Features of inhalant allergy on nasal endoscopy: a systematic review and meta-analysis.

BACKGROUND: Nasal endoscopy is increasingly accessible to ENT surgeons. The characteristics of the allergic upper airway are not well recognised. METHODOLOGY: MEDLINE (1946-2021), EMBASE (1974-2021), and the Cochrane Library were searched on 16th November 2021 to identify articles that reported endoscopic findings of patients with documented allergy who had undergone nasal endoscopy. The review followed the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy. Meta-analysis was performed by pooling sensitivities and specificities using the hierarchical summary receiver operating characteristics model. RESULTS: A total of 4108 articles were identified, of which 15 manuscripts met the inclusion criteria. The included studies involved 4660 patients who had undergone nasal endoscopy. Middle turbinate (diffuse/polypoid) oedema (sensitivity 58.0%, specificity 84.5%), watery secretions (sensitivity 65.7%, specificity 76.5%), inferior turbinate hypertrophy (sensitivity 86.2%, specificity 32.2%), and unspecified turbinate hypertrophy (sensitivity 82.0%, specificity 42.9%) were identified as the features with the highest predictive value of inhalant allergy. CONCLUSIONS: Diffuse or polypoid oedema of the middle turbinate or watery secretions seen on nasal endoscopy can be a useful adjunct in the identification and diagnosis of inhalant allergy. These clinical features should be part of the diagnostic workup for patients that includes a clinical history and surrogate markers of allergic sensitisation from the skin and serum.

Characteristics of macrolide responders in persistent post-surgical rhinosinusitis.

INTRODUCTION: The anti-inflammatory effects of long term low dose macrolide therapy have shown benefit in the management of diffuse panbronchiolitis. Dramatic responses to macrolide in the upper airway are seen but our understanding of the patient phenotype predisposing to macrolide response in chronic rhinosinusitis (CRS) is poor. METHODS: A case control study was performed in a tertiary level rhinology practice of consecutive chronic rhinosinusitis patients placed on a 3-month low dose macrolide therapy after failing at least 3 months of corticosteroid irrigation therapy post-endoscopic sinus surgery. Patients were defined as a macrolide responder when having near normal endoscopy after a 3-month period of clarithromycin treatment. Patient characteristics of smoking, asthma, atopy status, revision surgery, symptom severity (SNOT-22) along with biomarkers from serum and tissue histopathology results were compared between groups. RESULTS: Of twenty-eight consecutive macrolide treated patients, 19 responders were compared to 9 non-responders. The groups were similar in age, female gender, non-smoking, asthma, and atopy. Macrolide response was associated with a lack of tissue eosinophilia (more than 10/HPF) and lower serum eosinophilia. Neutrophil expression was similar in tissue and serum. Squamous metaplasia was overexpressed in non-responders. CONCLUSION: Low tissue and serum eosinophilia, and absence of tissue squamous metaplasia may predict a CRS phenotype suitable to a trial of long-term macrolide therapy when surgery and topical therapy has failed.

The impact of bitter taste receptor genetics on culturable bacteria in chronic rhinosinusitis.

BACKGROUND: Extra-oral bitter taste receptors have been associated with innate bacterial defence mechanisms. Genetic variation in T2R38 functionality has been shown to be associated with susceptibility to upper respiratory tract infections and chronic rhinosinusitis (CRS). We sought to independently assess the influence of bitter taste receptor genotype on the presence of culturable bacteria in the sinuses. METHODOLOGY: A cross-sectional analysis of patients with CRS undergoing surgery was performed. Middle meatal nasal swabs were sent for microbiological evaluation at the time of the procedure. Mucosal biopsies were taken and sent for bitter taste receptor genotype analysis. Sequencing of 3 polymorphisms in the TAS2R38 gene was performed to identify genotypes as super-tasters (PAV/PAV), non-tasters (AVI/AVI) or heterozygous expression (PAV/AVI). The presence of culturable organisms and common pathogens were compared with bitter taste receptor genotypes. RESULTS: 25 patients (age 52.4 +/- 18.28 years, 51% female) were assessed. Super-tasters comprised 16% of the group, 24% were non-tasters and 48% had heterozygous expression. A cultured pathogen was grown in 48% of patients; 32% gram-positive, 20% gram-negative, 28% grew Staphylococcus aureus and 12% Pseudomonas aeruginosa. A non-taster genotype was predictive of colonised pathogens. Tissue eosinophilia (more than 10 HPF) was seen in 48%. CONCLUSION: Even in a small sample of patients with CRS, non-taster T2R38 genotype appears to predict the presence of culturable bacteria colonising the sinus cavity at the time of surgery for their condition. A genetic link to patients more likely to become infected is likely.

