Is Preoperative Chemoprophylaxis Safe for Venous Thromboembolism Prevention in Patients With Head and Neck Cancer?

OBJECTIVE: To assess the safety of preoperative chemoprophylaxis (PEC) in head and neck cancer (HNC) patients undergoing oncologic procedures. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary academic center. METHODS: HNC patients with Caprini risk score (CRS) ≥5 who underwent inpatient surgery ≥3 hours between 2015 and 2020 were included. Patients were divided into 2 cohorts, PEC and control, based on whether or not they received a single dose of low molecular weight heparin or unfractionated heparin prior to surgery. The primary endpoint was the 30-day rate of major bleeding events. RESULTS: A total of 539 patients were included; 427 patients received PEC prior to surgery. The rate of major bleeding was 6.7%. The PEC cohort was more likely to have received concurrent aspirin or ketorolac (225 of 427 patients vs 36 of 112 patients; P = .0002), greater duration of chemoprophylaxis (7.8 vs 5.0 days; P < .0001), have higher CRS (7.2 vs 6.6; P < .0001), longer operative times (596 vs 512 minutes; P < .0001), higher blood loss (265 vs 214 ml; P = .02), and higher bleeding rates when compared to the control (34 of 427 patients; P = .03). On multivariate analysis, only PEC was associated with bleeding (odds ratio, 8.74; 95% confidence interval, 1.15-66.5). The rate of VTE was 1.3% and was not significantly different between cohorts. CONCLUSION: PEC was associated with an increase in bleeding and did not result in lower rates of VTE in patients with HNC. This study highlights the need to determine the optimal regimen of chemoprophylaxis in this patient cohort.

Noninvasive Temperature Measurements in Tissue-Simulating Phantoms Using a Solid-State Near-Infrared Sensor.

The monitoring of body temperature is a recent addition to the plethora of parameters provided by wellness and fitness wearable devices. Current wearable temperature measurements are made at the skin surface, a measurement that is impacted by the ambient environment of the individual. The use of near-infrared spectroscopy provides the potential for a measurement below the epidermal layer of skin, thereby having the potential advantage of being more reflective of physiological conditions. The feasibility of noninvasive temperature measurements is demonstrated by using an in vitro model designed to mimic the near-infrared spectra of skin. A miniaturizable solid-state laser-diode-based near-infrared spectrometer was used to collect diffuse reflectance spectra for a set of seven tissue phantoms composed of different amounts of water, gelatin, and Intralipid. Temperatures were varied between 20-24 °C while collecting these spectra. Two types of partial least squares (PLS) calibration models were developed to evaluate the analytical utility of this approach. In both cases, the collected spectra were used without pre-processing and the number of latent variables was the only optimized parameter. The first approach involved splitting the whole dataset into separate calibration and prediction subsets for which a single optimized PLS model was developed. For this first case, the coefficient of determination (R2) is 0.95 and the standard error of prediction (SEP) is 0.22 °C for temperature predictions. The second strategy used a leave-one-phantom-out methodology that resulted in seven PLS models, each predicting the temperatures for all spectra in the held-out phantom. For this set of phantom-specific predicted temperatures, R2 and SEP values range from 0.67-0.99 and 0.19-0.65 °C, respectively. The stability and reproducibility of the sample-to-spectrometer interface are identified as major sources of spectral variance within and between phantoms. Overall, results from this in vitro study justify the development of future in vivo measurement technologies for applications as wearables for continuous, real-time monitoring of body temperature for both healthy and ill individuals.

Facial Trauma During the COVID-19 Pandemic.

Study Design: Retrospective cohort study. Objective: The purpose of this study is to evaluate the impact of the COVID-19 global pandemic on the regional trends in facial trauma at a tertiary care, level 1 trauma center in Central New York. Methods: The study sample was derived from the population of patients who presented with facial trauma to the emergency department at the Downtown and/or Community Campuses of SUNY Upstate University Hospital between March 1, 2020, and May 15, 2020, and compared to two historical controls in 2018 and 2019. Descriptive and bivariate statistics were calculated for study variables in each cohort. Poisson regression was used to compare incident rate ratios (IRR) with 95% confidence intervals with significance set at P < .05. Results: Sixty five patients presented during the COVID-19 pandemic, while 83 presented in 2019 and 95 in 2018. For the study period, the most common mechanism was assault in 47.7%. IRR was significantly lower than in 2018 (IRR = 1.46, P = .018), but not significantly different from 2019 (IRR = 1.28, P = .14). During lockdown, IRR was significantly decreased compared to 2019 (IRR = 1.84, P = .0029) and 2018 (IRR = 2.16, P < .001). Conclusions: The volume of facial trauma seen in Central New York appears undeterred in the absence of "shelter in place" orders. Analysis of pandemic and regional trauma variations can offer valuable insight for improved resource allocation to better prepare for potentially high-risk procedures.

