment drives disparities in representation. This retention gap is partly due to a lower rate of college completion and partly through attrition to other majors. Although under‐represented students were less likely to enroll in field courses, field courses were associated with higher self‐efficacy gains, higher college graduation rates, higher EEB major retention, and higher GPAs at graduation. All demographic groups experienced significant increases in self‐efficacy during field‐based but not lecture‐based courses. Together, our findings suggest that increasing the number of field courses and actively facilitating access to students from under‐represented groups can be a powerful tool for increasing STEM diversity.

In-column dilution: Improving volume loadability in reverse phase gradient chromatography through the use of a silica pre-column

Volume overload is a critical limitation in Reversed Phase (RP)-HPLC purification of pharmaceutical compounds. Limited solubility of these materials in most injection solvents leads to large injection volumes in order to maximize throughput. However, peak distortion due to volume overload limits injection amounts, and results in suboptimal use of chromatographic instruments. Volume loading for RP gradient separations was significantly increased by inserting a silica column ahead of the RP separation column. The sole purpose of this column is to dilute the plug of strong injection solvent so that the actual sample constituents are retained when the diluted injection plug arrives at the RP column. This is similar to the concept of a “retention gap” in GC, yet this has never been applied to liquid chromatographic separations. Injection volumes were increased by almost a factor of 3 when using appropriately sized silica columns. A discussion of critical parameters that determine the effectiveness of this approach is provided. The concept is easily applied and does not require any system modifications. It is therefore well suited for open access applications where more instrument intensive approaches, such as “At-Column Dilution”, would be less desirable. We will also show that the generic concept which we have titled “In-Column Dilution” can easily be applied to increase the detection sensitivity for analytical application as well by allowing injection of larger sample volumes without peak deterioration for purifications.

Advancement in Determination of Phthalate Metabolites by Gas Chromatography Eliminating Derivatization Step.

A gas chromatography-mass spectrometry (GC–MS) method to determine polar and thermally unstable phthalate metabolites [monomethyl phthalate–MMP, monoethyl phthalate–MEP, mono-n-butyl phthalate–MnBP, mono-(2-ethylhexyl) phthalate–MEHP] has been developed. This is the first report presenting the separation of monophthalates without derivatization step and any additional equipment or special injection port. Injection parameters (temperature, pressure, time, and volume of injection), chromatographic separation (retention gap, temperature program), and MS detection/identification (working parameters, ion selection) were investigated. Mechanisms and phenomena occurring under different conditions in the GC injector were evaluated and discussed. The limits of detection (LODs) of MMP, MEP, MnBP, MEHP in the protocol were 0.049, 0.036, 0.038, and 0.029 ng (per 2 μL of injection), respectively. The response of the monophthalates was found to be linear in the tested concentration range (for MMP: 0.15–100 ng, MEP and MnBP: 0.11–100 ng, MEHP: 0.087–100 ng per 2 μL) with the coefficient of determination higher than 0.9817 and inter-day precision in the range of 1.4–5.4%. The developed method is fast, easy and repeatable. Moreover, it allows for the elimination of derivatization agents, reduction of toxic waste production and simplification of analytical procedure.

Simultaneous separation of small interfering RNA and lipids using ion-pair reversed-phase liquid chromatography

RNA interference offers a novel approach for the development of new therapeutics for targets that are otherwise “undruggable” using traditional modalities. The safety and efficacy of siRNA-based therapy mainly rely on lipid or polymer-based nanocarriers to overcome inherent barriers to a systemic delivery of siRNA. A multicomponent lipid nanoparticle (LNP) system is a promising delivery platform, typically consisting of a cationic lipid, phospholipid, PEG-containing short-chain lipid, and cholesterol. Characterization and chemical analysis of the LNP formulation is important to assure drug product stability, a key consideration for chemistry, manufacturing and control strategy. Here we report an ion-pair reversed phase UHPLC method capable of simultaneously separating both siRNA and functional lipids in LNPs with a minimal retention gap for two classes of biologically essential yet chemically distinct molecules. Key chromatographic parameters critical to the separation are discussed, including the structure of the ion-pair agent, stationary phase chemistry, column temperature and an organic additive. The results showed that the retention time of siRNA is tunable by using various ion-pair reagents. The retention factor of the siRNA exhibited a first order relationship with the number of carbons in the alkyl chain of the ion-pair reagents. In contrast, the type of ion-pair reagent has no significant impact on the separation of phospholipids. Separations using a BEH phenyl column and dibutylammonium acetate as the ion-pair reagent showed satisfactory selectivity for a range of double-stranded siRNAs and phospholipids, key components for lipid nanoparticle formulations. Furthermore, the method was applied to the separation of an experimental LNP formulation, demonstrating good selectivity for siRNA, functional lipids and their potential degradation products.

Black Teachers’ Retention and Transfer Patterns in North Carolina: How Do Patterns Vary by Teacher Effectiveness, Subject, and School Conditions?

Despite public interest and government action toward diversifying the teaching workforce in U.S. public schools, our knowledge about the retention and transfer patterns of Black teachers lacks specificity and clarity. In this study, I find that Black teachers’ annual retention rate was about 4 percentage points lower than that of White teachers in North Carolina elementary and secondary schools from 2004 to 2015. This Black-White teacher retention gap can largely be explained by Black teachers’ experience and education and the challenging school and community contexts in which these teachers worked. Compared with White teachers who had similar professional attributes and worked in similar school settings, Black teachers were more likely to stay in schools serving a larger proportion of Black students and to move to a school that served a higher proportion of Black students. The marginal probability of Black teachers’ retention received an additional boost with an increase in teachers’ observational ratings and math value-added scores. Stronger school leadership and higher-quality professional development predict a higher retention rate of more effective Black teachers.