Airflow and symptom outcomes between allergic and non-allergic rhinitis patients from turbinoplasty.

BACKGROUND: Inferior turbinate procedures are applied to relieve medically refractory nasal obstruction. However, the nature of congestion differs between allergic(AR) and non-allergic rhinitis(NAR). This study compares surgical outcomes between AR and NAR patients. METHODOLOGY: A case-control study of patients undergoing turbinate with or without septoplasty surgery for nasal obstruction was performed. Patient reported outcomes were: nasal obstruction, global nasal function(GNF), and sino-nasal outcome test(SNOT-22) with rhinitis, facial symptom, sleep and psychological sub-scores. Nasal peak inspiratory flow(NPIF) assessed nasal airflow. Measurements were obtained preoperatively and 3 months postoperatively. RESULTS: 190 patients were assessed. AR had worse obstruction and worse GNF. All outcomes improved post-surgery; nasal obstruction, GNF, SNOT-22, rhinitis-symptoms, facial-symptoms, sleep-function, psychological-function and NPIF. GNF improvement was greater in AR. NPIF improvement was similar between groups. CONCLUSIONS: Both AR and NAR patients gained benefit from surgery to relieve nasal obstruction. AR patients demonstrate greater improvement in GNF score but allergy management may contribute to this.

Association of gastro-oesophageal reflux and chronic rhinosinusitis: systematic review and meta-analysis.

INTRODUCTION: Gastro-oesophageal reflux disease (GORD) has been implicated in the development of chronic rhinosinusitis (CRS). The association of GORD with CRS is systematically assessed from the medical literature. METHODOLOGY: Embase and MEDLINE were searched using a comprehensive strategy limited to English language and Human subjects. Any study with original data on the experimental, diagnostic, treatment or prognostic association of CRS with GORD was included. Studies without a control group, case reports and review articles were excluded. RESULTS: The search returned 958 records, with an additional 10 found from bibliographic lists; this produced 32 studies. The included studies (n=32) consisted of studies reporting pathogenic factors (n=20), epidemiological association (n=8), prognostic interactions (n=3), and a combination of these outcomes (n=1). Potential pathogenic roles for GORD in CRS were supported; CRS subjects had greater prevalence of intranasal Helicobacter pylori and acid reflux than subjects without CRS. CRS is more prevalent in GORD sufferers than those without GORD. Evidence is conflicting for GORD as a factor in CRS treatment failure. CONCLUSION: The results support a significant association of GORD with CRS. Physicians should be cognizant of the potential for acid and non-acid reflux as a driving factor in CRS.

Periostin as a marker of mucosal remodelling in chronic rhinosinusitis.

BACKGROUND: Although extracellular matrix (ECM) proteins are associated with irreversible lower airway changes, the relationship with upper airway remodelling which occurs during chronic rhinosinusitis (CRS) is poorly understood. This study assessed the expression of ECM proteins periostin, fibulin-1, fibronectin and collagenIV in nasal mucosa of patients with and without histologic features of remodelling. METHODS: A cross-sectional study of sinonasal mucosal biopsies taken from patients, undergoing surgery for CRS was performed, where patients were grouped according to remodelling, defined by basement membrane thickening (BMT over 7.5 micrometer) and subepithelial fibrosis. An overall view and three random fields of immunostained tissue sections that included epithelium, basement membrane and submucosa, were imaged using Zeiss Zen software. The area and intensity of positive staining were scored by two blinded observers, using a 12-point ordinal scale of weak to strong. RESULTS: 65 patients (47.6 +/- 13.4years, 44.6% female) were assessed. Patients were grouped as controls 26.2%, BMT/no fibrosis 38.5% or BMT and fibrosis 33.8%. Stronger grade of periostin expression was associated with remodelling changes and tissue eosinophilia over 10/HPF. Fibulin-1, fibronectin and collagenIV did not differ. CONCLUSION: Periostin expression was associated with the presence of BMT, fibrosis and tissue eosinophilia and may identify patients undergoing remodelling changes.