Pituitary Gland Surgical Emergencies: The Role of Endoscopic Intervention.

True pituitary surgical emergencies are rare. These events can occur throughout the perioperative period and are broadly categorized by the timing of occurrence. Acute indications for emergent pituitary surgery include pituitary apoplexy, vision loss, and severe Cushing presentation. Emergencies may also occur intraoperatively, secondary to bleeding. Postoperative emergencies include epistaxis, pneumocephalus, and intracranial bleeding. Cerebrospinal fluid (CSF) leak occurs in about 37.4% of transsphenoidal sellar surgery, yet postoperative CSF leaks are less frequent at approximately 2.6%. As they occur often during pituitary surgery, CSF leaks alone are generally not considered a true surgical emergency unless associated with symptomatic tension pneumocephalus.

Products for Monitoring Glucose Levels in the Human Body With Noninvasive Optical, Noninvasive Fluid Sampling, or Minimally Invasive Technologies.

BACKGROUND: Conventional home blood glucose measurements require a sample of blood that is obtained by puncturing the skin at the fingertip. To avoid the pain associated with this procedure, there is high demand for medical products that allow glucose monitoring without blood sampling. In this review article, all such products are presented. METHODS: In order to identify such products, four different sources were used: (1) PubMed, (2) Google Patents, (3) Diabetes Technology Meeting Startup Showcase participants, and (4) experts in the field of glucose monitoring. The information obtained were filtered by using two inclusion criteria: (1) regulatory clearance, and/or (2) significant coverage in Google News starting in the year 2016, unless the article indicated that the product had been discontinued. The identified bloodless monitoring products were classified into three categories: (1) noninvasive optical, (2) noninvasive fluid sampling, and (3) minimally invasive devices. RESULTS: In total, 28 noninvasive optical, 6 noninvasive fluid sampling, and 31 minimally invasive glucose monitoring products were identified. Subsequently, these products were characterized according to their regulatory, technological, and consumer features. Products with regulatory clearance are described in greater detail according to their advantages and disadvantages, and with design images. CONCLUSIONS: Based on favorable technological features, consumer features, and other advantages, several bloodless products are commercially available and promise to enhance diabetes management. Paths for future products are discussed with an emphasis on understanding existing barriers related to both technical and non-technical issues.

Selectivity and Sensitivity of Near-Infrared Spectroscopic Sensing of ß-Hydroxybutyrate, Glucose, and Urea in Ternary Aqueous Solutions.

The next-generation artificial pancreas is under development with the goal to enhance tight glycemic control for people with type 1 diabetes. Such technology requires the integration of a chemical sensing unit combined with an insulin infusion device controlled by an algorithm capable of autonomous operation. The potential of near-infrared spectroscopic sensing to serve as the chemical sensing unit is explored by demonstrating the ability to quantify multiple metabolic biomarkers from a single near-infrared spectrum. Independent measurements of ß-hydroxy-butyrate, glucose, and urea are presented based on analysis of near-infrared spectra collected over the combination spectral range of 5000-4000 cm-1 for a set of 50 ternary aqueous standard solutions. Spectra are characterized by a 1 µAU root-mean-square (RMS) noise for 100% lines with a resolution of 4 cm-1 and an optical path length of 1 mm. Calibration models created by the net analyte signal (NAS) and the partial least squares (PLS) methods provide selective measurements for each analyte with standard errors of prediction in the upper micromolar concentration range. The NAS method is used to determine both the selectivity and sensitivity for each analyte and their values are consistent with these standard errors of prediction. The NAS method is also used to characterize the background spectral variance associated with instrumental and environmental variations associated with buffer spectra collected over a multiday period.

Crystal Structure-Free Method for Dielectric and Polarizability Characterization of Crystalline Materials at Terahertz Frequencies.