Group 2 innate lymphoid cells (ILC2s) are increased in chronic rhinosinusitis with nasal polyps or eosinophilia.

BACKGROUND: Chronic rhinosinusitis (CRS) is a heterogeneous disease with an uncertain pathogenesis. Group 2 innate lymphoid cells (ILC2s) represent a recently discovered cell population which has been implicated in driving Th2 inflammation in CRS; however, their relationship with clinical disease characteristics has yet to be investigated. OBJECTIVE: The aim of this study was to identify ILC2s in sinus mucosa in patients with CRS and controls and compare ILC2s across characteristics of disease. METHODS: A cross-sectional study of patients with CRS undergoing endoscopic sinus surgery was conducted. Sinus mucosal biopsies were obtained during surgery and control tissue from patients undergoing pituitary tumour resection through transphenoidal approach. ILC2s were identified as CD45(+) Lin(-) CD127(+) CD4(-) CD8(-) CRTH2(CD294)(+) CD161(+) cells in single cell suspensions through flow cytometry. ILC2 frequencies, measured as a percentage of CD45(+) cells, were compared across CRS phenotype, endotype, inflammatory CRS subtype and other disease characteristics including blood eosinophils, serum IgE, asthma status and nasal symptom score. RESULTS: 35 patients (40% female, age 48 ± 17 years) including 13 with eosinophilic CRS (eCRS), 13 with non-eCRS and 9 controls were recruited. ILC2 frequencies were associated with the presence of nasal polyps (P = 0.002) as well as high tissue eosinophilia (P = 0.004) and eosinophil-dominant CRS (P = 0.001) (Mann-Whitney U). They were also associated with increased blood eosinophilia (P = 0.005). There were no significant associations found between ILC2s and serum total IgE and allergic disease. In the CRS with nasal polyps (CRSwNP) population, ILC2s were increased in patients with co-existing asthma (P = 0.03). ILC2s were also correlated with worsening nasal symptom score in CRS (P = 0.04). CONCLUSION AND CLINICAL RELEVANCE: As ILC2s are elevated in patients with CRSwNP, they may drive nasal polyp formation in CRS. ILC2s are also linked with high tissue and blood eosinophilia and have a potential role in the activation and survival of eosinophils during the Th2 immune response. The association of innate lymphoid cells in CRS provides insights into its pathogenesis.

Intranasal corticosteroids do not affect intraocular pressure or lens opacity: a systematic review of controlled trials.

BACKGROUND: Intranasal corticosteroids (INCS) are prescribed for the long-term prophylactic treatment of inflammatory upper airway conditions. Although some systemic absorption can occur via topical routes, the clinical relevance is controversial. The effects of orally administered corticosteroids on intraocular pressure (IOP) and lens opacity (LO) are well established, but the impact of the INCS is less well defined. This study aims to systematically review the literature for evidence of adverse occular events with INCS use. METHODOLOGY: A systematic review of literature from Medline and Embase databases (January 1974 to 21st of November 2013) was performed. Using the PRISMA guidelines, all controlled clinical trials of patients using INCS, that reported original measures of IOP, LO, glaucoma or cataract incidences were included. Studies with adjuvant administration of oral, inhaled and intravenous steroids were excluded. RESULTS: 665 articles were retrieved with 137 were considered for full-text review. Of these, 116 (85%) were literature reviews and two were case reports. 19 studies (10 RCTs, 1 case-control, 8 case series) were included for the qualitative review, of which 18 reported data on IOP and 10 on cataract/LO. None (n=0) of the 10 RCT reporting data on glaucoma or IOP demonstrated changes in IOP compared to control. Also none (n=0) of the 6 RCTs reporting cataract or lens opacity demonstrated changes compared to control. CONCLUSION: Data from studies with low levels of bias, do not demonstrate a clinically relevant impact of INCS on neither ocular pressure, glaucoma, lens opacity nor cataract formation.

Modified Lund Mackay Postoperative Endoscopy Score for defining inflammatory burden in chronic rhinosinusitis.

OBJECTIVE: The Lund Mackay Postoperative Endoscopy Score (LMES) for chronic rhinosinusitis (CRS) is a poor measure of the patient experience. A proposed Modified Lund Mackay Postoperative Endoscopy Score (MLMES) aims to better describe the inflammatory burden in CRS. METHODS: A prospective study on CRS patients having endoscopic sinus surgery (ESS) was conducted. Endoscopy was recorded at the 6th and the 12th week post-op. The MLMES recorded changes in mucosa, mucus and purulence for each of the maxillary, ethmoid, sphenoid, frontal sinuses and olfactory fossa in post-ESS cavities. The correlation between MLMES and visual analogue scale of total rhinosinusitis symptoms, global anchor score of nasal function, Sino-Nasal Outcome Test 22 (SNOT-22) and nasal symptom score was analyzed. The inter-observer reliability, intra-observer reliability and correlation between the change in MLMES and in subjective measures were also investigated. RESULTS: Thirty patients were assessed. The MLMES significantly correlated with visual analogue scale, SNOT-22, global anchor and nasal symptom score. The change in MLMES correlated with the change in SNOT-22 and nasal symptom score. The inter-observer and intra-observer reliability were excellent. CONCLUSION: Objectives measurements for post-ESS patients can be reconsidered to represent the cumulative inflammatory burden of all sinuses. The proposed MLMES represents total sinus inflammatory burden and correlates well with patient reported outcome measures.

Nasal peak inspiratory flow (NPIF) as a diagnostic tool for differentiating decongestable from structural nasal obstruction.

BACKGROUND: Identifying the cause of nasal obstruction is critical before surgical intervention. Structural nasal obstruction, due to nasal valve stenosis, is unlikely to benefit from simple septoplasty and turbinate reduction. This study assesses changes in nasal peak inspiratory flow (NPIF) as a tool for discriminating decongestable versus structural obstruction. METHODOLOGY: Cross-sectional study of patients undergoing nasal airflow assessment was performed. Rhinomanometry, nasal obstruction visual analogue scores (VAS) and NPIF were performed pre- and post-decongestion. Population groups were defined with decongestable or structural obstruction by relative post-decongestion changes in airways resistance and symptoms. RESULTS: Fifty two patients were assessed, 24 with decongestable, 28 with structural obstruction. Pre- and post-decongestion NPIF were similar between groups. Absolute and percentage NPIF change were larger with decongestable versus structural obstruction. Sensitivity and specificity for predicting decongestable obstruction were 75.0% and 60.7% for NPIF increase >20 L/min; 75.0% and 64.3% for NPIF increase >20%. The respective positive predictive values were 62.1% and 64.3%. CONCLUSION: NPIF increase after decongestion is larger with decongestable than structural nasal obstruction. NPIF alone cannot discriminate the two conditions and does not replace more formal assessment.

Osteitic bone: a surrogate marker of eosinophilia in chronic rhinosinusitis.

BACKGROUND: Causes of osteitis in chronic rhinosinusitis (CRS) other than previous surgery are poorly defined. Patients with eosinophilic CRS (ECRS) have more severe disease and poorer outcomes despite repeated surgery. Associations between osteitis and markers of ECRS are not well described. METHODS: A cross-sectional study of CRS patients undergoing sinus surgery was conducted. Osteitis was scored radiologically using previously published measures. Associations between osteitis and histopathology, symptoms, endoscopy, CT mucosal score and seromarkers were analyzed. RESULTS: Eighty-eight patients were assessed of whom forty-five had osteitis. Patients undergoing revision surgery recorded higher osteitis scores. Patients with mucosal eosinophilia had higher osteitis score than those without. Patients with osteitis had higher serum eosinophil. Similar relationships were also found in primary surgery. Osteitis was associated with endoscopic and radiologic, but not symptomatic disease severity. CONCLUSIONS: Osteitis is associated with tissue and serum eosinophilia in both patients with and without prior surgery. Patients with these features may benefit from post-operative corticosteroid therapy to prevent osteitis.