Terahertz (THz) time-domain spectroscopy provides a direct and nondestructive method for measuring the dielectric properties of materials directly from the phase delay of coherent electromagnetic radiation propagating through the sample. In cases when crystals are embedded within an inert polymeric pellet, the Landau, Lifshitz, and Looyenga (LLL) effective medium model can be used to extract the intrinsic dielectric constant of the crystalline sample. Subsequently, polarizability can be obtained from the Clausius-Mossotti (CM) relationship. Knowledge of the crystal structure density is required for an analytical solution to the LLL and CM relationships. A novel crystal structure-free graphical method is presented as a way to estimate both dielectric constants and polarizability values for the situation when the crystal structure density is unknown, and the crystals are embedded within a pellet composed of a non-porous polymer. The utility of this crystal structure-free method is demonstrated by analyzing THz time-domain spectra collected for a set of amino acids (L-alanine, L-threonine, and L-glutamine) embedded within pellets composed of polytetrafluoroethylene. Crystal structures are known for each amino acid, thereby enabling a direct comparison of results using the analytical solution and the proposed crystal structure-free graphical method. For each amino acid, the intrinsic dielectric constant is extracted through the LLL effective medium model without using information of their crystal structure densities. THz polarizabilities are then calculated with the CM relationship by using the determined intrinsic dielectric constant for each amino acid coupled with its crystal density as determined graphically. Comparison between the analytical and graphical solutions reveal relative differences between dielectric constants of 3.7, 5.1, and 13.6% for threonine, alanine, and glutamine, respectively, and relative differences between polarizability of 0.6, 0.9, and 5.4%, respectively. These values were determined over the 10-20 cm-1 THz frequency range. The proposed method requires no prior knowledge of crystal structure information.

Association of Prolonged-Duration Chemoprophylaxis With Venous Thromboembolism in High-risk Patients With Head and Neck Cancer.

Importance: Venous thromboembolism (VTE) is associated with substantial morbidity and is the most common factor associated with preventable death among hospitalized patients. Data from otolaryngologic studies suggest that the risk of VTE may be underestimated among high-risk patients, particularly among those undergoing oncologic procedures. The incorporation of prolonged-duration chemoprophylaxis (PDC) into preventive therapy has been associated with substantial decreases in VTE incidence among patients undergoing oncologic surgery. However, bleeding remains a major concern among otolaryngologists, and substantial variation exists in the use of thromboprophylaxis. Objective: To assess the association between PDC and VTE in high-risk patients with head and neck cancer undergoing oncologic procedures. Design, Setting, and Participants: This retrospective cohort study identified 750 patients with biopsy-confirmed head and neck cancer and a Caprini risk score of 8 or higher who underwent inpatient oncologic surgery at a tertiary care referral center between January 1, 2014, and February 1, 2020. After exclusions, 247 patients were included in the study; patients were divided into 2 cohorts, traditional and PDC, based on the duration of prophylaxis. Univariate and multivariate analyses were performed to examine the development of VTE and bleeding-associated complications during the 30-day postoperative period. Data were analyzed from April 1 to April 30, 2020. Exposures: PDC, defined as 7 or more postoperative days of chemoprophylaxis. Main Outcomes and Measures: VTE and bleeding events during the 30-day postoperative period. Results: Among 247 patients (mean [SD] age, 63.1 [11.1] years; 180 men [72.9%]) included in the study, 106 patients (42.9%) received traditional prophylaxis, and 141 patients (57.1%) received PDC. The incidence of VTE was 5 of 106 patients (4.7%) in the traditional cohort and 1 of 141 patients (0.7%) in the PDC cohort (odds ratio [OR], 0.15; 95% CI, 0.003-1.33). In the multivariate logistic regression analysis, PDC was independently associated with reductions in the risk of VTE (OR, 0.04; 95% CI, 0.001-0.46). The incidence of bleeding events was 1 of 106 patients (0.9%) in the traditional cohort and 6 of 141 patients (4.3%) in the PDC cohort (OR, 4.64; 95% CI, 0.55-217.00). Conclusions and Relevance: The use of chemoprophylaxis for high-risk patients with head and neck cancer remains a high-priority topic. The results of this study suggest that PDC may be associated with reductions in VTE among this patient population. However, the associated increase in nonfatal bleeding events warrants careful consideration and further highlights the need to determine an optimal duration for chemoprophylaxis among this distinct cohort.

Identifying cohort differences in children undergoing partial intracapsular tonsillectomy vs traditional tonsillectomy for sleep disordered breathing.

OBJECTIVE: Partial intracapsular tonsillectomy (PIT) is a well-established technique for reducing post-operative morbidity in pediatric patients with sleep disordered breathing (SDB). Although tonsillar re-growth rates are reported as low, risks of symptom recurrence or need for completion tonsillectomy are clear disadvantages when compared to traditional tonsillectomy (TT). We aim to identify cohort differences to better guide clinical decision making and identify patient-specific factors that may influence this decision. A secondary aim was to evaluate potential risk factors for tonsillar regrowth. METHODS: Retrospective chart review of pediatric patients who underwent TT or PIT for SDB between 2015 and 2019 at a tertiary care academic medical center. Records were reviewed for age, gender, race, body mass index, comorbidities, diagnosis, apnea-hypopnea index, pre-operative Brodsky tonsil size, length of stay, post-operative hemorrhage, tonsillar regrowth, symptom recurrence, and need for completion tonsillectomy. RESULTS: 315 patients were included: 174 underwent TT and 141 underwent PIT. Patients undergoing TT were more likely to have a sleep study showing OSA (OR 3.01, p < 0.0001), asthma (OR 4.28, p = 0.000124), and other comorbidities (OR 4.06, p = 0.0258). The overall complication rate was 4.44% (14/315). Tonsillar regrowth was exclusive to the PIT group, occurring in 7/141 patients (4.96%). Age ≤4 years was significantly associated with increased risk of tonsillar regrowth (≤4 years: 7.69%, >4 years: 0%; p = 0.049). Race and pre-operative tonsil size were not associated with regrowth. CONCLUSIONS: Our study supports the low incidence of tonsillar regrowth in PIT and suggests an association with younger age. Moreover, we found that patients undergoing TT are more likely to be older, have OSA, asthma, and other comorbidities.

Comparing Kadish and Modified Dulguerov Staging Systems for Olfactory Neuroblastoma: An Individual Participant Data Meta-analysis.

OBJECTIVE: To compare the Kadish and the modified Dulguerov staging of individual participants to determine the impact of stage and other prognostic factors on disease-free (DFS) and overall survival (OS). DATA SOURCES: Systematic review of EMBASE, MEDLINE, Cochrane Library, and CINAHL databases. REVIEW METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) was followed for this study. Articles including patients with olfactory neuroblastoma (ONB) staged with both Kadish and Dulguerov staging systems were reviewed. The raw data from eligible studies were requested to perform an individual participant data (IPD) meta-analysis. RESULTS: Pooled data from 21 studies representing 399 patients with ONB undergoing treatment with curative intent showed that increasing age, treatment with chemotherapy, and positive or unreported margin status portended worse DFS (P < .05). Increasing stage for both Kadish and Dulguerov staging systems was prognostic for worse DFS and OS (P < .05), with Kadish C representing a heterogeneous group with regard to outcome and corresponding Dulguerov T stage. Using the Akaike information criterion, the Dulguerov staging system had superior performance to the Kadish system for DFS (1088.72 vs 1092.54) and OS (632.71 vs 644.23). CONCLUSION: This study represents the first IPD meta-analysis of ONB directly comparing the outcomes of Kadish and Dulguerov staging systems in patients treated with primary surgery. Both systems correlated with DFS and OS, with superior performance in the Dulguerov system. Furthermore, the Kadish C group represented a heterogeneous group with regard to outcomes after stratification by the Dulguerov system. Dulguerov T4 patients had the worst outcome, with most being approached with open resection.

Characterizing Bone Mineral Density Using Lumbar Spine Computed Tomography Attenuation in Patients With Distal Radius Fractures.

INTRODUCTION: This study examines how many patients with distal radius fracture (DRF) eligible for bone health evaluation could potentially be screened using bone mineral density (BMD) estimation by L1 vertebra computed tomography (CT) attenuation obtained for other purposes. MATERIALS AND METHODS: For all adult patients with DRF who presented over a 5-year period, we recorded the age, sex, dual-energy X-ray absorptiometry (DXA) results up to 3 years prior to injury or 1 year post-injury, and L1 CT attenuation on any CT including L1 that had been performed within 6 months of their fracture.1 We compared the availability of L1 CT attenuation measurement to the rate of DXA scan use. We calculated the percentage of patients with osteoporosis and compared attenuation results to DXA results in those patients where both tests were available. RESULTS: Of 1853 patients with DRF, an L1 CT had been obtained in 195 patients. Of the 685 patients who met criteria for osteoporosis screening, 253 (37%) patients had undergone only DXA screening, 68 (10%) patients had an L1 CT only, and 18 (2%) patients had both tests. Of the 86 patients who met criteria for osteoporosis screening and had an adequate CT, 67 (78%) demonstrated L1 attenuation <135 HU, and 79 (92%) had CT attenuation <160 HU. DISCUSSION: Our study found that 10% of patients with a distal radius fracture who met the criteria for osteoporosis screening had a CT scan that could be used to estimate bone density and that the majority of those patients met criteria for osteoporosis based on CT attenuation. CONCLUSIONS: Utilization of opportunistic BMD screening with L1 CT attenuation offers the potential to increase osteoporosis screening from 40% to 50% of eligible patients and make the diagnosis of osteoporosis in an additional 8% of patients with DRF at no additional cost.