Safety and activity of vandetanib in combination with everolimus in patients with advanced solid tumors: a phase I study.

BACKGROUND: Preclinical studies suggest that combining vandetanib (VAN), a multi-tyrosine kinase inhibitor of rearranged during transfection (RET) proto-oncogene, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR), with everolimus (EV), a mammalian target of rapamycin (mTOR) inhibitor, may improve antitumor activity. We determined the safety, maximum tolerated dose (MTD), recommended phase II dose (RP2D), and dose-limiting toxicities (DLTs) of VAN + EV in patients with advanced solid cancers and the effect of combination therapy on cancer cell proliferation and intracellular pathways. PATIENTS AND METHODS: Patients with refractory solid tumors were enrolled in a phase I dose-escalation trial testing VAN (100-300 mg orally daily) + EV (2.5-10 mg orally daily). Objective responses were evaluated using RECIST v1.1. RET mutant cancer cell lines were used in cell-based studies. RESULTS: Among 80 patients enrolled, 72 (90%) patients were evaluable: 7 achieved partial response (PR) (10%) and 37 had stable disease (SD) (51%; duration range: 1-27 cycles). Clinical benefit (SD or PR ≥ 6 months) was observed in 26 evaluable patients [36%, 95% confidence intervals (CI) (25% to 49%)]. In 80 patients, median overall survival (OS) was 10.5 months [95% CI (8.5-16.1)] and median progression-free survival (PFS) 4.1 months [95% CI (3.4-7.3)]. Six patients (7.5%) experienced DLTs and 20 (25%) required dose modifications. VAN + EV was safe, with fatigue, rash, diarrhea, and mucositis being the most common toxicities. In cell-based studies, combination therapy was superior to monotherapy at inhibiting cancer cell proliferation and intracellular signaling. CONCLUSIONS: The MTDs and RP2Ds of VAN + EV are 300 mg and 10 mg, respectively. VAN + EV combination is safe and active in refractory solid tumors. Further investigation is warranted in RET pathway aberrant tumors.

Artificial intelligence to detect tympanic membrane perforations.

OBJECTIVE: To explore the feasibility of constructing a proof-of-concept artificial intelligence algorithm to detect tympanic membrane perforations, for future application in under-resourced rural settings. METHODS: A retrospective review was conducted of otoscopic images analysed using transfer learning with Google's Inception-V3 convolutional neural network architecture. The 'gold standard' 'ground truth' was defined by otolaryngologists. Perforation size was categorised as less than one-third (small), one-third to two-thirds (medium), or more than two-thirds (large) of the total tympanic membrane diameter. RESULTS: A total of 233 tympanic membrane images were used (183 for training, 50 for testing). The algorithm correctly identified intact and perforated tympanic membranes (overall accuracy = 76.0 per cent, 95 per cent confidence interval = 62.1-86.0 per cent); the area under the curve was 0.867 (95 per cent confidence interval = 0.771-0.963). CONCLUSION: A proof-of-concept image-classification artificial intelligence algorithm can be used to detect tympanic membrane perforations and, with further development, may prove to be a valuable tool for ear disease screening. Future endeavours are warranted to develop a point-of-care tool for healthcare workers in areas distant from otolaryngology.

Referral of young people attending a sexual assault referral centre to mental health services.

Mental health issues following sexual assault in young people are common but early intervention may improve outcome. A retrospective case-note review of 58 female patients aged between 13 and 18 attending The Haven Whitechapel, a sexual assault referral centre, demonstrated past emotional problems in 72% of those seen, and current emotional problems in 95% of those being followed up. Fifteen percent were already involved with adolescent mental health services (AMHS). All patients requiring and not already receiving input were referred to AMHS or in-house. Of 23 patients referred to AMHS, eight (35%) were accepted and the patients attended, seven (30%) were accepted but did not attend, six (26%) were declined and the outcome of two referrals was unknown. The prevalence of emotional problems and inconsistent referral outcomes demonstrate a need for closer links with AMHS, clearer referral criteria and improved referral pathways.