Frontal Sinus Fractures: Evolving Clinical Considerations and Surgical Approaches.

Frontal sinus fractures are an uncommon injury of the maxillofacial skeleton, and account for 5-15% of all maxillofacial fractures. As the force of impact increases, fractures may extend beyond the anterior table to involve adjacent skull, posterior table and frontal sinus outflow tract (FSOT). Fractures at these subsites should be evaluated independently to assess the need for and type of operative intervention. Historically, these fractures were managed aggressively with open techniques resulting in obliteration or cranialization. With significant injuries, these approaches are still indispensable. However, the treatment of frontal sinus fractures has changed dramatically over the past half-century, and recent case series have demonstrated favorable outcomes with conservative management. Concurrently, there has been an increasing role of minimally invasive endoscopic techniques, both for primary and expectant management, with a focus on sinus preservation. Here, we review the diagnosis and management of frontal sinus fractures, with an emphasis on subsite evaluation. Following a detailed assessment, an appropriate treatment strategy is selected from a variety of open and minimally invasive approaches available in the surgeon's armamentarium.

DFT Computed Dielectric Response and THz Spectra of Organic Co-Crystals and Their Constituent Components.

Terahertz (THz) spectroscopy has been put forth as a non-contact, analytical probe to characterize the intermolecular interactions of biologically active molecules, specifically as a way to understand, better develop, and use active pharmaceutical ingredients. An obstacle towards fully utilizing this technique as a probe is the need to couple features in the THz regions to specific vibrational modes and interactions. One solution is to use density functional theory (DFT) methods to assign specific vibrational modes to signals in the THz region, coupling atomistic insights to spectral features. Here, we use open source planewave DFT packages that employ ultrasoft pseudopotentials to assess the infrared (IR) response of organic compounds and complex co-crystal formulations in the solid state, with and without dispersion corrections. We compare our DFT computed lattice parameters and vibrational modes to experiment and comment on how to improve the agreement between theory and modeling to allow for THz spectroscopy to be used as an analytical probe in complex biologically relevant systems.

Nocturnal Hypoglycemic Alarm Based on Near-Infrared Spectroscopy: In Vivo Studies with a Rat Animal Model.

A noninvasive method for detecting episodes of nocturnal hypoglycemia is demonstrated with in vivo measurements made with a rat animal model. Employing spectra collected from the near-infrared combination region of 4000-5000 cm-1, piecewise linear discriminant analysis (PLDA) is used to classify spectra into alarm and nonalarm data classes on the basis of whether or not they correspond to glucose concentrations below a user-defined hypoglycemic threshold. A reference spectrum and corresponding glucose concentration are acquired at the start of the monitoring period, and spectra are then collected continuously and converted to absorbance units relative to the initial reference spectrum. The resulting differential spectra correspond to differential glucose concentrations that reflect the differences in concentration between each spectrum and the reference. Given an alarm threshold (e.g., 3.0 mM), a database of calibration differential spectra can be partitioned into two groups containing spectra above and below the threshold. A classification model is then computed with PLDA. The resulting model can be applied to the differential spectra collected during the monitoring period in order to identify spectra whose corresponding glucose concentrations lie in the hypoglycemic range. In this work, the alarm algorithm was tested in two single-day studies performed with anesthetized rats. Glucose concentrations spanned the range of 1.6 to 13.5 mM (29 to 244 mg/dL). For both rats, the alarm algorithm performed well. On average, 87.5% of alarm events were correctly detected, and the occurrence of false alarms was 7.2%. False alarms were restricted to times when the glucose concentrations were very close to the alarm threshold rather than at random times, thus demonstrating the potential of the approach for practical use.

Polarizability of Aspirin at Terahertz Frequencies Using Terahertz Time Domain Spectroscopy (THz-TDS).