A systematic review of the evidence base for vidian neurectomy in managing rhinitis.

BACKGROUND: Vidian neurectomy has been proposed as a surgical option for rhinitis refractory to medical treatment. However, the evidence base for its benefit remains controversial. METHODS: A systematic review was performed. Studies reporting original data on patients with rhinitis treated by vidian neurectomy were included. Patient-reported outcome measures were the primary outcome investigated; specific peri-operative morbidities were the secondary outcome. RESULTS: A total of 1012 articles fulfilled the search criteria, 32 of which were included in the study. Patient-reported outcome measures were compared before and after surgery in eight studies. There were 529 patients represented in these trials. Significant improvement in rhinorrhoea was reported in all eight studies. Temporary dry eyes was reported in 24.63 per cent of cases (272 out of 1104 cases). There was no report of cranial nerve deficit or eye movement disturbance. CONCLUSION: Endoscopic vidian neurectomy does have a role in the surgical management of refractory rhinitis, particularly in patients with non-allergic rhinitis, but a well-designed cohort trial would be advantageous to clarify long-term outcomes.

Quantitative effects of unsaturated fatty acids in microbial mutants. VII. Influence of the acetylenic bond location on the effectiveness of acyl chains.

The ability of a series of 18 carbon acetylenic fatty acids to fulfill the unsaturated fatty acid requirements of Escherichia coli and Saccharomyces cerevisiae was investigated. Despite their high melting points (greater than 40 degrees C), several isomers of the acetylenic fatty acids were as efficient or more efficient in supporting growth than the analogous fatty acid having a cis-double bond. The efficiencies of the different positional isomers in supporting cell proliferation varied from essentially 0 cells per fmol for the 2-5 and 13-17 isomers to high values when the acetylenic bond was near the center of the chain: e.g. 45 E. coli and 5.5 S. cerevisiae cells/fmol for the 10 isomer. A striking ineffectiveness of the 9 isomer was observed with E. coli. The 7, 8 and 10 isomers were at least 10-fold more efficient than any of the other positional isomers in supporting the growth of E. coli. In contrast, the 9 isomer was among the most effective acetylenic fatty acids tested with the yeast mutant. Chromatographic analysis of the extracted lipids indicated that each of the acetylenic isomers tested (except delta2 and delta3) could be esterified by the prokaryotic and eukaryotic microorganisms. The content of unsaturated plus cyclopropane acids observed when growth ceased in E. coli cultures supplemented with growth-limiting concentrations of the acetylenic fatty acids ranged from approx. 15 mol% for the 8 isomer to approx. 35 mol% for the 14 and 17 isomers. The 8-11 isomers were observed to be esterified predominantly at the two position in phosphatidylethanolamine of E. coli and in phosphatidylcholine of S. cerevisiae.

Incidence of neoplasia in patients with unilateral epiphora.

BACKGROUND: Nasolacrimal duct obstruction is common and is usually a result of benign stricture formation.Although neoplasia near or around the lacrimal system may produce epiphora, the incidence of neoplasia from within the lacrimal system as a cause of nasolacrimal duct obstruction is not well documented. METHODS: A retrospective study was performed on all patients undergoing dacryocystorhinostomy with a history of epiphora. The incidence of patients with operative findings of intra-lacrimal neoplasm was sought. Histopathologically confirmed cases were included. RESULTS: The study comprised 537 patients, who underwent a total of 631 endoscopic dacryocystorhinostomy procedures between January 1998 and July 2013. Non-stenotic causes of nasolacrimal duct obstruction were encountered in 3.01 per cent of dacryocystorhinostomy procedures, and included neoplastic, inflammatory and infectious pathologies. Inverted papilloma was the most common cause, encountered in 0.79 per cent of dacryocystorhinostomy operations. CONCLUSION: These findings suggest that neoplasia is an uncommon but not a rare cause of nasolacrimal duct obstruction. Surgical teams performing high numbers of dacryocystorhinostomy procedures should be aware of such pathology and patients counselled appropriately.