A novel application of terahertz time-domain spectroscopy (THz-TDS) is described for the determination of permittivity and polarizability of organic crystals, as exemplified by measurements with the polymorph I form of crystalline aspirin (acetylsalicylic acid). The coherent nature of the THz pulse experiment, coupled with gated-detection, permits direct measure of differences in the phase angle of the electric field vector after passing through a pellet composed of the aspirin crystals embedded within an inert polymer matrix. An effective media model is used to extract dielectric information for the crystals from the measured time-domain signal that is representative of the entire pellet composition. Polarizability is then obtained for these organic crystals by using the Clausius-Mossotti relationship. Dielectric spectra and polarizability spectra are presented over the 0.3-3 THz frequency range (10-100 cm-1). The average polarizability values measured over the low frequency range (10-20 cm-1) are 22.4 ± 0.3 and 22.4 ± 0.5 Å3 for aspirin crystals embedded within matrixes of polytetrafluoroethylene (PTFE) and polyethylene (PE), respectively.

Septal fractures predict poor outcomes after closed nasal reduction: Retrospective review and survey.

OBJECTIVES/HYPOTHESIS: To determine outcomes of patients with displaced nasal bone fractures after closed nasal reduction (CNR). STUDY DESIGN: Retrospective patient review. METHODS: Review of all patients presenting to the emergency department of a tertiary-care, level 1 trauma hospital with a nasal bone fracture over a 2-year period, followed by telephone survey after CNR. RESULTS: Six hundred seven patients presented to the emergency department in 2015 and 2016 with a diagnosis of nasal bone fracture. Of these, 134 patients met inclusion criteria and underwent CNR without septal reduction. Those with sports-related injuries and those with a septal fracture identified on computed tomography imaging were significantly more likely to undergo CNR. Ninety-one patients completed the post-CNR telephone survey. Over 90% of patients were satisfied with the procedure. However, patients with septal fractures reported worse outcomes, as 53.6% versus 24.1% (P = .0025) disagreed that CNR improved nasal breathing. Of all patients, 11 (2%) eventually underwent septorhinoplasty, with the presence of septal fracture on imaging a significant risk factor. CONCLUSIONS: Nasal bone fractures are a common injury, often managed initially with CNR. Patients with septal fractures should be counseled on the high risk of posttraumatic nasal deformity and obstruction despite CNR. In addition, addressing a septal fracture found on imaging may be warranted with either closed septal reduction or early aggressive management given the poorer outcomes seen in the present study. Although these patients are more likely to have definitive treatment, many forego later intervention despite persistent symptoms, emphasizing the need for early intervention or close follow-up. LEVEL OF EVIDENCE: 3 Laryngoscope, 129:1784-1790, 2019.

Transoral resection of extensive pediatric supraglottic neurofibroma.

This case report describes the novel use of transoral robotic surgery (TORS) with delayed transoral laser microsurgery (TLM) for residual disease in the resection of a pediatric neurofibroma with supraglottic and parapharyngeal space extension. Postoperatively, the patient had excellent functional outcomes. This case demonstrates that pediatric TORS is feasible, safe, and complementary to TLM. Neurofibroma is just one of the diverse pathologic processes of the pediatric airway that can be managed via transoral surgery, and applications of TORS with TLM will continue to broaden as our experience develops. Laryngoscope, 2525-2528, 2018.

Molar Absorptivity Measurements in Absorbing Solvents: Impact on Solvent Absorptivity Values.

Molar absorptivity is a fundamental molecular property that quantifies absorption strength as a function of wavelength. Absolute measurements of molar absorptivity demand accounting for all mechanisms of light attenuation, including reflective losses at interfaces associated with the sample. Ideally, such measurements are performed in nonabsorbing solvents and reflective losses can be determined in a straightforward manner from Fresnel equations or effectively accounted for by path length difference methods. At near-infrared wavelengths, however, many solvents, including water, are absorbing which complicates the quantification of reflective losses. Here, generalized equations are developed for calculating absolute molar absorptivities of neat liquids wherein the dependency of reflective loss on absorption properties of the liquid are considered explicitly. The resulting equations are used to characterize sensitivity of absolute molar absorptivity measurements for solvents to the absorption strength of the solvent as well as the path length of the measurement. Methods are derived from these equations to properly account for reflective losses in general and the effectiveness of these methods is demonstrated for absolute molar absorptivity measurements for water over the combination region (5000-4000 cm-1) of the near-infrared spectrum. Results indicate that ignoring solvent absorption effects can incorporate wide ranging systematic errors depending upon experimental conditions. As an example, systematic errors range from 0 to 10% for common conditions used in the measurement of absolute molar absorptivity of water over the combination region of the near-infrared spectrum.