Hihg-speed GC/MS of gasoline-range hydrocarbon compounds using a pressure-tunable column ensemble and time-of-flight detection

A pressure-tunable series-coupled ensemble of two capillary GC columns is combined with a time-of-flight MS detector for the high-speed characterization of mixtures containing hydrocarbon compounds. The column ensemble consists of a nonpolar 5% phenyl poly(dimethylsiloxane) column and a very polar poly(ethylene glycol) column. The TOFMS instrument uses time-array detection to obtain up to 500 complete electron mass spectra per second. Instrument software allows for automated peak finding and the spectral deconvolution of severely overlapping unknown chromatographic peaks, if their fragmentation patterns are significantly different and if at least two spectra can be recorded between the peak apexes. By adjusting the carrier-gas pressure at the column-junction point, the separations between adjacent peak pairs can be adjusted to enhance the capabilities of the TOFMS detector. The sensitivity of peak-pair separation to changes in junction-point pressure is studied for combinations of alkanes, olefins, and aromatic compounds. When complete separation is required, the use of pressure-tunable column ensembles cannot always provide sufficient control of peak-pair separation for structurally similar compounds. However, complete chromatographic separation typically is not required with the TOFMS detection, and a pressure-tunable column ensemble is very useful for the high-speed characterization of hydrocarbon mixtures.

Programmable control of column selectivity for temperature-programmed GC

A computer-driven pressure controller connected to the junction point of a series-coupled ensemble of two capillary GC columns having different stationary-phase selectivity is used to obtain on-the-fly (programmable) changes in ensemble selectivity. Changes in the junction-point pressure result in differential changes in the local carrier gas velocity in the two columns, and this results in changes in the pattern of peaks eluting from the ensemble. When used with relatively fast temperature programming (30 degrees C/min), the pattern of eluting peaks can be very sensitive to the time at which a selectivity (junction-point pressure) change is implemented. These elution pattern changes are described for a set of six PCB congeners that elute with a small range of retention times. The components are considered as a group, and changes in their elution pattern are described for a single junction-point pressure change, which is implemented at various times after sample injection. If the pressure change is implemented after the components have migrated across the junction point, the final pressure has relatively little impact on the ensemble retention pattern. Pressure changes implemented prior to the components reaching the junction can have a large effect and usually result in a pattern of peaks similar to the pattern obtained when the final pressure is used for the entire separation. For pressure changes made when the group of components is near the junction point, the observed peak pattern may be very sensitive to the time of the pressure change. The time at which the junction-point pressure change occurs is varied in 1.0-s intervals. Artifacts such as peak doubling and peak focusing or broadening are observed if a migrating band is crossing the column junction point at the time of the programmed pressure change.

Peak capacity, peak-capacity production rate, and boiling point resolution for temperature-programmed GC with very high programming rates

Recent advances in column heating technology have made possible very fast linear temperature programming for high-speed gas chromatography. A fused-silica capillary column is contained in a tubular metal jacket, which is resistively heated by a precision power supply. With very rapid column heating, the rate of peak-capacity production is significantly enhanced, but the total peak capacity and the boiling-point resolution (minimum boiling-point difference required for the separation of two nonpolar compounds on a nonpolar column) are reduced relative to more conventional heating rates used with convection-oven instruments. As temperature-programming rates increase, elution temperatures also increase with the result that retention may become insignificant prior to elution. This results in inefficient utilization of the down-stream end of the column and causes a loss in the rate of peak-capacity production. The rate of peak-capacity production is increased by the use of shorter columns and higher carrier gas velocities. With high programming rates (100-600 degrees C/min), column lengths of 6-12 m and average linear carrier gas velocities in the 100-150 cm/s range are satisfactory. In this study, the rate of peak-capacity production, the total peak capacity, and the boiling point resolution are determined for C10-C28 n-alkanes using 6-18 m long columns, 50-200 cm/s average carrier gas velocities, and 60-600 degrees C/min programming rates. It was found that with a 6-meter-long, 0.25-mm i.d. column programmed at a rate of 600 degrees C/min, a maximum peak-capacity production rate of 6.1 peaks/s was obtained. A total peak capacity of about 75 peaks was produced in a 37-s long separation spanning a boiling-point range from n-C10 (174 degrees C) to n-C28 (432 degrees C).